Low Compression? Please help

[redhatman]

Hey guys, I am having a lot of difficulties with my Blaster. Its a 2002, supposedly has the hot rod crank, has Motion pro twist throttle, tors out, oil blocked off, idle kit, DG exhaust sytem, mixed 32:1 - 92 octane.

I was driving it the evening I bought it last weeked and about 30 minutes of runtime on it it started bogging and backfiring. I decided to shut it off, loaded it up and brought it home. I changed the plug with brand new ones several different times, and still wont run.

So far:
-Cleaned the carb twice by two different people, everything looks fine
-Checked reeds, resealed gasket
-Fixed exhaust leak out of engine
-Fresh Fuel
-New Plug
-Tightened the thing down that gives electricity to the plug so its nice and grounded
-Tors Out
-Cleaned air filter
-Cleaned Air box
-Took off panel to check flywheel, no play in it
-Has good spark
-Reset Carb to 1.5 turns out

The only thing left I believe would be compression, right? It is hard starting if I dont give up by the time it fires. While running it seems to run decent.

I noticed that if I put it in gear and try to push it, it will move fairly easily. For instance if I tilt my trailer down it will roll off in gear.

What else could I check? Whats the cheapest way to rebuild if I need to? I have no clue if this was bored out yet or not, and the guy I bought it from was as dumb as a brick.

Thanks a ton,
-Pat

 

[ron89]

yeah it sounds like its time for a rebuild .. .. i would say go with this .. Engine - Wiseco Piston Kits - ATV - Yamaha - Blaster
i just ordered my .090 piston from there .. but i would try a compression tester first befor u order any thing ..

 

[blasterfreek30]

if its rolling off the trailer in gear, i would say yeah no compression, time for a rebuild, defenitly go w wiseco for the piston kit!

 

[Lake]

how low should your compression be for a rebuild?

 

[blasterfreek30]

it really should be no lower than 100psi, good compression is between 120 and 150psi for stock

 

[redhatman]

Compression was reading around 90 on the first couple kicks, then steadily at about 60...Not sure though being the gauge would jump when I kicked it and go back to zero after i let off. I had to read it as I kicked.

How do I know if I have a "good spark" What should the voltage read? Also....How do I go about boring it out? Does the sleeve come out easily? Are there any guides as to how to measure the values and identify what to do? I will call NAPA tomorrow and ask if they can machine the sleeve.

I bring it to a machine shop right?

 

[blasterfreek30]

yes take the hole cylinder to a machine shop, u do not have to take out the sleeve, the shop will bore it for prolly about 50 to 80 bucks

 

[vspec]

don't go weisco for the piston,every time i rebuild anything with a weisco piston the wrist pin hole is always out of round,go with WSM.

 

[redhatman]

Isnt there anything else to try first? Maybe a head gasket or something? I dont want to bite the bullet right away and spend $150 on a "new" piston and sleeve...I just got it last week and it seemed to run fine.

 

[redhatman]

So I built a pressure tester and tried out the engine. There is a huge leak in the exhaust but other than that it seems fine. I tightened down the bolts but still nothing? Its a brand new gasket and high temp rtv on it... The engine will not hold 10 psi for more than a minute or two. Pressure tester is not leaking, nor the head or base or reed assembly seal.... just the exhust.

 

[ron89]

if it only has 10psi u need a rebuild for sure..

 

[redhatman]

if it only has 10psi u need a rebuild for sure..

That is all I pumped it up to with the pressure tester (tire chuck)

 

[blaster biotch]

if u are doing a leak down test you must make sure the piston is at tdc, all the way up to the cylinder head. there are no valvesso if the piston is too low in the cylinder it will pass right out of the exaust port. your best bet is to to a compression test by kicking the engine over a few times and seeing what it pumps up to. under 100 psi and a rebuild is necessary.and i would go with a weisco forged piston, there is nothing better.and spray a little carb cleaner in the intake and see if it fires up for a second. if so carb is clogged.and if you can put it in gear and it rolls eaisly and the engine is turning over (not clutch slippin) then i would say u need an over bore and new piston. or maybe u can get by with a hone and new rings.

 

[redhatman]

I got my atv all back together from cleaning the carb and pressure testing, also picked up some starting fluid. I sprayed some in and it fired but I killed it being it was like 11:45 pm and everyone in my house is trying to sleep. My next day off is friday to mess around with it.

What does that mean if it will start with starting fluid in the air intake and then run fine?

 

[igotacracker]

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