itsjustagreat1 Posted September 13, 2011 Report Share Posted September 13, 2011 Ok, I have a stock stroke drag port that I have recently had issues with. I have ran this motor on 19cc domes on 91 octane with +5 timing for the last 6 years. On spring break at little sahara, It blew out a dome oring while my buddy was running it and he didn't realize it happened so it had a melt down (pretty much no orings left, rings melted to pistons, etc.).It only had about 10-12hrs tops on a fresh rebuild. Anyway I rebuilt it again and went to sahara this weekend and dragged it like I have for the last 6 yrs and she started to misout . So I headed to camp to check it out and found that one of my spark plugs were only held in by a few threads. Ok, so tightened it back up and fired it up...BUT coolent blowing out the overflow. Tore it apart tonight and found the left dome oring half melted. So I figure it has to be detonation. So I checked to make sure my timing plate hadn't moved and it hadn't. The only other things I could think is that maybe my dyna fs cdi could be causing problems. It is still on stock setting though and have never had any problems with it. My other idea was that I had always gotten my 91 fuel from the local travel plaza, but they recently sold out to "LOVES Travel store" and the last 2 trips I have used their 91 fuel. Each trip, it blew after about an hour of riding. Could their fuel be over rated and actually not 91 octane? It has no ethanol in it and like I said before, I have been running the same setup for the last 6 years with no issues. Can anyone give me any suggestions? Oh, and also my jetting is correct I also checked the plugs. Quote Link to comment Share on other sites More sharing options...
Jereme6655 Posted September 13, 2011 Report Share Posted September 13, 2011 if your cylinders are backing out then you are detonating......id say either either gas or your timing ( i know you said it ran for 6 yrs on the same settings) my suggestion is that you try some new o-rings and back your timing down to stock and run it. AFTER you do a leak down.... Quote Link to comment Share on other sites More sharing options...
itsjustagreat1 Posted September 13, 2011 Author Report Share Posted September 13, 2011 (edited) Already put her back together tonight and pressured up to check seals and are fine. Also put in new orings and backed timing to +4. Weird thing is that I used to hot lap it on the drag strip for up to an hour or more and never had a bit of issues and now all of the sudden I can't even run for an hour of normal easier riding. Also not sure what you meant by cylinders backing out, but I think you meant plugs. Edited September 13, 2011 by itsjustagreat1 Quote Link to comment Share on other sites More sharing options...
lms1977 Posted September 13, 2011 Report Share Posted September 13, 2011 can't hurt to try new gas. did you do a compression test after the rebuild? you sure the base gasket is the correct thickness and you squish is correct? Quote Link to comment Share on other sites More sharing options...
itsjustagreat1 Posted September 13, 2011 Author Report Share Posted September 13, 2011 Yeah, checked comp. I am at + -- 155psi each cyl. I am at around 2k ft. Base gaskets are the same "stock Yamaha" gaskets that I have always used. I guess there is always a possibility that I just plain forgot to tighten my left plug, but I kinda doubt it because I am pretty picky and seem to always double check things. Quote Link to comment Share on other sites More sharing options...
Jereme6655 Posted September 13, 2011 Report Share Posted September 13, 2011 my bad....i meant have your SPARK PLUGS ever backed out...... Quote Link to comment Share on other sites More sharing options...
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