Mercruiser 4.3l power problems

[apollo5646]

Hello all,

I am having a weird problem with my boat. I took it out this weekend for the first time in about 2 years. Had to have the out drive rebuilt (long story). The motor it self is only about 25 hours old. The problem that I am experiencing is that it will start like a charm first crank no matter what. When i first get going it runs good top end is not there seems like i only get about 25 mph to 30mph on the top end in a 19 ft boat seems weird. Anyway i will be able to cruise for a while like that no probs may be an hour or so. Then the boat will lose power while on plane if i back that throttle down to idle and bubble it does it just fine all day but try to get back on it just doesn't have any power unless i pump the throttle then the motor will rev up then back down so if i keep pumping i can get back on plane and make a hasty retreat to the trailer. It was hot yesterday 80 and 90's so I don't know if its vapor lock or dirty fuel or a pump. Not real sure were to start with it. Any help would be great with this problem or the lack full top end.
The collected brain power on this site I'm sure that we can nail this down. Thank you to all who lend your time and knowledge to help someone out.
John

 

[dr_bowtie]

Re: Mercruiser 4.3l power problems

sounds like a dirty carb....more so the main jets...

pumping the throttle pumps the squirters and gives you an extra shot and thats why the motor revs up and then dies back down...

you may need to clean the carb or check fuel pressure to make sure your not having fuel delivery issues...like bad fuel pump...or clogged screen in the tank..

 

[apollo5646]

Re: Mercruiser 4.3l power problems

any ideas on the easiest way to clean the carb?

 

[cooter2506]

Re: Mercruiser 4.3l power problems

tear it apart and rebuild it. Soak all parts in carb cleaner overnite ad blow out all passages with air hose. Then put back together using a rebuild kit.

 

[apollo5646]

Re: Mercruiser 4.3l power problems

Dang I was hoping to not have to tear into it like that. I'm real good on FI stuff not carbs though. I guess that the result of growing up with only FI motors. Oh well, is hard to do or is it pretty straight forward? any site that I could look at that would have info on how to do it?

Thank you all so much for all the help!!!

John

 

[cooter2506]

Re: Mercruiser 4.3l power problems

Look up your carb kit here on iboats. In the kit will be a really good set of instructions on how o do it.

 

[dr_bowtie]

Re: Mercruiser 4.3l power problems

yes carb rebuilding is easy...take pictures and lay the parts out is the best thing you can do...only a few parts in that need particular attention like the pump check ball and spring...


clean all the passages with Gum-Out and follow by compressed air...just to make sure...

for the air bleed screws count the turns in and then pull them out and clean them as well and the passages...then put them in and back them out the turns you counted before...easy and set the float

 

[dubs283]

Re: Mercruiser 4.3l power problems

before we start re-building carbs lets troubleshoot the fuel system first

is the fuel in the tank two years old??

did you check/replace the fuel filters??

it could be you do need a carb re-build but why spend the time and money if you don't have to?

 

[apollo5646]

Re: Mercruiser 4.3l power problems

I was going to check the fuel filters tonight when i get home from work based on the great info i have found on this sight. cudos to you all.

As I can gather there is the canister water separator, and the little one in the carb it self, right? or is there an in line one that i can see under the floor?

I did fill it up with fresh gas yesterday not sure how much was in it at first.

you all will have to for give me a little i let it get a little neglected over the past few year. Darn deployment to Iraq.

 

[apollo5646]

Re: Mercruiser 4.3l power problems

OK so I changed the two filters and gave it a try on the water. No change.
Today I took a Look in the tank the gas doesn't look to bad and tank seem clear on the bottom. I couldn't get to the pick up as it seemed that the opening was welded to the tank. I did notice that the anti siphon valve was not working had some metal shavings in it that was preventing to valve from moving. replaced that will try it tomorrow. Is it possible that this stupid little valve was the source of my problem?

 

[cooter2506]

Re: Mercruiser 4.3l power problems

Very well could be your problem. Mine was bad and gave me some real bad surging at WOT.

 

[apollo5646]

Re: Mercruiser 4.3l power problems

Sea trials yesterday went great!! No problems I guess that the anti siphon valve was the culprit. Now to figure out what is holding the top speed back. Will try it with my gps this weekend and figure out how good the speedo is. Thanks for all your help!!