Snowmobile Forum banner

1 - 7 of 7 Posts

·
Registered
Joined
·
2 Posts
Discussion Starter · #1 ·
Hello -

Nice forum. I've been researching an issue with a sled I recently bought and following advice from other posts to troubleshoot. I've run out of ideas though. Sorry this post is so long but wanted to give all the details.

First the background: Bought a used sled a month ago and when PO went to demonstrate the throttle cable ferrule broke. He knocked $100 off so we closed the deal. Took it home and rigged a temp fix but this left throttle partially opened on start. It was hard to start, my guess is because throttle was cracked, and needed starting fluid. When it started though it took off like a rocket and I drove around the yard for a bit. While I waited for cable on order I took off carbs and cleaned them per instructions on forum for Mikuni's. Also drained gas tank to be safe, installed new filter and all new fuel lines (they looked brittle). New plugs too (BR9ES). I also removed bolts on each side of case that allow you to drain any excess gas. In putting them back the one closest to magneto broke leaving a piece of stud in hole. New cable arrived and put it on and visually synced the slides.

Started right up and idled pretty good. I was just starting to go when I heard a loudish bang sound once and then it sounded different. Checked and noticed that the case bolt that had sheared was gone (I assume blown out and not sucked in) and difference in sound was this opening in case. The sound I heard once could have been the bolt blowing out and hitting something because it was kind of a bang like metal on metal but I could not find the piece of bolt. So I shut it off and located a replacement bolt same exact size and seated it and sound was normal.

Started right up but now it won't go with my weight and has no power. I am running on one cylinder on PTO side. I am confirming the one cylinder after every step below by pulling the wire from the mag side and sled still idles. When I try pulling the PTO side (with mag side on) it dies right away. With PTO side connected it will idle just fine on the one cylinder. I'm using an insulated wire puller and still feeling a noticeable shock so I believe I have a good CDI.

Here is what I have tried so far:

1. Ran compression test (120 mag side, 118 PTO side).
2. Checked plugs and PTO side looks new but mag side is wet. Replaced both to be safe. No change
3. Swapped carbs, no change.
4. Swapped plug wires, no change.
5. Took off carbs and flanges and inspected piston travel. Do not see anything broken or abnormal but it is difficult of course to get a good view. Not really seeing a lot of the skirt on travel to tell if it is damaged.
6. Attempted to pull Y-pipe but of course one nut is stripped so I can't get it off completely. Removed muffler though and peering in and watching piston travel on each side I can see a bit more than carb side but still nothing looks out of ordinary. Still not seeing a lot of the skirt though to tell if it is damaged.
7. I also try idling it and spraying starter fluid all over case to see if it is seals and anything changes with idle but not noticing any difference at all.

Another observation is with airbox off and idling it appears that I have suction on PTO carb inlet but not really on carb on mag side. For example if I switch to carb cleaner and spray the PTO side carb it will start to die and recover. On mag side nothing happens (which isn't really a surprise since that cylinder is not working) but trying to give all details. Any thoughts what might be next? Not adverse to tearing it apart and I am mechanical but wondering if there might be something else to try.

Thanks for any suggestions.
 

·
Registered
Joined
·
350 Posts
sound like a piston is broke to me...had a polaris last year with broke piston it was cracked in the ring groove and did build compression just wldnt run right it wld blow gas out the carb while the others sucked, but the hole bolt thing is wierd so idk for sure but just throwing that out ther in case u get into then engine its a a place to start.
 

·
Registered
Joined
·
2 Posts
Discussion Starter · #4 ·
Thanks for the suggestions. When I had the intake boot off it didn't seem damaged but I also did not swap these. I will pull and inspect again and swap to be safe. Also check the Y pipe carefully.

Of course I'm trying anything I can before opening the engine up but am prepared to do that if needed.

Thanks again for the help.
 

·
Registered
Joined
·
115 Posts
Keep us informed. I have two 340 engines under my bench now with the same problem. One will run on the mag side and the other on the clutch side. Both have fire and compression and gas. I wasted the best part of a winter on the first engine, got no sledding in. Last winter I dropped in a running engine from a scrapped machine so my daughter and wife could go driving. This year I bought a 89 Sport GT, needed a crank seal on clutch side. Hmm, I put in new seals and new rings while I had it apart. This was the 2nd engine listed. I did like you swapped out everything, no change. GRRRR I yanked that POS out and put in an engine from an Indy Lite, since tracks are obsolete they make great donor parts. LOL
PS I started to wonder if my mechanical abilities were failing me, but I rebuilt a 488 Trail engine also and it's working fine. Sorry I'm of no help, but your not alone!!LOL
 

·
Registered
Joined
·
115 Posts
I thought that also. Put a dial indicator on each cylinder and there was no difference. I only did that on my first engine along with all the other stuff my local dealership mechanic suggested, even the stuff that didn't make sense.
 
1 - 7 of 7 Posts
Top