470 Rotax Motor Idle And Rotary Valve Timing - Snowmobile Forum: Your #1 Snowmobile Forum

1972 Skidoo 399 · 07-16-2012, 11:42 PM

Hi there bought a sled for 100 bucks few months ago with a locked motor, came to the conclusion it was toast, so i bought a beater sled with a rebuilt bottom to top Rotax 470, but heres the problem.....

didnt run when i got it, compression tested 155 - 160 both sides. Cleaned the carbs there was about an 1/8 inch of green stuff in the bowl and all inside the carb never seen that before had to scrape it out when a screw driver before using my carb tooth brush believe it or not, but there completly clean now.

He said he Advanced the rotary valve some to give some more throttle response and that it did but it idles VERY high, the carbs where out of sinc so i fixed that, the idle screws are 1 3/4 turns out and high speed jet is 1 1/2 turns out.

Is this causing it, I noticed that the throttle cable comes down to where the rotary valve is right ontop of the intake manifold and i was going to adjust it but then i thought, is this for the oil injectors? if i adjust it there will it mess something up??

anyone with ideas?

**smallengineguy** · 07-17-2012, 06:24 AM

That cable goes to the oil injector, so don't touch that! It may have an air leak somewhere. Start it and spray carb cleaner around the crank where the clutch attaches, as well as into the recoil area. If the idle changes, the crank seal is leaking. Advancing rotary valve timing won't make it run faster.

1972 Skidoo 399 · 07-17-2012, 11:31 AM

Ok I will try that but will have to adjust the idle first incase it does speed up, itl go right through my other sled into my garage wall!

What is the normal idle adjustment for these carbs?
and should the crank seal leak, how would I go about replacing it? I know the clutch will have to come off but have never replaced one of these before.

davidnnoah · 07-17-2012, 08:11 PM

Not sure what year 470 you have but the air screw should be 1.5 out from 90-93 94 and 95 gets complicated from 3/4 to 1 and 5/8 depending on model.

Idle varies as well but most sleds are good around 18. Set with idle screws, not air screw. Good luck.

1972 Skidoo 399 · 07-17-2012, 08:50 PM

My Sled is a 86 but the motor im pulling from the parts sled is an 84 and i dont know if 470's where made in 84, it is no later then an 89 but thanks for the advice I appreciate it!

**smallengineguy** · 07-18-2012, 06:19 AM

If the crank seal is gone, you need to remove the motor and take off the bottom of the case to replace it.

1972 Skidoo 399 · 07-18-2012, 10:29 AM

Oh, Well that sucks... I havnt started it up yet though and tryed spraying some wd40 at it but I will later on today. Hopefully it is a carb adjustment and now a crank seal.

I forgot to mention the motor and primary get real hot after running for maybe 45 seconds, like if I touched them I would Burn my Hand....... is this because its idling to high ? I never had a sled that got warm like that in a matter of seconds

**RJ Gleason** · 07-18-2012, 11:16 AM

Check that end bearing too while you have the case split to replace the seal, I'l bet it's bad.

1972 Skidoo 399 · 07-18-2012, 01:21 PM

I just nocited that a Line with a spring that comes off the oil resivour that goes to the rotary valve is broken, not the bottom but the top, would that cause it to lean out?

but I prefer to avoid spliting the cases untill it is the last resort because of replacing gaskets and everything

davidnnoah · 07-18-2012, 05:39 PM

[QUOTE=
I forgot to mention the motor and primary get real hot after running for maybe 45 seconds, like if I touched them I would Burn my Hand....... is this because its idling to high ? I never had a sled that got warm like that in a matter of seconds[/QUOTE]

Running that hot is crazy. You're lean and causing damage. Best find the problem.