mabee a bad stator that isnt putting out enough power at low rpms to fire the plugs, bet once the rpm's is increased it has a bit more voltage.

not sure, just an idea, mabee a larger idle jet might be an idea.

 

Starving out at idle. Check that the air screw is open far enough. that is the small screw closest to the airbox. It should be 3/4 to 1 full turn out. Turn it out in 1/4 turn increments.

 

What color should the spark be when you are just pulling the cord to crank the engine over? I seem to be getting a medium strength spark, mostly yellow in color.

 

the spark will be yellow or blue, depending on how fast you can turn it over.

 

The air screw does not seem to make alot of difference. I have had simular results with it in all positions from completely closed to 4 turns out. I did turn the idle way back down today from what the shop had set it. When I primed the engine with the squirt bottle and fired it off it ran VERY fast. I had to kill the ignition to keep it from shooting off the trailer and out of the garage. It was close. I agree that it seems to be a starving at idle situation. I just can't seem to find the cause. Is the idle jet changeable on this carb? I can't imagine it being too small as I live at 8500 ft. elevation. Are there sources for possible vacum leaks I could look for? What is the valve (?) below the carbs that is also controlled by the throttle? How do you synchronize these carbs?

Thanks to all who can help or even give me a guess that I haven't thought of.

 

I guess I should have mentioned that the sled only has 1700 miles on it.

 

That is the oil pump. the carbs can be set by feel, using your fingers, set the slide to the same hight with the idle screws and then gently squease the throttle. Bothe of the slides should move at the same time. If not, you can adjust them with the screw opn the top of the carb where the cables go in. One of the things that you can check is that thw floats in the bowls are set correctly. You remove the carbs and take the bowl off and turn it upsidedown and set it on a level surface. The arms that move the needle valve should be parallel to the body, or slightly down at the tips. If they are up at the tips, that is why there is not enought fuel to make it run right.

 

I will check the float levels tomorrow. Am I thinking wrong though that too low of a fuel level in the bowl would more likely cause a problem during extended wide open throttle than it would at idle?

 

It will cause a problem at both ends of the rpm, but if it is low, it can cause idle problems.

The only other thing is that the low speed jet is partially clogged. You can use compresssed air to check this by removing the screw and blowing out from the inside of the carb.

 

When you have the carbs off to check the floats, pull the pilot jets and run a small strand of fishing line or very small wire (one strand of a twisted wire) to clean the jet. Fuel at idle is metered by the pilot jet, they are very small and sometimes even after cleaning, they have a restriction. You could even toss a couple of new pilot jets in as a diagnostic, they are not expensive. Being as it runs great at higher rpm, focus on the low speed circut (pilot jets); your floats are probably ok if you are getting adaquate fuel at high RPM.

 

Also may have saturated floats! I've seen it before!

 

Well, I took the carbs off today and checked the float level. Both were fine, fuel bowls were full. I removed the pilot jets and blew them out. Also ran air through the carbs. Didn't find any junk at all. The pilots did appear to be completely clear. I synchronized the carbs so both started to move after squeezing the throttle about 1/4".

I put it all back together and primed it with the squirt bottle. It fired up enough to fill the carb bowls. I put it on full choke and fired it up. Only took about 6 pulls. After a few seconds I switched it to half choke. It seemed to settle down and idle fair at half choke, about 2100 rpm. After a couple minutes I switched the choke off and the rpm shot up to 4200 for about 5 seconds then it started to fall off and about 5 seconds later was dead. I restarted at half choke 4 more times with identicle results. Could this be in the settings on the carbs? The small screw on the right side is 1 turn out and the large screw on the left side is 1 1/2 turn out. Which of these screws is which and where should they be set?

Thanks for any help or SWAGs.

 

The small screw next to the aribox is the mixture screw, should be 3/4 to 1 turn out as you have it.
If you work the throttle after you cut off the choke, will it still run?
If not, you still have a plugged pilot jet.

 

I can keep it running with the throttle without the choke on but it requires finesse especially if the rpm fall below 2500. Since the pilot jets have been verified clean, is the problem likely in a passage that feeds fuel to them? The sled did sit for about 2 years before I got it. Is the solution to completely tear down the carbs and soak them in solvent for a couple days? Any guesses why this wasn't taken care of when the shop rebuilt the carbs?

Dang, I'm tired of messing with this thing. Once I get it running right I will be regearing both sleds. Sure hope we get the snow to make all this worth it this winter.

 

I was going to suggest that next. I think it's the actual passage the jet goes into. Get some spray carb cleaner and spray into that jet hole and let it sit. You may have to get some small wire. etc to try to open the passage. Then use some compressed air to blow it out really good. If you can open the passage up, I think you'll have it.

 

Like you and SEG said, if your pilots are clean as a whistle, the passages may need to be cleared.

They make some killer carb cleaners that come in about a gallon can (I use Chem-Dip, purchased at an auto parts store). The can comes with a basket, you put the parts you want cleaned in the basket and let it soak. It's deadly on varnish, much more so than the aerosol can stuff. Follow directions, and don't put any rubber or plastic parts in; you won't like it when you pull 'em out

If you put the lid back on the can to let the stuff work, be careful taking the lid off... the chemical reaction will build up some pressure and any cleaner on the rim of the can can fly up and get in your eyes. The instructions state to open the opposite side of the can slowly to prevent this, and wear safety glasses!

 

good trouble shooting for 580 cat carbs.

as said in the header , good tech support and info. here . have the same sled only a 96 thats been sitting for @ 5 years . slipped my mind to yank the carbs and soak em . have lots more to deal with before even trying to start this kitty. LOL , looking forward to your support .

 

have you figured it out yet??


mabee crank seals if you havnt cheched that yet, it sounds like a carb problem but mabee not.

 

Finally found it

Well, we finally found the problem. It was the clutch side crank seal. What a huge pain in the neck for a $21 part. Thanks to all who tried to help.

Dave

 

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