Idle problem...at wit's end

[birdguy45]

I have been tearing my hair out for the last few days trying to figure out why I can't get my A to idle properly. The engine has about 600 miles on it since a complete overhaul by a professional garage (Hansen's in Ramona, CA); it had a complete electrical system restoration about a week ago by a professional Model A mechanic (Ron Alley in Culver, OR). Ron also rebuilt the carb and assured that all the jets are the correct size and correct heights, as well as setting the float height using a sight gauge. The carb works perfectly on one of his A's, but on mine there is a problem. The timing has been set correctly, and the distributor has high-quality modern points and condensor. The compression was tested a couple of days ago, measuring 90, 80, 90, 90 pounds. Interestingly, when shorting each plug to the block, numbers 1,2, and 4 cause the expected slight decrease in engine speed; shorting #3 stalls the engine immediately. I have tried another distributor upper body and cap, thinking there might be a problem with leakage...no joy.

After considerable time adjusting the idle speed and mixture, I can get the engine to idle (fully retarded) at about 400-450 RPM, but it lopes when idling; on the road, with the timing at full advance, the engine runs great and has excellent throttle response. I have attached an audio file (zipped to allow posting) that captures the sound of the loping (15 sec recorded next to the engine followed by 15 sec near the tailpipe.

Any ideas or suggestions for ways to further troubleshoot the problem are most welcome. TIA for any help!

[DaWizard]

I would ask a couple questions.

What is the gap on the plugs?
What is the gap between the rotor and the cap?
Are you using stock cap and blade "wires"?
Is that sound at full retarded?

That doesn't sound bad if it smoothes out at advanced.

[birdguy45]

Thanks for the quick reply, DaWizard! Answers follow.

I would ask a couple questions.

What is the gap on the plugs? .030
What is the gap between the rotor and the cap? don't know, but all are equal by eye
Are you using stock cap and blade "wires"? yes and yes
Is that sound at full retarded? yes

That doesn't sound bad if it smoothes out at advanced.

[DaWizard]

Ok, what plugs are you running?
You really should check the gap between the rotor and cap, that needs to be less than the gap on the plugs.
I would take the plugs to .035 gap

Taking the plugs to .035 may smooth it out if the gap on the rotor to cap is at or more than .030.

One other question, what is the GAV set at?

[DaWizard]

There are a few things that contribute to loping. Since you have a strong spark, and shorting the #3 plug and having it stop the engine tells me that something in the distributor isn't playing well with the others. What I would do is unhook the #3 blade from the distributor while running and see what happens. Now you are going to tell me it can't be done without getting shocked, so I will let you in on a secret. As long as no other part of your body is against the car, even with the insulation of a pair of jeans you will get zapped. See, the coil is putting out enough to jump a .035 gap, so you need to be further than that from the car, you can remove the strip from the distributor.

I am wondering how the engine runs with the #3 unhooked.

Couple other things. You say a fresh build with only 600mi. Well, that engine is still kinda tight, do you use MMO in the gas?
Why is that #2 cylinder only 80#?
What head do you have on it?
Have you used the starter fluid trick to see if you have an intake leak?
Has the engine overheated since the rebuild?
What do you use for engine temp monitoring?
How many times have you torqued the head, and to what torque?

Rereading your post, I found something else, you can't set the float height using a sight gauge, it will tell you how much gas you have in the bowl, but not much more, and if it runs fine on his car and not yours, you have an intake leak. Which gasket do you use to between the manifold and carb? If you have one of the copper type, I recommend using a paper style and using a slight bit of assembly lube to seal it up.

[DaWizard]

For the carburetor there are basically 3 measurements that need to be perfect.

The float needs to be FLAT 1" from the top. That means taking the measurements at at least 3 places. I have a dial caliper that I set at 1" and measure at the outer tip to the edge of the seam on the float, then back to either side of the float pivot. I have found that when you turn the carb top upside down, the float needs to be not just closed, but flat to the top.

The other two settings are the Main Jet needs to be set at 3/8 (.375) from the top lip of the bowl, and the Cap jet needs to be 7/16 (.4375) from the same bowl top.

These are the correct dimensions for setting up the carburetor. If the float needle is closed and you have 5/8" of fuel, it still won't be right, you need to be parallel with top for the float to close properly with an even pressure on the needle.

[Mitch]

As Wiz mentioned at full retard you will get that little lope. From the information provided i wonder if you have a problem at all. How does it idle at 1/4 advanced? I didn't see it mentioned but what carb are you running?
I only full retard it for start up and sometimes right before shut down but not always

[Sunnybrook Farm]

You might want to put the timing pin in to where it engages the hole in the timing gear and then remove the #1 plug and verify that the piston is at dead top. This will make sure the gear is on the right tooth of the crank gear. It is probably fine but I have hear of them being one tooth off. Also if you had weight removed from the flywheel, it might not idle like original. It does sound like the distributor but I can't imagine what it would be other than the cam touching something as it spins by #3.

[BILL WILLIAMSON]

WHOA, BACK UP, if the carb runs good on the other car, then it must be OK!
I'd first try checking for INTAKE leaks, with a CHEAP Stethescope, using just the open hose (no probe)
Bill W.

[DaWizard]

WOW, was I up late last night, or what? Sorry folks for getting so long winded, I don't know what came over me.

[Ray Horton]

I can't open the sound file, but any properly tuned Model A should lope without stalling when fully retarded, and run smoothly when the spark lever is about 9:00. I'm not sure you have a problem. How long have you been into Model A's?

There are many helpful and knowledgeable A guys in Bend. Bill Barlow is one of the best. Are you a member of the High Desert A's? If not, join up, and ask one of your local experts.

[Ed H]

WHOA, BACK UP, if the carb runs good on the other car, then it must be OK!
I'd first try checking for INTAKE leaks, with a CHEAP Stethescope, using just the open hose (no probe)
Bill W.

That was my first thought, vacuum leak.

[Mitch]

Here ya go
https://www.vintagefordforum.com/for...-leak-detector
OR

better yet smoke it


9D33D9E5-81D9-4B68-80F8-4990F4CCC6AEL0001.jpg

[Mitch]

I/m still thinking you may not have an issue, but keep us posted on any new developments

[birdguy45]

Just a quick note to let y'all know what has been going on. Between visits to the vet with a sick dog and trying to keep him comfortable at home, I managed to get to Ron's and we found one problem: an air leak in one of the intake manifold ports (visible in the attached photo at about 10:00). We put on another manifold and the loping decreased significantly, but it's still there. I will reset the timing soon and see if I can finally even it out.

I really appreciate all of the interesting ideas and suggestions presented by y'all...I have learned a lot. This is my first Model A, and I have much more to learn! I'll keep you posted with my progress.

[DaWizard]

Yes, that looks like it is cracked back further than just the visible area in the picture, a good source of problem. Thanks for the update.

[tbirdtbird]

Thanks for the update.
1) I would still use the timing pin as mentioned to double check the indexing of the crank gear with the timing gear on the cam. It is easy for a mechanic to get it one tooth off.
2. You did not say if you only just changed out the intake manifold, or both the intake and the exhaust as a pair.
For best performance, the two manifolds need to be assembled together, taken to a machine shop, and have both surfaces trued at the same time. Else you can have small devilish intake or exhaust leaks. If the engine is running better, you may decide to skip this step, but it is worth the effort. Unless they are machined together they are seldom in the same plane.
3. I too wonder why the compression readings are not all the same on a new rebuild. I'd start by repeating the compression test. Be sure all 4 plugs are out, and that the throttle is wide open, and give the motor at least 3 full revolutions when cranking, but usually until the gauge stops rising.
4. I am totally baffled as to why shorting #3 stops the motor dead. I would get a spark tester and put it in the high tension wire to the center of the dizzy cap to visually see if it is the spark actually failing from the coil. If so, I suspect there is some sort of short, crossfire, leakage, or something going on. It may require more testing. Post more info about that and we can walk you thru it step by step.
5. This is your first A, but from the way you have written it seems like you have worked on cars before. Why else would you have a compression gauge in your back pocket. A spark tester is a handy diagnostic tool to have.
6.Wiz, are you non-conductive? Is that why you be the Wiz? LOL. Every time I have removed a plug wire or strap by hand I have gotten zapped. It is 10,000 volts trying to find a home. If you use a plastic handled screwdriver you can slip them off. However, having said that, this can be detrimental to the coil because that voltage has to go somewhere and it can backfeed and damage the insulation of the coil windings. Better to just short the plug with a screwdriver

Here is a link to typical spark testers
https://www.amazon.com/s/ref=nb_sb_n...s=spark+tester

[DaWizard]

Oh no, I am definitely conductive. If I don't consciously keep away from the fender, that will jump up and bite me. I may just be a bit more resilient than most, having been zapped by some nasty voltages.

[tbirdtbird]

Haha, OK you must have long arms! LOL

[DaWizard]

Oh no, regular length, I have just learned how to bend at the waist!

[Rowdy]

Glad you found it. Sorted through all of my intakes last week and scrapped two with simular cracks. One had been brazed, but there was still remnants of the crack near the ID of the flange. Debated about wheather to keep it or not. Finally decided to pitch it and avoid a possible future problem. Rod

[birdguy45]

Time for a catch-up to let y'all know how my problems have been resolved. The upshot is that I now have a Model A that idles correctly and runs like a top on the road. It has been a long and windey road, but with the help of a couple of local folks and the excellent advice and suggestions here on the forum, the journey has been worth it. The following list (in no particular order) summarizes what was done to fix the problems:

1. Followed Les Andrews instructions to set timing. Found points gap to be a tad tight; set to .020. Rotor-to-cap gaps very tight; filed rotor to get about .025-030 gap and cleaned cap contacts with emery paper. Adjusted steering column position to ensure full range of advance/retard with hand lever. Set timing using light bulb to have points open at second click of hand lever.
2. Replaced exhaust and intake manifolds with good used ones. Local machinist milled ports to make all co-planar to ensure tight fit to block. Replaced and torqued to spec both cold and hot. Tested for intake leaks with ether and found none.
3. Replaced carb with known good unit from another car...works perfectly. Will revisit original carb and figure out what's wrong and fix as time permits.
4. Replaced spark plugs with new Champion 3X plugs (O'Reilley's Auto Parts had best price I could find after checking Snyder's et. al. and several places on internet). Gapped to .035 per instructions that came with plugs. Not sure if it was worth $24/plug to make the change, but they sure do look pretty.

Well, that pretty much sums it up. It has been a real learning experience and I feel much more confident in my ability to keep the old girl running now. Again, thanks to all who provided support...I hope to be able to pay it forward as I can. Happy motoring to all!

[DaWizard]

Glad to hear it is running better now and you have it sorted out. One thing that I was also wondering is, when you set up that carb, be sure to get the jets set up for your altitude too. Depending on your altitude, the jets sizes will make a driving difference too.

[Mitch]

Thanks for the follow up report, i am glad you got things figured out. One can never go wrong by checking the basics and now that your timing is set to specs it will not move. Just keep an eye on your point gap periodically and make sure you use a little cam lube for the rubbing block. On the manifolds i never torque them as the les torque listing is on the strong side. Just a click of the wrist feel type thing is sufficient.
OH and your 3X plugs are worth every penny so keep'em all waxed up and pretty.

[Dennis]

Wax on 3X? Ok I can do that. What brand and where do I get it?

[birdguy45]

Glad to hear it is running better now and you have it sorted out. One thing that I was also wondering is, when you set up that carb, be sure to get the jets set up for your altitude too. Depending on your altitude, the jets sizes will make a driving difference too.

Interesting thought, Wizard. Is there a chart someplace that describes the relationship/recommendations between altitude and jet sizes for all the jets? I'm at 3500' most of the time here in Central Oregon, but can get as high as 5000' on occasion.

[Mitch]

Call Renners and they will hook you up!

[DaWizard]

Birdguy45, PM me your email addy and I will send you the sheet I use.

[Dennis]

Excellent advice from Mitch! I plan on doing some high altitude driving in the future and will have at least one extra carb to change along the way jetted for the higher elevation. I'm not even going to mess with it, just going to call Renner's.

[birdguy45]

OH and your 3X plugs are worth every penny so keep'em all waxed up and pretty.

OMG...waxing my plugs. That appeals to my OCD nature!

[old31]

Birdguy, can you send another mp3 file so that we can hear the new idle.

[old31]

Thanks for the update.
1) I would still use the timing pin as mentioned to double check the indexing of the crank gear with the timing gear on the cam. It is easy for a mechanic to get it one tooth off.
2. You did not say if you only just changed out the intake manifold, or both the intake and the exhaust as a pair.
For best performance, the two manifolds need to be assembled together, taken to a machine shop, and have both surfaces trued at the same time. Else you can have small devilish intake or exhaust leaks. If the engine is running better, you may decide to skip this step, but it is worth the effort. Unless they are machined together they are seldom in the same plane.
3. I too wonder why the compression readings are not all the same on a new rebuild. I'd start by repeating the compression test. Be sure all 4 plugs are out, and that the throttle is wide open, and give the motor at least 3 full revolutions when cranking, but usually until the gauge stops rising.
4. I am totally baffled as to why shorting #3 stops the motor dead. I would get a spark tester and put it in the high tension wire to the center of the dizzy cap to visually see if it is the spark actually failing from the coil. If so, I suspect there is some sort of short, crossfire, leakage, or something going on. It may require more testing. Post more info about that and we can walk you thru it step by step.
5. This is your first A, but from the way you have written it seems like you have worked on cars before. Why else would you have a compression gauge in your back pocket. A spark tester is a handy diagnostic tool to have.
6.Wiz, are you non-conductive? Is that why you be the Wiz? LOL. Every time I have removed a plug wire or strap by hand I have gotten zapped. It is 10,000 volts trying to find a home. If you use a plastic handled screwdriver you can slip them off. However, having said that, this can be detrimental to the coil because that voltage has to go somewhere and it can backfeed and damage the insulation of the coil windings. Better to just short the plug with a screwdriver

Here is a link to typical spark testers
https://www.amazon.com/s/ref=nb_sb_n...s=spark+tester

Tbird do you recommend any particular tester? They seem the same but different.