no compression....sometimes. why???

2 replies to this topic
  • thumper4life

Posted June 20, 2002 - 07:28 AM


took subframe and carb off to do bk mod and jet it, my dad decided to unscrew the idle all the way. so after we got it back together we tried to set the idle back to where it should be which resulted in me kicking it about 40 times.
but my question is, sometimes when he would turn the idle up after another failed start, i would go to kick it and there would be no compression, well a little bit but i could kick right through it. its fine now and works fine and the BK mod rips, but i wanted to know WHY there was no compression sometimes after turning the idle up

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • JSTheJack

Posted June 20, 2002 - 08:10 AM


You know, I posted that same question about a week ago when I read other messages about no compression. I'd bet the exhaust valve with the compression release is not totally seating, or there is carbon built up on the exhaust valve seat.

That has got to be the only rational reason for the loss of compression that later returns. I can't believe the valves would stick unless they're bent...I mean, valve springs are really stout.

  • thumper4life

Posted June 20, 2002 - 08:35 AM


yeah, after searching on this site (that search comes in handy AFTER i post :) ) i found that a valve was most likely sticking, and your reasoning is perfect because my bike was running SUPER rich and there was a crap load of carbon in the header. and when i was flushing it out with my hand after sprayin all the gas in it after the bk mod and flushing it out with no plug in it, it became hard so i hit the comp release and pushed it through a few times. so that and the carbon build up could be the reasons it was sticking. at least its fine now :D

Related Content


Megabomb Fitment by 288yz450

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 1 reply

Should I buy this bike? help....... by Numsa Hul

Dirt Bike   General Dirt Bike Forums   What bike should I buy?
  • * * * * *
  • 10 replies


Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • Hot  30 replies

Chubby dad, looking at bikes , First trip to the orange/black forum ! by Slow_ride

Dirt Bike   Make / Model Specific   KTM   250-530 EXC/MXC/SXC/XC-W/XCR-W (4-Strokes)
  • Hot  28 replies

2016 YZ450 by CaptainKnobby

Dirt Bike   Dirt Bike Technical Forums   Suspension
  • Hot  59 replies

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.