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Thread: 87 Mighty Max, Cylinder 3 Misfiring...

  1. #1

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    87 Mighty Max, Cylinder 3 Misfiring...

    So, I picked up my little Mighty Max earlier this week, and originally knew that it had a miss, but assumed it was a faulty plug, wire, cap, or rotor. So, I replaced them all. Didn't fix this issue. Checked the fuel because it had been parked for awhile, and the gas is perfectly fine. Checked for fuel pressure and it seems fine because its pumping out plenty of fuel. The Spark plug for that cylinder is sparking, I checked the compression. All cylinders are reading all the same pressures. The carb is kind of dirty, but I don't think that would be causing that one cylinder to be missing. I'm running out of idea and patience.. Any ideas or help would be amazing. Thanks!!

  2. #2

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    Does it miss straight from a cold start or is it only after warming up? It could be pre-igniting from carbon build up. I would give the carb a good hose down with a can of carb cleaner and put an additive into the tank to see if you can clean out the combustion chambers. And are you still using the original ignition coil? They break down after 10-15 years of use and get tired. Weird it's only missing on one cylinder and you seem to have eliminated the usual culprits...

  3. #3

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    I believe it does still have the original coil, but I'm not certain.. I had taken the carb and intake off of the engine yeaterday just to inspect and it looked as if the intake was leaking so I had to replace the mating gasket.. But, as it was apart I did clean out the carb, flushing carb cleaner through just about every orifice I could find, and also removed the egr tube and valve on the exhaust side of the engine just to inspect, then I reassembled everything, cranked it and fired right up. Idk exactly what I did, or what I cleaned, but it worked. Thank you for getting back to me quickly!!!

  4. #4

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    My next bet was a manifold gasket leak but you beat me to it. Glad you got it sorted

  5. #5

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    Spoke to soon.. I go to start it today and it's missing in cylinder 4 now. I take the carb back off. Flush it out and it's still doing it. I honestly don't know what changed from 600pm yesterday to 500pm today. Its very aggravating... Anyone have any input please?

  6. #6

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    I found the actual culprit last night. So, this is hard to believe, but I can remove the spark plug wire from either the cap, or the plug itself, hold it away from its connection spot, and be able to watch the arc flow, and the cylinder will fire, but once I fully connect either the spark plug end to the plug, or the cap end of the wire to the cap, it will start missing once again. I'm not sure what would cause anything like this... Mind boggling really.

  7. #7

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    I wonder what would cause that to happen. Maybe you could e-mail whoever made those plug wires and see what they say.

  8. #8

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    It's strange the misfire has moved from one cylinder to another and a period where it ran perfectly in between. Because it's not misfiring on all cylinders it sort of eliminates a tuning issue or the coil/distributor. I know you have replaced the plugs - did you use OEM equivalents? And did you check the gaps before installing them? Sorry about the barrage of questions but it's a process of crossing off factors until the problem is fixed.

  9. #9



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    try a different set of wires - also check the play in the distributor. Is there strange wear in the cap or burn marks on the cap inside terminals or the rotor?
    Pennyman1
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    Living the D-50 lifestyle since 1980

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