Husky 371XP Shi...jet hit the fan

[bowenp]

Hay all,
Looking for a little advice, I just finished working over a 371XP, milled cylinder to .020, adjusted timing on the exhaust port, squared up the exhaust and intake, put the Walbro 12B on it, set it fat for the tuning session. It warmed it up, then I set the low speed, and slowly leaned out the high. It 4 stroked up to 15-16 thousand and the I heard a pop and plastic started flying.

Looking over the remains, I think the plastic "jet" next to the flywheel started vibrating and hit the fan, or a loose starter rope got sucked into the flywheel. The second picture is a mod of the jet. I trimmed it down and used some silicon on it for better support.

Any ideas?

 

[Westboastfaller]

Good one.. I've never managed to do that in 21 yrs pro use with the 371/372.

I suppose they were all new parts too. My only concern would be does the mod one still have the male end we see in top example? (Looks like it would still) as well the top end of the air scoop should be screwed on I'm certain. Is that still intact? or that could have been the problem of not in the bottom properly I'm saying it's only a few dollars part. Why risk something like that again. But if its fastened properly and can funnel 36000 litres of oxygenated air per day then sounds good.
Good thing you have the non rev limiter with that build or it would rattle to pieces at 13500

 

[bowenp]

What was left of the scoop was still screwed down.
The mod one does have the little male end (from spare part saw).
I think it was the rope that did it, but I thought I would ask about the scoop cause it seemed it could move enough.
But on a side note, darn thing runs good with just this little "clean up" porting and the cylinder work.
Almost scary how many r's it can turn and still 4 stroke.
Might have to get a Wisco piston and some hybrid bearings for my personal saw.

 

[Westboastfaller]

I doubt it would be the scoop that caused it. I now vaguely recall at least once doing the exact same back about 8 yrs ago on a winter Seismic job. I know I had one that had a few broken bottom air louvers out of the starter cover. I would wear shorts under my Fallers pants in the winter instead of long underwear and I would always forget to do up my fly and tie the string. Of course what was supposed to stay in would come out (No not 'that') and what was supposed to stay out would come in.
The string would get sucked in all the time and wake me up. It was my que to zip the fly. It wouldn't get caught just bounce of the flywheel and scare me.
My luck did run out eventually and it caught and pulled it right out of the shorts.
I was thinking what if the other end was tangled around my 'junk'?
A guy that has his snow boots so packed with chips that he can barely get them off at night may no notice something liket that. You focus so much on one thing that you condition to block out a lot of abnormal things that would usually be beyond bothersome.
Yes now that I think of it more it was pretty destructive. I'm sure it was about the same apart from the pull cord but broke both starter pawls. I had to get my Mechanic to bus me up some parts.

I would bet money it was from the shroud in your case. Crack or pinched? the plastic would have caught the cord.

Anyway it should be a strong saw in the wood..
Is it right at the end of the 4 stroke at that rev? Work saw for what kind of cutting work? It's on older bottom end?

 

[Big_Wood]

make sure your starter pawls are nice and straight before installing anything new on there otherwise it will just do it again. Here’s an obvious example but they don’t need to be that bent to cause issues.