2-stroke troubleshooting help for a quad

I picked up a KFX 80 (same as Suzuki LT 80) quad for my kids. It was a non runner and it is still NOT RUNNING

The bike has over 150# of compression cold, which apparently is excellent and on the high side. It is electric start and that works (actually grenaded then replaced it.)

I still have a no start problem so I just put mix down the hole. Still nothing. I have visible spark and checked 2 plugs one brand new.

Fuel, spark, air and timing. The key looks to be in tact, so while I haven't inspected timing I suspect its fine.

Any tips to trouble shoot? If weak spark is there a poor man's test? Can Reed valves play into a no start condition if I put the mix down the plug hole??

 

Pull the exhaust and check the piston. I have seen scored pistons still make good compression on the gauge.

 

Check the coil, they will sometimes show good spark, but will not fire under compression. There was a thread elsewhere that had Mastermind confused, that turned out to be the flywheel. The magnets had somehow reversed polarity.

 

The piston is clean both intake & exhaust, also the exhaust is unrestricted.

 

Ok.... how do I do that? I do think I need to take a closer look at the stator.

 

Make sure the flywheel key is not sheared.

 

Sometime the power band wears out on those 2 strokes.


A cracked reed valve could affect this. I assume you cleaned or rebuilt the carb?

 

Yeah, pretty sure he checked the carb out. That was in another thread but iirc he cleaned it out. Yes, I'd check the reed valve.

The gas flows freely? I assume the file filter was checked and that the petcock will drain.

 

Reeds look great, carb has been rebuilt and cleaned, gas gets to the carb and possibly to the plug. The reeds snap back in place when lifted and I see nothing wrong with them.

As of right now, this is not fuel related as I am putting in a tsp of mix down the plug hole. This should also bypass any issue with the reed valves... I think?

I will check the key next. Before digging deeper I am also going to try to bring extra ground wires over to ignition and block.... just because electrical gremlins and bad grounds go hand in hand.

I appreciate any tips, keep them coming.

The coil measurs slightly low, it is the type where I have to remove the tip of the spark plug. I dont like that as the fit isn't as tight.

 

No spark under compression, just verified with a spark tester probe which I forgot I even had. Real strong light when the plug is not seated in the block.

Good tip, but now to find out why.

 

Try grounding the key better, but I suspect the coil is the culprit.

 

you beat me to it

 

CDI and coil are separate, the service manual is terrible but lots of info on the net.

 

Have you tried a new plug? I've seen "fouled" (shorted internally, not just dirty) plugs bite even the best mechanics in the butt.

 

Tried the original and a brand new one.

 

Yeah, so it would look to be. I can't get the flywheel off and not sure how.

I had a brilliant idea to chisel the sheared key off on the shaft thinking it was not allowing the flywheel to pull off cleanly. No go, not sure if rust plus some remaining metal resistance, very little access to hit it with a BFH... I am at a loss unless I weld something to it to pull from front.

Any ideas?

 

You may have to weld a couple of nuts to it to pull it. Then grind off the nuts after you pull it off.

It's kind of a common issue on many makes of small motors like this.

 

I found 2 types of pullers for it but I'm not sure either type will work.

I don't see any holes in the flywheel so this one won't work.

SUZUKI LT80 KAWASAKI KFX80 LT KFX ENGINE MAGNETO FLYWHEEL PULLER 87-06 | eBay

I don't see any threads on the center of the flywheel either.

SUZUKI LT80 KAWASAKI KFX80 LT KFX ENGINE MAGNETO FLYWHEEL PULLER 87-06 | eBay

Can you very carefully pry on it while tapping on it? I'm not sure that welding to a flywheel is a good idea.

What I mostly do on a chainsaw is thread the nut on the end of the crank and hold the saw by the flywheel. I put a socket on the nut and tap on it. I'm not sure if you could do something similar.

 

The other option is drilling and tapping threads into the flywheel.

Welding onto a flywheel to remove a stuck one is pretty common fix. Then grind what you welded off after you pull it.