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  1. #1

    Default BMW D50-2 - Stuck on full throttle!

    I recently purchased a boat with a D50 engine. The engines had water in the oil (a lot!) for 1-2 years, and before use we had the cyl head off and overhauled it, and replaced the cooler (wich was the cause of the water in the engine).

    When we tried to start it the first time, the bloody thing started on the first rev. It then virtually exploded up to ~5000 RPM, and we had no way to stop it. Pulling the stop wire made no difference, and the accel lever was in Idle. We finally reduced the RPM`s to 3000 or so by blocking the air supply by hand, and stopped it by cutting off the diesel supply.

    We then started dissassembling the pumps,. guvernor lever etc etc. The lever was stuck due to rust, so we put everything, including the crankcase in diesel for a week. We then inspected and reassembled everything, zeroed the pumps and so on. As far as we could see, everything was in top condition. The only thing we did was to release that little piston on the pump-camshaft that was stuck.

    So we started the engine again, and this time it worked fine. At this time we had the boat on shore, so we connected a water hose, and let it idle for an hour or so. At this point, we could use the throttle as normal, rev it to 2-3000 and back down with no problems at all.

    Then we changed the oil, put the boat back on the sea, and stared it again.... And once again, the bloody thing revved out on us, luckily we were prepared and choked it on the air supply. Pulling the stop did not stop it, but choking it while pulling the stop helped. So, once more, everything into pieces, inspect, and reinstall. Nothing appeard unnormal at this point. The piston was in the rearmost position, not stuck in the front position like the last time, and everything moves perfectly as far as we can tell.

    So now, we have tried, disassembled and reassembled at least 15 times. Still it revs out. Could someone please help us understand how the throttle system works on these engines, so we can troubleshoot it? Any ideas on what can be wrong on this engine?


  2. #2

    Default Re: BMW D50-2 - Stuck on full throttle!


  3. #3

    Default Re: BMW D50-2 - Stuck on full throttle!

    ok... not sure what is causing the problem... but it sounds like you need an emergency shut down valve on this engine to prevent the runaway problem... check out my website esdvalvellc.com

  4. #4

    Default Re: BMW D50-2 - Stuck on full throttle!

    Just a little update, here is how we fixed it:

    The throttle is semicontrolled by a centrifugal weight system in the dieselpump camgear. Im not 100% shure why its there, it may be a centrifugal rev limiter or perhaps its purpose is to make the engine start easier. Or both. Anyways, when the engine is off, the throttle gouvernor is stuck on full throttle. Once you start the engine, its pulled back to neutral by the centrifugal weights. I think.

    This is where our problem was. Inside the camgear there is a rod attached to a spring. This rod connects to the throttle gouvernor rod. This rod was seized by rust, and as a result the centrifugal weights could not pull the throttle back to neutral upon startup.

    We found this same problem on another engine nearby. He said he`s had intermittent problems with the engine taking off on him. Some rust was found inside the rod, and it appears to be the solution.

  5. #5

    Default Re: BMW D50-2 - Stuck on full throttle!

    We have a D35-2 that did exactly the same thing....in Baja. We tried everything, including taking injectors and pumps to states for inspection (no reliable mechanics for Bosch down there in BCN).
    Anyway - I can't see the centrifugal you are talking about through the engine ports where the governor mounts or the governor rod is under the cold start.
    Any chance you can help me out here.
    This engine was running fine until we got to Baja and into some of the thickest kelp beds we've ever seen, not to mention lots of lobster pot (floats).
    We can get it to run normally by hold down the electric shut off and working the throttle until it gradually responds normally (comes down to idle). Next time we start it up though and it's off to the races. The rev limiter works, fortunately and she runs dam smooth a 3k rpms
    Any thoughts?
    Muchas gracias

  6. #6

    Default Re: BMW D50-2 - Stuck on full throttle!


    It sounds like you have the same problem as us. Added is a link to the D35 / D50 engine manual.

    1. Go to page 69. Remove the timing cover
    2. Go to the bottom of page 83. Figure 141, 142 and 143 is for the gouvernor centrifugal weight assembly.

    If this assembly is stuck, the engine will be stuck on full or partial throttle. I think. There are no good explainations in the manual. Anyways, we cleaned this assembly for rust, lubricated it with grease and the engine has run fine since.



  7. #7

    Default Re: BMW D50-2 - Stuck on full throttle!

  8. #8
    Join Date
    Jun 2008
    Island Heights, NJ,

    Default Re: BMW D50-2 - Stuck on full throttle!

    A bit of clarification to help you understand. The "throttle" on a gas engine engine controls the engine speed by limiting the airflow to the engine and hence the horsepower and only indirectly the engine RPMs. A diesel is controlled by setting the speed of the governor directly. Mechanically controlled diesels have a governor with weights that are forced outwards the faster the engine spins. The "throttle" control limits how far these move and hence the max RPMs of the engine. Diesels suck in the same amount of air regardless of the setting of throttle and "speed" is controlled by governor varying the amount of fuel injected. Gas engines require a precise air/fuel ratio to run, diesels don't and ideally run with a surplus of air. So.... in a diesel, the governor is everything.

    There have been cases in old truck diesels, of the engines not shutting off even when fuel is cut off in engines with badly worn rings, wherein the engines run uncontrolled on crankcase oil sucked up past the rings and burned as fuel.
    Capt Bob
    1969 23ft ChrisCraft Lancer
    Merc 5.7L 260HP/ Volvo 280
    1972 22ft Bristol
    Honda 7.5HP 4 stroke Long shaft

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