2000 SXR 700 "thumps" during slow take off

CharlieSmith

CharlieSmith

New member
Joined
Feb 13, 2011
Messages
5
Age
62
Location
Greece NY
Hello all. I am new to the sport of snowmobiling. I bought 2 used sleds last year and only have about 1200 miles under my belt. So please forgive my ignorance of some of the terms used to describe my problem.

Some background information that may or may not have led to the problem........Prior to the season, I replaced the hyfax in my 2000 SXR by removing the suspension. I had no problem removing the suspension and it was a breeze to remove/replace the hyfax. Putting the suspension back in was another story. I'll leave story that for another time.....

Anyway, I now hear and feel a very distinct "thump, thump, thump" on slow start. The noise seems to go away after ~ 20 mph. At first the thumping noise would go away completely after putting some miles on the sled. I was recently riding it and noticed after about 10 miles, the noise did not go away....so maybe the problem is getting worse?

I've checked the belt and see no missing sections and it still looks good (it was put on new late last season).
I've checked to see if any of the track studs and track paddles were bent/damaged, thinking maybe one was hitting the tunnel....all good.
I've adjusted the track, both side to side and tension, per the Yamaha maintenance manual.
I've played with track tension to see if I could get the problem to go away by loosening the track (the tension spec in the manual seemed too tight)

Any help/advice is appreciated!
 

First off, Welcome!! I was thinking belt but..... Have you tried putting the sled on a stand and running it? get someone to operate the throttle. Are your hyfaxes the right length? They arent hanging out the back end to far are they? Bearings were good when you put them back in? You didn't knock a stud protector off the front cooler did you? I'm sure somene else will chime in, my brain is foggy right now. Need more coffee.
 
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FJViper said:
First off, Welcome!! I was thinking belt but..... Have you tried putting the sled on a stand and running it? get someone to operate the throttle. Are your hyfaxes the right length? They arent hanging out the back end to far are they? Bearings were good when you put them back in? You didn't knock a stud protector off the front cooler did you? I'm sure somene else will chime in, my brain is foggy right now. Need more coffee.
Click to expand...

Thanks for the welcome and the quick response! I did put it up on a stand and ran it.....no "thumping" noises were heard or felt, so it seems it just happens when the sled is under a load. The hyfaxes were OEM Yamaha and pre-cut to length and beveled on the end. I also made sure they were the same length as the ones I took out. The bearings seemed good.

Now, about the cooler stud protector. I'm not sure if I knocked it off or not as I wasn't aware there was one. Is there an easy way to check?

Also, something else I failed to mention in my original post (sorry): I drove the sled around at slow speeds with the cowl up and the belt guard up. While watching the clutches, the drive clutch (the one coming off the engine) would squeeze the belt just a little during the thumps. In other words, it looked like it would engage the belt a little more during the thumps. I wasn't sold on this being the problem, because (in my pee brain), the clutch may do that because it was seeing more load at the time of the thump?

Thanks again.
 
tractordanp said:
i would say you have a flat spot on your belt switch it out and try it
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You know, the more and more I think about it (and type about it), swapping the belt would be the easiest thing I could do to eliminate/prove the belt as the problem.

Not sure why I didn't just swap it out. I visually inspected it and called it good. I guess I was thinking the worst having just re-installed the suspension and not knowing of any event that could have flat spotted the belt.

I will swap it the next chance I get, but it might be a while...........our little bit of snow we have is suppose to melt today with temps above freezing the rest of the week.
 
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Back off the nut on your chain case adjustment. tighten the bolt up by hand and tighten the nut. Doesn't take but a little slop to make noise.
 
Thank you all for the replies!

I will swap out the belt, check to see if the problem goes away. If not, I will adjust the chain tension. I'll check back in with the verdict.

Thanks again. I really appreciate all the feedback! ;)!
 
Well...don't I feel like a dumbazz. :o|

I replaced the belt and the "thumping" went away.

I guess I was confused because the problem started right after I re-installed the suspension and I was focused on the suspension. The old saying about cant see the forest for the trees comes to mind. ;)!

Not sure what's wrong with the belt. It looks mint. No flat spots. No damage at all.

Now, I need some snow so I can properly "test" it out!

Thanks to all! :rocks:
 
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