buffer screw adjustment

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Active member
Dec 11, 2020
Hayward, ca
Looking for input, attempting to adjust the buffer screw on a 8V71 that has fast idle & buffer switch for Jakes. After a few attempts to have the fast idle work but couldn’t get the Jakes to shut off at idle, only at fuel off, would the buffer switch activate. Then it happened, the next start RUN AWAY, pushed the emergency stop, nothing, ran to the back manual trip flapper, guessing 3000 RPM by that time. When the flapper engaged, it slowed the engine down to around idle (with lots of black smoke) but would not shut down. Ended up unscrewing the fuel filters, finally slowly the engine can to a stop. Today reprimed back off buffer screw (to be safe) and she firered up normally. Still can’t get the Jake buffer switch to engage at idle. I have all the books, GM manual, Detroit service manual, and Jacobs instruction manual, am I missing something, says tighten buffer screw to no more than 15 RPM increase, I stopped at 10 RPM increase. So why did the emergence stop not work, well the solenoid was bad. In 10 plus years with this coach, I never thought about checking that solenoid. And why did I have run away? The injectors were not stuck, the engine is not weak (inframe around 15 years ago, low mileage).


Site Team
Feb 22, 2016
For some reason a few posts seem to have gone unanswered which is unusual here.

Have you managed to sort out your problem or are you still hoping for an answer?


Well-known member
Sep 14, 2009
Cedar City, UT
Might as well erase the post,, the poster found his answer on another board that I frequent.. I doubt that anyone here would know or understand the intricacies of a two stroke Detroit engine with a Jacobs braking system and the governor that regulates it,, that's where the buffer adjuster screw is...>>>Dan
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