[McDale78]

Hey all, new to the forum here; thanks for any help you can offer ahead of time!!

I’m having a strange issue with my Rotax 800. The issue is that it wants to continue to pull and keep going for a second or so AFTER letting go of the throttle. It seems to idle ok (now: see below) but not perfect. It’s fine when using a small amount of throttle to just put around. But when you walk on it and pull hard it seems to continue to burn fuel even with the throttle closed for a second or so!

I’ve tested the throttle cable and the slides and can clearly see the linkage snapping back just fine. So, I don’t think this is a throttle cable issue.

It was having issues idling after it sitting for a couple of years this time. (Kids!). So I pulled the carbs off and cleaned them up fully. They did have a little old fuel scunge down in the bowls but using carb cleaner and solvent the fuel passages and jets are now squeaky clean.

After putting them back on this issue I described now happens. However my brother borrowed and tried the sled last year too and said it was doing this exact thing then too and was scary so the

My theory is that maybe there is some sort of air leak between the reeds and the carbs…maybe the carb mount boots? Any good way to test this? I was thinking of maybe spraying some ether in that area ahead of the carbs and see if it revs up? Or maybe something to do with the DPM system? (Don’t really know how the DPM works..)

thinking the boots might be the case because:
-a couple years ago I burnt up the stock motor and this is a new shortblock
-all the original accessories including carbs boots etc were from the original motor
-it seemed to be running hot the first couple rides after changing the engine out
-now this problem with “run on” of fuel burn…

Any ideas, confirmation, or other ideas would be greatly appreciated.

McDale

 

[racnooc]

If you look at the carb boots they might be starting to de laminate or have cracks in the rubber. The only test i know of is just a visual. Maybe take them off so you can get a really good look at the underside of them. If you need replacements Boysen cages are metal and they have some for your sled on their web site. I have a pair on my 800 and have been happy with them so far.

 

[McDale78]

If you look at the carb boots they might be starting to de laminate or have cracks in the rubber. The only test i know of is just a visual. Maybe take them off so you can get a really good look at the underside of them. If you need replacements Boysen cages are metal and they have some for your sled on their web site. I have a pair on my 800 and have been happy with them so far.

Cool, thanks. I’ll look into those if mine are faulty.

Does my line of thinking sound right? Do you think issues with the boots would cause that? I don’t want to pull all that stuff off there if the issues it’s causing are unrelated…

 

[racnooc]

It sounds like the boots, that is how mine acted when the boots were letting go. Mine were starting to separate on the top so they were easy to see. You can do a search for "Carb Boots" on here and find a lot of posts about carb boots.