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Discussion Starter · #1 ·
What would be the better motor for my wifes sled. its a 94 xlt sp. has i believe the 580cc in it but not sure. It seems to have a bog at the bottom end. had the clutch rebuilt last winter and the bog was still there. or i have a 91 rxl 650 motor that needs a new top end. has 9000 miles and is low on comp. Is it worth rebuilding the 650 or do i figure out what is wrong with the 580. Any suggestions on the 580 bog would be help full. any advice is greatly appreciated. Thanks in advance [thumb]
 

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Have you played with the carbs to fix the bog? but it is probably bogging due to warm summer temps. and yes, 94 xlt is the 580cc.
 

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All depends... It's going to cost about the same to rebuild the top ends on the two motors, when you're done do you want power or longevity?

For power. Rebuild the 650..

For longevity, rebuild the 580.
 

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Discussion Starter · #4 ·
I did play with them last winter and the bog never went away. Went and bought a good comp tester and the cylinders all have about 118-120 psi cold. I took the carbs off last winter when i got it and cleaned them well. ran with the bog all winter and didnt seem to hurt it. still has good comp. it has a light blue clutch spring (no not what the rate is) but it still bogs when its jack up-track off the ground. My next thing to do is to buy all new needles and jet for it or use the 650 carbs to see if that works.
its the wifes sled so longevity would be good but its also the back up sled for me so power is good to. Might just do both and have one as a back up motor
 

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I would check the seals on the clutch side of the crank shaft. They tend to have that issue when they go. To check this issue is to spray carb cleaner around the back side of the clutch when running and if the seal is bad you will hear the motor bog or rev up. Also spray around the crank case to see if there is any leaks in the case. My thoughts that the 580 is going to be better on gas and the 650 will be faster. So it is all in what you want.
 

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120 is decent compression, but a broken skirt will cause a bog and won't effect compression tests. Have you checked that?
 

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Ugly_old_Poo_kid said:
All depends... It's going to cost about the same to rebuild the top ends on the two motors, when you're done do you want power or longevity?

For power. Rebuild the 650..

For longevity, rebuild the 580.
I'm curious as to why you say the XLT motor will have better longevity than the 650. Having owned a 91 650 with Aaen pipes and a 95 XCR 600 with Aaen pipes both ran well and gave me a little trouble. Both sleds were good and would have been more reliable if not piped, but the fun factor was better with the pipes. The 650 was purchased new and the XCR was 1 season old but had a new short block from the well known crank issues. I replaced the original "A" pistons to "C" pistons in the 650 after breaking a skirt and burned one pto piston on the XCR during a few friendly lakes drags.
 

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For the bog, check the belt, if the belt isn't adjusted right, or is worn it will bog off the line, and maybe go a little stiffer on the primary spring, raising the engagement may help also.
 

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Ugly_old_Poo_kid said:
120 is decent compression, but a broken skirt will cause a bog and won't effect compression tests. Have you checked that?
[thumb] That is exactly what I would be checking. I had a 580 with a bad bog and it was due to a broke piston skirt. Compression still should 120. Take the pipe off and the carbs and look into the cylinders. Check to make sure all of the skirts are still intact.
 

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tnmemr said:
Ugly_old_Poo_kid said:
All depends... It's going to cost about the same to rebuild the top ends on the two motors, when you're done do you want power or longevity?

For power. Rebuild the 650..

For longevity, rebuild the 580.
I'm curious as to why you say the XLT motor will have better longevity than the 650. Having owned a 91 650 with Aaen pipes and a 95 XCR 600 with Aaen pipes both ran well and gave me a little trouble. Both sleds were good and would have been more reliable if not piped, but the fun factor was better with the pipes. The 650 was purchased new and the XCR was 1 season old but had a new short block from the well known crank issues. I replaced the original "A" pistons to "C" pistons in the 650 after breaking a skirt and burned one pto piston on the XCR during a few friendly lakes drags.
There's 580's that have passed the 15,000 mile mark without rebuilding... And there's those that will do it again after a rebuild.

That's longevity stories I never heard about the 650.
 

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Discussion Starter · #12 ·
Hangman said:
Does the 580 bog when taking off slowly or when slapping the throttle wide open? 118-120 isn't too bad yet.
Maybe this will help:

View attachment 20108121222408_24996.pdf
Thanks for the file. ill read it and try tuning the carbs a see what happens.It mostly bogs when you punch it, but if you gradually get on it, it dosent do it. also if you keep the rpms up its fine.

Ugly_old_Poo_kid said:
120 is decent compression, but a broken skirt will cause a bog and won't effect compression tests. Have you checked that?
Havent checked the pistons ill check those tonight when im cleaning the carbs for the 100th time.
dtmmil said:
For the bog, check the belt, if the belt isn't adjusted right, or is worn it will bog off the line, and maybe go a little stiffer on the primary spring, raising the engagement may help also.
the belt looks new but it could still be the wrong one. ill check tonight also. how do i check to see if the belt is adjusted right? The clutch seams to engage pretty late already, like around 2500-3k or so, maybe.
I also sprayed either all around the engine and no raising of rpms there. so no leaks on the out side. thanks again for all you help.
Will running it with a busted skirt hurt it in any other way should it be replaced asap?
 

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You need to check the belt deflection, and set that to specs, generally if the belt is riding about 1/16" to 1/8" over the secondary clutch your good, and engagement is way low, my xcr was at 5000, hell, my 700xc is low at about 3800. I would say you want it to engage at no less than 4000 with the triple, maybe more.
 

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like dtmmil said, 2500 to 3 is to low and would cause your bog. Id change your primary spring to get it to 4000 at least,I have a polaris blue spring in my 93xlt kicks in at 4 and has no bog.
if you do have a busted skirt change the piston now!
 

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Discussion Starter · #15 ·
No busted skirts. checked both sides (carb side and exhaust side) and all looks good. changed the carbs to a set i had off the 91 rxl 650. their bigger but they fit for testing and still has bog. even if the engagement is low or the spring is week, shouldn't having the track off the ground with no pressure help the bog a little?
 

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We have used this set-up and variations of it with XLT/XCR sleds in the past with good results. We found that most 34mm carbed XLTs perform beat when engaging @ 4200 or higher and 38mm XLT/XCRs @ 4700+.


HSP white primary 140/285
10M-5 weights
42/34 progressive or Polaris T1 helix
HSP white secondary #2 40/100
Gear to 20/39 or 21/41 (1.95 ratio)
Lean the needles at least 1 slot on the E-clip or go down on the nozzle size.
Mains 1 size smaller for sure
Keep an eye on the plugs and piston wash for jetting.
 

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Discussion Starter · #17 ·
So whats the standard size carb for a 94 xlt? the 34mm right? and the 650's got 38mm. So what spring should i run to get 4200rpms? looked at the spring chart and cant figure it out. Im not that smart.[beatup]
 

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yes 94 xlts had 34's
 

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Discussion Starter · #19 ·
tried a light blue (i think ) spring and it brought the engagement up but still bogin. gona try screwin wit the choke cables tomorrow. maybe those are out of alignment or sumthin.
 

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Remember also, its warm out, so it will be running real rich so the response isn't going to be what it will when its cold either.
 
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