Mercruiser 3.0 Issue, Maybe Carb.

[Gagnon_716]

Long Time Observer Here.

1992 Mercruiser 3.0L Alpha 1 Gen II
Engine S/N: 0D713989
Outdrive S/N: 0D665639

I am the second owner of a 1992 Larson All American 170. I purchased the boat 4 years ago. It ran great for the first 2 seasons. By the end of the third season, when the engine was hot the boat would flood, and become ridiculously hard to start.
I assumed the obvious bough a model specific kit from M***s C**********S.com. pulled the carb and rebuilt it to spec over the winter of 2014-2015.
Something went wrong. Last summer i ran the boat and now have absolutely zero hole-shot, at WOT the boat will not go over 3000 rpm.
I double checked the float level against the merc spec and everything was spot on.
I noticed the transom of the boat was covered with black ?soot? I pulled all the plugs, numbers 2 and 3 were completely carbon fouled, # 1 & 4 looked great.
With spring (boating season) fast approaching here in Canada, and the boat soon to be taken out of storage. I am trying to figure out if there is something completely obvious That i have missed. Or if it is time to put down the wrenches and call a mechanic.

Any help would be great.

 

[Fastatv]

Long Time Observer Here.

1992 Mercruiser 3.0L Alpha 1 Gen II
Engine S/N: 0D713989
Outdrive S/N: 0D665639

I am the second owner of a 1992 Larson All American 170. I purchased the boat 4 years ago. It ran great for the first 2 seasons. By the end of the third season, when the engine was hot the boat would flood, and become ridiculously hard to start.
I assumed the obvious bough a model specific kit from M***s C**********S.com. pulled the carb and rebuilt it to spec over the winter of 2014-2015.
Something went wrong. Last summer i ran the boat and now have absolutely zero hole-shot, at WOT the boat will not go over 3000 rpm.
I double checked the float level against the merc spec and everything was spot on.
I noticed the transom of the boat was covered with black “soot” I pulled all the plugs, numbers 2 and 3 were completely carbon fouled, # 1 & 4 looked great.
With spring (boating season) fast approaching here in Canada, and the boat soon to be taken out of storage. I am trying to figure out if there is something completely obvious That i have missed. Or if it is time to put down the wrenches and call a mechanic.

Any help would be great.

How about a pic of that boat...LOL I have the same boat but it's an 89 model....great little boat. If you built the carb correctly, and verified the float again, and it's correct, then I might suspect the choke isn't fully opening, or you may have it clocked incorrectly. Also could be an issue with the accerlator pump ( the hole shot problem ). When you installed the pump, did you ensure the pump edges were all facing downward....no part of the pump "rolled" back up on you/and linkage is correct and in the correct hole for your application? And were you sure when you re-installed the air horn ( top of carb ) that you went straight down, ensuring the power piston was "dead" on top of the power valve? Let us know what you find and good luck!

 

[airshot]

Because you mentioned cylinders 2-3 were carbon fouled and 1-4 looked good, I would recommend doing a compression check. The 3.0 engine is noted for blowing the steel head gasket out between 2-3 and this low compression causes fouling and poor performance. I know because I had the same thing happen last summer but in a slower fashion. Thru the course of the summer the engine became harder to start and did not want to idle and kept fouling the 2-3 plugs. Ran a compression check and sure enough 2-3 were low. Over the winter I pulled the head and sure enough there was an 1/8" wide burn thru the steel gasket right at the closest point between 2-3. I had the head redone with new valves, springs etc and resurfaced. It is currently sitting in the boat ready to be put back together. I can't say for sure whether this is your problem or not, but a quick compression check is all it would take to confirm.

 

[airshot]

Hey there Fastatv I think we met at the atv connection forum as well...(kymco 450i).....glad to see you are a "toy" man same as I am with atvs and boats.

 

[Rick Stephens]

I would recommend doing a compression check.

Concur.

 

[Fastatv]

Hey there Fastatv I think we met at the atv connection forum as well...(kymco 450i).....glad to see you are a "toy" man same as I am with atvs and boats.

Yep, it's me...LOL And cars, jeeps...LOL

 

[Gagnon_716]

No Title

How about a pic of that boat...LOL I have the same boat but it's an 89 model....great little boat. If you built the carb correctly, and verified the float again, and it's correct, then I might suspect the choke isn't fully opening, or you may have it clocked incorrectly. Also could be an issue with the accerlator pump ( the hole shot problem ). When you installed the pump, did you ensure the pump edges were all facing downward....no part of the pump "rolled" back up on you/and linkage is correct and in the correct hole for your application? And were you sure when you re-installed the air horn ( top of carb ) that you went straight down, ensuring the power piston was "dead" on top of the power valve? Let us know what you find and good luck!

Thanks for the replies! Fastatv. Nice to hear from another happy Larson owner! The edges of the accelerator pump were all facing downward, once the winter cover comes off I will verify the choke and do a compression test as Airshot mentioned.

The boat has been great for us, and we really don't need any more power then the 3.0 was originally providing.

Thanks again guys I will check back in in the coming warmer months!