What would cause this...carburator

T

tyler

Senior Member
Got my electrical problems fixed, buttoned everything back up and to my amazment, the car started. Thought I' let it run for a while as it hasn't been run all winter. Started it with the gav open a little less than three quarters turn, after it warmed up a bit, closed the gav to 1/4 turn, where it normally runs well when warm. Was running fine but after 5 minutes or so it started running rough and to smooth it out, I had to OPEN the gav 3/4 turn.
What would cause this and what can I do to fix it? All stock setup, carb rebuilt last year.
Thanks

Tyler
 
Opening the GAV, riches the mixture, so it sound like the Carb. was leaning out. Check your Carb. and see if the main jet is getting clogged up with something. The Zenith Carb. is very easy to clean and blow out all the passages. The new gas with ethanol is bad to leave deposits in the float bowl. I redid a Carb. last year the looked like it was full of baking soda. I soaked the Carb.in white vinegar for a few hours and it cleaned up really nice and worked great.
 
Starting to run rough after warmup can be due to premature fuel vaporization (fighting words) or thermal expansion either opening up a vacuum leak or creating a poor electrical connection. The fact that opening the GAV cured it, eliminates the last one but leaves the first two, IF the behavior is reproducible after car sits over night again.

If it runs rough from the get-go the next time you start it, I would suspect a piece of crud has found its way into one of the carb jets. Try the carburetor Heimlich: momentarily race motor via throttle shaft while simultaneously completely covering carb air intake with palm of hand and then quickly pulling it away before motor dies. Probably smart to wear a glove in case of backfire. The tremendous vacuum created by racing the motor WILL pull anything caught in the jets on through. Might have to repeat a few times.

Steve
 
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When mine acts that way I find it's usually the in- carb filter and take it out,blow through it and it's ok then. Only happens when about 1/4 or less in the tank. I know,I know! I need to clean the tank!
 
I'll try all your suggestions in the morning and see what happens. I'll report back with my findings. Thanks again, guys.

Tyler
 
Contenderizer, that was what I was going to say also. Once she is warmed up and expanded it sounds like a vacuum leak developed hence the need to correct the A/F ratio.... check the throttle plate shaft area, carb to intake gasket, intake to block gasket and possibly the vacuum wiper and associated lines.
 
O.K., what's the best way to check for a vacuum leak and where is the throttle plate shaft? I put all new manifolds and gaskets on the engine last summer, was very carefull to make sure everything snugged up several times after running the car some. Don't have a vacuume wiper so that's out. Thanks again.

Tyler
 
tyler said:
O.K., what's the best way to check for a vacuum leak and where is the throttle plate shaft? I put all new manifolds and gaskets on the engine last summer, was very carefull to make sure everything snugged up several times after running the car some. Don't have a vacuume wiper so that's out. Thanks again.

Tyler
Click to expand...

The throttle shaft is connected to the arm, which connects to the linkage on back to the gas pedal.

To check for a vacuum leak I like to use a propane torch UNLIT. Just turn the torch valve open a little and use it to sniff around the carb and manifold. If there is a leak, it will suck in the propane and make the engine run faster and smoother.
 
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