Slight bog off idle
Thread Starter
Race Director
Joined: Dec 2003
Posts: 14,148
Likes: 936
From: Fremont Ca
2022 C4 of the Year Finalist - Modified
Slight bog off idle
I've got an 81 4-speed and at times it seems to bog down slightly when taking off in first gear. The carburetors been rebuilt and TPS adjusted to correct voltage. I've tried adjusting the air/fuel mixture using a dwell meter but can't get a correct reading. Currently air/fuel mixture screws are at 3 turns out. At one point I completely isolated all vacuum ports coming off the carburetor. Any tips would be greatly appreciated.
Race Director
Joined: Nov 2006
Posts: 13,229
Likes: 7,825
From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
2024 C3 of the Year Finalist- Modified
2022 C3 of the Year Finalist - Modified
Cruise-In VIII Veteran
100 percent stock electronic carburetor.
Did these actually ever run perfectly?
Sorry.
If it were mine it would quickly become not 100 percent stock.
Have you tried using a AFR Meter to judge rich or lean?
Considered using a 80 and earlier carburetor or aftermarket carburetor? Or even changing over to EFI?
Did these actually ever run perfectly?
Sorry.
If it were mine it would quickly become not 100 percent stock.
Have you tried using a AFR Meter to judge rich or lean?
Considered using a 80 and earlier carburetor or aftermarket carburetor? Or even changing over to EFI?
Thread Starter
Race Director
Joined: Dec 2003
Posts: 14,148
Likes: 936
From: Fremont Ca
2022 C4 of the Year Finalist - Modified
100 percent stock electronic carburetor.
Did these actually ever run perfectly?
Sorry.
If it were mine it would quickly become not 100 percent stock.
Have you tried using a AFR Meter to judge rich or lean?
Considered using a 80 and earlier carburetor or aftermarket carburetor? Or even changing over to EFI?
Did these actually ever run perfectly?
Sorry.
If it were mine it would quickly become not 100 percent stock.
Have you tried using a AFR Meter to judge rich or lean?
Considered using a 80 and earlier carburetor or aftermarket carburetor? Or even changing over to EFI?
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Thread Starter
Race Director
Joined: Dec 2003
Posts: 14,148
Likes: 936
From: Fremont Ca
2022 C4 of the Year Finalist - Modified
Thread Starter
Race Director
Joined: Dec 2003
Posts: 14,148
Likes: 936
From: Fremont Ca
2022 C4 of the Year Finalist - Modified
I can't get an accurate dwell reading,it's jumping all over the place. I've been told I need to replace the O rings on the AIR/BLEED valve,there's a vacuum leak somewhere and there's a good possibility it might be coming from here. When bringing the RPMs up the dwell meter moves up with the revs. It's my understanding that when the carburetor was rebuilt the O rings for the AIR/BLEED valve should have been replaced but they weren't. No too happy with the shop that rebuilt the carb.
Racer
Joined: Apr 2006
Posts: 477
Likes: 43
From: Millbrae California
the dwell reading should read in the 5 degree range if it is running to lean because the computer is commanding a richer mixture, a dwell reading in the 45 degree range is commanding a leaner a/f mixture. If you disconnect the m/c solenoid the carb will go full rich, be sure the air pump is not pumping up stream into the exhaust manifold (pinch the air pump hoses closed)) it would cause the o2 sensor to see the extra air as a lean condition. i have never seen a dwell reading that jumps all over the place.
Thread Starter
Race Director
Joined: Dec 2003
Posts: 14,148
Likes: 936
From: Fremont Ca
2022 C4 of the Year Finalist - Modified
the dwell reading should read in the 5 degree range if it is running to lean because the computer is commanding a richer mixture, a dwell reading in the 45 degree range is commanding a leaner a/f mixture. If you disconnect the m/c solenoid the carb will go full rich, be sure the air pump is not pumping up stream into the exhaust manifold (pinch the air pump hoses closed)) it would cause the o2 sensor to see the extra air as a lean condition. i have never seen a dwell reading that jumps all over the place.
Thread Starter
Race Director
Joined: Dec 2003
Posts: 14,148
Likes: 936
From: Fremont Ca
2022 C4 of the Year Finalist - Modified
@olescarb I didn't make to connection until now. You've done some work on a Holley I had years ago,NOVA JOE recommended your shop. I wish I would have remembered your shop when I had this Rochester rebuilt. I'm waiting on some parts,I haven't done anything with the car for a few days but will look into the EGR valve before and replace the O rings on the AIR/BLEED valve before I take it apart. If it does need some work I'll most likely bring it by. Thanks for the info,greatly appreciated.
Thread Starter
Race Director
Joined: Dec 2003
Posts: 14,148
Likes: 936
From: Fremont Ca
2022 C4 of the Year Finalist - Modified
I may have found the issue. I removed the idle air bleed valve to get a look at the O rings and one of them was completely worn. I used some silicone on the O ring to get it to seal and the car runs better with a smoother idle. I've ordered a rebuild kit with the O rings. Thanks for the tips/info,greatly appreciated.