One BBl Carb Question
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Senior User
Joined: Jun 2002
Posts: 330
Likes: 1
From: Chandler,Arizona - USA
One BBl Carb Question
My truck's idle has been surging and generally idling pretty bad. I checked the vacuum lines, changed the fuel filter, sprayed Gum-out in the carb and on the linkages. I also sprayed gumout in that valve on top of the air cleaner. This did not help much. I went ahead and turned in the air fuel mixture screw in all the way to lean it out. Crazy thing is that the truck ran good when I did that. I backed it out about maybe a half turn, and now the truck idles much better.
My question is that when the screw is turned clockwise to lean out the mixture, the engine should shake, shudder, and almost stall. I had that screw turned in all the way, and it ran fine. Did something internal in the carb get messed up? This is a re-man carb with about 20,000 miles on it. It is a non-feedback carb. Thanks in advance for your replies.
My question is that when the screw is turned clockwise to lean out the mixture, the engine should shake, shudder, and almost stall. I had that screw turned in all the way, and it ran fine. Did something internal in the carb get messed up? This is a re-man carb with about 20,000 miles on it. It is a non-feedback carb. Thanks in advance for your replies.
Elder User
Joined: Apr 2004
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First thing I would do is check and make sure all the carb screws are tight. After that where is the idle speed set, if it is too high the idle air adjustment won't make any change. Knowing the way these carbs come loose I don't think you will have to go much further
Posting Guru
Joined: Apr 2003
Posts: 1,153
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From: Venezuela
That sounds like a fuel level at bowl is to high, you can chech this very easy.
1º Remove air filter or air hose adapter, (Depends on year)
2º Star engine and let it run for about 10 minutes at idle (650-750RPM)
3º Using care and a flash light, put yourself right over the Carb barel and take a closer look where the Main Jet spread fuel.
If fuel level is too high, you will see fuel been drooped down. This cause a rich condittion and the the mixture screw can't work properly.
If so, correct this conddition first and then will see what more appears...
1º Remove air filter or air hose adapter, (Depends on year)
2º Star engine and let it run for about 10 minutes at idle (650-750RPM)
3º Using care and a flash light, put yourself right over the Carb barel and take a closer look where the Main Jet spread fuel.
If fuel level is too high, you will see fuel been drooped down. This cause a rich condittion and the the mixture screw can't work properly.
If so, correct this conddition first and then will see what more appears...
Thread Starter
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Senior User
Joined: Jun 2002
Posts: 330
Likes: 1
From: Chandler,Arizona - USA
The carb is on tight. Everyone into cars and trucks here are saying the float is the most likely culprit. I never messed with adjusting the float level before. I still have my old feedback carb, the float assembly should be similar to the non-feedback carb. I'll play around with the old FB carb and my Chilton's manual, and see how that goes. Do you use a feeler gauge for a float level adjusting tool? Thanks for your help everyone!
Posting Guru
Joined: Apr 2003
Posts: 1,153
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From: Venezuela
The float level stated on most calibration charts, in my own experience is a bit high. I guess this is because the aftermarket carburetor kits use low quality needle valves causing a bit of fuel leak.
Using the stated value, the float will hang PARALELL to gasket surface, but I found calibrating it a bit low than that works better for me.
The idea is put the level as high as possible BUT not so high to drip fuel while idling... Be sure the Feedback solenoid is disconnected while you are trying to find the proper level, or consider disable the ECM so it doesn't interferes...
Using the stated value, the float will hang PARALELL to gasket surface, but I found calibrating it a bit low than that works better for me.
The idea is put the level as high as possible BUT not so high to drip fuel while idling... Be sure the Feedback solenoid is disconnected while you are trying to find the proper level, or consider disable the ECM so it doesn't interferes...
Freshman User
Joined: Feb 2007
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i am having this same problems with rough idling. there are 2 screws on the side witch one is which?
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Posting Guru
Joined: Apr 2003
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From: Venezuela
Hi Jondawg, you should try to make first a search with " +Rough +Idle " words, you will find a lot of things to be checked looking for this issue.
Regarding the screws: That one which bolt directly into carburetor body is "Mixture Screw" the another one is "Idle Adjusting Screw". Both of them can be seen from Right Fender.
There is another that can be seen from the Left Fender, side to Climatic Control, this is the "Fast Idle Adjusting Screw"
Get a Carburetor Kit you will find a brochure with Part List.
Regarding the screws: That one which bolt directly into carburetor body is "Mixture Screw" the another one is "Idle Adjusting Screw". Both of them can be seen from Right Fender.
There is another that can be seen from the Left Fender, side to Climatic Control, this is the "Fast Idle Adjusting Screw"
Get a Carburetor Kit you will find a brochure with Part List.
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Postmaster
Joined: May 2004
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Are they building different carbs for Venezuela? Under Hugo's orders?
My 1 bbl has one screw facing the passenger front...kinda hidden...it is the IDLE mixture screw only.
There are two screws facing the drivers side....one is the idle SPEED, the other is the fast idle SPEED. The former dead ends into the carb body.
No screw adjustment for running mixture adjustment.
De nada!
My 1 bbl has one screw facing the passenger front...kinda hidden...it is the IDLE mixture screw only.
There are two screws facing the drivers side....one is the idle SPEED, the other is the fast idle SPEED. The former dead ends into the carb body.
No screw adjustment for running mixture adjustment.
De nada!
Elder User
Joined: Feb 2007
Posts: 629
Likes: 2
From: DFW Metromess, TX.
If this is a variable venturi carb, it's the jets and or the one of the sensors. I had the problem with my 82. Rebuilt the carb at a local shop for like $180.00 back in 1990. Problem solved. They said the venturi goes south after it wears, and doesn't work as engineered. Rebuilding kit replaces the venturi...
Maybe you could buy a kit for like $50.00 now and diy.
Maybe you could buy a kit for like $50.00 now and diy.
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Senior User
Joined: Jun 2002
Posts: 330
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From: Chandler,Arizona - USA
Back from vacation! I took a look at the carb, which is a non-feedback carb. It did have fuel coming out of a nipple down in the center of the barrel. It also had fuel coming out of the thin nipple on the passenger side of the carb. I adjusted the air/fuel mixture to 1 1/4 turns out. Fuel still comes out of the small thin nipple on the passenger side of the carb only. The idle still fluctuates.
Looking at my old feedback spare carb I have lying around, inside where the float is, there is a black hose that goes to the nipple on the passenger side of the carb. Is this part of the accelerator pump assembly? This is the part that is still dripping fuel.
Looking at my old feedback spare carb I have lying around, inside where the float is, there is a black hose that goes to the nipple on the passenger side of the carb. Is this part of the accelerator pump assembly? This is the part that is still dripping fuel.