Mercruiser 3 liter bogs and stutters under load

bensoldboat

Recruit
Joined
Jul 13, 2013
Messages
3
I have a standard ignition 3 liter mercruiser, new factory rebuilt carb, new plugs, condenser, coil, points, wires, and rotor. I have made attempts to replace the gas, but have only gotten about 5 gallons out by putting some air pressure to the vent and running the fuel line out the back. I've seen no water in the five gallons of gas that I've gotten out. Both fuel filters are new. When I'm in it by myself and hit the throttle it starts off strong then stutters for sometime 6 seconds and then takes off like a beast. If I try and run it at 20 miles an hour the engine sounds like its missing at times then takes off and runs right at other times. The timing is set at 6 btdc and I've taken the distributor apart to see if the mechanical advance is loose and it seems to be clean and working right. I have not taken the timing light to see if its advancing as it should while powered up. It does run a little rough at low idle. The wires are in the correct order. I'm thinking I have a stuck lifter. I 've done no compression checks. Any help would be appreciated I at a loss. With three people in the boat it will pull a wakeboarder out but not above 15 mph because the engine is sputtering. Three people in the boat and it stutters and bogs for a little longer than with just myself then finally takes off like a rocket. Thank you for your suggestions....
 

alldodge

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Staff member
Joined
Mar 8, 2009
Messages
40,582
I have a standard ignition 3 liter mercruiser, new factory rebuilt carb, new plugs, condenser, coil, points, wires, and rotor. I have made attempts to replace the gas, but have only gotten about 5 gallons out by putting some air pressure to the vent and running the fuel line out the back. I've seen no water in the five gallons of gas that I've gotten out. Both fuel filters are new. When I'm in it by myself and hit the throttle it starts off strong then stutters for sometime 6 seconds and then takes off like a beast. If I try and run it at 20 miles an hour the engine sounds like its missing at times then takes off and runs right at other times. The timing is set at 6 btdc and I've taken the distributor apart to see if the mechanical advance is loose and it seems to be clean and working right. I have not taken the timing light to see if its advancing as it should while powered up. It does run a little rough at low idle. The wires are in the correct order. I'm thinking I have a stuck lifter. I 've done no compression checks. Any help would be appreciated I at a loss. With three people in the boat it will pull a wakeboarder out but not above 15 mph because the engine is sputtering. Three people in the boat and it stutters and bogs for a little longer than with just myself then finally takes off like a rocket. Thank you for your suggestions....

:welcome: to iboats

Need an engine serial number or at least a year
Sounds like a fuel issue, either carb, pump, restriction or bad gas. Why did you pump the fuel from the tank? Pull the fuel filter off and pour contents into a clear container to see what you find. If you can buy or get a Vacuum/fuel pressure gauge, place it inline between the fuel pump and carb. Look for pressure between 4-7psi. Have you tied running it from a 5 gal can?
 

Bondo

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Staff member
Joined
Apr 17, 2002
Messages
70,468
I have a standard ignition 3 liter mercruiser, new factory rebuilt carb, new plugs, condenser, coil, points, wires, and rotor. I have made attempts to replace the gas, but have only gotten about 5 gallons out by putting some air pressure to the vent and running the fuel line out the back. I've seen no water in the five gallons of gas that I've gotten out. Both fuel filters are new. When I'm in it by myself and hit the throttle it starts off strong then stutters for sometime 6 seconds and then takes off like a beast. If I try and run it at 20 miles an hour the engine sounds like its missing at times then takes off and runs right at other times. The timing is set at 6 btdc and I've taken the distributor apart to see if the mechanical advance is loose and it seems to be clean and working right. I have not taken the timing light to see if its advancing as it should while powered up. It does run a little rough at low idle. The wires are in the correct order. I'm thinking I have a stuck lifter. I 've done no compression checks. Any help would be appreciated I at a loss. With three people in the boat it will pull a wakeboarder out but not above 15 mph because the engine is sputtering. Three people in the boat and it stutters and bogs for a little longer than with just myself then finally takes off like a rocket. Thank you for your suggestions....
Ayuh,... Welcome Aboard,..... Ya skipped the Most Important part,....
 

bensoldboat

Recruit
Joined
Jul 13, 2013
Messages
3
Thank you for the replies. I did the compression checks, and ended up with a blown head gasket and burnt valve. Took the head in, had it planed, a valve job and checked for leaks. 3 weeks later, I put it back on, take it back out and the same exact thing happened, but not as bad as before. It ran rough under load with some (i'm calling internal backfiring, or slight popping). I get it home readjust the rocker arms which I had too tight,(also did another compression check- which was fine) and while it ran much smoother, it still sputtered and "missed" under load. The first time out of the hole, I thought I had gotten it....it accelerated nicely and went to top speed. Then I let it settle back down in the water and give it full throttle and the sputtering was back. I changed the spark plugs *(again), with no change. Any more suggestions would be greatly appreciated.....
 

alldodge

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Staff member
Joined
Mar 8, 2009
Messages
40,582
Thank you for the replies. I did the compression checks, and ended up with a blown head gasket and burnt valve. Took the head in, had it planed, a valve job and checked for leaks. 3 weeks later, I put it back on, take it back out and the same exact thing happened, but not as bad as before. It ran rough under load with some (i'm calling internal backfiring, or slight popping). I get it home readjust the rocker arms which I had too tight,(also did another compression check- which was fine) and while it ran much smoother, it still sputtered and "missed" under load. The first time out of the hole, I thought I had gotten it....it accelerated nicely and went to top speed. Then I let it settle back down in the water and give it full throttle and the sputtering was back. I changed the spark plugs *(again), with no change. Any more suggestions would be greatly appreciated.....[/QUOTE]

Have you tried any of things I mentioned in post 2 ?
 

bensoldboat

Recruit
Joined
Jul 13, 2013
Messages
3
A590653 is the engine serial number, and its an 1986. I have a newly rebuilt carb on it, and both filters have been changed. I tried pumping the gas from the tank thinking I would find water, at least that is why I did that, although I didn't find any water in the fuel. I will pull the fuel filter from the carb and see if all looks good there, then switch out the fuel pumps. I don't have an inline pressure gauge and not sure how I would work that without getting a replacement fuel line since its metal. Sorry I haven't seen a fuel pressure gauge used. I'm assuming it would have to go between the pump and carb where my metal line is now. Are you saying to run it off a 5 gallon can to bypass the pump ? Like hold the tank so it gravity feeds into the carb? Thank you again! The other fuel pump I have around came off an engine that was running fine.
 

mkfs9

Seaman
Joined
Jul 8, 2005
Messages
64
Is your exhaust manifold old, could be water seeping into your engine if they are rusted out inside.
 
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