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I have a 1988 model 1640.

When I shutoff the threshing system at full throttle, the engine rpm's will run up to 2900 instead of staying at about 2700. This has just started to happen in the past week.

Engine has 3900 hours on it and it was overhauled at 2700 hours.

The engine has run up a couple of time while harvesting also-mainly when I went down a decline.

I can hear the engine run up, sounds like it going to race higher and higher. I reach over and cut the throttle back and it drops down.

Is there an adjustment on the fuel pump maybe? My guess is that it's inside the fuel pump. Possibly a weak/broken spring.

Thanks.
 

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I think you're right about the trouble being inside the fuel pump - to me it sounds like the regulator isn't doing it's job properly.
I don't know the specific pump, but a worn or broken part (spring, lever etc.) inside sounds like a good guess to me...

Let us know what you work out!

- Peter
 

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That engine has a rotary American Bosch Model 100 pump on it. The governor weights are driven by a gear with a preloaded slip clutch. Over time the preload will weaken which allows the weight retainer to slow down and will not govern high idle. The pump needs to come off and get repaired.
 
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