Issue with acceleration 2010 3.0 Mercruiser

[viper1216]

Having an issue with my engine and kind of at a loss as to what it could be. Beginning of the season, replaced the fuel water separator filter and plugs like I do every year. Had some running issues after it was in the water so ended up rebuilding the carb. When putting carb back on, found the distributor was loose. Redid the timing per manual. Boat ran like a champ...better than it has in years. Had a spout of crappy weather and she sat for about 2-3 weeks....took boat out last week and it legit felt like we were running with a dead elephant in the back. Wouldn't get above 3300rpm or 19mph. Was swimming around it and noticed a crap ton of seaweed ont he outdrive and my trim tabs. Today, took it out and dove down and scraped all the crap off. Got her up to 4200 rpm and about 29mph which is pretty normal I think. Was a bit choppy and I had about half the weight capacity on the boat. Acceleration still sucks though. When I give it full throttle to take off...it feels like its bogging down...and you can hear it.....takes about 4-5 seconds and will get up to speed and seems fine after that. I rebuild the carb every year on this boat, and the only thing I did different this year was cut off the crappy guard over the mixture screw that doesn't allow you to take it out and replaced the screw. Figured it was 10 years old so time for a new one. Would that cause the issue? And if so...why was it running fine and now it's not? That's what is hanging me up.

Thanks!!

 

[Rick Stephens]

Might dump contents of water separator and see what you got. Seems the only thing different is sitting for a few weeks.

I'd a never left the limiter cap on a carb screw either.

 

[viper1216]

Thanks Rick. I'm going to run some Seafoam through it. Maybe some ethenol got into a jet again.

 

[Rick Stephens]

Thanks Rick. I'm going to run some Seafoam through it. Maybe some ethenol got into a jet again.

No such thing as a mechanic in a can. Dump your fuel filter into a clear container, see what you have there. If it has any crud or water in it (same thing really), might have to rebuild the carburetor. Water will mess up your carburetor.

 

[viper1216]

I know I'm just wondering if there is maybe some funk in the carb from sitting and maybe it will clean it out. I don't want to have to get a whole new rebuild kit again,

 

[Rick Stephens]

You know what they say: wish in one hand, poop in the other. See which fills up faster. . The carb either needs cleaning or it doesn’t. If you did it recently you might get away with popping it open and not tearing up the gasket.

 

[viper1216]

Ok...played with it today for a bit. I checked the mixture screw...per what I have read, it is supposed to be out 1 1/2 turns. And then adjusted from there as needed. Mine was turned out 2 1/2 turns. Took the screw out completely just to check for debris...clean as a whistle. Put it back in. Brought it out 1 1/2 turns and started it up. Was running a little rough. Opened it up to just a smidge over 1 3/4 and was all good. Took boat out and same issue. Brought it back in, put into base timing and checked with a light. Was at 2 degrees ATDC where I set it. (and per spec) I advanced it to 0 degrees. Brought it back out. Top end was way better...solid 4300 rpm and 32 mph in a slight chop and sounded good and great throttle response at anythign above 2k rpm. But hesitation was still there. If I'm at throttle and just in gear running at 1500 rpm...if I punch it, there is literally a 2 second delay. Kinda throaty response from the engine...count to 2 and it jumps from 1500 to 2k and keeps accelerating. Verified it would do that every time...it did. If I slowly advance the throttle it seems to accelerate pretty smoothly, so only hesitates when I go right to full throttle. Checked the drain on my water separator...little bit came out but nothing seemed like crud or anything. It was clean. Carburator was rebuilt in mid-may. Fully disassembled and cleaned and rebuilt kit installed. There is maaaybe a tank and a half of fuel through it since. So any other idea what me be causing that 2 second delay?

 

[viper1216]

Oh, and I checked for fuel in the throat. Hitting throttle produces 2 streams of fuel for about 2-3 seconds or so.

 

[Ron in TN]

Rebuilt my carb late last year. Engine ran better than ever for a month or so and then developed idle issues. Turned out to be debris in one of the transition acceleration ports - the little holes that provide extra fuel until the accel pump takes over. It took opening a supposedly CLEAN carb twice before I finally found a tiny spec of something. Was frustrating but simple.

Not saying this is your problem but could be a similar situation in that some foreign material has dislodged since the rebuild. Good luck.

 

[viper1216]

Interesting. It could very well be that. I actually ended up looking and found I have 3 holes on my accelerator pump linkage. It was in the middle. I moved it to the outer hole which adds an extra 0.5cc of fuel. Now it has the tiniest bit of delay. Like maybe 3/4's of a second. Close enough for now. Not like I'm pulling a skier or something. I plan on taking it off and rebuilding it after I winterize the boat and letting it stay in the basement over the winter.