rpm's running high at idle!!!! - HCS Snowmobile Forums

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Old 01-31-2010, 07:30 PM   #1 (permalink)
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When I run my sled just below freezing the rpm's gradually fall down to the recommended idle speed of 1600 rpm. But the colder it gets the worse the problem gets. This weekend if i blipped the choke on the rpms went directly down to 1600, but immediately climbed to high 2000's even as high at 3000!!!!!!! I was afraid I might over heat the engine as I'm now of the opinion that the jet's are too small. I bought this sled used and it had a melted piston so I'm been very timid and cautious when riding. I read somewhere that if you need to quickly choke the engine to get the rpms to return to idle the jets are too small. Is this true? and could there be another reason???? If this is a jetting problem should I go buy the "recommended stock jets" or pull apart the carbs and just up size 1 or 2 sizes???

Tomorrow I'm putting new plastic skis' and track, and since I'm already going to be working on it I might as well figure this problem out while it's being taken off the trails anyways.

Thanks,

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Old 01-31-2010, 08:02 PM   #2 (permalink)
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i tell people all the time jets dont just magicaly change sizes, Only way they change is if you change them. Unless it did this since you got it and dont know what kind of jets are in it?

Might just need a cleaning. Or you have a cracked carb boot or its sucking air somewhere.

Check your carb boots from the inside for cracks. If none, spray a starting fluid or carb cleaner on the ends of the crank and see if your idle changes (if it does its a clear sign your seals are sucking air).

Spray behind the clutch, and take the pull cord assembely off, then emergency start the engine and spray that end of the crank
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Old 01-31-2010, 08:19 PM   #3 (permalink)
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Quote:
i tell people all the time jets dont just magicaly change sizes, Only way they change is if you change them. Unless it did this since you got it and dont know what kind of jets are in it?

Might just need a cleaning. Or you have a cracked carb boot or its sucking air somewhere.

Check your carb boots from the inside for cracks. If none, spray a starting fluid or carb cleaner on the ends of the crank and see if your idle changes (if it does its a clear sign your seals are sucking air).

Spray behind the clutch, and take the pull cord assembely off, then emergency start the engine and spray that end of the crank[/b]
Listen to this kid! Talking like he knows something. LOL.

Actually, he's spot on. All good advice right there.
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Old 01-31-2010, 08:43 PM   #4 (permalink)
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Listen to this kid! Talking like he knows something. LOL.

Actually, he's spot on. All good advice right there.[/b]
:beer_cheers:
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Old 01-31-2010, 09:21 PM   #5 (permalink)
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I did a total rebuild including crankcase. ALL seals and gaskets have been replaced including the oil seals on the crankshaft. And I retorqued everything on the engine after 3hrs of use. Today while I was loading the sled in the back of my friends truck it was not idling nearly as high and it was 15 deg. C. or 25 deg. F warmer!!!! So I really hope that it's not sucking air! When i rebuilt the engine the Carb boots looked like new. I have not touched the jets since I bought it with the blown engine and I did not check the what size the jets were, but I'm running the sled only a couple hundred feet above sea level at temperatures from -5 deg. C to -25-30 deg. C./ 25F down to -10ish deg. F. So when I'm looking at the jetting charts I'm in the larger jet range am I not?

But I will definitely try the advice for checking for an air leak. I just HOPE and think thats not the case..... I will also recheck the carbs for dirt, but I've got less than 7 hrs (100 miles) on it and I replaced all fuel lines and cleaned the gas tank/fuel pump/ and carbs during the rebuild. I was being this through because I didn't know how long the sled had been sitting since it last ran or why it burnt down.
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Old 01-31-2010, 09:24 PM   #6 (permalink)
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Like I said, do a plug check. It'll save you in the long run.
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Old 02-01-2010, 02:23 AM   #7 (permalink)
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Is it the 93 indy trail fan cooled?
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Old 02-01-2010, 11:23 PM   #8 (permalink)
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Yes it is the 93' 488 fuji fan cooled.

Spent 4 hrs today putting on new skii's and track. But didn't have the energy to really get into the carbs. I was able to bring it into a heated mechanics shop......SO nice being able to work on the sled with a t-shirt on!!!!

I wasn't able to run it today, but the plugs didn't have any blistering both were wet after sitting for 24-30 hrs; with out being run, and that was only to run the sled up to the truck. Which doesn't really tell me anything, I adjusted the pilot jet down from the stock 1 turn out to 3/4 and then 1/2 this did have an effect but not too much. But I didn't get a chance to actually drive the sled around. I did change the plugs from BR8ES to BR9ES today. I will try to check for air leaks tomorrow....

If I find an air leak at the carb boots, is there an easy fix or am I into ordering new boots? I.e. gluing them to the shroud???????

I'm hoping to go up north on Wednesday, so I need to get this problem under control soon.......

Thanks, for any and all help, it's much appreciated!!!!
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Old 02-02-2010, 06:00 AM   #9 (permalink)
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if the sleds cold and u moved 20 feet that tells uu nothing about plugs and jetting realy, plugs can foul under strain but still spark and look like they should work.
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Old 02-02-2010, 09:33 AM   #10 (permalink)
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Current Sled(s): 2002 Pro-X 440 EFI ; 2012 PRO RMK
Previous Sled(s): 1993 Polaris Indy trail
Location: Vancouver, BC. Canada
12-13 Mileage: 450+
11-12 Mileage: 800
10-11 Mileage: 1200
Age: 26
Riding Since: 1991
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"and that was only to run the sled up to the truck. Which doesn't really tell me anything, " did you read that part of my reply? Anyways, I'm going to check for airleaks today and get into the carbs to find out what size the jets are. will give an update later.
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