Engine misses when hot

Joe Immler said:
OK I did the vacuum tests and here is what I got:
Idle cold 18Hg
180degrees 16 Hg
190 degrees 16-17 Hg Rapid oscillation
210 degrees same result
190 degrees after driving same results
So...valves?
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Valves is my vote.........jerking needle only when hot makes me think valve adjustment etc....:eek::D
 
The valve set up is pretty simple. But..what should I look for? What suggestions for checking them out? This will be a winter project since there is another month to drive it.
 
You need to check the clearances. If you continue to drive it, you risk burning seats or valves. Then you'll have to yank the engine. Right now for a few hours' work you might get away with no further work.

I assume you have adjustable lifters?
 
Joe, with all the above posts, and all the things you have tried, it seems like you have the possibilities pretty well covered. So, my WAG leans towards 'valves'. But, what?, in relation to valves? Bad adjustment? Too tight would tend to support the symptoms (I think). Or, 'hanging' valves? (stem-to-guide too tight) Seems to me, if the valve adjustment is too tight, you should have seen it with a fluctuating needle during the vacuum test. (rapid intermittent dropping from normal) On the other hand, too tight, combined with the posts by Dick S, could easily give the symptoms you report.
If I was looking for something to try, and this is another WAG, Maybe a strong dose of MMO in the gas, or diesel in the gas, and repeat the 'hot' test. This would be a relatively cheap and easy try. By strong dose of MMO, I mean something like a pint or more, to 10 gal of gaso (not the 4 oz, recommended on the bottle). Or, if diesel, I mean 10 percent (or more), like 10 gal gaso and 1 (or more) gal diesel. This 'try' would be for the theory of 'hanging' valves. If the problem is 'too-tight', this 'try' would probably do nothing.
Let me ask... Why the valve job? Is there any chance there is some problem with the 'workmanship'? This might lead me to think about the valve adjustment.
Is this the same engine that you got from Jon? If so, I thought you had considerable history of 'no-problems' with this engine. And, again, if so, then did all of this start AFTER the valve job? And, using Jon's logic, this would lead me to think there is something wrong with the valve job.
And, another thought & question... What are your driving habits? In socal, I think it would be normal for you to spend a lot of time on a freeway. Right? This would tend to 'negate' hanging valve problems. In OH, are you doing a lot of highway driving? Or, is it a lot of driving at low speed, around town, to the store and back, etc.? My experience has been that if I drive my heap mostly on the highway, I don't have hanging valve problems. But, if I do a lot of short distance driving, I get problems with the valves, missing, popping, etc. As soon as I return to the highway, and sometimes add a gal of diesel (or MMO), valve problems go away.
Just my .02. As you can tell, I'm just tossing out what are likely stupid ideas.
Hope you are doing well. We miss you. Bob
(PS, side note... One day, at Jon's shop, there sat Dudley's 38, for a valve adjustment. Seems that there are folks out there that do it incorrectly, and as soon as Jon did a proper adjustment, Dudley's car suddenly ran great. Food for thought.)
 
BobH I did get some MMO per Alan's suggestion. I will dump more in the tank and also in the carb. I had the engine out last year for installation of the 4th rear main seal and some ****** work. At that time the valves were done. The mechanic that did the work is an old Ford Guy like Jon and I feel confident with his work. As for the driving I have gone to some distant car show and the combined mileage is probably about 280 miles of 60 mph driving. As I said this will be a winter project as there are a few local shows in October. We'll see what the MMO does. I miss you and Darlene . I saw your message but did not know how to answer. See? I am still the same Dummy you remember!!
 
I had a similar issue I was able to solve simply, but I'm not sure you can adopt my solution. I'm running a helmet dizzy but with an adapter for an external coil. I simply moved the coil bracket to a cylinder head from its position immediately above the dizzy. The increase in air flow keeping the coil cooler was enough to take care of things.

I was prepared to start the usual round of things to fix "vapor lock". Nothing other than moving the coil was necessary.

Tom
 
Please advise...can I use a vacuum test to tell difference between electrical misfire (say coil or condenser caused) and misfire caused by valves hanging?
This would be very useful, please go through the procedure if possible.

Thanks, Tom.
 
Drizzle some Marvel Mystery Oil down both sides of the carb while running and put about a pint in the gas tank. Sticky valve problem gone in less than 10 miles. Then put it in every tank of fuel. G.M.
 
Tom Walker said:
Please advise...can I use a vacuum test to tell difference between electrical misfire (say coil or condenser caused) and misfire caused by valves hanging?
This would be very useful, please go through the procedure if possible.

Thanks, Tom.
Click to expand...

Maybe, maybe not
 

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GM I tried your suggestion to use MMO. I put over a 24 Oz. in a full gas tank and also dribbled 8 0z. in the carb. Drove 53 miles and missing came on at 180 degrees as usual. Worth a try though. Lot's of exhaust smoke!! Local environmentalists probably had chest pains.
 
Heat relayed, sounds like coil, condenser or the start of vapor lock. Does it get worse when it gets hotter, say up near 200?? G.M.
 
GM Yes it gets worse as it gets hotter. I have tried 2 rebuilt Skip Haney coils and one new one. As I said in the original post I have tried 3 condensers. I also heated up the coil and condenser to 215 degrees with a heat gun yesterday and the car ran fine. Also if it were vapor lock I would think the electric fuel pump would overcome this. Also,the problem continues as the car is driven which also seems to rule out vapor lock.
 
Joe Immler said:
GM Yes it gets worse as it gets hotter. I have tried 2 rebuilt Skip Haney coils and one new one. As I said in the original post I have tried 3 condensers. I also heated up the coil and condenser to 215 degrees with a heat gun yesterday and the car ran fine. Also if it were vapor lock I would think the electric fuel pump would overcome this. Also,the problem continues as the car is driven which also seems to rule out vapor lock.
Click to expand...

I would test one of the condensers off the car with an the old needle type ohm meter. Heat the condenser up to about 160 degrees, this is where you can't hardly pick it up for about 2 seconds. Touch the probes to the body and lead and every time you reverse the leads the needle should jump up about 3/4" and slowly drop down to zero. They will all do this cold so check it cold first the problem starts when they get hot it should work the same cold and hot to be good. G.M.
 
GM I finally got around to testing the 3 condensers I have per your instructions. They all tested OK. Thanks for that info though as I had never heard of this. This will go in the file of stuff I have on the in's and out's of Flatheads.
 
Is it possible that the coil is breaking down at high temperatures? I had this problem and checked the distance the spark would jump when the car was cold and when it was hot. The spark was weaker when the car was hot. I initially believed it was a condenser problem, and changed it. No difference. I changed the coil and the problem went away.
donQ
 
I have exactly the same symptoms as Joe, so am following this thread. One thing, does the body of a condenser need to be attached to ground?

Thanks, Tom.
 
donQ I doubt that it is the coil. In my first post I said I have installed 2 different Skip Haney rebuilt coils with no change. I also borrowed a proven reliable coil and tried it with no results. Also, as mentioned earlier I heated a coil with a heat gun and it did not change things. I am pretty much to the point where I am going to dig into the valves this winter. Will let you all know what I find.
TOM My condenser as well as others I have seen are only mounted with the bracket
bolt not the body. Others may have a comment on this.
 
I am having this problem to. lots of new parts. I just closed the plug gap to .025 and seams better I will try mmo in gas tomorrow .very interested in this thread thanks
 
MMO usually works just drizzling down both sides of the carb and in the gas cures the slightly sticky valves. I have done a lot of engines that sat 50 or more years. Some wouldn't even turn over. Everyone runs and has been driven many trouble free miles except one. That one was a 8BA that mice got in and peed on the lifters. I never had time to really get serious on that one but may try again this winter. The real MMO treatment is with a parts washer syphon gun. Put the syphon tube down in a quart MMO bottle, spray down both sides of the carb with the plates open, in all spark plug holes. Turn the engine a little to open the valves that were closed and spray again. When spraying down the carb you will see the mist come out the spark plug holes. Let it sit over night, crank the engine over and give it another treatment. This should do the job. G.M.
 
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