Vintage Dirt Bike Q & A

Our 1981 CR80 has a high speed surging problem, and it's not a little problem. At high rev it starts this Whaaa, Whaaa, Whaaa crap. Carb is clean as a whistle and float valve is seems to be working properly. Starts easy and idles fine. Advice needed on how to troubleshoot this. TIA.

John Sullivan

their are only a few things that would normaly cause this. 1 replace spark plug and GAP to speck. check your exhaust system make sure its clear. make sure all grounds are CLEAN. then make sure your getting a good flow of fuel from the tank. i'm asooming that it ran good before so we could probibly rule out the main jet

Great advice, I'll run down the list. I spoke with a guy that works in Honda service and runs several 2-stroke bikes. He said he had a similar experience way back and it ended up being his kill switch going bad. I'll update when I finally figure out this problem.

Just as an additional note - if the carb is OK (I'd double-check the float level just in case), you might want to inspect for air leaks around the carb throat, manifold, reeds, and left crankshaft seal (I've never tried it, but apparently WD-40 can be sprayed around a suspected leak area; rpm change = leak). You may also be able to check the right seal by leaning the bike way over to the right with the motor running to see if you get any addditional exhaust smoke and/or a change in the way the motor runs.

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric