Idle adjustment problem

R

REByar

Member
I have a 1928 Tudor. The idle is too high. If I lower it, it will easily go into first gear. But when I have to come to a stop the engine will die. Like it has run out of gas. I can move up the idle but then I grind the gears to get it into first. But it will run fine and if I have to stop the engine will not die. I have adjusted the advance a little but that does not seem to make any difference. I have had the car about 3 years. Soon after I purchased it I cleaned out the gas tank, cleaned and sealed the iron sed bowl and installed new fuel lines and installed a rebuilt Zenith carb. I had the engine rebuilt about 9 months ago. Before the rebuild sometimes if the engine had been running more than 20 min this would not always be a problem. I could get the idle set for the most part. But since the engine rebuild it is a problem all the time. I am sure it is an adjustment issue but I just do not know what to adjust. Any advice would be greatly appreciated.
Thanks
REB
 
Your brakes are too good and make you stop too quickly.:D

My 28 will do the same thing when I stop quickly. I let the engine brake until I'm about 10 or 15, then I shift to neutral and brake easy. The engine will slow some as I'm decelerating, but it won't die. If I have to brake quickly then I can either tap the throttle before hitting the brake pedal, or pull the throttle lever down a click.
 
Well now after reading your other drivability thread, i thnk you have more going on than the float. It would be better to post all the information in one thread.
http://fordbarn.com/forum/showthread.php?t=215519

Try contacting the local club to help you out with a diagnosis instead of replacing parts

Checking for spark and fuel is a basic first step when a car wont start
 
I recently had a similar issue happen after fiddling with the gav and idle mixture screw. Long story short, i believe you're Gav and idle are not set properly. My thoughts are your A dies when the idle is low because it's getting too much gas not starving. Hence the fouled plugs. My suggestion is start with a fully seated gav. Back it out 1/4 -1/2 turn. Then seat the idle mix screw. Back that out the recommended turns which I believe are 3 full turns. Set the screw on the carb that adjusts the accelerator to a little before the lowest setting. Start there. Hopefully that gets you driving around decent. The final adjustments I believe are recommended once the engine is at normal operating temps. I would leave the gav alone and only tweak the idle and accelerator adjustments. Hope that helps.
 
That dieing problem is quite common, especially if you have GOOD brakes. That's why Henry re-designed the carb.
I used to just leave the throttle down a couple of notches, while driving, EASY!
Bill Fastidle
 
I am a little confused about this stalling when braking hard. My car does this only when cold or sometimes when stopping going down a very steep hill. Some say the carb is too rich some say to lean. It seems to me that when you put on the brakes the gas in the float bowl would move away from the jets thus making your mixture too lean. So making the float level a little higher and or the idle jet a little richer would help. Am I missing something?
 
It's just the gas sloshing around in the LOOONG fuel bowl & driving the float CRAZY. Tillotsons DON'T do that, because of the design of the fuel chamber & the float.
Bill W.
 
BILL WILLIAMSON said:
That dieing problem is quite common, especially if you have GOOD brakes. That's why Henry re-designed the carb.
I used to just leave the throttle down a couple of notches, while driving, EASY!
Bill Fastidle
Click to expand...

I'd think if it was a bad carb design, then ALL Model A's would exhibit the "stall when stopping" problem.

Sort of like blaming drivability problems on "crap gas". Plenty of A's out there running "crap gas" with no drivability problems.

A Model A should be able to idle quite slowly and stop quickly (slide tires) without stalling.

I'd start with the carb. All internal passages clear? Throttle shaft not loose? Float level set correctly? Jets not clogged or damaged? No vacuum leaks?

If that checks out...Points set to spec? Timing to spec? Valve adjustment to spec? Good, even compression on all cylinders?
 
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A small intake leak can cause this also. At road load, the leak means nothing, but at idle, it is a big part of what the engine gets. Too lean. The easy thing to do is to make sure the two surfaces of the flanges where the carb attaches to the manifold are flat. Clean them up with a file. File until the whole surface is shiny. For the manifold, use a light and mirror and a big file. Then use a new gasket. Beyond this, it could be a small air leak in your manifold gasket.
 
wmws said:
I am a little confused about this stalling when braking hard. My car does this only when cold or sometimes when stopping going down a very steep hill. Some say the carb is too rich some say to lean. It seems to me that when you put on the brakes the gas in the float bowl would move away from the jets thus making your mixture too lean. So making the float level a little higher and or the idle jet a little richer would help. Am I missing something?
Click to expand...

That is exactly what I figured when I had this problem years ago but I followed the advice given by a Model A guru and lowered the fuel level. It worked.
 
I had the same problem in my Model A of 1929. When the engine was in idle, had too much air, because the idle screw was very unscrewed. I solved it by screwing the idle screw all the way to the bottom and leaving it tight between a turn or a turn and half unscrewed. Engine at working temperature and open gav 1/4 turn when you are doing the adjustment.
 
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Synchro909 said:
That is exactly what I figured when I had this problem years ago but I followed the advice given by a Model A guru and lowered the fuel level. It worked.
Click to expand...

By lowering the fuel level, do you mean you adjusted the float to give more or less than 5/8" fuel level from the bowl half?

Thanks.
 
I inadvertently installed the jets incorrectly (yes, they will screw in the carb body in the wrong position and will run) after engine rebuild. Took two days to troubleshoot the problem. Installed the jets in the correct hole and it ran fine. No more stalling. Hope this is your problem so you can get it resolved. Tom
 
X2 on what Bill has said. I have fixed a few A's now that had this problem by simply lowering the idle speed.

Idle fuel comes from secondary well which is not immediately effected by bowl level or slosh (takes a little time to adjust level thru jet). GAV is directly effected by bowl level and slosh very quickly.

It is interesting to note based upon porting in the intake that Henry intended the motor to idle very slowly - throttle butterfly barely cracked open.

I personally do not like idling that slow (generator) and will increase it until the GAV has only a slight effect - I make out just fine with fast stops.
 
I'm a big fan of the Marvel carbs for the reason you state...they don't die on hard brake...because the float is mounted on the side, not lengthwise.
Can be found on Ebay or rebuilt at rennerscorner.com.
 
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