OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions on Other Engines Dieseling 2 Cycles

I may be posting this in the wrong forum but it should relate to all 2 cycles.

I just repaired my first dieseling 2 stroke. Just wonder if anyone here have ever seen one doing this?

Even the dealer couldn't repair this 6 month old Hedger trimmer engine.

The strange thing it would only diesel after warm up and at only full throttle.

AVB when you say dieseling I assume you mean when it is hot, you turn the kill switch off and it continues to run. I can't remember coming across the problem but I can see how it could happen. Ok I will bite what was the fix, did closing the choke slow it enough to bring it to a point where the ignition would shut it off ?

You're just the fellow I figure I would snag on this fishing trip, Norm.

Here was what happening. After the engine warm up at first it start surging. Then after little longer running at full throttle take off like an Emu slowly running along and when you touch him kick it into higher speed. The hedger was actually sounding like it hitting over 120000 rpms. When you release the throttle it slow back into normal speeds including idling correctly.

When I put on an inductive tach after finding out it had a speed limited coil on it I found that the coil was completely shutting down during these high speed bouts. It actually was still running even if I pull the plug lead off the plug until I release the throttle then of course it would die without the plug wire connected. Of course with an inductive tach with the coil shut down involved I couldn't get an actual max speed but sure was trying to shake it apart. Now the initial surging at full throttle was the coil limiter doing its job trying to prevent the hedger from going above 9300 rpm.

For me it turned to be one those little NGK 10mm spark plugs that was the root cause. Changed the plug and then I couldn't even get above idle speed but this because of a plugged spark arrester. Once it was cleaned and the new plug all is well. I have seen some pretty behaviors from these CMR6H plugs.

First time I ever seen dieseling in a 2 cycle in 9 yrs I have been doing this small engine work.

I have seen my Emus do this change of running speeds as my brother was trying to catch one on a 4 wheeler ATV. When he reach out and touch one it kick it into full speed left the ATV and my brother eating his dust.

Another strange thing was this hedger actual would hit at start up with the choke close and the plug wire disconnected. Would not start and run though.

I take my hat off to you AVB, takes a lot of determination to go through the process to figure what is going on when all it needed was a new spark plug. Easy in hindsight but because it is running you believe the plug is ok. NGK used to be a top notch plug but their reputation has taken a battering over the last 10 years or so because of the fake NGK plugs and the problem with the fake ones they are very hard to spot and it is only on the packaging that you can spot the fakes. From memory the box color is a shade different and there is something in the writing that is wrong. I stopped using NGK some years ago because of this problem.