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Uneven Speed on my ST4

schmidt

Member
I have noticed that on our ST4 when climbing a moderate hill at about 10 to 15 mph’s a “chugging” motion. Almost like I was being erratic with the accelerator, when in fact I have it very still. Could this be caused by the track or the drive chains being to loose? Any thoughts would be appreciated.

Brad
Mountain Home Lodge
 

Melensdad

Jerk in a Hawaiian Shirt & SNOWCAT Moderator
Staff member
GOLD Site Supporter
Brad, some others with more experience my have better guesses, but it seems to me there are several possible choices.

1. Engine issues, if the engine is running smoothly during his problem then rule this out.
2. Clutch/transmission issues, this is no different than a manual transmission car, under load if you have a transmission problem with a car that has a manual transmission then a jerky ride is not uncommon.
3. Variator/variator belt issues. This seems to be more likely than a chain drive issue. If you had a few teeth knocked off a drive sprocket then you'd be slipping on ONE track, not on both tracks, so the erratic movement would tend to drive the Snow Trac one direction only. The Variator system controls both tracks and should then affect both sides.

Just my thoughts . . . now I need my morning coffee.
 

Wannafish

Floppy Member
SUPER Site Supporter
B_Skurka said:
Brad, some others with more experience my have better guesses, but it seems to me there are several possible choices.

1. Engine issues, if the engine is running smoothly during his problem then rule this out.

Bob,
I wouldn't rule this out without a little investigation.
It sounds to me like either a vacuum leak; a leak in the fuel line allowing air to enter; or more likely a partially plugged fuel filter. These issues MAY not be evident until asking the engine for additional power over a long period of time (such as going up a hill), in which case they wouldn't show up under normal conditions.

Rick

FWIW - I have never seen and ST4, let alone worked on one, so I am only going on what little knowledge I have of engines.:wave:
 

bczoom

Super Moderator
Staff member
GOLD Site Supporter
Wannafish said:
FWIW - I have never seen and ST4, let alone worked on one
But he did sleep at a Holiday Inn Express last night. :yum:

If you're on level ground and from a dead stop, try to get to full speed as fast as you can, what happens?
 

Wannafish

Floppy Member
SUPER Site Supporter
bczoom said:
But he did sleep at a Holiday Inn Express last night. :yum:

If you're on level ground and from a dead stop, try to get to full speed as fast as you can, what happens?

:yum: Yeah - What He said! :yum:

That brings up a good point. Level ground versus sloped. Might need the float in the carb adjusted if it only does it going up a hill...:blahblah:
 

schmidt

Member
Hi Gang,

Thanks for all the great suggestions and I'll get to work later today with some testing. The engine shows no signs of poor performance and I need to confirm that this is only happening on the up hill. Its tough when this is the only ST4 I have been in, so I have nothing to compare to. On a side note, good snow here with about 12-15" on the ground and hopefully more by the end of the week.

Thanks,
Brad
 

Melensdad

Jerk in a Hawaiian Shirt & SNOWCAT Moderator
Staff member
GOLD Site Supporter
Brad, is it pulling/jerking to one side? If so, then one of the chains or the gears maybe the problem.
 

schmidt

Member
Hi Bob,

I didn't get a chance today to do more tests, but I am suspicious about the chains. Its seems to me that one chain has more slack in it then the other. I need to take the machine out and run it straight for 30 feet+ a confirm this. The machine seems to track pretty straight. But, I wonder if there is too much slack in one or both of the chains thus creating an oscillating (chugging)that starts to happen, especially at certain speeds and loads (i.e.: up hill). Thanks Brad
 

BigAl

Gone But Not Forgotten
SUPER Site Supporter
I am betting on a plugged fuel filter . My ole Nissan truck ,that I had many years ago, did the same thing . A new filter fixed the problem .
 

schmidt

Member
Hi Al,

Thanks for the idea and I will give that a try. Also, the fuel has been in there most of the summer and I will burn through that today and get some new in and see if it improves.

Thanks,
Brad
 
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