This cylinder I have came with a motor I bought 5 yrs ago, I thought , what the heck, put a piston in it and see what it does. I did not bother to put new reeds in it. Upon inspection of the reeds, one of them has small break forming on the top edge. When I bought this motor, it came with a set of reeds with a stiffener, I assume these would be high tension reeds. The next time I go out, I will try these reeds, see if it makes a difference, I have an extra reed cage that I have already mounted a set of new low tension reeds.

Gary

#55 Honda CR80

Just checked my wiring, all connections good, with good grounds.

Plug gap .022, spec .024-.028

The motor doesn’t always  break up under WOT, it’s just this RPM range of 10,000-11,000 , it happens sometimes feathering throttle out of corner prior to nailing it. The reeds in the motor had 30 hrs on them, they were damaged, I have changed them with ones that came with cylinder,  I will try them out and see if the problem persists.

If the problem continues, I will check out the electronics, but I doubt if that is the problem, it worked fine before. (every mechanic loves that line) lmao!

I have a kill switch, like before, it worked fine before, I will disconnect it see if it makes any difference.

The motor has run a few what I would call clean laps without breaking up, and when it does, it runs like a raped ape, lots of midrange and top end. I find myself over revving between shifts at 13,500, motor still pulling.

Gary

#55 Honda CR80

1st time out with top end, new seals, 30 hrs on crank.

At the end of break in, when I started picking up RPM’s, I first noticed this problem, never experienced anything like this before, never ran this cylinder before. I have had this cylinder for 5 yrs and finally had the juevos to put this massively ported cylinder on a motor. I don’t know if there is a problem with the cylinder and that is why it came as an extra in a “motor package”.

One thing I forgot to mention, the cylinder has an “o” ringed head,  I am experiencing a minor coolant leak on the exterior between the cylinder and head, with no coolant loss and no coolant in combustion chamber.

Gary

#55 Honda CR80

UPDATE:

During the past 5 months, have tried many things to figure this out, turns out it must be the black box. It runs good some times, and other times runs like crap. I put on an old Vortex ignition box and ran great, then the cylinder cracked along the intake port, put on my other cylinder, ran great, changed back to the old black box, ran great, changed complete motor and after break-in, runs like crap again. The same thing, around 10,000 rpm it starts to flutter. New motor has different stator and pick-up, the only thing that is the same is the black box and coil. Have 2 spare black boxes, I feel confident changing that black box will fix the problem.

Gary

#55 Honda CR80

Greg I believe you are absolutely correct about the cracking along the intake port, the cylinder had been welded on 1 side already, cracked thru that weld and started cracking on the other side of the cylinder as well. Like I said, this ported cylinder was an extra offered in the purchase of “motor package with extras”. I put this cylinder on to see what it would do, unfortunately the ignition took a dump the same time I put this cylinder on. I was quite impressed with the performance gain, 1/2 second a lap and lots of rpms.

Gary

#55 Honda CR80