HELP Sled Runs WOT!

[m-waage2]

Hi everyone,
Just got done with my 700 rotax motor. I ported and polished, RKT head with 13.2 domes, Crankshop pipes, one piece Cabontech reeds on modified cages, yadayada...

Anyhow I go to fire it up and it takes off, pegged, 9 Grand. Hit the kill switch and it keeps running, pull the tether, pull off the plug wires, still 9 grand! Good thing I didn't put the belt on! Finally choke it off when i grab the throttle.

So I look at it for a bit.

Start it up again, 9 grand. But now it shuts off with the kill switch.

Scratch Head...

The final verdict is it runs almost wide open, If I grab the throttle it will spin up a little bit more. Will shut off on the kill switch. No obvious air leaks that I can see. Tore it down again and the base gasket and head gaskets look ok but I am replacing them anyhow. Crank seals were good when I put them in, or so they appeared to be. Throttles are not sticking. I can find anything that would leak enough air to let it run almost unthrottled.

Just wondering If anyone has had this before or anyone has some suggestions at to what it may be.

On another note This is a DPM motor and the main jets in the roundslide carbs are 280. On my 01 700 I built the same last year It had DPM flatslide rack carbs. I was running 540 main jets in that. Though those are big It just seems that 280 Is too small. I'm riding in Two Harbors MN, at about 1000 feet. Any comments?

Thanks all!

 

[06MXZXRenegade800]

Hmmm, roundslide carbs eh... Sure one of the slides isnt in backwards casing it to stay wide open?

Been there done that one before, except on a dirtbike that i had to bombstart, that was a fun ride...

 

[Motley Doo]

Yup, my bet is one/both slides are in backwards. Been there, done that!

 

[BankBuster]

Yep, my thoughts when I read the subect too,,, buddy had a barrel installed the wrong way on a carbed sled (sitting up on a pin) and the sled nearly went throught the garage door, LOL,,, (belt WAS on),,,

 

[m-waage2]

Slides are in the right way and close fully.

Just checked the bottom end, filled it up with gas and no leaks.

Any other ideas?

 

[winter brew]

It has to be getting air from somewhere....I would do a leak down test.

 

[06MXZXRenegade800]

Definately have an air leak somewhere, a fair sized one too...


Sure your not missing a plug on an extra crank case pulse nipple? I know the series3 engines have a few 'spares' depending on the options with the sled (e-rave, electric fuel pump, ect)

 

[Bambino]

I had a slighltly bent needle jet once that caused the same thing. Not to familiar with your carb though.

 

[m-waage2]

How would you do this leakdown test?

 

[06MXZXRenegade800]

basically, you want to block off the exhaust and the carbs and shoot a bit of air through one of the sparkplug holes (dont go crazy, a couple psi should do, or you will be redoing seals!) then listen for leaks around the gaskets and seals.

 

[Motley Doo]

Wow, that must be a helluva leak to make the thing run wide open! I read back through and you said you were running 280's? If so, those are WAY to small, put something pretty big in it and see if it calms'er down, possibly just wicked lean, but still, turning that hard?

 

[06MXZXRenegade800]

mains wont matter, if the slides are really all the way down its just the idle circuit doing the work.

 

[sledcrazzy]

Well that sounds like fun, The mains are proly abit small but will not cause your problem, no way no how. Look for air leaks, did you tighten the cage bolts, how about the bent needle, i had a sled come in that had just enough bend in the needle to burn down, and it will hold a slide up.

 

[m-waage2]

Yeah I have visually checked the carbs (not while it is screaming I guess) and they are closing and working fine.

It's stumping me...

I checked all the nipples and all are plugged up, fuel pump, two little oil nipples are together, and the big one get thes oil reserve bottle... (Premix Motor)

 

[Motley Doo]

Yeah, I thought about that a bit more and no way the mains would do it, the motor is just feeding off the lower circuits with the carbs closed. So then what does the rest of the jetting look like(just thinking out-loud), but the motor MUST be getting air from somewhere else, motor won't spin without air. What do the plugs look like? White, any "other" material buildup? Huh, this is driving ME nuts!

 

[bri74]

Ok we you might want to start from scratch here... unhook throttle cable and run the rack by hand. another thing is when you start it does it wind right up or do you bump the throttle a little to make it start and run?. also check the springs on top of the carb slides?
I know you probably dont want to do this but your then gonna have to look into the throats of the carbs when its running and see what they are doing. Have someone else start her while your looking in the carbs, maybe use a mirror so your head isnt near any rotating parts!!And no long hair down there by the clutch or jewelry!

 

[sledhed]

Boost bottle missing, cracked, not sealing in the fittings on top of the reed boots? Maybe reed cage issues?

 

[tiewire]

is there any way the throttle cable could have got out of ajustment? i had a similar problem and it was the ajustment just below the throttle. don't know how it moved but when your taken things apart stuff happens.

 

[muttrmk]

It has to be your carbs. Air leak (other than carbs) will not pull fuel through. you must have had it very hot to run without plug wires. Did that once with a jet ski when it was not in the water. got so hot that it would detonate the fuel on it's own.

My guess is that the carbs were stuck open and when you were frantic, they dropped back down. Scarry but have you fired her up again now that it seems OK.

My .02

Mutt