[crashcourse101]

I know there are several causes for what I am about to ask but I am hoping to take the steps to figure it out without changing several things at once.

I have a 93 Mariah barchetta 181 with a 4.3 Merc 2barrel and a 1.84 gear ratio.
I am getting 4500 with the 19p factory prop and 36 mph
I am getting 4450 with a 21p and about 40mph
both aluminum and gps verified.
Both props jump out of water with no hesitation.
Those figures do not matter if I am full or empty with gear and or people.

I have read several posts of people running much better then this and I feel it should also.

The boat has 221 hrs on it, it sat for 10+ years in the water. When I purchased boat there was so much scale on the hull it would not go over 27 mph.
I have cleaned the hull, changed plugs, oils, filters, and now I want to make this a perfect as the boat can be.

When cruising at 4000+ rpm I get a cough/lean pop through carb and no more power then I posted. I feel this boat should reach 4800 rpms and be cruising mid 40's with no issues.
What should be my next step?

I wont be able to get the boat out for a few weeks and am planning to do a carb rebuild first.
The man I purchased the boat from said all he did to get the boat going was drain the tank and started cruising.
I did not notice any water or particles when I inspected the gas from the filter and have power timed it in the water with no result.

[jsewall82]

Sounds like it might be the jets in the carb. I would rebuild the carb. is the fuel new or is it still old? if its old put some sea foam or some type of additive in it maybe to clean it up some.

[crashcourse101]

The fuel is all new it does have stabil and I have added seafoam in the past. I ran the boat for 5 hours this past weekend.

[crashcourse101]

Update!

I pulled the carb and upon the internal inspection the carb guru seems to believe it has been rebuil recently.. Ha I laughed because the carb has never I mean never been off the boat. everything on the boat is that clean and I could tell when removing the carb there were no witness marks from reinstallation.

With that being said he did not find anything that could be causing my issue internal to the carb unless there is a small spec of something in the jets.

I am wondering how do I inspect my antisiphon valve and where is the exact location?

[ColoradoDiablo]

It's usually located right at the tank. The fitting that comes out of the tank a lot of times contains the siphon valve.
This is how my Diablo is.
I'm kinda leaning toward the fuel in the tank like jsewall82.
Bad fuel does strange things for sure. The fuels of today don't last half as long as it use too. I always put in Seafoam when my boat sits for any length of time. It's my friend. LOL

[crashcourse101]

lol, and is mine also, I was hoping it was but like I said I put 120 dollars worth and 5 hours on my boat Memorial day weekend. I am starting to lean more toward just good full tune up.

I was talking with a guy that knows enough(scares me to trust) and he was thinking maybe something with my oil pressure sensor getting to the sweet spot and not realizing it has the oil pressure to continue to pump fuel.

I will continue to update so people with similiar issues will be able to troubleshoot. It seems this is a problem several people have with no resolution posted.

[crashcourse101]

Colorado Diablo,

What kind of rpm/speed are you seeing in your boat?
I am assuming they are very similar

[ColoradoDiablo]

They are crash. But I am at 5-7000 ft all the time. I run a 4 blade SS 17p for most lakes I go too. But I do have a 15p and a 19p for other areas I visit on occasion. I am running at 4700rpm at 7000ft with the 17p.
Easy enough to bypass the oil pressure switch if you think it could be a issue. Just jumper the wires.

[crashcourse101]

Update!!

I am still at 4400 rpm with an entire ignition tune up and a retune on the timing with a fresh carb rebuild. I found a service bulletin on the 2 barrel merccarb that says popping over 4000 rpm under a certain engine serial to reduce the jet size to 1.60 instead of 1.65 mm.

This makes me go hmmmm... I called several mercruiser dealers service dept and spoke to 5 techs that had no clue. I really wanted to pick some brains about the carb. I think I have also uncovered something else about my engine but have not confirmed to now. A retired gm mechanic came to my rescue the other day at the slip and noticed I may not have the balance shaft engine the boat had originally came with(oh great) .

I have ordered the jets anyway and plan to try them. I firmly believe I should be capable of revving my engine till it pops, am I right to believe this? Regardless of the motor that is in boat I should be able to maximize the motor to the prop and get every ounce of power the boat has turning 4800?

Remember, free revs only to 4300 before I start getting a rich popping and can rev to 4700 as its stumbling all over itself.

Any input on my ramblings will be greatly appreciated.

About what I thought was lean could have actually been rich. When cruising at 3/4 throttle and stab to wot I get a surge pull then it comes back in for cruising enjoyment. With that but being said I can load it up by pumping throttle one time so now I have reason to believe rejetting is the correct way.

[mikeyt]

At first thought i would have said its the coil breaking down but popping at WOT is 'usually' a lean fuel condition. I always thought the 1.60 jets were the correct ones for the 4.3 2bbl. When u did the 'complete tuneup' did you change the distributor sensor? That's something else that can lead to this condition.