83 120hp mercruiserI/O bogging

[SRT8]

OK I just spent over an hour reading the search results for this problem but can't find the answer to my ? so I will ask hear again . My motor is hesitating if I give it throttle fast and if I crack it WOT it will stall .This is what I have done already
-rebuild carb
-rebuild feul pump replaced filter
- all new fuel lines
-water seperator fiter replaced
-new plugs
-cleaned tank & fuel pick up


I rebuilt the carb and pump myself and it was the first time I did either but I am pretty sure I did it right .I am leaning towards a timing issue but I am no marine mechanic if I can't figure it out myself or through the forum I will take it in to have the marina that has worked on it since new .
hope you guys can help so I don't have to take it to the shop Thanks.

 

[Fordiesel69]

Re: 83 120hp mercruiserI/O bogging

Just because you did all that does not mean its getting fuel correctly. Verify with an actual pressure guage.

Also your mechanical advance counterweights in your distributor could be gummed / rusted up from sitting all winter. I personally would check those, as well as the point gap.

 

[SRT8]

Re: 83 120hp mercruiserI/O bogging

well the boat sat for 4 years with out being run which is why I had to do all those things to get it running the distributor was replace but like I said it sat for 4 years I will check it out tomorrow can the counter weights be cleaned with contact cleaner ? I have to do the points gapping anyways just haven't tried it yet thanks I will also verify the fuel pressure do you know what it should be ?

 

[45Auto]

Re: 83 120hp mercruiserI/O bogging

Do a compression check and make sure you don't have a weak cylinder. I had the exact same motor in a 16' Mark Twain (1983 2.5L 120HP Mercruiser) and it did the EXACT same thing as yours. Turned out the #4 cylinder had 60 PSI and the other 3 had about 150 PSI when I did the compression check. With the weak cylinder it didn't have the power to accelerate the boat and would just bog when you gave it throttle.

 

[SRT8]

Re: 83 120hp mercruiserI/O bogging

It is only if I give it throttle really quick if I just give it smooth steady throttle it jumps right up in plane and takes right off I will def put that on the list though I hope it's nothing like that I would imagine thats not a cheap fix.

 

[cr2k]

Re: 83 120hp mercruiserI/O bogging

You probably didn't get all the crud out of the accelerator pump system.
Did you use the new pump plunger? Some of the kits are coming with weak springs and you may need to change it and use the old spring off the accelerator pump. You may notice it is much stiffer.

You need to make sure with carb dip and compressed air that this circuit is clean. Did you pull the little T shaped one way valve out form under the main venturi part?

I am like 99.9999999999999% sure it is in the accelerator pump circuit.

 

[SRT8]

Re: 83 120hp mercruiserI/O bogging

You probably didn't get all the crud out of the accelerator pump system.
Did you use the new pump plunger? Some of the kits are coming with weak springs and you may need to change it and use the old spring off the accelerator pump. You may notice it is much stiffer.

You need to make sure with carb dip and compressed air that this circuit is clean. Did you pull the little T shaped one way valve out form under the main venturi part?

I am like 99.9999999999999% sure it is in the accelerator pump circuit.

Yeah the old plunger was completely seized tight and the rebuild kit was a mercruiser kit it was the only 1 availible and I cleaned everything very very good the vacuum line that came off the pump was all clogged with junk and I replaced it and cleaned both the fittings for it and with the carb every part that would come off came off and it soaked in carb cleaner and was washed with parts cleaner and dried overnight before I put it back together I will try the distributor and points gapping tomorrow and see if I can get the feul pressure checked and I will let you guys know if it's running better or not next week thanks for the replies I hope it's an easy fix but probably not .

 

[45Auto]

Re: 83 120hp mercruiserI/O bogging

With the boat off, have someone advance the throttle while you look inside the carb. You should see a jet of gas spray out of the accelerator pump orifices. There's some little passages under the plunger that are pretty much impossible to clean out if they are corroded shut.

 

[bhoppe]

Re: 83 120hp mercruiserI/O bogging

SRT8,

I have the same issue with my '85 120hp mercruiser I/O w/ mercarb. Have you been able to solve this issue?

Brandon