Snowmobile Fanatics banner

1 - 20 of 20 Posts

·
Registered
Joined
·
36 Posts
Discussion Starter #1
Running hot, plugs are coming out hot..
machines looses rmps after 3/4 throttle, hits about 8500rmps then dies off from there. No real top end power. main jets are 420's? i think...
gas is clean, carbs look good, strong spark..just no top end and running lean.
any ideas? or things to look for? thinking of bumpin' up to 500 mains...
 

·
Registered
Joined
·
567 Posts
What altitude are you running at and what's all done to your sled that you know of
 

·
Registered
Joined
·
4,016 Posts
First of all, you're revving about 400 RPM too high, and asking for trouble revving it that high.

No reason you should need 500 mains.

What altitude do you ride?

What is your current clutching and jetting setup?
 

·
Registered
Joined
·
36 Posts
Discussion Starter #4
i don't know the clutching set up...why would the power die off when it gets to the top end with the clutch? we are just runnin' it track off the ground..
jetting was 420's tried the 500s and it made it worse, the bog anyway.
its got a MBRP can on it and gutted air box...so far thats all i can tell...we disconnected teh ATACC just to eliminate that problem.
riding from sea level to 2500 feet about.
 

·
Registered
Joined
·
36 Posts
Discussion Starter #6
need to put this sled on the snow by monday and we are at a loss right now for ideas....?
 

·
Registered
Joined
·
2,125 Posts
powderburner said:
need to put this sled on the snow by monday and we are at a loss right now for ideas....?
Don't know much about your sled. Is it a 700 or 800? Again, 8500 rpms is high for any twin. Have you done a piston wash test for burn? Are you using the correct spark plug and its hot/cold rating? Ethanol Gas burns hotter than a non oygenated fuel. Just some ideas to start
 

·
Registered
Joined
·
36 Posts
Discussion Starter #8
we put new pistons and rings in and check cylinders everything looks good. spark plugs are whats listed to be in it...
 

·
Registered
Joined
·
2,973 Posts
Install 450's, add a couple grams weight to the clutching. And running it on a stand doesn't do do justice to any sled without loading the engine and clutches.
 

·
Registered
Joined
·
4,016 Posts
Spot on Marv.

420's are too lean for that elevation and 500's are way too rich.
 

·
Registered
Joined
·
36 Posts
Discussion Starter #11
well its on the stand now because when i ran it on the ground i could feel the bog after the 3/4 throttle..and the stand is the easiest way to see if the bog is still there...and it is.
the 500's didn't richen it up...same problem as before. could this be an oil pump deal or something of that nature?
 

·
Registered
Joined
·
4,016 Posts
You need to ride the thing to tune it.

Nobody tunes on a trackstand.
 

·
Registered
Joined
·
36 Posts
Discussion Starter #13
well we are just trying to get the bog out first...it bogged on the ground, bogs on the stand..figure if we can get it off at the stand, it might be gone on the ground. least be a start...
plugs are coming out hot even with the 500's in it.
 

·
Registered
Joined
·
4,016 Posts
What do you mean by "hot"? Like, they're literally hot? Or they're burning the electrode off? Looks lean?

If it's lean with 500 main jets, you have an air leak somewhere or the jets are partially plugged.
 

·
Registered
Joined
·
36 Posts
Discussion Starter #15
sorry, they are coming out lean...whiter...
air leak? its got a gutted air box, carb boots are good...where else would i be looking?
jetts are all clean and seem to be doing fine...
 

·
Registered
Joined
·
395 Posts
just going by what I read on here. Check the exhaust valve bellows for rips/tears. That will kill your topend and rpms and anything else past 3/4 throttle
 

·
Registered
Joined
·
4,016 Posts
Are these new plugs you're using? New plugs take a while to show color. Don't assume you're lean if they're brand new plugs.

Spray the carb boots and PTO crank seal with ether, if it revs up, you have an air leak.
 

·
Registered
Joined
·
9,980 Posts
If it's turning 8500, you need to look at the clutching..
 
1 - 20 of 20 Posts
Top