Invader Rebelling

[mswyka]

Good morning.  Today I find myself in an unusual situation with a sled that does not want to perform.  Not performing is not new, I have had plenty of sleds over the years that had one problem or another.  The thing that makes this unusual is the sled that has decided not to go, our 80 Invader.  This sled has been old reliable for as long as I can remember.  However, I dropped it off at camp in the late fall of 2024 and on the first outing it would not go over 30 mph.  So we pulled it back into the shop and as I had time to work on it ended up swapping in a new fuel pump and a fresh set of carbs and replacing fuel and primer lines.  All seemed to be solved although by that time the snow was gone and it didn't get any additional running.  Fast forward to February 2026 and I am ready to go but the sled refuses to make RPMs.  Starts easily, idles - a bit low, but idles, but refuses to make enough RPMs to move.  No apparent other issues with the sled.  Looking for suggestions.

[mswyka]

I am working through assumptions little by little as time allows.  Last night I had a few minutes and in that time I was able to identify/confirm the following:

1.  20k ohms between the two spark plug leads
2.  Both cylinders are sparking
3.  200 PSI compression on both cylinders
 
Last fall we replaced the carbs with carbs that had new jets and new needle/seat, replaced fuel pump with new Mikuni pump, and replaced primer lines with new tygon lines.  Primer pumps properly but the old primer lines were cracked. I have a few other things that I know to check.

[Interceptor398]

I would wonder about the primer and the fuel.

[mswyka]

Yes, I had suspected as well.  New fuel, primer tested, primer lines replaced, carbs replaced, new jets, new needle/seat, new fuel pump.  Pulled exhaust to confirm no exhaust restriction.  I am embarrassed to say that after all that it turned out to be a bad plug.  With all the other work, once the fresh plugs went in, it screamed off like it always had.

[Interceptor398]

Interesting