1974 JD 300 Sputter and backfire

Maj_hazard · Post by **Maj_hazard** » Mon Feb 26, 2007 11:05 am

Top of the day gents..

I'm posting a problem I may have without knowing if I really have a problem.. Let me explain..

I was riding my JD 300 last night with my wife and 3 year old on board. I took the sled through some deep snow and after a few minutes the sled began to miss and sputter.. I turned back onto the main trail and the problem got worse and I swear I got a backfire out of the exhaust system. I shut the machine down and waited about 10 minutes. The sled restarted without issue and I got the old girl (the sled) back to the cottage. On the ride back the sled didn't feel like it's peppy old self but the idle was fine and smooth...

I had to head back into the city so I had no chance to look things over to see what may be wrong..

I was hoping the issue was related to an over heated engine (outside temp -2 C) , a snow plugged exhaust or fouled plugs...

Any other suggestions as to what I should check ???

After melting a piston last year I'd hate to go down that road again..

BTW... I've heard mention of performing a chemical cleaning of parts reused after a system melt down... Can any of you give any details ????

Cheers and Thanks

Mike

400brian · Post by **400brian** » Wed Feb 28, 2007 4:59 am

Hi Mike

My first guess is that you got it hot. Our '72 400s would do the same thing in deep snow, or breaking trail, especially in warm conditions.

Other things are certainly possible, see how it runs next time. I suppose you could have done permanent damage, but hope not. Look at the plugs for anything abnormal looking.

After a seizure, it is mandatory to mechanically and chemically clean the aluminum out of the jug before honing and reassembly. Otherwise, the aluminum in the pores of the jug will cause the piston to gall, and failure may occur in short order.

Maj_hazard · Post by **Maj_hazard** » Wed Feb 28, 2007 12:02 pm

Hi Brian..

Thanks for the reply.. I was begining to think I must of pasted wind some place in my original posting as no one seemed to want to jump in...

I've got my fingers crossed that it was just an overheated engine.. I'm sure I shut it down before things got ugly...

It kills me that I had to leave the cottage before I could have a look at what may have gone wrong.. Possible what ifs will haunt me till I get back up..

I will check the plugs as I also wonder if I'm still running rich and may have fouled.. I just hate any clockwise turns of the needle valves after last years lean melt down..

I'll also check compression..

If I did melt down I may need to pick some more at your Kohler carcus.. You know your current door stop/boat anchor.....

What is used for the chemical cleaning ????

Cheers

Mike