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Flames out of exhaust?

Discussion in 'The Garage' started by vincejames, Aug 18, 2016.

  1. vincejames

    vincejames XS650 Addict

    It took me a while to get my XS650 running right. With the help of everyone on this forum, luckily, I think I finally got her running the way she should be. With continuous changes to the carburetor, I finally think I figured out the perfect set up. First I adjusted my cam chain to spec, timing etc., Now I'm running a 145 main jet and a 45 pilot with the fuel/mixture screw 2.25 turns out on my bs38s. - a little large, but with a 2-1 exhaust it ran the best this way.

    My question: after riding at night I found that my 2-1 exhaust is shooting flames. I'm thinking that I have too much gas, I kind of like it though. I'm thinking it is certainly not good for the bike. The exhaust is not baffled. But I'm thinking even a baffle will not cure the problem. Opinions?

  2. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

    Not uncommon for short, unbaffled exhausts. Can be aggrevated by ignition misfires and leaky exhausts.

    Kinda cool, tho. I used to get them with my panhead's open dragpipes. You can see them in daytime on a Stearman. I remember dad's commenting on the flames coming from his P-51's Merlin engine's short exhausts...
  3. peanut

    peanut XS650 enthusiast & inveterate tinkerer Top Contributor XS650.com Supporter

    I'd say burnt exhaust valve or exhaust valve not seating properly is a distinct possibility .
    Try adjusting your valves a little looser or do a compression test to eliminate that possibility.
    Yamaha were constantly changing the recommended valve lash settings throughout the model years often by just 1 thou up or down.

    These days it is popular to see the advantage in running the valves at .006" inlet and .012" exhaust which were the recommended settings for the early models.
    You lose no power but as the valve is seated a little longer the engine should run a little cooler and there is much less chance of burning out a valve or having one not close fully.
  4. vincejames

    vincejames XS650 Addict

    Cool. I will take a look at the valve clearance and see what I can find.

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