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Thread: MSU 800 cutting out when hot

  1. #1
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    MSU 800 cutting out when hot

    My 5,000 mile 2014 MSU800 is now cutting out (nearly stalling) at speeds under 20mph after running a few hours. No other symptoms other than sometimes I have to crank the ignition up to 10 seconds for it to start and gas mileage has dropped from around 16 to 11mpg. I had similar problems 7 months, 1,000 miles ago where it would eventually die and would not restart until it cooled for around 20 minutes. Then it would start, run and die a few minutes later. Back then I changed out the crank position sensor and haven't had the problem for 7 months, 1000 miles. So this time I replaced that crank position sensor with a spare I carry. Again, after I run for a few hours, it acts like it wants to stall, then recovers at low speed. Once on the highway, the problem did not reoccur until I returned to the campground and drove at 15 mph for a mile or so. Is there another solution, or should I assume my spare crankshaft position sensor is also bad? I've heard they can be bad when new. I had recently replaced a leaking radiator cap which had allowed about a pint of coolant to escape and triggered the high temperature light, and it ran fine next few similar rides afterward. Any thoughts? I plan to put some fuel system cleaner in and also call motorcycledoctor.com as they have been helpful in the past.
    Last edited by 2014msu800; 04-05-2018 at 05:43 PM.

  2. #2
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    Update. Called Craig at motorcycledoctor.com and he will send me another crank position sensor and recommended I check the valve clearance as well.
    Last edited by 2014msu800; 04-08-2018 at 10:24 AM.

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    Cleaned dirty air filter (didn't look restricted), added AMSOIL QuickShot fuel system cleaner and stabilizer to the fuel tank and replaced the hardly used 40 mile crank position center with a brand new one delivered last week. Removed valve cover on front cylinder and both exhaust valves were opened to 0.25mm so tightened them down to 0.18 so barely back in spec. The shop said they adjusted the valves 1000 miles ago. Do they go out of adjustment that quick and does the gap increase like it seemed to in mine? When the exhaust valve gap was open, the intake valve gaps were completly closed and I didn't try to rotate the engine to check gap when open. Craig said I could just tap the ignition to rotate and open the gap, but I was chicken to do that so left it alone. Is that the right technique? Is that done with the spark plugs disconnected and out? I've adjusted valves on my BMW by just putting bike in higher gear and rotating the back wheel to measure the gap in the cam. Would this also work on my MSU?

    Put everything back together, starts right up. Went on the state road for a quick trip to the gas station a mile down the road and got up to 68mph. I guess every thing good so far. Need to ride it to use a full tank of gas at slower speeds to see if I fixed the problem of it wanting to stall when the engine is hot at low speeds after a few hours riding.

  4. #4
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    40 mile ride today. Ran great! Fuel economy also seems to have returned.

  5. #5
    Respected Member kelleymotorsports's Avatar
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    we have seen several issues with bad fuel. and yes valves can go out of adjustment and typically they tend to go tighter over time as the valve will eventually hammer into the seat and wear that down and the face of the valve. being slightly loose could cause some lose of power but typically would make a chattering sound if to far out of adjustment (on the loose side)
    Kelley Motorsports LLC 563-920-3412 sales@kelleymotorsports.com
    Sales, Parts, and Service www.kelleymotorsports.com

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    Thanks. For some reason mine wear looser. I took it into a shop 1000 miles ago because it refused to start. He measured compression, said it was low and feared major problems. He adjusted the valves and it started easily and regained the power I thought was lost going from sea level to 5,000 feet. So I guess the valves were again loose due to loss of compression.

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