Tuning a Holley 750

Posted By: RapidRobert

Re: Tuning a Holley 750 - 01/25/11 01:52 AM

What 602heavy said, pump shot related. I'm assuming floats/jets are good & no vac leak.

Posted By: BSB67

Re: Tuning a Holley 750 - 01/25/11 02:41 AM

OP said

"The off-the-line hit is great. "

Usually not the pump if it only happens at cruise, in my experiance.

Posted By: RapidRobert

Re: Tuning a Holley 750 - 01/25/11 02:44 AM

Quote:

"The off-the-line hit is great.

Yeah I missed that part

Posted By: Chilort

Re: Tuning a Holley 750 - 01/25/11 04:05 AM

Holley's FAQ says this:

"QUESTION I have a vacuum secondary carburetor that bogs when the secondaries come in. What will cause this?
ANSWER Bogging and hesitation are caused by the secondaries coming in too quickly. You can install a heavier secondary spring and this will prevent the secondary from coming in too soon. If the engine is sluggish in response at full throttle then the secondaries may not be opening soon enough. You will then need to go to a lighter spring. The spring kit is part number 20-13 which will have 7 different springs to fine tune with."

Is this possibly what I'm chasing?

Posted By: forphorty

Re: Tuning a Holley 750 - 01/25/11 05:25 AM

Make sure nothing is clogged. Sometimes a shot of carb cleaner into the air bleeds will do a world of good. If it sneezes through the carb as you go to WOT, that is a momentary lean condition. Secondaries opening too fast will cause it. Secondaries opening too slow will just make the car slow.

Posted By: StealthWedge67

Re: Tuning a Holley 750 - 01/25/11 04:43 PM

Quote:

Holley's FAQ says this:

"QUESTION I have a vacuum secondary carburetor that bogs when the secondaries come in. What will cause this?
ANSWER Bogging and hesitation are caused by the secondaries coming in too quickly. You can install a heavier secondary spring and this will prevent the secondary from coming in too soon. If the engine is sluggish in response at full throttle then the secondaries may not be opening soon enough. You will then need to go to a lighter spring. The spring kit is part number 20-13 which will have 7 different springs to fine tune with."

Is this possibly what I'm chasing?

Start with the obvious and easy fix, then work from there. Pump shots and cam changes will tailor the enitial and mid throttle tip in, but if its coughing when you nail it all at once to the floor, the most likely problem is that you're secondary's are opening too fast.

Put the strongest spring possible in the vacuum canister and see if the problem goes away. If it does, then we know we're on to the right issue. From there, start weakening the spring, I'd go (2) springs at a time, until the problem starts to show itself again. Back off to the last spring that didn't bog..... done. From here, you can start to mess with pump shots and cams, and nozzle sizes. Being off on those shouldn't cause a complete cough, though. Those are things that will add throttle response if tuned properly, but it sounds to mee like the secondary spring is your issue. Especially if those other items are at stock spec. for an 80508.

It seems to me that a good running 440 really should be able to take all of 750cfm right away, I had the same carb on my old 383 with the lightest spring available in the vacuum can, and it would take a tromp to the floor without hesitation. But, your gearing being so far out of line with the rest of your combo is likely to blame. Going to a set of 3.55's would make a world of difference, and still allow 60 MPH fairly comfortably. I'd look to change the gearing ASAP.

Posted By: Chilort

Re: Tuning a Holley 750 - 01/26/11 01:31 AM

Well, according to Holley the 80508S (my carb) comes with a black secondary spring. And the stiffest spring in the 20-13 Holley spring kit is the black one.....

Posted By: 602heavy

Re: Tuning a Holley 750 - 01/26/11 01:57 AM

Fix a paper clip or similar (tie strap) to the arm on vaccume pod & go take it for a blast , if the paper clip has moved down rod the secs are opening , you will also be able to tell how far if any they opened.

Have you checked for slack in the pump arm?.............maybe try a higher rated power valve or try going up 6 sizes on primary main jets.

Posted By: YO7_A66

Re: Tuning a Holley 750 - 01/26/11 01:58 AM

Have you pulled the existing spring to confirm that it is the black one?

""Primary jets are 74 (original jets were 70) and it has a metering plate for the secondaries that works out to a 75 jet.""
A 75 secondary jet seems lean on a built 440 to me.

What color pump cam and what size squirter do you have in it?

Are you are getting 12"hg in N or D?

I think that one of your circuits is lean. Either the pump cam is too small, the PV is too low, or the secondary plate is too lean.

Posted By: Chilort

Re: Tuning a Holley 750 - 01/26/11 02:14 AM

I haven't done much of anything at all yet. It has been raining quite a bit here. And I've got a job interview on Friday to turn my current position into a full time position so I've been a little busy with the prep-work for that.

I have thought that the metering plate might be a little small. But I don't want to have to buy a bunch of metering plates. I really have the option of getting a conversion or just stepping up to an 830 (Quickfuel) or 870 (Holley) carb.

I have not confirmed that the spring in the carb really is the back one. I won't get around to checking until late Friday afternoon or Saturday.

Thanks for all the suggestions so far.

Posted By: YO7_A66

Re: Tuning a Holley 750 - 01/26/11 02:20 AM

I believe that you have plenty of carb tuning left before you consider another carb. You could buy a metering plate for the secondary and this way you can rejet the secondary until you get it correct. Many carb companies sell the metering plates.
Please let us know the answers to my previous response.

Posted By: Pacnorthcuda

Re: Tuning a Holley 750 - 01/26/11 02:43 AM

Quote:

With that cam the lowest gear I'd run would be 3.55's. 3.91's would be ideal. I doesn't start working until about 2k...so keep that in mind.

I agree, I run that same cam in a 440, and the powerband starts at 1900-2000 rpm. Normally not an issue in an automatic (converter would normally slip past 2K under heavy foot) EXCEPT that you have those really tall gears and you don't state the diameter of your rear tires.

You might want to see if the bog occurs under 2000 or not.
The issue can be fixed with carb tuning if not, but if you are lugging the motor that much at 'cruise' it may require 3.23's

Posted By: Magnum

Re: Tuning a Holley 750 - 01/26/11 05:02 PM

I had a similar problem. In neutral the engine would take a quick snap of the throttle. In low gear, again no problem. In a higher gear a quick snap and it would cough.

Do not accept it will not work with a tall gear. My truck is a manual trans and even in 5th, I overcame the bog.

My resolution about 15 replies down this thread.

Posted By: Chilort

Re: Tuning a Holley 750 - 01/27/11 03:31 AM

Quote:

I had a similar problem. In neutral the engine would take a quick snap of the throttle. In low gear, again no problem. In a higher gear a quick snap and it would cough.

Do not accept it will not work with a tall gear. My truck is a manual trans and even in 5th, I overcame the bog.

My resolution about 15 replies down this thread.

Your description of what is happening is much closer to what my vehicle is actually doing than what I described. I will have to look into this.

Posted By: Chilort

Re: Tuning a Holley 750 - 01/29/11 01:30 AM

Okay, I finally had time to mess with this a bit this evening before it got dark.

The spring in the vacuum canister is the black one, which is the heaviest in the kit.

The secondaries are opening (maybe 3/8"). I used a zip tie on the shaft and it moved down for sure.

I get 12 inhg in neutral and around 10-11 in drive.

I was wrong when I "updated" about my bog. It is when I'm in 3rd gear and nail the throttle. Nothing happens and then off like a raped ape. It only sneezes out of the carb when the engine is cold. Once it is warmed up it just goes flat instead of sneezing.

The carb is a stock setup. I don't know about the pump cam as that isn't listed in the specs with the carb and I don't know where to look. If the "squirter" is the "pump discharge nozzle" it is an 0.031. The power valve is a 65.

The tires are tall. This is in a truck ('68 Swepty).

I haven't pulled a plug in awhile to look but the last time I looked they looked very clean. The engine builder I work with has told me they should look clean when the engine is running right as opposed to the light brown that I've always heard.

I'm not opposed to getting a secondary metering plate with jets. Or a taller gear for that matter but I still need to be able to run 75mph on the interstate with all the other morons in Atlanta.

Thoughts?

YO7_A66, where you from in Indiana? I spent a good portion of my life in Corydon, went to college in Terre Haute (at RHIT), then lived in Kokomo for a bit too.

Posted By: Chilort

Re: Tuning a Holley 750 - 01/29/11 05:07 PM

Also, I live very close to a Summit outlet. I can get parts quickly and actually have some time this weekend to work on this. If I were to get a secondary plate that would allow me to change jets should I get one from Holley that doesn't have a power valve or one from Quick Fuel that does have a power valve?

Posted By: YO7_A66

Re: Tuning a Holley 750 - 01/29/11 08:54 PM

If you have 10"hg in D than the 6.5 should be fine.
You can figure out the pump cam by looking at the drivers side of the carb, just behind the throttle linkage bracket on the primary butterfly. There should be a small plastic cam that is held into position with one screw that is on that same throttle linkage bracket. You might be able to see the color better by standing in front of the engine and looking just to the left of the throttle bracket. It could be pink which seems to be a standard pump cam color.
If you are going to buy parts, it might be cheaper to start with the pump cam kit from Holley. It comes with 6-8 different colors of pump cams and they are very simple to swap in and test the 3rd gear bog issue. I think once you have that tuned better than maybe purchase the secondary metering plate (no need for the pv on the sec side) and you can figure about 6-10 jet sizes larger on the sec side than what you have in the primary side if you need to order a couple of jets to test with.
Start with one change at a time and the pump cams should be under $20. Once you know what color you currently have, then we can help you with a guess on the next one to test.
You can use the attached chart to help select a pump cam. The pink cam (for reference) is the "slowest" cam for delivering fuel. You can see this by referencing the chart and looking at the left hand side at the Throttle Degrees versus the number under the pink cam. The numbers under the cam colors are easier to read if you just use them as a "number" (so many cc's of fuel). If you look at the 10 degree number of the pink cam and the orange cam (.050 sersus .022), you will see a big difference of how much fuel each cam will activate at 10 degrees of throttle movement. This chart will help you make a guess at your cam change as long as you know your current cam color and you know that your current cam is setup correctly with the linkage. You want the cam to activate fuel as soon as the throttle moves. You have to readjust the cam pump arm after each cam swap. All you have to do is shorten the pump arm bolt (clockwise on the bolt), then swap cams, then readjust the pump arm bolt so that you get a squirt as soon as the throttle is moved. You may have to make your final adjustmet when the engine is running. If your car is bogging just off idle, then pick a cam with more fuel delivery at 10 or 20 degrees or so. If you need more fuel at 40 or 50 degrees of throttle, then reference the chart to pick the next cam.

Attached File

6445354-5273820-HolleyPumpCams.pdf (230 downloads)

Posted By: Chilort

Re: Tuning a Holley 750 - 01/30/11 02:41 AM

The cam looks pink to me. What would you recommend?

I also got a secondary metering plate conversion. I'm thinking of starting with 82s. I've got a part throttle knock at around 75mph that some others have thought might be a lean condition as the secondaries start to come in. I'm actually thinking of starting with converting the secondary over before I start messing with the pump shot.

Thanks for all the help.

Posted By: Chilort

Re: Tuning a Holley 750 - 01/30/11 07:07 PM

Now that I have the carb off, the pump cam looks orange.

Posted By: Chilort

Re: Tuning a Holley 750 - 01/30/11 08:53 PM

Okay, I put 82 jets on the secondary side. The soft spot is still there but doesn't seem quite as bad. I think I'm going to change the pump cam from the current orange to blue. The bigger jets did not alter my knocking issue.

Posted By: YO7_A66

Re: Tuning a Holley 750 - 01/30/11 09:20 PM

""The bigger jets did not alter my knocking issue.""

If you have pinging, then you either have too much timing too quick or you are lean.

The orange cam is the second most aggresive cam for the 30cc pump and I would have guessed that cam would have taken care of the issue. If the orange did not cure it, I would guess that your primary side jets are still too lean. You have to remember that the pump is just a "bandaid" to tranfer the carb from circuit to circuit.
I would suggest that you now bump up your primary side jets and retest. That blue cam will run out of fuel by 50% throttle movement which may affect your kickdown performance at highway speeds, or when you are above 50% throttle.
Also, the 82 jets are only activated after the black spring allows the secondaries to kick in. So you are using your primary jets most of the time with that black spring installed. This is why I suggest that you look at the primary jetting.
You could also swap out the 6.5pv for a higher rated unit since you have 10-11in of vacuum in gear. I would not go past an 8.5 because they are not super accurate.

Posted By: Chilort

Re: Tuning a Holley 750 - 01/30/11 10:16 PM

Spark plug color is light gray/light brown. Looks on the okay to slightly lean side. I think I'm going to pump up the primary jets to 76. I've played with the timing itself until I'm blue in the face. I've got it slowed down more than the Mopar kit will allow and have even modified springs. ... but I think I'm getting closer with all of this.

Posted By: Chilort

Re: Tuning a Holley 750 - 01/30/11 10:53 PM

With 76s the hesitation is now almost completely gone.

And to be honest, even though the carb came with the black secondary spring, I threw in the brown (next to heaviest) right after I got the spring kit.

I'm wondering if I should try 77s or 78s now on the primary and then bump up the secondary side to 84s.... thoughts?

YO7_A66, thanks for the tuning 101 lessons.

Posted By: Chilort

Re: Tuning a Holley 750 - 01/31/11 12:40 AM

Okay, I went with the 78s on the primaries and 84s on the secondaries. The hesitation is now nearly gone. I can only get it to do it some times and when it happens it is slight and much quicker to recover.

Would 86s be a good direction?
I'm wondering if the brown pump cam might help overcome this slight and infrequent issue.

My rattle is still there but more slight as well. My initial timing is 21* and the all in is 35* and it doesn't come all in until 3500rpm or so. I made a ping monster because the pistons are really far in the hole.

I guess it is a matter of looking at plugs, driving, and looking at plugs.

Posted By: YO7_A66

Re: Tuning a Holley 750 - 01/31/11 01:14 AM

What octane are you running?

You might need to run a cooler spark plug. What heat range are you running? If you are running too hot of a plug, the pinging will only get worse during the Spring and Summer temps. A cooler plug will allow you to run a quick timing curve and also allow less jetting to some degree.

The brown cam is for the 50cc pump.

Your timing curve looks good!!

Posted By: Chilort

Re: Tuning a Holley 750 - 01/31/11 01:40 AM

I run 93 from Shell. The plugs are what Eddy called for Champion RC12YC (IIRC). I tried a 9 but everyone told me that it would be too cold.

Posted By: YO7_A66

Re: Tuning a Holley 750 - 01/31/11 02:32 AM

Since your are running the highest octane from the pump, I would suggest that you either keep jetting up the primary until it stops pinging, or try a cooler plug.
A plug is only too cold if the plug keeps fouling.
You have to feed a hot plug with more fuel.

Posted By: Chilort

Re: Tuning a Holley 750 - 01/31/11 03:10 AM

Okay, I still have the 9s on the shelf. I'll keep at it. But now things wait for the upcoming weekend.

Posted By: Magnum

Re: Tuning a Holley 750 - 01/31/11 03:31 PM

You set your jets for most power. Fattening them up to cover a bog will just use more fuel. Same with bigger shooters.

Before the washer trick. I was able to cure my bog with a 35 shooter but come on. I have a stock 5.9L with a vacuum carb. It shouldn't need so much shooter to cure a bog that was like yours, only under that one condition of fighting the tall gear. That's when I decided to preload the spring a bit. Ultimately I was able to go back to a smaller shooter too.

When you snap the throttle open. Can you see the spring compressing?

Posted By: Chilort

Re: Tuning a Holley 750 - 01/31/11 03:53 PM

Quote:

When you snap the throttle open. Can you see the spring compressing?

I will have to look next time I am messing with it. The accel pump has a red spring. I know when I move the throttle at all (without the engine on) I can hear it squirt fuel.

Posted By: Junky

Re: Tuning a Holley 750 - 01/31/11 04:50 PM

Quote:

I was able to cure my bog with a 35 shooter...

Same here.

Posted By: Chilort

Re: Tuning a Holley 750 - 02/01/11 08:50 PM

I can't find any information in the instruction sheet for the size of the shooter that comes in this carb. How do I identify that?

Posted By: YO7_A66

Re: Tuning a Holley 750 - 02/01/11 11:53 PM

The shooter (squirter)should have a two digit stamping on it. The stamping would be on the side that is facing the middle of the carb.
(28=.028", etc.)
I have a carb that both squirters came from QF with no stamping which means .031" to them.

Note: the larger the squirter the "quicker" it will deliver the fuel and visa-versa.

Do you have any extra squirters to try?

Posted By: Chilort

Re: Tuning a Holley 750 - 02/02/11 02:06 AM

Quote:

The shooter (squirter)should have a two digit stamping on it. The stamping would be on the side that is facing the middle of the carb.
(28=.028", etc.)
I have a carb that both squirters came from QF with no stamping which means .031" to them.

Note: the larger the squirter the "quicker" it will deliver the fuel and visa-versa.

Do you have any extra squirters to try?

Nope. But, it is raining here and is supposed to rain through Saturday so I couldn't try anything out even if I wanted to.

Posted By: DOUGG

Re: Tuning a Holley 750 - 02/02/11 02:20 AM

That carb should have came with a 31 squirter.

Posted By: Chilort

Re: Tuning a Holley 750 - 02/03/11 07:53 PM

Is there any advantage to this kind of squirter:
http://www.holley.com/121-135.asp
versus this kind of squirter:
http://www.holley.com/121-35.asp

I currently have the style similar to the 121-135.

What kind of jetting on the primary and secondary is just so high that it would indicate that I need to start looking for other sources for problems? My highway ping is still there (though it seems better in some ways) and I'd like to fix it.

Posted By: YO7_A66

Re: Tuning a Holley 750 - 02/03/11 09:12 PM

Did you confirm that the fuel is squirting as soon as the spring is depressed?
I had a vacuum secondary carb that I had to shim the primary side spring to get it to work properly too.
-------------------------------------------

""My highway ping is still there (though it seems better in some ways) and I'd like to fix it.""

If you are still getting the ping at highway cruise/WOT, and since you are running the orange pump cam, then a larger squirter would delivery that pump shot quicker. I would try a 035 or a 040 (with hollow screw) for your next testing. If one of these fixes the ping, then you can back down on your main jetting as long as your plugs are looking good. Your pump cam might get smaller too with the bigger squirter.
It appears that it wants more fuel but the guess is "when" it wants more fuel.

BUMP for the reference on the 440/750 (Holley #80508S) jetting.

---------------------------------------------
I found this info about the straight versus tube online:

The "straight" type are basically first design, and are for straight boosters. The "tube" type was developed to aim a straighter stream of fuel against the booster, usually a dropped booster venturi. As the fuel hits the booster venturi, it atomizes better than the straight type.

I have also read that most cases you can use the style that the carb came with.

Posted By: Chilort

Re: Tuning a Holley 750 - 02/03/11 10:40 PM

Quote:

Did you confirm that the fuel is squirting as soon as the spring is depressed?
I had a vacuum secondary carb that I had to shim the primary side spring to get it to work properly too.

Yes, it is squirting right away. The spring compresses and then slowly lets out.

Quote:

"My highway ping is still there (though it seems better in some ways) and I'd like to fix it."

If you are still getting the ping at highway cruise/WOT, and since you are running the orange pump cam, then a larger squirter would delivery that pump shot quicker. I would try a 035 or a 040 (with hollow screw) for your next testing. If one of these fixes the ping, then you can back down on your main jetting as long as your plugs are looking good. Your pump cam might get smaller too with the bigger squirter.
It appears that it wants more fuel but the guess is "when" it wants more fuel.

If it is pinging at WOT I cannot hear it. The ping starts when I am running around 75mph in 3rd and have to increase the throttle a tad to go up hill or pick up speed a little more. Then it rattles like a coffee can full of bolts. I would guess engine speed is about 2700rpm based on gear and tire size. Engine vacuum is still over 15inhg when this happens. If I get into the throttle more I can make the rattle go away. I'm guessing still to lean on the primary side. I'm currently still running the 78 jets on the primary and 84 on the secondary. I did drive the truck today and will check some plugs when I gethome.

Quote:

The "straight" type are basically first design, and are for straight boosters. The "tube" type was developed to aim a straighter stream of fuel against the booster, usually a dropped booster venturi. As the fuel hits the booster venturi, it atomizes better than the straight type.

I have also read that most cases you can use the style that the carb came with.

Mine came with the straight types, so I guess I'll go with that.

Posted By: RapidRobert

Re: Tuning a Holley 750 - 02/03/11 10:49 PM

Quote:

The ping starts when I am running around 75mph in 3rd and have to increase the throttle. If I get into the throttle more I can make the rattle go away.

Try turning the vac can 3 turns CCW w a 3/32" allen wrench

Posted By: RapidRobert

Re: Tuning a Holley 750 - 02/03/11 10:59 PM

The Q (to me) is is it a lean prob or timing. I'd suspect timing (if your octane is adequate). I'm wondering if a slightly stiffer spring combo would help (& I'm assuming your total (w vac adv unhooked/capped as it is now) is correct for the eng family 35-SB 36-38-BB.

Posted By: Chilort

Re: Tuning a Holley 750 - 02/03/11 11:03 PM

I'm running about 35* total advance all in around 3500rpm. I have it slowed way down with a heavy spring package and spring perches bent a bit to get it that slow.

I've run more and less total timing and I've never been able to make the ping go away with timing. I'm hoping it is lean and I can get some of my timing back once I figure out what is going on.

Posted By: RapidRobert

Re: Tuning a Holley 750 - 02/03/11 11:08 PM

Yeah you are not overboard w timing. Holler how it turns out. Didn't read all the posts & dont know if more octane is a practical option for you but that's my guess

Posted By: Chilort

Re: Tuning a Holley 750 - 02/04/11 02:02 AM

Pulled 8 plugs and they look gray to me. No signs of light brown/tan color. I must still be too lean. I'm thinking of going with 82s on the primary and 88 on the secondary side......

Posted By: BSB67

Re: Tuning a Holley 750 - 02/04/11 02:13 AM

Something else is wrong. you need to start looking for something else. I'd be surprised if that carb needed to be changed 2 jet sizes.

What is your fuel pressure when you are cruising and at part throttle?

Posted By: YO7_A66

Re: Tuning a Holley 750 - 02/04/11 02:26 AM

""The ping starts when I am running around 75mph in 3rd and have to increase the throttle a tad to go up hill or pick up speed a little more.""

Your running Champion RC12YC plugs,high pump octane (93), 9.2 compression, no vac advance, timing at 3500, orange pump cam/031 squirter, 78 primary jets, and you still have pinging at light accel at 2700rpms and 15hg vacuum. HMMMMMM.
This problem may get worse as the outside temps go up, unless you are lean. I still suggest that you try the 035 or 040 squirter.
My second thought is that the plugs are tooooo hot in the range.
----------------------------------------------
What heat range Champion spark plugs are other members running on the street? Are 12's too hot?

Posted By: calrobb2000

Re: Tuning a Holley 750 - 02/04/11 02:39 AM

hi
what is your cranking compression psi ?

per haps you have too much cyl psi ?

may need to back off timing to 32-34 deg total .

Posted By: Chilort

Re: Tuning a Holley 750 - 02/04/11 03:23 AM

I just tried some Autolite plugs that are in the same heat range as a Champion 9 because I have them sitting around. ....same result.

I bumped up the primary to 82 and secondary jets to 88. .... same result (and too dark out to tell if I was leaving a cloud of black smoke behind me).

I've never checked the cranking pressure. The cam was installed straight up and verified that it is straight up.

I've never checked the fuel pressure either. I don't have a port and I don't have a fuel pressure gauge that reads this low (mine is for fuel injected stuff). The fuel pump is a new Carter replacement style pump.

I do need to get a bigger squirter but that'll have to wait for the weekend.

Posted By: Chilort

Re: Tuning a Holley 750 - 02/04/11 05:13 AM

This has a rear sump pan and a windage tray. We had to heat and bend the rear sump pickup a bit to get the tube to clear the windage tray and still stay off the bottom of the pan. I wonder if at specific engine speeds the oil pump pickup is oscillating and hitting the windage tray. That pickup is a snake-y thing and I could see it doing that. But even if it did I doubt it would be loud enough for me to hear.

I'm grasping at straws.

Posted By: SomeCarGuy

Re: Tuning a Holley 750 - 02/04/11 05:42 AM

I did a quick scan of the thread, didn't see these things, forgive me if this was covered already.

-looks like you changed the vac spring before the engine was ran w/ this carb. Very easy to get the diaphram off center. Could have a huge vac leak at the pod.

-are you running a choke? I was having fits w/ my 3310 and another member pointed out that there is a hole that needs to be plugged if it is removed. Looks like a screw hole, I didn;t even think it was anythign until that was pointed out. I put a self tapping screw in and my carb now runs fine.

-I bet you have a vac leak someplace. If not at the above spots, someplace. Have you went over all of the intake areas with carb cleaner to check?

-how sure are you that the TDC mark is reliable? Maybe you have a bunch more timing than you think.

-have you tried different gas stations?

I really find it hard to believe that a 9.2 to 1 engine w/ aluminum heads pings on 93 octane w/o any vac advance at all. The jets you have in there just sound way too big. The plugs should be pretty dark, unless extra air is coming in somewhere. There has to be something missing in this picture.

Posted By: Chilort

Re: Tuning a Holley 750 - 02/04/11 03:25 PM

Quote:

-looks like you changed the vac spring before the engine was ran w/ this carb. Very easy to get the diaphram off center. Could have a huge vac leak at the pod.

-- nope, changed it while it was on the engine.

Quote:

-are you running a choke?

-- running a choke.

Quote:

-I bet you have a vac leak someplace. If not at the above spots, someplace. Have you went over all of the intake areas with carb cleaner to check?

-- I have not done this.

Quote:

-how sure are you that the TDC mark is reliable? Maybe you have a bunch more timing than you think.

I am not sure. But the initial makes sense based on other's setups. I dialed it in with the max vac then pull back 1 inhg method. Total mechanical is then relative to the initial. Maybe it is still too much and I could try to take even more out.

Quote:

-have you tried different gas stations?

-- Yes

Quote:

I really find it hard to believe that a 9.2 to 1 engine w/ aluminum heads pings on 93 octane w/o any vac advance at all.

--- Me too. I didn't check any plugs after I finished up last night. I guess I'll start plugging off ports (not that this has many accessories) to see if maybe that's the issue.

Posted By: B5 Bee

Re: Tuning a Holley 750 - 02/04/11 03:29 PM

You need to find the problem.
Lower rear gears and spark plugs won't fix a carb problem.

There are two things that will make it sneeze back when you punch it, slow timing and/or a lean condition.

10 sizes larger on the jets is crazy. It may eliminate the symptoms but the problem still exists. Seldom does any motor with a Holley perf carb need more than 4 jets sizes up.
My first guess is you have a problem with the power valve circuit. A bad power valve, a power valve with too low of a rating, or a stopped up passage.
My second guess is it's lean on the accelerator pump circuit. Nozzles should be big enough if it doesn't sneeze when you hit it from an idle. Make sure have a pump cam that still has travel from half to full throttle.
If you want to eliminate the chance it's the secondaries opening too soon, disconnect them and try it on primaries only. BTW, the spring has only a small effect of when the secondaries open. The main control is something called a kill bleed. Although one will effect the other, basically, the kill bleed controls when the secondaries start to open, the spring controls how long it takes to get them fully open.

Remember that there are 5 fuel delivery circuits in a Holley.
-idle ports, from the idle mix screws
-transfer slot, near the idle ports
-acclerator pump system, delivers fuel to squirt nozzles
-power valve system, delivers fuel to boosters
-main jets, delivers fuel to boosters

The goal is to find and fix the problem, not just eliminate the symptoms.
You have understand how something works before you can fix it, GRASSHOPPER.

Posted By: Magnum

Re: Tuning a Holley 750 - 02/04/11 04:09 PM

If your spring is compressing, I'd aim your efforts there.

Let's assume the spring is weak or there is too much resistance in the squirter circuit. Switching to a hollow shooter screw AND/OR shimming the spring will help.

Unlike bigger jets and bigger shooters. This modification will not consume more fuel.

Posted By: Chilort

Re: Tuning a Holley 750 - 02/04/11 11:20 PM

I'm really unfamiliar with the power valve system. When does it start to work and what would be symptoms of a bad power valve? [Edit - never mind, just read through some info on Holley's site and it sounds like mine is still working and wouldn't be the cause of my problem regardless.]

I can't really try anything until it quits raining here and that's going to be a few days.

Posted By: Chilort

Re: Tuning a Holley 750 - 02/05/11 04:51 PM

Going to go pick up a 3.23 gear set in a 489 case today. Isn't likely to solve all the issues but will be a better overall gear set for my combo.

Posted By: SomeCarGuy

Re: Tuning a Holley 750 - 02/05/11 04:57 PM

Pick up a can or two of carb cleaner while you are out.

Posted By: Chilort

Re: Tuning a Holley 750 - 02/05/11 05:29 PM

Maybe I never said I did that but I sprayed the entire thing down with a can of carb cleaner while I had it off the engine to convert it to 4150 and rebuild my fuel line last weekend. It made no difference in how it works. But it is all shiny and clean on the inside now.

Posted By: SomeCarGuy

Re: Tuning a Holley 750 - 02/05/11 06:22 PM

You need to check for leaks. Not about cleaning anything. You are about 99% sure to find that you have a vaccum leak.

Posted By: Chilort

Re: Tuning a Holley 750 - 02/06/11 01:13 AM

Gotcha.

Posted By: 69B3GT

Re: Tuning a Holley 750 - 02/06/11 02:18 AM

Quote:

it won't get any better until you get some gear. Putting a 2.73 in a 440 car is like having a pretty girl friend that has bad breath. yeah you can get past it but it will take a second or 3.

Words cant describe how hard I just laughed

Posted By: Chilort

Re: Tuning a Holley 750 - 02/06/11 08:36 PM

Quote:

You need to check for leaks. Not about cleaning anything. You are about 99% sure to find that you have a vaccum leak.

I worked my way around the carb ... no problem.
Went around the outside of the intake manifold ... no problem.
Sprayed into the valley tray area ... problem.

Time to try to fix it.

Posted By: Chilort

Re: Tuning a Holley 750 - 02/06/11 09:28 PM

Nothing in the intake runners to indicate that it was sucking oil. I'd used a full set of intake minfold gaskets on both the top and bottom of the bath tub pan. I guess I need to figure out how that is going to work because what I had on clearly didn't. And I used Gasgacinch to seal it up even.

Posted By: Pacnorthcuda

Re: Tuning a Holley 750 - 02/06/11 09:45 PM

Quote:

Nothing in the intake runners to indicate that it was sucking oil. I'd used a full set of intake minfold gaskets on both the top and bottom of the bath tub pan. I guess I need to figure out how that is going to work because what I had on clearly didn't. And I used Gasgacinch to seal it up even.

It could be the gaskets moved over time and led to the leak. Very common. I superglue the fiber gaskets to the valley pan before install so I KNOW they wont move.

Posted By: screamindriver

Re: Tuning a Holley 750 - 02/06/11 09:56 PM

Spray copper adhesive holds them tight also...

Posted By: Chilort

Re: Tuning a Holley 750 - 02/07/11 01:05 AM

Time to run it over to the machine shop I guess. I resealed the entire thing with new gaskets and it still pings when driven and still bogs slightly when I spay carb cleaner under the intake.

Posted By: SomeCarGuy

Re: Tuning a Holley 750 - 02/07/11 02:39 AM

Quote:

still bogs slightly when I spay carb cleaner under the intake.

Posted By: Chilort

Re: Tuning a Holley 750 - 03/06/11 12:21 AM

Okay, I sealed up the intake one more time. Now, I cannot find a vacuum leak at all.

Still pings.

I installed a 3.23 gear set.

Still pings, but at a different speed (though I cannot tell you exactly because I forgot to pick up the speed-o gear for this setup -- tires are 26" tall).

Posted By: 7e5dartsport

Re: Tuning a Holley 750 - 03/06/11 05:23 AM

i read about it since the beginning and because you tried different timing positions, i dont think its timing-related. a couple of years ago, ihad a similar bog at part throttle and a bigger shooter didnt correct it. a high flow power valve did, and i suggest you try holley number 125-165. first confirm it is the primaries that are lean by disconnecting the vaccuum pot from the secondaries by removing the small clip at the end of the shaft.make sure the secondaries cannot open and go for a ride. if it still bogs or pings you know the problem lies in the primary circuit and you should try the hi-flow power valve. you could also try to momentarily plug the pcv hose with a pair of vise-grips, it should help too.

Posted By: Chilort

Re: Tuning a Holley 750 - 03/06/11 09:02 PM

I disconnected the secondary vac can and locked the blades shut. I went for a drive and it pings just like it always does.

I've never heard of one of these high flow power valves.

By the time I'm done with this there will be nothing original left of my 750 Holley that "works" right out of the box.

Posted By: SomeCarGuy

Re: Tuning a Holley 750 - 03/06/11 09:23 PM

At this point I'm going to say you need to look into the PV as has been suggested and also look at the TDC mark.

Try backing down the timing and see if it goes away. If it does and runs good(not a slug), chances are the TDC mark is off.

It has been awhile since this got going, so i don't remember what the plugs look like. Are they bright white and clean?

Posted By: Chilort

Re: Tuning a Holley 750 - 03/06/11 11:46 PM

I've pulled the timing back to 19* initial and 33* total. It still pings. It wasn't a slug at that timing though. My initial timing, the vacuum at initial, etc. all suggest to me the TDC mark is fine.

I haven't checked a plug in it in a while but they are so dirty from all of that I've done I'd really have to throw in a new set and check.

I think I'm going to take it to a local guy that does a lot of work on these BB Mopars and let him have a look. His opinion over the phone was that with pistons .100 in the hole it is always going to ping.