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Bog when Engine is Warm #1667982
09/06/14 10:49 AM
09/06/14 10:49 AM
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North Carolina
cjskotni Offline OP
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Guys,

I may have fixed my vapor lock issue with the vapor separator and return line setup. I have noticed another tiny issue that is a little annoying now..

I notice when the engine is totally warm, maybe after 10 minutes of runtime, it has a bog when you blip the accelerator pedal. This happens right off idle or even if you're cruising. When the engine is cold/warming up it is spot-on but when it gets hot...this 1/2 second bog when you give it pedal. However, once the bog ends, the motor is strong and pulls pretty hard.

The carb is a Holley 850 4150 vacuum secondaries. I have the silver (middle tension) spring installed right now. Am I right in thinking this might be an issue with secondaries opening too early maybe? If so, why only when the motor is warmed up?

I have the spring kit and the quick change housing installed so if this might be my issue, what would you guys recommend as far as the spring to use?

Thanks as always!

Re: Bog when Engine is Warm [Re: cjskotni] #1667983
09/06/14 11:08 AM
09/06/14 11:08 AM
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Bend,OR USA
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Make sure the accelerator pump adjuster screw is adjusted properly (Holley says to hold the throttle open at WOT, check it and adjust the screw so it has .015 room with a feeler gauge stuck between the screw and the pump arm ) I have seen a bog caused by to much squirt also


Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: Bog when Engine is Warm [Re: cjskotni] #1667984
09/06/14 11:46 AM
09/06/14 11:46 AM
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Lincoln Nebraska
RapidRobert Offline
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Quote:

Am I right in thinking this might be an issue with secondaries opening too early maybe? If so, why only when the motor is warmed up?


As you know a cold eng requires a richer mixture & with it being OK when cold the choke enrichment may be taking care of that then warmed up/no choke it is too lean OR if no choke is being used it might be too rich which is what is needed when cold but when warm that is too rich (not likely here) but I'd confirm the float level(s) and definitely the pump shot (tip in should be immediate/good duration). I would unhook the secondaries to take them out of the picture and find out what in hg it bogs at and did you mention what PV is in there. A slight vac leak might be a possibility but easy stuff first. Holler with any news


live every 24 hour block of time like it's your last day on earth
Re: Bog when Engine is Warm [Re: cjskotni] #1667985
09/06/14 12:47 PM
09/06/14 12:47 PM
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Prospect, PA
BSB67 Offline
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Quote:

Guys,



Am I right in thinking this might be an issue with secondaries opening too early maybe?






It is unlikely if it happens right as you blip the throttle. Does it happen if you are low speed cruising and you give the throttle a quick stab to half throttle?

If so, it is likely lean idle and transition circuits in the carb. It is very popular to increase the squirter size to fix this problem, but in my experience it usually just masks the true issue.

As mentioned float level and opening vacuum of the PV should be checked

Last edited by BSB67; 09/06/14 12:51 PM.
Re: Bog when Engine is Warm [Re: BSB67] #1667986
09/06/14 01:12 PM
09/06/14 01:12 PM
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North Carolina
cjskotni Offline OP
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When the engine is warm, it will bog off idle @ low speed cruising or even at higher speeds like 30-40mph.

Right now I have a 42 squirter, arm is adjusted, and 8.5 PVs. Idle vacuum on this motor is 14-16in.

Re: Bog when Engine is Warm [Re: cjskotni] #1667987
09/06/14 01:51 PM
09/06/14 01:51 PM
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BSB67 Offline
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You really did not answer the key question. Will it bog/hesitate at quick part throttle?, or just WOT.

Don't remember the specifics of your car, but it is hard to imaging that a 42 squirter is necessary.

Depending on your gear ratio and other factors, you could still be mostly in the transition at 30 - 40.

Re: Bog when Engine is Warm [Re: BSB67] #1667988
09/06/14 03:30 PM
09/06/14 03:30 PM
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cjskotni Offline OP
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Quote:

You really did not answer the key question. Will it bog/hesitate at quick part throttle?, or just WOT.






I don't ever really "floor" this car but I can tell you that it bogs at quick part throttle for about a 1/2 second or so and then picks right up and pulls hard. This feels a bit like what I had last year when I had a 32 squirter on the carburetor and I fixed it by going up to eventually settle on the 42. The 32 was the original squirter size and was confirmed to be too small on the dyno by the shop who tuned the engine originally. I tried a 38/40/42 and the 42 seemed to act the most responsive at the time....


In my fuel system troubleshooting I have swapped to a factory style hemi pump with return line/VS (from the Holley w/o return) which seems to be lower pressure according to my fuel pressure gauge. I have no idea if this is affecting anything or not.

Re: Bog when Engine is Warm [Re: cjskotni] #1667989
09/06/14 04:06 PM
09/06/14 04:06 PM
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Quote:

Quote:

You really did not answer the key question. Will it bog/hesitate at quick part throttle?, or just WOT.






I don't ever really "floor" this car but I can tell you that it bogs at quick part throttle for about a 1/2 second or so and then picks right up and pulls hard. This feels a bit like what I had last year when I had a 32 squirter on the carburetor and I fixed it by going up to eventually settle on the 42. The 32 was the original squirter size and was confirmed to be too small on the dyno by the shop who tuned the engine originally. I tried a 38/40/42 and the 42 seemed to act the most responsive at the time....


In my fuel system troubleshooting I have swapped to a factory style hemi pump with return line/VS (from the Holley w/o return) which seems to be lower pressure according to my fuel pressure gauge. I have no idea if this is affecting anything or not.




Not to sure a dyno is the best way to determine squirter size and duration. I've been to a couple of dynos, and I would also caution that a dyno guy is not necessarily a good carb tuner by default.

Your fuel pump is not the problem.

Re: Bog when Engine is Warm [Re: BSB67] #1667990
09/06/14 04:25 PM
09/06/14 04:25 PM
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God's Country Maryland
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At idle, your accelerator pump arm should have NO play in it. It must start moving the instant the throttle starts moving. Look down the carb with a flashlight to confirm there is actually fuel being squirted into the carb, you can do this with the engine turned off. That 8.5 power valve may need to be replaced with a 9.5 or even a 10.5. A vacuum gauge will help here or just try the 10.5 to see if it helps. If the squirter is too big it can be confirmed with someone watching the exhaust for a puff of black smoke when you "blip" the throttle.


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Re: Bog when Engine is Warm [Re: GODSCOUNTRY340] #1667991
09/06/14 05:47 PM
09/06/14 05:47 PM
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North Carolina
cjskotni Offline OP
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Alright. I went and inspected the adjustment on the pump arm and it seemed to be adjusted right where the arm would start to get depressed instantly when moving the throttle.

Now this is something I have always wondered about but the accel pump arm has a little play in it. In other words, it can be pushed down a bit (maybe .030-.040) from its resting position before I 'feel' resistance like its pushing the diaphragm.

I had the throttle arm adjusted so it was holding the accel pump arm just 'south' of that resting position but maybe .020-.030 from where it began to feel resistance. There as no gap at all between the throttle lever arm and the accel pump arm. I went ahead and backed off the adjuster nut 1/2 a turn or so which puts more tension on that arm and brings it where it will start to feel that resistance as soon as the throttle is moved.

Does that sound right? Hopefully this makes sense...

So anybody care to explain why if this was misadjusted, why it would be crisp while the engine was cool and get a bog when warmed up? This particular circuit should operate identically hot or cold, right?

Thanks for the suggestions so far.

Re: Bog when Engine is Warm [Re: cjskotni] #1667992
09/06/14 06:20 PM
09/06/14 06:20 PM
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BSB67 Offline
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Does the carb have a choke? If the choke is actuated before it is warmed up, you cannot compare.

Re: Bog when Engine is Warm [Re: BSB67] #1667993
09/06/14 07:44 PM
09/06/14 07:44 PM
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cjskotni Offline OP
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Quote:

Does the carb have a choke? If the choke is actuated before it is warmed up, you cannot compare.




Electric choke. It starts to come off after about 20-30 seconds.

Re: Bog when Engine is Warm [Re: cjskotni] #1667994
09/06/14 09:00 PM
09/06/14 09:00 PM
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Your choke could be richening the idle/transfer circuit when the engine is warming up. Then when the engine is warm and the choke is open, the engine could be seeing a lean spot off idle and during tip in.

I always adjust my pump cam linkage when the engine is idling and with a flash light. I lean over the engine "just enough" to see the front squirter while shining the flash light on that squirter. Then I move the linkage and watch how soon the fuel starts to pump out. If the fuel does not pump out as soon as I move the throttle, then I readjust it and check it again. I move the nut about 1/8 of a turn until I see fuel.

What pump cam color do you have? Do you have a hollow squirter screw with the 42? If not, then you won't see much of a difference in pump shot larger than a 37 squirter.
Note: A 42 is a large squirter. Maybe it is time for a pump cam swap.


1970 YO7 A66 [Canadian Export] F8 Challenger
340 (Currently in shop for stroker assy.)
Re: Bog when Engine is Warm [Re: YO7_A66] #1667995
09/07/14 12:54 AM
09/07/14 12:54 AM
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cjskotni Offline OP
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I will have to try your method of adjusting that accel pump arm.

I do have the hollow screw and run a pink cam. I always though the 42 seemed big... but it seemed to be what it wanted....

What else could be wrong that the large pump shot might be compensating for? I had the carb jetted on the dyno with wideband O2 sensors so I am pretty sure the jetting is right...

Any ideas?

Re: Bog when Engine is Warm [Re: cjskotni] #1667996
09/07/14 01:39 AM
09/07/14 01:39 AM
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Quote:

I will have to try your method of adjusting that accel pump arm.

I do have the hollow screw and run a pink cam. I always though the 42 seemed big... but it seemed to be what it wanted....

What else could be wrong that the large pump shot might be compensating for? I had the carb jetted on the dyno with wideband O2 sensors so I am pretty sure the jetting is right...

Any ideas?


Did the dyno have your exhaust system hooked up? Did you dyno tune it with teh air cleaner on and hot air from the radiator blowing over the carb air cleaners? If not you may need to retune it in the car I get my motors close on the tune up on the the dyno wideban and then finish the tune up in the car, with or without my dual wideban hooked up, the butt dyno can be fairly accurate in the car


Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: Bog when Engine is Warm [Re: cjskotni] #1667997
09/07/14 09:30 AM
09/07/14 09:30 AM
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Quote:



What else could be wrong that the large pump shot might be compensating for?




Really?




Quote:

I had the carb jetted on the dyno with wideband O2 sensors so I am pretty sure the jetting is right...





Jetting should be very close and likely not the problem IMO. However, there is no down side to stepping up the jets in the primary side at some point just to see, but I don't think you are there yet. Curious, do you know what changes they made in jetting at the dyno?

Is this the 870 Avenger carb?

Re: Bog when Engine is Warm [Re: BSB67] #1667998
09/07/14 10:11 AM
09/07/14 10:11 AM
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cjskotni Offline OP
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The dyno shop jetted it up a few sizes to 82 in front 88 rear. I don't remember what it was but I do recall it was lean before.

The carb is a Holley 4150 850cfm. It is not the 870 Avenger.

One of the issues I ran into with the carb was it had a really weird tune on it from the factory. Holley recommended it for my motor so I bought it. However, this carburetor is the same unit they put on the Chevy 502 crate motors so it wasn't configured like your standard Holley. Just weird things like 3.5PVs, super duper light vac secondary spring, etc...

Re: Bog when Engine is Warm [Re: cjskotni] #1667999
09/07/14 10:40 AM
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The PINK cam is the ""least"" aggressive off idle of the entire selection of pump cams!!!!!

I would suggest a white or red (very similar to each other and twice as aggressive off idle than the pink cam.) cam on position #1. If that helps but not all the way, then I would suggest the Orange pump cam which is more aggressive than the white or red cams and it also has more overall pump volume (which you may or may not need), But for testing purposes, I would leave the 42 in there and just swap out pump cams for now.
Note: you will need to shorten the pump arm screw to install the larger pump cams. Maybe 1/2 turn before insalling the white or red cam and then once the cam is in, readjust.


1970 YO7 A66 [Canadian Export] F8 Challenger
340 (Currently in shop for stroker assy.)
Re: Bog when Engine is Warm [Re: cjskotni] #1668000
09/07/14 12:02 PM
09/07/14 12:02 PM
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Do you know how many turns out the idle mixture screws are?, and what the A/F ratio is at idle(from the dyno session)?

Better yet, do you have the A/F graphs?

Last edited by BSB67; 09/07/14 12:04 PM.
Re: Bog when Engine is Warm [Re: BSB67] #1668001
09/07/14 01:17 PM
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cjskotni Offline OP
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Idle mix screws are about 1.25 - 1.5 turns out from bottom. I have the graph but it only shows 3500 RPM+ so it might not be that useful here.

Another thing we may be grappling with is the tune was done with a marginal fuel pump which failed totally shortly afterwards. I also later found the ignition as marginal and had to go to a lower ballast resistor to get the coil output voltage back up. At the time of tune, the output was in the 10-15kV range...new ballast...in the 45kV range. No idea if this will affect anything here or not.

I have thought about experimenting with the cams but I didn't know enough to make an educated guess as to which one to try. I am appreciative of the specific suggestion on which color to try. My friend has the set of cams so I will see if I can steal his set to play with...

Thanks for the help so far....

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