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| Bog during off-idle WOT https://slantsix.org/forum/viewtopic.php?t=42010 |
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| Author: | Josh P [ Wed Sep 22, 2010 3:01 pm ] |
| Post subject: | Bog during off-idle WOT |
Seems like a lot of people have been having bog and stuttering problems lately, and so am I... So I've got a very brief bog/hesitation which only occurs during WOT when coming off-idle. I'm thinking its the vacuum advance because I hooked up my timing light and when cracking open the throttle my timing seems to retard itself and then start climbing. Any ideas on checking the VA without removing it? The other question is, which VA to use? The previous owner added an old Chrysler electronic ignition and electronic distributor but I'm not exactly sure what year or engine (though I'd guess a mid '70s slant because it has a dual ballast resistor) the parts came from. So is there a preferred VA pod and will any Chrysler style VA pod work? EDIT: I just noticed that there is absolutely no bog when in reverse... seems odd... Any reason the tires spin in reverse but the engine stutters when in drive? |
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| Author: | wjajr [ Wed Sep 22, 2010 6:01 pm ] |
| Post subject: | |
What make carburetor do you have? Automatic or manual transmission? Reverse is a little lower geared than first, rpm is a bit higher, and engine may be out of the transition circuit. This is when the carburetor is changing from idle circuit to main jets. Perhaps the carburetor is feeding off the main jets just enough to keep from leaning out. As the throttle opens from idle, a lot of air is introduced into the idle air fuel mixture before the main metering jets can supply enough fuel to keep the proper stoichiometric mixture. One way to over come this is to have a good shot of raw fuel injected as the throttle plates open by the accelerator pump. Sometimes the pump shot is correct, but there is still a bog. With a Holley carburetor, this happens when too much of the idle transfer slot is exposed below the throttle plate when the idle speed adjustment screw keeps the throttle plates too far open. Other brands of carburetors I can’t speak to as I haven’t had an opportunity to play with them, but I suspect that they to have a similar system. Try lowering the idle speed with the idle speed adjustment screw to lessen the exposure of the idle transfer slot, and adding a degree or two of timing advance to bring back up the idle speed if needed. Also a rich condition can cause a bog, too much pump shot, and not enough air flow through the carburator. |
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| Author: | Josh P [ Wed Sep 22, 2010 8:03 pm ] |
| Post subject: | |
Transmission is an automatic. Carb is a Carter BBS, and I rebuilt it only about 2,000 miles ago. It didn't used to have this bog. The problem seems to have popped up sometime between the rebuilt and now (didn't notice 'cause I wasn't driving it very hard). The bog only happens when I really stomping on the gas while the car is stopped at idle. I don't believe the position of the throttle plate is my issue... also advancing my timing much more would cause it to ping... |
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| Author: | Josh P [ Fri Oct 01, 2010 3:06 pm ] |
| Post subject: | |
Found the issue, my accelerator pump vent was set too low, after adjusting to the correct height all is right (mostly). I'm still not convinced my vacuum advance is functioning correctly, but oh well. |
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