Another Engine Revving Problem - Perkins 4108

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neil1967

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In May this year, the High Pressure Fuel Pump on my Perkins 4108 expired at the end of a trip from the Netherlands to Falmouth. As far as I am aware, it was original and had done 2980 hours over 32 years. The pump was replaced and I subsequently sailed to Portugal, with quite a lot of motoring (56 hours in a 120 hour trip), with no problems. I have sailed infrequently since (about 8 hours on the engine), but on starting the engine today, all was not well.

The starting procedure for the 4108 is to have the throttle set to full (to engage the cold start mechanism) and the engine normally races/bounces to 4000 RPM, before being being throttled back - this also kicks the rev counter into action. Today the engine started, but the RPM only built steadily to around 2000 RPM, under no load. Putting it into gear the max revs were about 1000-1200. (Hopefully) coincidentally when I tried to stop the engine (electric solenoid) that didn't work either, but I found that the clip that connects the chain to the solenoid had come adrift. Having reconnected that, the engine stopped normally.

Having started and stopped the engine a number of times, the max no load RPM has now built to 3000, but it builds steadily to 2500 and then slowly creeps up from there. In gear max RPM is about 1500. Normally cruising RPM is around 2000. I have checked the primary fuel filter (Racor) - it looked fairly clean (it was changed at the same time as the fuel pump), but I changed it anyway, with no improvement. Prop is also clear. Any pointers as to where I should look next would be much appreciated!
 
I tend to be sceptical regarding coincidences and engines. Have you tried pushing the valve rod in while trying to raise the revs, and does it feel like it's reaching the ends of its travel properly.
 
Thanks - the engine stop is by pulling on the rod, rather than pushing, so it is difficult to see how that could be the cause, but I agree with your scepticism and will give it a try!
 
My thinking is that if the mechanism (spring?) that's supposed to keep the rod pulled in during normal running isn't working, then when the solenoid released the tension the linkage would hang loose and could disengage. You should be able to pull it out and when you release it I'd expect it to pop back in with a positive click.
 
You've got it! The stop lever on the fuel pump is not fully returning after being operated, so whatever mechanism the fuel pump uses to stop the engine is not being fully disengaged. When the stop lever is manually returned to its full extent the engine revs freely and fully. Now to determine why - hopefully just a tired spring. Many thanks for the advice - much appreciated :)
 
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