The Ford Barn

kimlinh · 08-20-2017, 06:25 AM

My newly rebuilt engine does not idle well. Sometimes it will idle slowly and sometimes it needs to be faster to keep from stalling (During the same trip with the car). I think the idle hole is worn a little over sized and maybe that is part of the problem, but I don't know. I have played with the GAV, float level, advance, etc. But I'm not sure where these will work best. I'm looking for some advice on getting a good, constant, reliable idle at something less than 2000 RPM. I suspect the carburetor is the main problem but I'm not sure.

Thanks in advance

Mike V. Florida · 08-20-2017, 06:40 AM

It is my opinion that the engine is still breaking in and as such you are having idle problems.

Patrick L. · 08-20-2017, 06:44 AM

Getting one of these monsters to 'idle at something less than 2000 RPM' should not be a problem.
That said, I don't think I'd want one that idles for any length of time at less than 200 rpm.
If it idles in the 400-500 rpm range then I don't see a problem.

I'd recommend looking at the throttle shaft bushings, throttle plate centering in the venturi, correct idle mix adjustment, distributor shaft bushing condition.

Bob Bidonde · 08-20-2017, 07:28 AM

Mike has it right. The motor will be somewhat erratic until it breaks-in. I adjust the carburetor idle mixture with the GAV 1/8 of a turn open. Set the idle speed fast enough to prevent stalling, and use the hand throttle to optimize the idle speed while driving.

Before adjusting the carburetor, be sure that the ignition timing is set, the spark plugs gaps are set, and the motor is at operating temperature.

Jacksonlll · 08-20-2017, 08:12 AM

Make sure you don't have an intake air leak. Could be the manifold, (hard to find), the gaskets, or a leak where the carb attaches to the manifold. File both surfaces flat,(clean them up) then use a new gasket. An engine at idle does not like extra air.

Marshall V. Daut · 08-20-2017, 09:33 AM

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What carburetor are you running? If it's a Tillotson, then in addition to experiencing new, tight engine symptoms (as has been suggested), it's very likely that the mounting flange is warped into a "saddle" shape. Because the Tillotson replacement carburetor is made of pot metal, it is prone to warpage due to the heat transferred from the exhaust manifold flange. This will most definitely cause erratic idling. Air will be sucked in through the gap in the low point of the "saddle" warpage. Putting in a second manifold flange gasket between the carb and exhaust manifold usually won't compensate enough for the gap.
To check, remove the carb and gasket. Lay a metal (not wood) straight edge across the length of the carb's flange. Doing this with the edge down, not the breadth laying flat. You are trying to create an inflexible straight edge to use as a trueness guide. A metal ruler works well here. Then take a strong light and shine it from behind. If you can see light in the center above the throttle hole, the flange is drooping in the center.Alternately - and perhaps better - run a feeler gauge underneath the straight edge, say .005" to start. You will not be able to get it underneath at the flange's mounting holes (the high spots), but will undoubtedly be able to easily slip it under the straight edge in the middle (the low spot). That small of a gap is a not a problem. Go to a thicker feeler gauge and test again. Chances are, you will find a gap of way, way more than .010". You will be shocked at the droop.
To correct the problem, secure the carb in a vise. Be sure to protect it with towels or wooden blocks. Pot metal breaks easily under pressure! Use a very sharp file and carefully run it across the top of the flange lengthwise. The first few passes will create shiny ends, but leave the center dark because the file passes right over the droop. Keep filing until the entire flange is shiny silver. Try to stay as flat and level as you can with the file so that you don't create a slant. Turn it upside down on a known good flat surface and shine a light on one side. The carb should sit level and not allow light to pass beneath the center of the flange. Replace the gasket and re-mount the carb. Start the engine and re-adjust the GAV, idle mixture screw on the side of the carb and the idle speed set screw once the engine has warmed up a bit. You will notice a better, more steady idle.
If, however, you have an original and far superior Zenith (when PROPERLY rebuilt) carb, ignore all this information. Zeniths do not warp here. The problem will be found inside, especially if a rebuild kit has been installed. These are usually made of any parts from any vehicle (usually tractors) that will screw into place, regardless of orifice size or jet length and flow rate. Use original parts if possible. Be sure the Zenith's passageways are clean and the other parts fit properly. That's the secret to making a Zenith work the way it was designed. 5,000,000 Model A's didn't leave the factory with a terrible idle and malfunction for millions of owners for almost 90 years.
Marshall

larrys40 · 08-20-2017, 09:54 AM

Agree with Mike and the guys above. New engines need 500-1k+ miles break in. It is noticeable how much better they run once you have some miles on them. Having said that I usually get things dialed in so they run smoothly anyway even when fresh. It's a balance of good ignition with a well rebuilt distributor, carb done well (as Marshall noted) and as Jackson noted make sure you don't have any air leaks. Manifolds are planed and decked and checked with a straight edge and feeler guage test ( I use .0025 as my guide) and also the associated vaccuum line and rubber hose to the wiper including the wiper motor is not leaking.

Make sure your manifolds are tight and carb as well. I think with all that done and timed properly with good fuel/air mixture you will find it to be much better.

Good luck and happy break in motoring!
Larry Shepard

RawhideKid · 08-20-2017, 11:01 AM

IF you find that the carb mating surfaces are warped, an easier way of resurfacing that face is a piece of wet/dry sand paper and a small pane of glass. Lay the glass down flat, place th sand paper on the glass, and rub the top of the carb on the glass, this way, even if you should get it cocked to the side, the surface will remain flat.

Big hammer · 08-20-2017, 11:20 AM

Fresh rebuild engine, it's time too rebuild the accessories!

mike657894 · 08-20-2017, 03:32 PM

you cant idle below 2k? my car sounds like its coming apart if I get it to 2k in the garage. I idle around 800rpm. Im with jack on the intake leak. thats when my car had a high idle.

msmaron · 08-20-2017, 05:11 PM

Quote:

Originally Posted by larrys40

Agree with Mike and the guys above. New engines need 500-1k+ miles break in. It is noticeable how much better they run once you have some miles on them. Having said that I usually get things dialed in so they run smoothly anyway even when fresh. It's a balance of good ignition with a well rebuilt distributor, carb done well (as Marshall noted) and as Jackson noted make sure you don't have any air leaks. Manifolds are planed and decked and checked with a straight edge and feeler guage test ( I use .0025 as my guide) and also the associated vaccuum line and rubber hose to the wiper including the wiper motor is not leaking.

Make sure your manifolds are tight and carb as well. I think with all that done and timed properly with good fuel/air mixture you will find it to be much better.

≈
Good luck and happy break in motoring!
Larry Shepard

Best Advise so far!!

kimlinh · 08-20-2017, 05:42 PM

Mike- I was kidding about the 2k . My car just doesn't idle consistently. I don't know the RPM, I don't have a tachometer. The engine will be Idling good one minute and then start stalling the next. sometimes I must use a high idle and sometimes it will idle slower. I'm not trying to get a very slow Idle, I just want something that seems normal and doesn't stall. I don't think its an intake leak, but I could have missed it. I'll check again.

08-20-2017, 06:25 AM	#1
kimlinh Senior Member Join Date: Nov 2014 Location: Middlebury,Connecticut Posts: 100	Advice on Idle settings My newly rebuilt engine does not idle well. Sometimes it will idle slowly and sometimes it needs to be faster to keep from stalling (During the same trip with the car). I think the idle hole is worn a little over sized and maybe that is part of the problem, but I don't know. I have played with the GAV, float level, advance, etc. But I'm not sure where these will work best. I'm looking for some advice on getting a good, constant, reliable idle at something less than 2000 RPM. I suspect the carburetor is the main problem but I'm not sure. Thanks in advance

08-20-2017, 06:40 AM	#2
Mike V. Florida Senior Member Join Date: May 2010 Location: South Florida Posts: 14,054	Re: Advice on Idle settings It is my opinion that the engine is still breaking in and as such you are having idle problems. __________________ What's right about America is that although we have a mess of problems, we have great capacity - intellect and resources - to do some thing about them. - Henry Ford II

08-20-2017, 06:44 AM	#3
Patrick L. Senior Member Join Date: May 2010 Location: Largo Florida Posts: 7,225	Re: Advice on Idle settings Getting one of these monsters to 'idle at something less than 2000 RPM' should not be a problem. That said, I don't think I'd want one that idles for any length of time at less than 200 rpm. If it idles in the 400-500 rpm range then I don't see a problem. I'd recommend looking at the throttle shaft bushings, throttle plate centering in the venturi, correct idle mix adjustment, distributor shaft bushing condition.

08-20-2017, 07:28 AM	#4
Bob Bidonde Senior Member Join Date: May 2010 Location: Long Island, NY Posts: 3,463	Re: Advice on Idle settings Mike has it right. The motor will be somewhat erratic until it breaks-in. I adjust the carburetor idle mixture with the GAV 1/8 of a turn open. Set the idle speed fast enough to prevent stalling, and use the hand throttle to optimize the idle speed while driving. Before adjusting the carburetor, be sure that the ignition timing is set, the spark plugs gaps are set, and the motor is at operating temperature. __________________ Bob Bidonde

08-20-2017, 08:12 AM	#5
Jacksonlll Senior Member Join Date: Jul 2012 Location: Michigan-- Member of Oakleaf of MARC Posts: 1,686	Re: Advice on Idle settings Make sure you don't have an intake air leak. Could be the manifold, (hard to find), the gaskets, or a leak where the carb attaches to the manifold. File both surfaces flat,(clean them up) then use a new gasket. An engine at idle does not like extra air.

08-20-2017, 09:33 AM	#6
Marshall V. Daut Senior Member Join Date: Apr 2011 Location: Davenport, Iowa Posts: 2,110	Re: Advice on Idle settings Sponsored Links (Register now to hide all advertisements) What carburetor are you running? If it's a Tillotson, then in addition to experiencing new, tight engine symptoms (as has been suggested), it's very likely that the mounting flange is warped into a "saddle" shape. Because the Tillotson replacement carburetor is made of pot metal, it is prone to warpage due to the heat transferred from the exhaust manifold flange. This will most definitely cause erratic idling. Air will be sucked in through the gap in the low point of the "saddle" warpage. Putting in a second manifold flange gasket between the carb and exhaust manifold usually won't compensate enough for the gap. To check, remove the carb and gasket. Lay a metal (not wood) straight edge across the length of the carb's flange. Doing this with the edge down, not the breadth laying flat. You are trying to create an inflexible straight edge to use as a trueness guide. A metal ruler works well here. Then take a strong light and shine it from behind. If you can see light in the center above the throttle hole, the flange is drooping in the center.Alternately - and perhaps better - run a feeler gauge underneath the straight edge, say .005" to start. You will not be able to get it underneath at the flange's mounting holes (the high spots), but will undoubtedly be able to easily slip it under the straight edge in the middle (the low spot). That small of a gap is a not a problem. Go to a thicker feeler gauge and test again. Chances are, you will find a gap of way, way more than .010". You will be shocked at the droop. To correct the problem, secure the carb in a vise. Be sure to protect it with towels or wooden blocks. Pot metal breaks easily under pressure! Use a very sharp file and carefully run it across the top of the flange lengthwise. The first few passes will create shiny ends, but leave the center dark because the file passes right over the droop. Keep filing until the entire flange is shiny silver. Try to stay as flat and level as you can with the file so that you don't create a slant. Turn it upside down on a known good flat surface and shine a light on one side. The carb should sit level and not allow light to pass beneath the center of the flange. Replace the gasket and re-mount the carb. Start the engine and re-adjust the GAV, idle mixture screw on the side of the carb and the idle speed set screw once the engine has warmed up a bit. You will notice a better, more steady idle. If, however, you have an original and far superior Zenith (when PROPERLY rebuilt) carb, ignore all this information. Zeniths do not warp here. The problem will be found inside, especially if a rebuild kit has been installed. These are usually made of any parts from any vehicle (usually tractors) that will screw into place, regardless of orifice size or jet length and flow rate. Use original parts if possible. Be sure the Zenith's passageways are clean and the other parts fit properly. That's the secret to making a Zenith work the way it was designed. 5,000,000 Model A's didn't leave the factory with a terrible idle and malfunction for millions of owners for almost 90 years. Marshall Last edited by Marshall V. Daut; 08-20-2017 at 04:38 PM.

08-20-2017, 09:54 AM	#7
larrys40 Senior Member Join Date: May 2010 Location: St Charles , Missouri Posts: 1,998	Re: Advice on Idle settings Agree with Mike and the guys above. New engines need 500-1k+ miles break in. It is noticeable how much better they run once you have some miles on them. Having said that I usually get things dialed in so they run smoothly anyway even when fresh. It's a balance of good ignition with a well rebuilt distributor, carb done well (as Marshall noted) and as Jackson noted make sure you don't have any air leaks. Manifolds are planed and decked and checked with a straight edge and feeler guage test ( I use .0025 as my guide) and also the associated vaccuum line and rubber hose to the wiper including the wiper motor is not leaking. Make sure your manifolds are tight and carb as well. I think with all that done and timed properly with good fuel/air mixture you will find it to be much better. Good luck and happy break in motoring! Larry Shepard

08-20-2017, 11:01 AM	#8
RawhideKid BANNED Join Date: Apr 2017 Location: Lower Left Coast Posts: 469	Re: Advice on Idle settings IF you find that the carb mating surfaces are warped, an easier way of resurfacing that face is a piece of wet/dry sand paper and a small pane of glass. Lay the glass down flat, place th sand paper on the glass, and rub the top of the carb on the glass, this way, even if you should get it cocked to the side, the surface will remain flat. __________________ Before Walmart you had to buy a ticket to the fair to see a bearded lady!

08-20-2017, 11:20 AM	#9
Big hammer Senior Member Join Date: Jun 2014 Location: Land of Lincoln Posts: 3,131	Re: Advice on Idle settings Fresh rebuild engine, it's time too rebuild the accessories! __________________ Don't force it with a little hammer tap, tap, tap get a bigger hammer tap done

08-20-2017, 03:32 PM	#10
mike657894 Senior Member Join Date: Oct 2015 Location: Bay City Michigan Posts: 1,050	Re: Advice on Idle settings you cant idle below 2k? my car sounds like its coming apart if I get it to 2k in the garage. I idle around 800rpm. Im with jack on the intake leak. thats when my car had a high idle.

08-20-2017, 05:42 PM	#12
kimlinh Senior Member Join Date: Nov 2014 Location: Middlebury,Connecticut Posts: 100	Re: Advice on Idle settings Mike- I was kidding about the 2k . My car just doesn't idle consistently. I don't know the RPM, I don't have a tachometer. The engine will be Idling good one minute and then start stalling the next. sometimes I must use a high idle and sometimes it will idle slower. I'm not trying to get a very slow Idle, I just want something that seems normal and doesn't stall. I don't think its an intake leak, but I could have missed it. I'll check again.