Hey all, I've got an odd issue going on with a new top end on a yz 125. It was running alright before the top end, definitely lower on power. The new top end went well, nothing to note, and I did the full recommended break in, also tuning the Lectron carb a bit richer since that was an issue prior to the top end. I've checked spark plugs, and it's not running rich or lean it seems, but there's some unburnt fuel leftover on the plug. The engine pulls excellently, significantly harder than before, but at about 2/3 throttle, power fully cuts out. It's more than a bog, the engine fully splutters to just about idle. It makes a buzzing burp sound, and takes a moment before rpm's can go up again. This cannot be replicated when the bike is in neutral. I'm guessing it could be power valve issues. I'm really limited on time to work on it with everything else in life going on, so nailing down a solid theory is my best bet. Cheers.
I can try and get some videos this weekend when I'm back home if the snow doesn't make it unrideable.
Definitely something you did while replacing top end if it did not exhibit this before top end service. Start simple, check wiring, maybe something came unplugged? Fuel flow? Gas cap vent hole..vapor locking? What else changed? Can you verify powervalve is working correctly?
how soon after starting your ride does it start cutting?
your jetting could be spot on but it sounds similar to an issue i had with my yz years ago (albiet with stock carb) the float was out of spec and i would drain the bowl of fuel and it start cutting out.
also check the power valve was re-installed correctly
also with the age the magneto could be failing too
I'll be home this weekend and can diagnose. Wiring should be all good. Fuel is working correctly. I just realized it could be the powerjet in the lectron carb. It might be tuned way too rich and is flooding the engine when pulling vacuum. I returned the lectron to their recommended tuning settings after the top end, accounting for elevation, but that might be the issue.
The Shop
Luxon 4-Post Bar Mounts
$189.95 - $239.95
DeCal Works Huge Plastic Inventory of UFO and Polisport kits.
Free shipping: VITALMX
It's cutting power when at operating temp, and doesn't improve at all when warmer. The float has been spot on. I did replace the stator a year ago and it has excellent spark. As said in a a different reply, I just realized it may be the powerjet in the lectron carb. I've got the stock carb, but it isn't jetted well at all and I don't have the correct throttle cables, but if all else fails, I'll try and throw that on.
Post a reply to: Phantom power issue (2005, YZ 125)