Compression

[predator]

my son has a 98 blaster. when we ran a compression check on it. kicking it over it has 25 psi, (i know it way way low). but when put in gear and turning it over that way it has 50 psi, (i know it still way low). it will not start by kicking. but will start by pop starting it. it also has a high idle problem. my question is. why is the compression way higher when we turn the engine over by turning the rear wheels?

 

[blasterdude14]

well its by doing that its likely heating the motor up a little which would cause the piston to expand which would result in a higher compression thats the only thing i can think of.

 

[predator]

but we only have to pull it a couple of feet before it starts. i mean like only ten feet

 

[blasterdude14]

dont take long just depends on how fast you get it moving fast enough to where it will start.

 

[CHutzell]

you have to keep kicking it over until the guage quits going up with the throttle all the way open

 

[yb200]

you have to keep kicking it over until the guage quits going up with the throttle all the way open

yep.........................................

 

[predator]

we had it on stands and was turning it over with our hands by spinning the wheels. i forgot to mention that

 

[TeamCarr]

check your reeds. my mechanic always tells me to check that first when you have low compression. my bike had no compression but i could push start it still. the piston was fried.

 

[Scspeed]

your prolly due for a top end rebuild, you might be able to get by with just getting rings depending on the cond. of your cylinder walls and piston.

This is easy and cheap to do. Just do it.

 

[predator]

thats what i came up with. just looking for a cylinder that we can have bored. as the one we have is already 60 over

 

[370]

you can bore a .060 over cylinder.. you should have 2 bores left.. pull starting or "pop" starting sometimes works when you have a very weak topend. but the truth is you need to replace the topend on that machine..