2 Stroke engine problems. Help!

[Jer]

It's been 6 months since it last ran, but on that last day it ran great.

My 2001 CR500 won't run. If you prime the cylinder by rocking it in gear, it will fire. Shortly after, it will bog and stall.

Another problem about every 10th kick while trying to start the bike, it will make a very loud backfire sound. I going to assume this isn't a good thing, but not sure with these bigbores.

I pulled the topend apart and the piston top is black as night. The cylinder walls look ok, no grooves, but they do show wear.

When I turn the crank with the topend off, it's coated in lots of oil.

The only thing this year thats really different, is the oil I ran yesterday when I tried starting it. ShellM . It's pretty thick, maybe thats the problem?

:scream: :scream:

Jer

 

[dell30rb]

Take the entire carb apart and clean, rebuild it. Did you check the plug?

 

[Jer]

whoops, guess I shoulda been more clear. :eek:

I took the carb apart, checked it over, looked ok.

Tried a few different plugs, the one I was first using was pretty fouled, so I slapped a new one in. No difference.

Jer
:think:

 

[Jer]

I would guess the backfireing (or whatever it is) while kicking it over isn't a good sign. I've never noticed this on any of my 2-strokes in the past. Unless it's bigbore specific ?

Jer

 

[Adrenaline]

Try running a compression test, I don't know the numbers off the top of my head but later on today I will look at Eric's book and find them for you. If the compression is not it i would look into, do you have spark? Air? and then fuel?
I hope that shell is premix oil and not motor oil. If it's motor oil then there is your problem most likely. I would use HP2 or even better Motul 800 2T
Good luck!

 

[Jer]

Once I get the topend back together, I'll run a compression on it. It is getting spark and fuel.

The shellM is premix, I run it in other 2 stroke 125 kart engines, but perhaps the 500 does not like it. :eek:

Can anyone comment on the backfire'ish behavior i'm getting while kicking it over? It happened off and on since the day I got the bike.

Jer

 

[Buzz Bomb]

Maybe when you kick it enough times, some unburnt gas gets into the exhaust pipe and when you kick the bike over it ignites the gas in the pipe as well as the gas in the combustion chamber. Just a guess, but I would check the piston/cylinder clearance to make sure your top end is still OK. Other then that, check your jetting and go back to your old oil. Maybe you got some bad gas? What octane is your gas?

 

[Adrenaline]

If gas is igniting in the exhuast then your timing is wrong si give that a check

 

[skhasky]

A couple of thought...

1) Make absolutely sure yout pilot jet is not clogged
2) make sure your floats arent leaking (remove and shake -listen for gas)
3) take your pipe off and inspect. Before I used a plug, I had a mouse nest in mine over the winter.
4) Your gas is fresh -right?