The Ford Barn

Larry Seemann · 10-07-2011, 06:25 PM

KP, pulling the choke enriches the mixture. Therefor what you're describing indicates a lean mixture situation which is usually caused by a vacuum leak. A vacuum leak can be in the wiper circuit (if the car has a vacuum wiper), or leak where the manifold bolts to the block, or where the carb bolts to the manifold. Do you perchance have a Tillotson carb? They are famous for warping at the flange that bolts to the manifold and sucking in air there.

kp · 10-07-2011, 07:25 PM

Zenith Carb. Dont have vacuum wipers ,outlet is plugged on the manifold.Took a sanding block to carb. flange looked ok ,so did manifold. dissambled carb. today and let it soak in Carb cleaner for about 4 hours blowed it all out ,reassembled according to Andrews book,it does ok if I dont get on it, but if you floor it goin about 35 it coughs and spitts back ,if you feather it it will eventually pick up speed ,compression tested to 55 to 60 on all 4 .Strarts fine and Idles ok ,maybe I'm expecting too much,but I think it still has a problem.At least it runs with the GAV about 1/4 open now where I had to run it couple of turns before. Maybe tomorrow I will try spraying WD 40 around the manifold trying to check for leaks. Bout got me Stumped .

Bill OH · 10-07-2011, 10:05 PM

I use a Triplett Model 60 on the highest DC scale - needle does not move very much.

Bill OH · 10-07-2011, 10:10 PM

I use a Triplett Model 60 and start with the highest DC scale - needle does not move very much.

Purdy Swoft · 10-07-2011, 11:05 PM

I think that the problem is the float setting. you say in a previous post that the float is set at one inch. I believe that the Zenith float should be set at about 5/8 . This would cause a lean condition when you try to accelerate. Not enough gas in the carb because the float is set too low in the bowl of the carb.

jmeckel · 10-08-2011, 09:18 PM

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I had this same problem with my 1929 Tudor, I checked every single wire, replaced condensor, etc. The problem was caused by a new set of points, the soft copper strap that runs with the flat spring was just a tiny bit too long and would short out. All I had to do was put a little bend in the strap to take up the slack, have put on about 400 miles since and no more problems. I have a new point set waiting in case another problem comes up from bending the conductive strap.

Perfdavid · 10-15-2011, 02:41 PM

Well, since I originally posted this thread the problem has been solved.
First I need to thank the awesome crew in our local Ford Model A club here in Baton Rouge.
The people are so nice and knowledgable. I learned so much in this first tune up day I attended.
So, the carb was taken of, we took it completely apart cleaned it and put new gaskets in it. We checked the timing again and cranked it off. Still backfired and didn't have anything near the power of the Ford Speedster I got to drive today. I had one of the really knowledgable guys ride with me and he is adjusting the GAV because it felt like it wasn't getting gas. After some turning and noticing no difference, wham she get full power and took off like a champ. No backfiring and the power increased bigtime. Here is the funny part or kick myself in the head for feeling stupid part but the darn knob was turning but the arm wasn't. Apparently there was a crack in the knob and it wasn't turning the GAV arm. The only thing that makes
Me feel not so bad is that a few of the experienced guys didn't catch it neither. But, guess it never hurts to do do a carb overhaul.
Anyway, thanks for everyone's input on here.

1931 flamingo · 10-15-2011, 04:46 PM

Thanks for getting back with the 'solution".
Paul in CT

48Ratfink · 10-15-2011, 05:05 PM

Quote:

Originally Posted by Perfdavid

Well, since I originally posted this thread the problem has been solved.

After some turning and noticing no difference, wham she get full power and took off like a champ. No backfiring and the power increased bigtime. Here is the funny part or kick myself in the head for feeling stupid part but the darn knob was turning but the arm wasn't. Apparently there was a crack in the knob and it wasn't turning the GAV arm. The only thing that makes
Me feel not so bad is that a few of the experienced guys didn't catch it neither.

Funny I was just going to suggest that!!!Ha,Ha,

J/K!
Now go drive it!!

10-07-2011, 06:25 PM	#21
Larry Seemann Senior Member Join Date: May 2010 Location: Spokane, WA. Posts: 496	Re: Idle screw and backfire KP, pulling the choke enriches the mixture. Therefor what you're describing indicates a lean mixture situation which is usually caused by a vacuum leak. A vacuum leak can be in the wiper circuit (if the car has a vacuum wiper), or leak where the manifold bolts to the block, or where the carb bolts to the manifold. Do you perchance have a Tillotson carb? They are famous for warping at the flange that bolts to the manifold and sucking in air there. __________________ Larry Seemann

10-07-2011, 07:25 PM	#22
kp Senior Member Join Date: May 2010 Location: Kingsland ,Tx. Posts: 234	Re: Idle screw and backfire Zenith Carb. Dont have vacuum wipers ,outlet is plugged on the manifold.Took a sanding block to carb. flange looked ok ,so did manifold. dissambled carb. today and let it soak in Carb cleaner for about 4 hours blowed it all out ,reassembled according to Andrews book,it does ok if I dont get on it, but if you floor it goin about 35 it coughs and spitts back ,if you feather it it will eventually pick up speed ,compression tested to 55 to 60 on all 4 .Strarts fine and Idles ok ,maybe I'm expecting too much,but I think it still has a problem.At least it runs with the GAV about 1/4 open now where I had to run it couple of turns before. Maybe tomorrow I will try spraying WD 40 around the manifold trying to check for leaks. Bout got me Stumped .

10-07-2011, 10:05 PM	#23
Bill OH Senior Member Join Date: May 2010 Posts: 453	Re: Idle screw and backfire I use a Triplett Model 60 on the highest DC scale - needle does not move very much.

10-07-2011, 10:10 PM	#24
Bill OH Senior Member Join Date: May 2010 Posts: 453	Re: Idle screw and backfire I use a Triplett Model 60 and start with the highest DC scale - needle does not move very much.

10-07-2011, 11:05 PM	#25
Purdy Swoft Senior Member Join Date: May 2010 Location: Alabama Posts: 8,099	Re: Idle screw and backfire I think that the problem is the float setting. you say in a previous post that the float is set at one inch. I believe that the Zenith float should be set at about 5/8 . This would cause a lean condition when you try to accelerate. Not enough gas in the carb because the float is set too low in the bowl of the carb.

10-08-2011, 09:18 PM	#26
jmeckel Senior Member Join Date: Sep 2011 Location: Luck WI Posts: 550	Re: Idle screw and backfire Sponsored Links (Register now to hide all advertisements) I had this same problem with my 1929 Tudor, I checked every single wire, replaced condensor, etc. The problem was caused by a new set of points, the soft copper strap that runs with the flat spring was just a tiny bit too long and would short out. All I had to do was put a little bend in the strap to take up the slack, have put on about 400 miles since and no more problems. I have a new point set waiting in case another problem comes up from bending the conductive strap.

10-15-2011, 02:41 PM	#27
Perfdavid Member Join Date: Sep 2011 Location: Louisiana Posts: 54	Re: Idle screw and backfire Well, since I originally posted this thread the problem has been solved. First I need to thank the awesome crew in our local Ford Model A club here in Baton Rouge. The people are so nice and knowledgable. I learned so much in this first tune up day I attended. So, the carb was taken of, we took it completely apart cleaned it and put new gaskets in it. We checked the timing again and cranked it off. Still backfired and didn't have anything near the power of the Ford Speedster I got to drive today. I had one of the really knowledgable guys ride with me and he is adjusting the GAV because it felt like it wasn't getting gas. After some turning and noticing no difference, wham she get full power and took off like a champ. No backfiring and the power increased bigtime. Here is the funny part or kick myself in the head for feeling stupid part but the darn knob was turning but the arm wasn't. Apparently there was a crack in the knob and it wasn't turning the GAV arm. The only thing that makes Me feel not so bad is that a few of the experienced guys didn't catch it neither. But, guess it never hurts to do do a carb overhaul. Anyway, thanks for everyone's input on here.

10-15-2011, 04:46 PM	#28
1931 flamingo Senior Member Join Date: May 2010 Location: new britain,ct 06052 Posts: 9,428	Re: Idle screw and backfire Thanks for getting back with the 'solution". Paul in CT