47 V8 ignition mystery

[slowforty]

Not to hijack this thread, But I had a bad Ignition Resistor that took me quite a while to diagnose, The car is a 40 Deluxe,(Helmut Dist) that I have owned for 35 years. The car would run and start well but would not run over 60mph (After about 20 minutes of running,so it was operating temp). I replaced the carb. distributor. wires, and coil with no results. Finally I was told to strap out the igniton resistor, Bingo! Issue solved by replacing the resistor.

[Jack E/NJ]

Craig>>>Again, the engine worked perfect . . . for a very short time before starting to misfire again. >>> problem stayed with the cylinder, not the wire.>>>>What else could that pattern suggest?>>>


Nothing --- based on all you've tried and observed so far. Always same cylinders. So tend to agree with Mart. Something other than ignition. Might be sticky valve stems after getting warmed up. Since it's easy, maybe try running some MMO in the carb & tank for a while to see what happens.

[Old Henry]

Originally Posted by slowforty

Not to hijack this thread, But I had a bad Ignition Resistor that took me quite a while to diagnose, The car is a 40 Deluxe,(Helmut Dist) that I have owned for 35 years. The car would run and start well but would not run over 60mph (After about 20 minutes of running,so it was operating temp). I replaced the carb. distributor. wires, and coil with no results. Finally I was told to strap out the igniton resistor, Bingo! Issue solved by replacing the resistor.

Thanks for the thought. I have bypassed my coil resistor several times to see if it makes any difference. The problem is actually worse without the resistor which surprised me. It certainly didn't get any better bypassing the resistor.

[flatford8]

Craig, I apologize if I missed this in previous posts but, have you tried moving the spark plugs to different cylinders?......I believe I read that you are using Autolite 216’s?......I’ve had issues with Autolites with the electrode pulling out of the plug while removing the boot. This has happened with 1 or 2 plugs in two different sets of eight. I switched to Champion H10’s but will probably use NGK on my next go ‘round. I realize these probably aren’t staying with your “as built” philosophy but maybe it will help you find the problem.
Good Luck..........Mark

[Old Henry]

Originally Posted by flatford8

Craig, I apologize if I missed this in previous posts but, have you tried moving the spark plugs to different cylinders?......I believe I read that you are using Autolite 216’s?......I’ve had issues with Autolites with the electrode pulling out of the plug while removing the boot. This has happened with 1 or 2 plugs in two different sets of eight. I switched to Champion H10’s but will probably use NGK on my next go ‘round. I realize these probably aren’t staying with your “as built” philosophy but maybe it will help you find the problem.
Good Luck..........Mark

Thanks for your suggestion. Early on I switched spark plugs around and it made no difference. In fact, I pulled the wires off the spark plugs and held them near head bolts and the intermittent sparking is coming out of the end of the wires not even attached to the spark plugs. So, the spark plugs are OK. The wires are OK. The coil is OK. The distributor seems OK. I don't know what's wrong.

I've sent some questions to Michael at third GEN to see what he thinks about my distributor he worked on.

[Als48]

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Craig, Have you done a compression test when the engine has been misfiring? That would be good information to have. Dont' remember you mentioning whether you had or not.

Al Hook

[alchemy]

I’m a complete hack, but I’ve heard that 87 percent of ignition problems are the carburetor.

[Jack E/NJ]

alchemy>> I’ve heard that 87 percent of ignition problems are the carburetor.>>>


Might be if half the carb is dedicated by the manifold to feed cylinders 8-6-3-7. Firing order with emphasis on problem cylinders.
1-5-4-8-6-3-7-2

[Mart]

Originally Posted by Jack E/NJ

alchemy>> I’ve heard that 87 percent of ignition problems are the carburetor.>>>


Might be if half the carb is dedicated by the manifold to feed cylinders 8-6-3-7. Firing order with emphasis on problem cylinders.
1-5-4-8-6-3-7-2

No, Jack. each side of the carb feeds alternate numbers in the firing order.

One side: 1,4,6,7
Other side: 5,8,3,2

If you look at those groups of numbers they both contain the two end cylinders from one side and the middle cylinders from the other.

So it is unlikely that one side of the carb is at fault.

[cmbrucew]

Sitting in the drivers seat the right hand side is 1234, the left side is 5678 from front to back. The crab cap should be numbered. One wire at a time.
Bruce

[FlatheadTed]

Looking at Henry first post he says the cam was so worn he couldn't set the points, in all the years I have been doing distributors I have never seen this I have only seen points that are badly made and dont set up ,he said it was running fine prior .They stopped doing this on Air Craft because of introduced faults .I have told this story before but I got called out to to a 36 v8 were it had a bad mis he changed carbs ect he .I took my Carb my dizzy wires (known to be good ) the miss was still there on # 6 it compression checked good, I pulled a plug and noticed the valve not going down he pulled the manifold and the top Guide keeper was stuck in the spring . he assembled it and said it still had a mis I suggested that he had introduced dirt into the crab, sure enough! Ted

[Old Henry]

Originally Posted by Als48

Craig, Have you done a compression test when the engine has been misfiring? That would be good information to have. Dont' remember you mentioning whether you had or not.

Al Hook

I hadn't done a compression test but just did. It showed the following pressures in each cylinder:

1-90
2-90
3-90
4-100
5-90
6-96
7-95
8-95

Any clues there?

[Old Henry]

Originally Posted by Old Henry

I've sent some questions to Michael at third GEN to see what he thinks about my distributor he worked on.

I haven't had any response from Michael regarding my distributor that he worked on to see if he thinks anything could be wrong with it causing my chronic missing problem. Hopefully, he'll respond soon. I've only got three weeks to solve this problem before I have to put Old Henry in a coma for two years while my wife and I go to serve voluntarily in the Philippines for two years.

[Old Henry]

Originally Posted by Mart

It could be that the problem lies with the carb or a vacuum leak or something like that, and all the shenanigans with the distributor have been a red herring.

I hope you can eventually get to the bottom of it and can post a positive result at some time.

Mart.

I just rebuilt the carburetor at the beginning of all of this and it seems to be working just fine. Any carburetor problems I've ever had caused gradual or sudden loss of power, not this "stumbling" that I'm getting. Have I missed something?

[tubman]

This is really "off the wall", but try running it without the air cleaner for a while. I had a problem with an occasional "stumble" on my Corvette and finally tracked it down to a restrictive air cleaner. It drove me crazy for almost 2 years until I found the problem.

[Old Henry]

Originally Posted by tubman

This is really "off the wall", but try running it without the air cleaner for a while. I had a problem with an occasional "stumble" on my Corvette and finally tracked it down to a restrictive air cleaner. It drove me crazy for almost 2 years until I found the problem.

Thanks for the idea. I have actually been running it without the air cleaner for a week. I just put it back on. No difference.

[Jack E/NJ]

Craig>>>Again, the engine worked perfect . . . for a very short time before starting to misfire again.


Still might be sticky valve stems after getting warmed up. Try running MMO thru carb & mixed in tank to see what happens.

[Old Henry]

Originally Posted by Jack E/NJ

Craig>>>Again, the engine worked perfect . . . for a very short time before starting to misfire again.


Still might be sticky valve stems after getting warmed up. Try running MMO thru carb & mixed in tank to see what happens.

Will do. Thanks for the reminder.

[Brian]

Back in the '70's, I remember reading an article in a NZ Hot Rod magazine about the editor having trouble getting his flathead to run sweet....tried everything to no avail, culminating with removing the intake manifold and applying grease to both sides of the gasket and rebolting it down which cured the problem! Now, i dunno if that is your problem here, but that article has always stuck in my mind, and I always grease that gasket when fitting.

[FlatheadTed]

I dont see any issues with the compression ,.rebuilt carb with ?? ,Dont rule out the carb they can show the same symptoms as electrical.