Results 1 to 4 of 4
  1. #1

    changed top end, rough idle and deto sounds

    Well I changed my pistons and rings and all gaskets, put it all back together, started it up and heard sounds of detonation with a high rpm. Stopped the engine, pulled the plugs and found oil or fuel/oil mix on them. Tried starting it again and had similar sounds but when I pulled the choke the rpms went down and the deto stopped. But after a few seconds the engine shut down but no deto sounds. Did it again and same result. No deto with choke pulled, but it died. Plugs still are wet with oil or oil/fuel mix. I put some oil in the gas tank as a breakin method. I also checked the spark by hand( i know not that safest way), but i put one plug wire on the ground rod and the other in a plug and held it while cranking. I didnt see a spark at the tip, but i did feel a surge through my hand. Is this normal? Is the wire bad?


  2. #2
    96XPSS's Avatar
    Join Date
    Feb 2006
    Location
    Warner Robins, GA Home of the 2007 All-Star Little League World Champions!
    Posts
    4,361
    Quote Originally Posted by cretamk View Post
    Well I changed my pistons and rings and all gaskets, put it all back together, started it up and heard sounds of detonation with a high rpm. Stopped the engine, pulled the plugs and found oil or fuel/oil mix on them. Tried starting it again and had similar sounds but when I pulled the choke the rpms went down and the deto stopped. But after a few seconds the engine shut down but no deto sounds. Did it again and same result. No deto with choke pulled, but it died. Plugs still are wet with oil or oil/fuel mix. I put some oil in the gas tank as a breakin method. I also checked the spark by hand( i know not that safest way), but i put one plug wire on the ground rod and the other in a plug and held it while cranking. I didnt see a spark at the tip, but i did feel a surge through my hand. Is this normal? Is the wire bad?
    And why would you rev brand-new rings and pistons to a high rpm with no break-in time?

  3. #3
    SURFnTURF's Avatar
    Join Date
    May 2007
    Location
    Australia
    Posts
    878
    +1
    11
    Quote Originally Posted by cretamk View Post
    Well I changed my pistons and rings and all gaskets, put it all back together, started it up and heard sounds of detonation with a high rpm. Stopped the engine, pulled the plugs and found oil or fuel/oil mix on them. ?
    Did you check piston/ cylinder clearances ???? I bet your undersize on your pistons compared to your bore sizes and you are hearing piston slap and not detonation.If you had detonation little chunks of piston would be chipping off the top of the piston above the exhaust port.

  4. #4
    Still crazy after all these beers Mac Daddy Racing's Avatar
    Join Date
    Jul 2007
    Location
    St. Paul MN
    Posts
    290
    Piston slap is often heard on the 800's and 951's. Also, did you use new gaskets on the intake or re-use the old ones? Had a 951 with a vacuum leak around the reed cage that caused high R's. Have you checked for a leak while running? I use starting fluid (Ether) and spray around the seals. If the R's climb then you found your leak.

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. FS 1300 top end, core cylinders and cases
    By philip_gpr in forum Yamaha Classifieds
    Replies: 8
    Last Post: 07-28-2010, 09:22 AM
  2. 08 250x rough idle and power losses
    By roleary in forum Kawasaki Open Discussion
    Replies: 3
    Last Post: 06-13-2010, 06:31 PM
  3. FS 04 1200 top end with head and carbs
    By malibu65 in forum Yamaha Classifieds
    Replies: 5
    Last Post: 09-22-2009, 11:33 PM
  4. Replies: 0
    Last Post: 02-11-2009, 10:00 PM
  5. 94 650 xp rough idle and flat spots
    By hotrod_sxty8 in forum 2-Stroke Performance
    Replies: 8
    Last Post: 05-20-2007, 11:27 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •