4.3 hesitation from idle and surging rpms at WOT

[jkust]

Hi all it, would seem that my carbed 2bbl 2003 Mercruiser is starting to act up. It's the same set up as it has been for several years and the prop is the same and undamaged. It's at about 200 hours on the meter and had a full 200 hour tune up at the 100 hour mark because it needed outdrive work and it was more economical to do a full tune up which included the outdrive work in the service package at the time.

Last season it would have a quick hesitation if accelerating from neutral. I didn't address it and let it slide since I couldn't find anybody willing to work on it in the fall. I haven't checked but guessing acceleration pump or ball valve but don't know where either of those are located on the carb or how to test for a stuck ball valve.

This season now in addition to the hesitation from idle, I can't get WOT rpms of 4850 any longer. I get about 4800 if alone after a long, long run (i've tested it twice when alone) and about 4400 if I've got the family with. I'd always get 4850 on the nose no matter the load previousy...it would just take longer to get there with a heavier load and was quick to get there with a light load. Obviously then top speed is down as well.

When I am at WOT then trying to eek out some more rpms which I can't seem to do, the tach will surge a couple hundred rpm's from 4400 to 4700 but never seemingly truly go beyond 4400.

My questions then are where are the acceleration pumps in the 2bbl carbs and what can I do to then also try to diagnose and free a sticky ball valve? Lastly then, the WOT issue is new, what causes the low WOT and surging tach?

I'd swear it is smoking white smoke more when I start it cold as well.

 

[wahlejim]

When the RPMs surge, do you hear the increase or is it just the gauge that is moving?

 

[s.hadley81]

What wahlejim said is right on is it the gauge moving or is the motor changing rpm and at 4850rpm you are over revving that motor just cause it will reach those rpm that doesn't mean that what your wot should be

 

[jkust]

Just the gauge is moving and I don't hear any change in Rpm's. 4850 on the 4.3 is the appropriate max rating which is the result of getting the correct prop set up...I've owned this since it had only break in hours on it so know how it should behave having put 170 hours on it so far. I've had props that could overrev it but then the rev limiter kicks in anyway to stop that from happening.

 

[81 Checkmate]

The acelerator pump and check ball is in the carb. You can rebuild a 2 bbl on your own if you have some mech skills. Take carb off and locate the serial number and order the kit. Lots of u-tube videos out there on how to rebuild.