4.3 revving up in neutral after a run at speed

[QBhoy]

Guys
I've posted the same issue in the VP section and not had much luck, so trying in the mercruiser section.
My friend has a VP 4.3 205hp 4 barrel carb engine (similar to Merc 4.3 as we all know). Problem seems to be that after a run up on plane, when slowing down and putting into neutral, the revs shoot up to around 2000rpm. Obviously not ideal,...wouldn't dare put into gear at those revs and a nightmare when coming into dock.
I haven't given the problem to much time and haven't had a proper look, so trying to figure it out in my head.
The only way to stop it doing this is to switch off then on again. It then instantly returns to normal idle rpm !
I'm thinking it surely can't be a mechanical problem like cable or butterfly sticking ?? Why would turning a key off and on have a mechanical effect on this ?
Other thoughts might be that this engine has an electrical fuel booster pump. I'm not sure why, I used to have the same engine and it didn't.
Any suggestion welcome and appreciated.

 

[QBhoy]

It's coupled to a 290dp. I had originally thought it may be cone clutch or drive oil contamination/thinning but again, why would turning off and on remedy ?

 

[alldodge]

If you don't get the answers you want in the VP section you don't post the same question in the Merc section.
http://forums.iboats.com/forum/engi...volvo-penta-4-3-carb-revving-high-after-a-run

Next I would say that you have been provided a suggestion about the cable but have yet to try the suggestion, only asked another question. Its a carb motor, and it runs fine, yet when you slow down the motor still wants to run fast. This in most cases is the throttle plate in the carb is not closing back down. Why turning the motor off causes it to idle back down is yet to be determined, but looking at the cable is the first step

 

[GA_Boater]

What AllDodge said. Read the Help Tip on top of the page.

Closed.