H missing badly

ycanby

New User
Hello, I have a '41 H with an H4 magneto. Low hours on engine and Mag rebuild. It started missing badly all at once, perhaps down to two cylinders. The mag checks out good. Adjusting the timing on the mag does no good. Was wondering if the mag drive gear could have sheared a key and slipped on the shaft? Is this a possible problem on these.
Thanks ahead for the help, and Merry Christmas to you all!
 
Start it and take a well insulated screw driver and short out each plug wire at the spark plug to the head. Determine which cylinder makes a difference in the idle and which do not. Now I?m talking about the old bare 90 degree plug terminals. Or if it has the newer style insulated boots on the plugs you will need to pull the plug wire and boot off of the plugs and then gently push them back on the plug so they barely are on the porcelain. Then use an insulated winter glove to pull the wire off each plug. The you ground out or unhook each cylinder one by one, the ones that don?t make a difference are not firing. Pull those plugs and see if they are fouled most likely black and sooty from over choking. If the plugs look good and to be truthful this should probably be done first before pulling the plugs. Assure the misfiring cylinders are getting a good blue spark that will jump a quarter inch. If this has all been already checked then testing the manifold to head seal should be another thing to check by spraying either around it at idle. During this test if the engine speeds up at any point you have found a leak. If you have a compression tester the you can also check that. Next would be to check the valves are set to correct clearances, which really as a best practice should be checked before a compression test. It?s sort of a...dog chasing his tail...thing. Someone with a lot of engine experience may not always follow steps the way a book lays them out if he knows where or when a short cut test can lead him to a final answer quicker and easier. Note, checking the spark with a winter glove may still allow you to experience a shock from the spark, if you are faint at heart to being exposed to this, you better find a mechanic to help you out.
 
The mag fires on TDC and there is no adjustment to it is fine or it would not start and run. So check your compression and valve setting. Next would be to check the plugs while they are out to see if they all look alike. What kind of work are you doing with the tractor. Are the wires new and copper centers. You didn't say but how many checks have you done
 
Had that problem with my H a number of years ago, all ready to take it apart and do major repair, found out that the nearly new Champion spark plugs were no good, put in Autolite, never had a problem with it skipping again. Still could be other things, but just passing on my experience.
 
I just put in Autolite 3116 plugs yesterday and did away with the D15y champions. Two of the champions had raw gas on them, figured they were the ones missing, the other two were a bit sooty, but not bad for being in 17 years. The tractor ran better for a little while, though still started hard. Then it got to missing again. I doubt it will even start today. Thanks!
 
Do some simple trouble shooting. Pull a plug one at the time and see which cylinder is not firing. You may find when you pull them the cylinder that is not firing will start to fire as you pull the plug wire. If it does good chance you have a bad/fouled plug. Also do you have true wire plug wires on it. If you have the car/truck type on it that could be your problem. Also pull each plug and look at them to make sure they look like they should and not all black and oily or black and sooty. Now days I switch all my tractor when I replace spark plug to NGK brand plugs they tend to work better then any other brand
 
(quoted from post at 07:17:17 12/24/17) I just put in Autolite 3116 plugs yesterday and did away with the D15y champions. Two of the champions had raw gas on them, figured they were the ones missing, the other two were a bit sooty, but not bad for being in 17 years. The tractor ran better for a little while, though still started hard. Then it got to missing again. I doubt it will even start today. Thanks!

Plug wires need to be solid copper. Not the stranded automotive style.
 

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