Farmall A idle miss

kopeck · Jul 7, 2012

My '47 A has been driving me nuts. For the last year or two it had a little miss in the idle doesn't matter the idle speed either. If you put it under a load, doesn't have to be to much, even just a small hill it cleans up.

I've rebuilt the carb and the magneto got a tune up (cap, rotor, wires and condenser).

at first I thought it could be the governor but if I don't see the rod moving at all unless it's at a very slow idle and the engine stumbles. I've even held the rod steady just to make sure. I was thinking an air leak might be doing it as well so I tried the propane test and didn't get anywhere.

Here's an A (not mine) that seems to have that same unevenness to it:

http://youtu.be/DQ0-EbhH3gU

My BN doesn't seem to do this and it has a tired engine where as my A was rebuilt 10 or so years ago.

Any ideas?

K

Janicholson · Jul 7, 2012

first since it is consistant, Use a spark plug from the good running engine. put it onto #1 plug wire and lay it on the block. if two cylinders now misfire, go to the next plug toward the rear. WHen it only misses on one cylinder, you have found the one causing the grief. Replace that plug with the one you know is OK. If this makes the mis go away, the plug was bad. If it still misses, I would next adjust the valves correctly and see if that is the answer. Pay attention to the adjustment on the cylinder that misses. The only last item I can think of without being there is to see if the intake manifold is cracked internally allowing exhaust to get into the intake, leaning it down at high vacuum. Jim

gene bender · Jul 7, 2012

Take all plugs out lay them in order on the hood then look for the bad one. You should see the ones that arent as good as the others maybe just one is bad thats why you need them all out in order mite even have bad valves or tappets mite ned to be set.

kopeck · Jul 7, 2012

I did replace the plugs so I don't think it's a bad plug. I'll try eliminating cylinders though, I didn't think it missed consistently enough to chase it down but I should hear something.

Double checking tappets is a good idea too, didn't think of that as it kind of just came on.

Thanks,

K

gene bender · Jul 7, 2012

I would still pull them and compare that could tell you there is a bad plug or bad wire. How are the tappets are they set at .14

DanR · Jul 8, 2012

New plugs does not mean good plugs. I know of one discount auto chain that buys seconds from Champion. The store manager told me so.

kopeck · Jul 8, 2012

I had just a minute to play with it today. All 4 plugs has some effect when they were unplugged but #1 was noticeably less effected. So it looks like something fishy is going on with #1.

I did have the plugs out a few days ago (wouldn't start, pretty sure dad flooded it) and I did notice anything way off while they were out but I'm running Autolites and the black base can be hard to read.

I'm kind of guessing it might be a valve that's not set right at this point, I mean minus a cracked ring or something like that I don't see what else would isolate one cylinder. I know it still could be a plug but I did change them all out and it ran exactly the same afterwards.

K

gene bender · Jul 8, 2012

So take the #1 plug and change with #2 then see if #2 has the miss wouldnt be the first time to have a bad new plug. If #1 still has a miss replace the wire. Are you using a Mag or a Dist? Bad bushings in a dist will make an engine run funny. I hook a timing lite to each wire and watch the fire can find bad wires easy or a bad worn dist by just observing the fire. I work on these engine a lot and thats just another method of troubleshooting i have learned. What kind of reading do you get with a compression tester no tricks just want similar readings on all cycls.

Farmall A idle miss

kopeck

Member

Janicholson

Well-known Member

gene bender

Well-known Member

kopeck

Member

gene bender

Well-known Member

DanR

Member

kopeck

Member

gene bender

Well-known Member

Similar threads