yfz has no compression... leakdown test was good!?!?!?!?

[Hozed]

ok... i was riding.. started loosing power... check compression 90lbs. after talking to the dealer they assured me it was probably just the rings even though the old ones looked fine. put it back together... 90lbs compression.

head/valves are fine, rings are fine... i put it together correct, timimg is good...
did a leakdown test an hour ago, held all the pressure we gave it... looked great... did another compression test at the dealer and they got between 65 - 80 on 2 different testers.

what is wrong? decompression seems to be working good...
dealer is lost... they gonna call yamaha tomorrow but we all know how smart they are...

help me!!!

[airheadedduner]

Need to make sure they are using short rubber hoses on their compression testers. I have found a difference of about 30-40psi because of that. Does it run or have you even tried to start it? It is very hard to get very high compression numbers with an autodecomp system, you may not be able to do one. You can't even check raptors without doing a leakdown. I don't think yamaha even gives a compression spec on the yfz in the factory service manual. Last time I tried to look it up I couldn't find it.

[BSTURDIVANT]

Try locking the counterweight open on the compression release with tape or wire tie and recheck! Also check for restrictions on the intake side- had 1 guy suck in a plastic bag that he forgot to remove!!

[Hozed]

i got it figured out...
would you beleive that the cammod causes a 50 lbs compression loss while not running?

that still doesnt explain why i was loosing power though... we will see how she goes in a day or 2.

[5valves]

I am kinda at a lose on why you think its a compresion problem?
I would be looking at ignition first.
these bikes have been known to have an ignition problem.
do you have a teather kill switch? are your head lights installed, and do you run with them on.
Yamaha has sent out a press release stating you need to run with the lights on or install there new resistor kit.
theres lots of info around about the ignition problems.
i got the kit from Bob at Magnolia.

[Hozed]

there is no problem now... it was false compression readings because of the cammod... i dunno why i was loosing power... but we will see what happens when i get it all set n ready to go.
but yes... ignition did come into my mind and was the next step.

[airheadedduner]

Originally posted by 5valves
I am kinda at a lose on why you think its a compresion problem?
I would be looking at ignition first.
these bikes have been known to have an ignition problem.
do you have a teather kill switch? are your head lights installed, and do you run with them on.
Yamaha has sent out a press release stating you need to run with the lights on or install there new resistor kit.
theres lots of info around about the ignition problems.
i got the kit from Bob at Magnolia.

But.........ignition problems tend to be all or nothing most of the time. Did they show you your old parts? It does sound like a compression loss or a mild sizure.

[Hozed]

no problem now... i dont think... it has good compression... it was the cammod...
i did my own work so i got the old parts.

[SRH]

what comes in that resistor kit?


and when you do the cam mod doesnt it cause the decompressor to be in a diff spot or something?

[Hozed]

Originally posted by SRH
and when you do the cam mod doesnt it cause the decompressor to be in a diff spot or something?


exactly... my dealer told me the little bit that it moves it would only throw it off at most 5 lbs.