The Classic "can't keep it idling" question.

[Elenor84]

Hey guys, I need some advice. I have a 1980 Ski-Doo Everest 500 that I'm trying to get running so my dad can come out riding with me. Its in ok shape and over the last little while I've been fixing it up. Everything is pritty muc good except I'm having trouble getting it to idle without stalling.

I'm wondering if there is an adjustment that I missed or something.

I can get it started and it runs and if I just hold the throttle slightly it will keep running. I'm not even holding the throttle enough for the clutch to engage. I believe its running alittle lean because when it starts to die, I simply press the primer plunger alittle bit(to dump some fuel in)it will pep right up and keep running. I have messed around with the air idle screw and done exactly what the shop manual says but still with no luck. I've brought the "E" clip on the main jet down a bit so to richen the mixture and still won't quite idle.

Does anyone have any thoughts on this or had a similar problem?

I've replaced the Ignition coils and put in freash fuel.

Maybe fuel pump not keeping up? Maybe replace it?

Again, It just seems to want a bit more fuel to keep running. How do I richen the mixture up a bit?

Thanks for any help !

 

[Trashy]

Have you tried replacing all of your fuel lines. They will get old, and brittle. thus allowing air in. Also, I would check the rubber boot's going from the air box to the carb, as well as the intakes. Float level, could also have a small impact on idling.

 

[Elenor84]

Have you tried replacing all of your fuel lines. They will get old, and brittle. thus allowing air in. Also, I would check the rubber boot's going from the air box to the carb, as well as the intakes. Float level, could also have a small impact on idling.

Thanks for the Reply, actually I have replaced all of the fuel lines and I replaced the gasket from the carb to the engine.

I did not replace the ruber from the airbox to the carb though. Maybe I will check that tomorrow.

How do you adjust the float level? Or is there a way of controlling that?

Thanks

 

[Modman]

Is this a mikuni carb or does it have the old Tillotson style carb on it?

If its a mikuni then you have to replace the pilot jet and adjust the air screw possibly. The air screw should be on the airbox side of the carb slide, a fuel screw will be on the motor side of the carb slide. They are 2 very different things, typically mikunis have the air screw though. You have to turn it in to make it richer.
It doesn't sound like you missed anything, if the fuel pump was going it would get worse as you increased the RPM, the fact that it starts running better means its likely not the fuel pump. You have to watch these sleds for vapour lock in the hot spring time temps, but usually that happens when its really hot and not an idle issue, they just bog out at high rpm.

I almost wonder if it almost sounds like you just need to increase the idle speed a little, they should be idling around 2000 rpm. You can do this by the idle screw or tighten up the cable adjuster. This is a simple solution and might solve the problem. I don't think the problem is electrical from what you describe.

I ran these sleds for years back in the 80's, my first sled was a 1978 440 TnT, they are not hard machines to work on and there's not a lot to them.

I hope that helps.

 

[Trashy]

Thanks for the Reply, actually I have replaced all of the fuel lines and I replaced the gasket from the carb to the engine.

I did not replace the ruber from the airbox to the carb though. Maybe I will check that tomorrow.

How do you adjust the float level? Or is there a way of controlling that?

Thanks

If you have a manual, it will tell you what your float gap should be at. As well drain the bowl, and put some rubbing alcohol in it(tank), just incase of water. Gas line anti-freeze will lower your octane numbers, and push the water out, where rubbing alcohol won't drop your numbers.

One last thing.......Go with Modman's advice. He does know his chit.

 

[Elenor84]

Is this a mikuni carb or does it have the old Tillotson style carb on it?

If its a mikuni then you have to replace the pilot jet and adjust the air screw possibly. The air screw should be on the airbox side of the carb slide, a fuel screw will be on the motor side of the carb slide. They are 2 very different things, typically mikunis have the air screw though. You have to turn it in to make it richer.
It doesn't sound like you missed anything, if the fuel pump was going it would get worse as you increased the RPM, the fact that it starts running better means its likely not the fuel pump. You have to watch these sleds for vapour lock in the hot spring time temps, but usually that happens when its really hot and not an idle issue, they just bog out at high rpm.

I almost wonder if it almost sounds like you just need to increase the idle speed a little, they should be idling around 2000 rpm. You can do this by the idle screw or tighten up the cable adjuster. This is a simple solution and might solve the problem. I don't think the problem is electrical from what you describe.

I ran these sleds for years back in the 80's, my first sled was a 1978 440 TnT, they are not hard machines to work on and there's not a lot to them.

I hope that helps.

MOdman, thanks for the responce, sounds like you know these machines very well. So I'm faily new to tinkering with these snowmobiles so I got a couple basic questions regarding your responce.

First off it is a Mikuni Carb.

You mention to tighten up the cable adjuster. Is this something you would do on the top of the carb where the cable goes in? If so I'll try that. And I'm wondering if I shouldn't just go down the the shop and just buy a new complete carb. Just so I'm no messing around with replacing stuff here and there. But if I don't do this, it may help to replace just the pilot jet?

Thanks again.

 

[Elenor84]

Also this is what the shop manuel says to adjust the idle speed.

C) Idle Speed Adjustment
Turn idle speed screw clockwise until it
contacts the throttle slide then continue
turning two (2) additional turns.
This will provide a preliminary idle
setting. Start engine and allow it
to warm then adjust idle speed to 15002000
R.P.M. by turning idle speed
screw' clockwise or cou nter-clockwise.

Am I reading this correctly? How can you turn a screw until it contacts something and then turn it more? Am I missing something? Because when it talks about the air screw it says to put it all the way in and then back it out 1 turn. The wording does not seem correct on these instructions.

I have tryed turning the idle screw all the way in and then backing out 1 full turn, 1 and half turns, 2 turns. It seemed to run best at 2 turns but still wouldn't idle.

 

[Trashy]

Also this is what the shop manuel says to adjust the idle speed.

C) Idle Speed Adjustment
Turn idle speed screw clockwise until it
contacts the throttle slide then continue
turning two (2) additional turns.
This will provide a preliminary idle
setting. Start engine and allow it
to warm then adjust idle speed to 15002000
R.P.M. by turning idle speed
screw' clockwise or cou nter-clockwise.

Am I reading this correctly? How can you turn a screw until it contacts something and then turn it more? Am I missing something? Because when it talks about the air screw it says to put it all the way in and then back it out 1 turn. The wording does not seem correct on these instructions.

I have tryed turning the idle screw all the way in and then backing out 1 full turn, 1 and half turns, 2 turns. It seemed to run best at 2 turns but still wouldn't idle.

Turn it back in a 1/2 a turn, and small adjustment from there.

 

[Trashy]

You should be around 1.5 turns out from lightly seated.

 

[Elenor84]

Ok I'll give a few of these tips a shot tomorrow and let you know how it goes.

 

[mrsummit700]

Are most sleds idling at 2000rpm? My summit 700 seems to idle smoothly at 1500rpm?
Just wondering Thanks

 

[rusty]

dropthe needle to the 3rd spot and be very sure the idle jet it clean. the barrell should be bottomed in the carb
where are you?? i know what is wrong

 

[Modman]

Also this is what the shop manuel says to adjust the idle speed.

C) Idle Speed Adjustment
Turn idle speed screw clockwise until it
contacts the throttle slide then continue
turning two (2) additional turns.
This will provide a preliminary idle
setting. Start engine and allow it
to warm then adjust idle speed to 15002000
R.P.M. by turning idle speed
screw' clockwise or cou nter-clockwise.

Am I reading this correctly? 1) How can you turn a screw until it contacts something and then turn it more? Am I missing something? 2) Because when it talks about the air screw it says to put it all the way in and then back it out 1 turn. The wording does not seem correct on these instructions.

I have tryed turning the idle screw all the way in and then backing out 1 full turn, 1 and half turns, 2 turns. It seemed to run best at 2 turns but still wouldn't idle.

1) Yes you can keep turning it in more. there is a spot on the slide where the idle screw contacts it, that spot is tapered upward, so as you turn the screw in, it pushes the slide farther up in the carb throat and lets more air in, there fore increasing the idle speed.

2) The air screw regulates how much air passes into the carb at idle. The air screw, pilot jet and idle speed screw control the lower throttle positions to about 1/4 throttle, the main jet controls 3/4 throttle to wide open and the needle and tube control about 1/2 throttle to 3/4 throttle. Adjusting the main jet will not help your idle problem, since there is not enough air velocity in the carb throat to pull fuel up the needle jet at idle.

I have attached the mikuni tuning manual for roundslide carbs. The very last page describes which fuel circuits control which throttle openings. This is the comprehensive manual for the VM roundslide carbs, it should help you trouble shoot the problem.

http://www.mikuni.com/pdf/vmmanual.pdf

I still think you should try adjusting the cable tension first though, since it's the cheapest solution. You are correct, there is a barrel adjuster and threaded stop nut on the top of the carb where the cable goes in, you need to back off the stop nut and then back the barrel adjuster out so that it takes up the slack in the cable. If you can do this when the sled is running you should hear the idle speed increase as this will raise the carb slide (just like the idle speed screw).

Optional part once you get it idling correctly: Some guys (like me) only adjust the cable tension to regulate the idle speed, I never use the idle screw. This way the slide is suspended from the cable, and not resting on the idle screw. When you hit the gas, there is no cable slack to pick up the carb slide and therefore your throttle response is slightly increased.

Hope that helps.

 

[Elenor84]

Success!!!

I got it running. I should really say we got it running. I went to the shop and got a new main jet and new pilot jet and I'm 99% sure it was the pilot jet that was causing so many problems. As soon as I took it out and held it to th light I couldn't see any light through it. Replaced it put the carb back in and it fired right up!(once the float bowl was full of course)

Man, thank you guys so much for the help! I really appreciate it.

So now I guess the next question is, when can we got out riding???

Here's a couple pics of the culprit

 

[Elenor84]

You should be around 1.5 turns out from lightly seated.

So as mentioned above I got it running really smooth, but kinda interesting. To get it just perfect, I'm like 3.5 turns out. Not sure if thats ok or what not, but it runs great.

And maybe a dumb question but, the sled does not have a tach, how can I determine what rpm it is running at? Do I need to get a tool to hook t the spark plug wires or something?

 

[Trashy]

So as mentioned above I got it running really smooth, but kinda interesting. To get it just perfect, I'm like 3.5 turns out. Not sure if thats ok or what not, but it runs great.

And maybe a dumb question but, the sled does not have a tach, how can I determine what rpm it is running at? Do I need to get a tool to hook t the spark plug wires or something?

You can hook up a temp external tach, and see what your idling at. As long as you are running smooth, and the clutch does not want to engage at idle, or want to lurch forward, you should be fine.

Also, now that you have it dialed in at idle. Don't forget to do random plug checks, after warmed up to operating temps.

I'm glad it all worked out for you.