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Engine Temps

Discussion in 'The Garage' started by SupsChad, May 10, 2022.

  1. SupsChad

    SupsChad XS400 Enthusiast

    So I got everything running good but I just want to know what you think is a high engine temp and if the spark plugs look lean. After riding the bike for 20min and giving it some juice, the spark plug sensor is reading about 310 when its 88F degrees. Using a laser temp I was getting about 290 around the spark plug and pretty much the same on the fins next to the exhaust. Secondly, do these spark plugs look lean? Ive looked at charts and honestly unless Im dumb, they didnt look like any of them. If so, Ill have to adjust the air mixture screw correct? What I have read is turning that screw on the top of the carb thats closest to the cylinders counter clockwise will richen it and clock wise will make it lean. Now please explain to me how that makes any sense. Its a Air/Fuel screw. Im assuming that screw has no impact on fuel, only air. So how does screwing it out counter clockwise richen it when a rich mix means more fuel than air? I feel you would need to screw it in to produce a more rich mix.

    The spark plugs in person look more greyish than they do in the pics

    Attached Files:

  2. SupsChad

    SupsChad XS400 Enthusiast

    I just rode this bike for the first actual time on the road for about an hour. Temp never got above 320f and stayed more around 305f while riding and its about 90f outside. Any help would be great
  3. CaptChrome

    CaptChrome XS400 Addict

    The plugs to me look pretty good as a starting point. IMG_3404 has that nice brownish color that you want to shoot for. The other plug looks a little rich with some black soot on it. So I think you are pretty close as you want them both having a nice even brownish color. A black plug is rich, a whitish residue is lean and brown is just right.

    Everything at this point gets pretty tedious though, when you adjust the mixture on one carb, it might throw off the carb balance and timing. I would make an adjustment to the one cylinder, re-synch the carbs and check the timing, and then ride if for 30-60 minutes a pull the plug to see how it looks. Then repeat the process until both plugs are pretty much the same or until you can't take it anymore.
  4. SupsChad

    SupsChad XS400 Enthusiast

    Would you say 310f is a high engine temp? The only info I got was someone with the same bike getting 255-275f. And I cant really find what this bikes max temp is
  5. CaptChrome

    CaptChrome XS400 Addict

    Exterior spark plug and head temperature is not something I measure, so I have no idea of what is normal or not. I don't have a running bike at the moment, so I can't get a reading easily.
  6. flea

    flea XS400 Enthusiast

    at 310f it is definitly to hot , should be 220 f max at the head , dont know about at s/plug or exhaust ports , run at your temps will quickly cause damage , on my xs650 i use a oil temp gauge as your oil temp is also critical , the one i use is on a modified dip stick , oil temp should be 230f max ...at 240 -250f most oils will start to break down .. i would be checking timing first , then carbs to see if running to lean , another thing is check air flow to the engine , on my xs650 i put a tool roll under the head light , found my oil temp went up 20 deg f , needless to say it came straight off
    Last edited: May 19, 2022

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