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Re: Tuning a Holley 750 [Re: YO7_A66] #911878
01/25/11 10:14 PM
01/25/11 10:14 PM
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Cookeville
Chilort Offline OP
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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.

Re: Tuning a Holley 750 [Re: Chilort] #911879
01/25/11 10:20 PM
01/25/11 10:20 PM
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Indiana
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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.


1970 YO7 A66 [Canadian Export] F8 Challenger
340 (Currently in shop for stroker assy.)
Re: Tuning a Holley 750 [Re: Mr.Yuck] #911880
01/25/11 10:43 PM
01/25/11 10:43 PM
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Kirkland, Washington
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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

Re: Tuning a Holley 750 [Re: Pacnorthcuda] #911881
01/26/11 01:02 PM
01/26/11 01:02 PM
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Hamilton, Ontario Canada
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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.


69 Super Bee, 93 Mustang LX, 04 Allure Super
Re: Tuning a Holley 750 [Re: Magnum] #911882
01/26/11 11:31 PM
01/26/11 11:31 PM
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Cookeville
Chilort Offline OP
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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.

Re: Tuning a Holley 750 [Re: Chilort] #911883
01/28/11 09:30 PM
01/28/11 09:30 PM
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Cookeville
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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.

Re: Tuning a Holley 750 [Re: Chilort] #911884
01/29/11 01:07 PM
01/29/11 01:07 PM
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Cookeville
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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?

Re: Tuning a Holley 750 [Re: Chilort] #911885
01/29/11 04:54 PM
01/29/11 04:54 PM
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Indiana
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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.

Re: Tuning a Holley 750 [Re: YO7_A66] #911886
01/29/11 10:41 PM
01/29/11 10:41 PM
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Cookeville
Chilort Offline OP
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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.

Re: Tuning a Holley 750 [Re: Chilort] #911887
01/30/11 03:07 PM
01/30/11 03:07 PM
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Cookeville
Chilort Offline OP
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Now that I have the carb off, the pump cam looks orange.

Re: Tuning a Holley 750 [Re: Chilort] #911888
01/30/11 04:53 PM
01/30/11 04:53 PM
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Cookeville
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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.

Re: Tuning a Holley 750 [Re: Chilort] #911889
01/30/11 05:20 PM
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""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.


1970 YO7 A66 [Canadian Export] F8 Challenger
340 (Currently in shop for stroker assy.)
Re: Tuning a Holley 750 [Re: YO7_A66] #911890
01/30/11 06:16 PM
01/30/11 06:16 PM
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Cookeville
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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.

Re: Tuning a Holley 750 [Re: Chilort] #911891
01/30/11 06:53 PM
01/30/11 06:53 PM
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Cookeville
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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.

Re: Tuning a Holley 750 [Re: Chilort] #911892
01/30/11 08:40 PM
01/30/11 08:40 PM
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Cookeville
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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.

Re: Tuning a Holley 750 [Re: Chilort] #911893
01/30/11 09:14 PM
01/30/11 09:14 PM
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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!!


1970 YO7 A66 [Canadian Export] F8 Challenger
340 (Currently in shop for stroker assy.)
Re: Tuning a Holley 750 [Re: YO7_A66] #911894
01/30/11 09:40 PM
01/30/11 09:40 PM
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Cookeville
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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.

Re: Tuning a Holley 750 [Re: Chilort] #911895
01/30/11 10:32 PM
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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.


1970 YO7 A66 [Canadian Export] F8 Challenger
340 (Currently in shop for stroker assy.)
Re: Tuning a Holley 750 [Re: YO7_A66] #911896
01/30/11 11:10 PM
01/30/11 11:10 PM
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Cookeville
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Okay, I still have the 9s on the shelf. I'll keep at it. But now things wait for the upcoming weekend.

Re: Tuning a Holley 750 [Re: Chilort] #911897
01/31/11 11:31 AM
01/31/11 11:31 AM
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Hamilton, Ontario Canada
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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?


69 Super Bee, 93 Mustang LX, 04 Allure Super
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