OT - Old 2-stroke question

5 replies to this topic
  • sirthumpalot

Posted August 21, 2004 - 12:09 PM


I just dusted off my old 1985 YZ80 and spun a few laps in the back yard. Wow the memories! I think I'll bring it to the track next time out and run some laps with the kids just for kicks. :thumbsup:

Here's the problem. It's got an .06 oversized piston, boynsen dual stage reeds, a PSI pipe (very peaky, top end only) with an FMF silencer. It will idle as smooth as my 426 all day long, runs perfectly smooth on bottom. If I open the throttle from idle, it will pull hard right out to about 50% of the RPM that it's good for, where suddenly it hits a flat spot where it just about completely stops making power, then a couple thousand RPM later suddenly it jumps on the pipe and pulls as hard as an antique 80cc bike can pull. :devil: So the question is, what's up with the flat spot. It has been that way for as long as I can remember (even when I was a kid), a jetting issue I assume. I assume my main jet may be a little too small but I wanted to double check with the old 2-stroke crowd before I buy parts and head out to the track. :awww:

  • 426_Texan

Posted August 21, 2004 - 12:29 PM


I'm by no means an expert, but a flat spot in the middle of the RPM curve sounds more like an ignition problem to me.

My .02

  • sirthumpalot

Posted August 21, 2004 - 12:56 PM


HEY funny you mention that... It's got an Answer Roost Boost ignition module plugged into it, I forgot all about that thing! The silly stuff we bought as kids.... I'm going to go unplug that thing and see how it runs, thanks! :thumbsup:

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  • Hamish

Posted August 21, 2004 - 02:51 PM


I doubt the mj wouldnt be too small, otherwise it would fall on its face in the top end. IF you hold it wot in nuetral does it rev out or does it 8 stroke? If it revs out it's too lean.
Personally, if the iginition doesnt fix it I'd be looking at the needle position. It could even be a nature of the beast with the exhansion chamber you have.

  • felony

Posted August 21, 2004 - 08:17 PM


i can almost guarantee your float level is set too high,check it out,thats what it sounds like to me :thumbsup:

  • Jeffro426

Posted August 22, 2004 - 07:50 AM


It's got an Answer Roost Boost ignition module plugged into it, I forgot all about that thing!

Roost Boost!! :lol: :thumbsup: :awww: The greatest gimmick ever to grace our sport! :D :devil:

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