KAD43 RPM dips at 2000 while accelerating?

DavidJ

DavidJ

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While accelerating up my port engine reaches 2000 rpm then dips to 1800 then will work it's way back to 2000 and beyond. The compressor is kicking in ok at about 1700 or so (same as s'board engine). Performance after this 'fuss' is ok.
I've had this problem before which was cured by tightening the lower belt (to torque spec) I've now replaced all the belts and tightened to correct torque spec but it hasn't changed this characteristic. My props are a bit fouled but I don't see a connection to the problem.
Any ideas?
 
Are the revs actually dropping or just the rev counter? If its just the gauge which I think is driven by the alternator it does sound like a belt issue?
 
targa31 said:
Are the revs actually dropping or just the rev counter? If its just the gauge which I think is driven by the alternator it does sound like a belt issue?
Click to expand...

Good question. It feels like it's actually holding back, a bit like the feeling before going on the plane then it feels like it frees itself then off it goes. We are only talking about a few seconds.
 
Checked for air leakes? My kad42's have both needed the sc manifold resealing. (easy job) Small piece of paper held around the pipes will show where air is escaping. Mine leaks were both directly underneath the outlet pipe. Mind moving parts though!

Once the turbo kicks in the leak ceases to effect the performance of the engine.

Ok that's the extent of my knowledge! One of our experts will be along in a bit who will help.
Good luck.
 
I,am no expert after checking for air leaks + belt tension , compressor oil level etc ,but I would clean up the props first. Mint them up !
Then " Italien tune up " particulary if ifs been stood for a while
Give em 3200 - 3500 rpm for a couple of hours .
Could it be on the limit of overloading ? + dirty bum + minor prop fouling = hesitant hole shot
 
I would put a call out to Volvo Paul to get an expert opinion so as to go best prepared! We could be off the mark!
 
Yes I'm hoping for an input from spannerman or volvopaul as well as any other theories. I believe the turbo kicks in at 2000 but again I can't see why any fault there would tempoarily drag the revs down to 1800. It's almost like the s'board engine pulls it out of the 1800 rpm hole then off it goes again.....very difficult to describe.
 
Portofino said:
Could it be on the limit of overloading ? + dirty bum + minor prop fouling = hesitant hole shot
Click to expand...

This is interesting. I don't understand what "hesitant hole shot" is and also why an overload should cause the rpm to 'collapse'. The s'board engine has no sign of this characteristic.

I think you may have touched on the cause, I'm just interested in the physics.

Interested in others view of course, mighterly useful so far.
 
Might be worth checking the supercharger clutch and the belts again.
2000rpm is where the supercharger is under a lot of load, so if a belt or clutch is slipping, this is the rpm you will see it.

Double check what is going on with the smaller, flat, auxiliary drive belt, correct tension, water pump not wobbling around, etc.
If belt ok, you could try swapping the supercharger clutches between the engines.

.
 
Last edited:
FlowerPower said:
Might be worth checking the supercharger clutch and the belts again.
2000rpm is where the supercharger is under a lot of load, so if a belt or clutch is slipping, this is the rpm you will see it.

Double check what is going on with the smaller, flat, auxiliary drive belt, correct tension, water pump not wobbling around, etc.
If belt ok, you could try swapping the supercharger clutches between the engines.

.
Click to expand...

Good observation!
When the engine was quite new I had a clutch burn out due to a badly fitted circlip.........I just wonder if the same is happening again.
hmmmmm!
 
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