Black smoke and gav

Perfdavid

Perfdavid

Member
This past weekend we took off the carb (tilloston), took it apart, cleaned it and put on all new gaskets. Inoticed today that she is emitting dark exhaust. So, I adjusted the Gav and the idle screw. If I open the gav at all she starts to run rough. However, fully closed she likes. Also, when I cut off the gas and let her carb run out she quit emitting the smoke. Guess my point is, after adjusting the gav and the idle, she still puts out dark fumes while idling. She did not do this before this weekend.
Any ideas or suggestions? Thanks guys
 
Sounds to me like you got the float out of adjustment when you had it apart. This may happen when the float is set to high. I think that the key is that when you turn off the gas it runs better.
Darryl
Fairbanks
 
the way i adjust the float is get it level and then bend the tab till the gas comes half way up the float in the bowl, not the purists way of doing it but its quick and it works
 
Thanks guys. I just went outside and took off the carb and adjusted the float. I also think I was idling too low. So, I adjusted the screw a little. (actually, I adjusted the screw first and it was still kicking smoke). That's when I went to the float. Problem solved. Once I cranked her off, got her idling well, no smoke and she quit shaking too. Thanks again!
 
Ok, problem not solved. Running real rough. I adjusted the float again this time in the middle of my other two tries and it didn't help. Does anyone know the distance the model x carb float is suppose to be set?
 
Most carb kits come with a cardboard float gauge. I usually set the float top to be level when the carb is level. You might have a sticky needle valve.
 
The best that I remember, the float setting for the Tillotson model X and XF is one inch. Float setting is important but I don't think that it would cause rich ideling. If the float is too high it will cause leaks and stalling when the brakes are applied. When the float is to low it will cause a lean condition and backfire when you try to accelerate. It sounds like the GAV needle isn't properly seating.the needle housing may not be tightened down far enough and the adjusting needle may not be properly reaching the seat.
 
Rightly or wrongly, I usually check the float level by looking down the throat of the carburetor at the main jet. I have the carb on the bench on a test stand so that I can put gas in the carb and watch for leaks. If you look at sketches of a Model A carburetor in the manual you will see that the gas level in the bowl places the gas level in the main jet very near the top of the jet. This makes sense because when running, the gas has to be near the top of the jet for the carb vacuum to lift the gas out of the jet. If the gas is too high in the bowl, the gas will spill over the jet and the carb leaks. If the gas is too low, you will not be able to see any gas in the jet. Care must be taken to be sure the gas in the jet does not spill over if the car is parked on a hill! I try to get the the gas level within 1/32 in. of the top of the jet. Set the gas level using the correct dimensions and then check your work looking down the throat of the carb at the jet. Good luck, Ed
 
Took off the carb today. Tok it apart. Measured the float. Took apart the gav needle. Put it all back together and still running poor. Checked timing again and it is dead on. Have a friend from our club coming over tomorrow to have a look. Oh, and also bought another tillotson x from a guy in TX who rebuilds em. No core needed to be sent in and got it for $150. Can't hurt to have an extra one around even if I get this one fixed.
 
Thanks, Steve. Let me see what we find tomorrow. I am pretty green but am trying. My buddy is an expert, so I will post tomorrow what we find.
 
ok, once again, 3 basic things that make a carb run rich on a model a, the gav seat or rod is worn and letting to much gas in the engine, bad needle and seat, float to high or has some fuel in it and not letting the needle and seat close, you say it started after working on the carb, so go back over what you did, strip carb down and do it all over again
 
I have. Float is fine. Took GAV needle apart and it seats well. I have a new GAV rod on the way. Hopefully we will figure it out tomorrow. Thanks for everyone's help.
 
Well,problem temporarily solved. Took out the plugs and they were fouled pitch black.
Cleaned em and it ran well. But why did it run rich to begin with and will it happen again? Could having the gav open too much cause this? I experimented and opened it up and idled low, it blew out dark smoke. I closed it to 1/8 and idled a little higher and it didn't. I am concerned it might happen again. Where should my idle be. Real low or higher? Will a low idle cause it to run rich and carbon up the plugs?
 
i should idle around 450 rpm, if you cleaned the plugs recently and there sooty again you still have a rich running problem, and untill you find out why its runnibg rich the problem will keep returning
 
Perfdavid said:
Well,problem temporarily solved. Took out the plugs and they were fouled pitch black.
Cleaned em and it ran well. But why did it run rich to begin with and will it happen again? Could having the gav open too much cause this? I experimented and opened it up and idled low, it blew out dark smoke. I closed it to 1/8 and idled a little higher and it didn't. I am concerned it might happen again. Where should my idle be. Real low or higher? Will a low idle cause it to run rich and carbon up the plugs?
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When the GAV is opened too much after warm up it will cause the engine to have a slow lopey idle and puffs of black smoke will be emitted and the spark plugs will get black and sooty. It sounds to me like you are tring to use the GAV to control idle speed, this is incorrect procedure. I usually run the GAV 1/4 turn open after warm up. Ethanol laced gas may require the GAV to be opened a little more but not to the point that the engine begins to lope and smoke. Set the idle speed with the screw on the throttle lever on the carburetor. You can fine tune the idle circuit with the air adjust screw on the carb. I start the air adjust screw at 1 1/2 turns off the seat. Turning the idle adjust screw clockwise richens the idle mix, counter clockwise leans the idle mix. If the engine lopes and emits black smoke close the GAV. It may take a few seconds for the smoke to subside. If it runs good with the GAV closed completely that will be ok. Usually Tillotson carbs run leaner than Zenith carbs because the pot metal warps from heat and over tightening at the flange, this in turn causes vacume leaks and a lean condition. Good luck, maybe you just need practice adjusting the GAV .
 
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