Missing 800 revisited

[Bill Allis]

Thanks for all the advise. I have tried it all and it still is missing. Cleaned the points and they look good. I have a nice blue white 1/4 inch spark at all plugs.(only got bit once) Removed the plugs to clean and found they look good, not sootie. It seems to get worse the longer it runs. Chokeing did not help and I have removed the bottom plug on the carb and drained it.

Is there a chance the coil is weak, I know it is old? But the spark looks good.

 

[old]

Check your spark when it is good and hot if it is not the blue/white and jump a 1/4 inch gap yes the coil maybe getting weak but if it is still good I would maybe think about setting the valve rocker arms they might be getting tight and not closing as tight as they should

 

[amstrad]

Hello
I have a 861 powermaster. that used to miss. My problem was a cracked head and bad valves.

 

[Dean]

Again, did you replace or sandblast (not "clean")the plugs AFTER removing ALL of the old gasoline from both the tank and the carburetor?

Did you replace or sandblast the plugs after flooding the engine with modern gasoline?

Dean

 

[Tom-NorthCenTX]

Check coil. If OK, then put in new condensor, rotor, cap, points, plug wires. Tom

 

[Keith Williams]

What Plugs are you using?

When my 4000 4cyl starts to miss, the first thing to check is the plugs. That is where it starts. I am now using the AL 437's. Before I was using the ones that come in the kits from Ford.

Keith

 

[Jimmyjack]

Does the gas line still run behind the manifold? Does it get worse when it heats up? Many people have had problems with the gas boiling in the line, with ethanol gas. I relocated the line, and switched to ethanol free gas and my problems were solved.

 

[Jerry/MT]

If you have a FAT, BLUISH-WHITE SPARK, the color of lighning, I would say the primary ignitin circuit isn"t the problem.

I would suspect the bushing and/or shaft on the distributor might be worn. Rotate the engine til the points close. Then push radially (from the side) on the distributor shaft from several directions, watching the points. The points should not move. If they do, then you"ll need to replace the distributor shaft bushings and maybe turn the shaft also.

 

[ErnieD]

Time to rule out a bent push rod/stuck valve.

 

[MarkB_MI]

A second vote for sticking valve. Pretty common with engines that have been sitting. I suggest you find the missing cylinder(s) by pulling off the spark plug leads one at a time. It is almost certainly missing on at least two cylinders; a single cylinder missing on a 172 is hard to detect. I have had some success freeing stuck valves by squirting Marvel Mystery Oil into the spark plug hole of the offending cylinder.