crashmaggio
Recruit
- Joined
- Sep 30, 2020
- Messages
- 3
Hi All,
Sorry for the long post, just trying to get all the info out there in one shot that I normally see asked in these posts....
Long time listener, first time caller. I rebuilt a boat this summer that decided to go for a swim on it's own.
It's 4.3L Mercruiser Thunderbolt V - S/N 0M227756
After a few unsuccessful launches, here's where I'm at, hoping to pick the mind of the hive.
After getting the motor out of the water, it was drained, oil/filter has been changed to the point that I have 0 milking in the oil any more. Brand new fuel filter, fuel tank, lines, carb bowl and pump have all been drained and/or flushed. All hydraulic lines have been flushed with fresh oil, power steering was flushed with fresh oil. fresh oil in lower unit. Plugs have been pulled and are in good shape. I pulled the distributor cap and cleaned all the points and rebuilt the rotor. (I'm planning to change cap/rotor wires and plugs over the winter, ran out of "one more weekend" with the wife) I used the engine alignment tool when reinstalling the engine and new gimbal bearing and it will slide in and out with 2 fingers. I re adjusted all the throttle cables and shifter cables per the manual, I have nice tight engagement in the lower unit. Prop has no play on shaft.
The engine runs well on earmuffs in the driveway, I've had it running about 30 minutes 600rpm, no knocks, no ticks, beautiful smooth idle. The boat will sit and idle in the water all day same as in the driveway. I can cruise around the lake at around 2200 RPM 10MPH and it' would be happy to do that all day, not me.
Now the problem:
When I rev the engine to about 3/4 throttle, the boat will jump up on plane and gets up and goes for about 5-10 seconds around 3500-3600 RPM, then seemingly out of nowhere, it almost sounds like the motor trips on itself, and RPMs drop to around 2000RPM. If I leave the throttle in position, it'll struggle and work it's way up to RPMs again sometimes, but it normally dies.
If I cut the throttle back to an idle, it pretty much dies right away. Then it'll take 2-3 cranks of the motor to get it started again, rinse and repeat. I know the prop isn't cavitating because it was a strong running boat prior to the sinking, and RPMs never spike, they just kinda die.
My guess is I'm starving for gas, but I'm not getting the lean RPM revs that you would normally see when the mix gets lean. I'm also thinking I may have some contamination on the carb, maybe jets etc... when I drained the carb there was about 20/80 water gas mix in the bowl. Not sure how long it was in there. I'm going to get a carb rebuild kit and do a full rebuild based on this assumption.
Looking for other opinions or thoughts on what I could be facing here?
Any ideas how to test it without bringing the boat down to the launch for another unsuccessful launch?
Thanks in advance
Sorry for the long post, just trying to get all the info out there in one shot that I normally see asked in these posts....
Long time listener, first time caller. I rebuilt a boat this summer that decided to go for a swim on it's own.
It's 4.3L Mercruiser Thunderbolt V - S/N 0M227756
After a few unsuccessful launches, here's where I'm at, hoping to pick the mind of the hive.
After getting the motor out of the water, it was drained, oil/filter has been changed to the point that I have 0 milking in the oil any more. Brand new fuel filter, fuel tank, lines, carb bowl and pump have all been drained and/or flushed. All hydraulic lines have been flushed with fresh oil, power steering was flushed with fresh oil. fresh oil in lower unit. Plugs have been pulled and are in good shape. I pulled the distributor cap and cleaned all the points and rebuilt the rotor. (I'm planning to change cap/rotor wires and plugs over the winter, ran out of "one more weekend" with the wife) I used the engine alignment tool when reinstalling the engine and new gimbal bearing and it will slide in and out with 2 fingers. I re adjusted all the throttle cables and shifter cables per the manual, I have nice tight engagement in the lower unit. Prop has no play on shaft.
The engine runs well on earmuffs in the driveway, I've had it running about 30 minutes 600rpm, no knocks, no ticks, beautiful smooth idle. The boat will sit and idle in the water all day same as in the driveway. I can cruise around the lake at around 2200 RPM 10MPH and it' would be happy to do that all day, not me.
Now the problem:
When I rev the engine to about 3/4 throttle, the boat will jump up on plane and gets up and goes for about 5-10 seconds around 3500-3600 RPM, then seemingly out of nowhere, it almost sounds like the motor trips on itself, and RPMs drop to around 2000RPM. If I leave the throttle in position, it'll struggle and work it's way up to RPMs again sometimes, but it normally dies.
If I cut the throttle back to an idle, it pretty much dies right away. Then it'll take 2-3 cranks of the motor to get it started again, rinse and repeat. I know the prop isn't cavitating because it was a strong running boat prior to the sinking, and RPMs never spike, they just kinda die.
My guess is I'm starving for gas, but I'm not getting the lean RPM revs that you would normally see when the mix gets lean. I'm also thinking I may have some contamination on the carb, maybe jets etc... when I drained the carb there was about 20/80 water gas mix in the bowl. Not sure how long it was in there. I'm going to get a carb rebuild kit and do a full rebuild based on this assumption.
Looking for other opinions or thoughts on what I could be facing here?
Any ideas how to test it without bringing the boat down to the launch for another unsuccessful launch?
Thanks in advance
