'93 351 Engine Rough out of hole

[Maristar Toy]

I have a 351 w/carb on a Maristar. 330 hours. I've owned it 7 years and it's been great up to now. Boat starts up easily and idles. If I give it full throttle out of the hole, it will not take off: it sputters and runs rough. This happens warm or cold. If I plane the boat out slowly, then give it full throttle it takes off and sounds great.

The boat ran fine last year. This problem started new this year. I took it out first time and noticed problem. There was no water in the water fuel separator (I replaced it with the in-line filter too). The screens in the carb were perfectly clean. I cleaned the flame arrestor too. I changed the spark plugs before taking it out the first time this year. One plug did not have any engine fogging oil residue from winterization; the remaining 7 plugs were all oily from winterization. No remedy has worked. The marina has worked on it all week and cannot fix it: they say the ignition checks out ok and see nothing wrong with carb. I burned 13 gallons of new gas this year. I had the tank a little low at winterization with stabilizer.

As a maintenance item, last summer I cleaned the gas tank, and I took out the screen in the tank pickup. I also removed the anti-syphon valve at the tank.

Any ideas?

[skibtlvr4evr]

I had a problem with the vent on the gas cap. The rubber had expanded (alcohol in gas) and boat would be starving for fuel. I took cap apart and cut rubber back and no problems since. Good luck

[denverd1]

"If I plane the boat out slowly, then give it full throttle it takes off and sounds great."
could be a float problem in the carb.

Does is run fine at high RPM? If so, that would rule out fuel starvation.

[flipper]

Sounds like a carb problem to me.

[JimN]

Did it overheat recently? The fact that it didn't have any fogging oil tells me that it may not have good compression in one cylinder and if it's bad enough, it won't be drawing fuel in, either. One boat I worked on had new head and intake manifold gaskets with Permatex Ultra Copper sealant on them, which is a big problem. He overheated it, the sealant basically melted and the compression caused a leak between cylinders. Eventually, the head gasket eroded to the point that 1-1/2" was missing and while it idled great, it was really lumpy under load.

I think they need to look into why no fogging oil got on the one plug.

"As a maintenance item, last summer I cleaned the gas tank, and I took out the screen in the tank pickup. I also removed the anti-syphon valve at the tank."

You took the screen out and cleaned it or just removed it? I wouldn't recommend that, or removing the anti-siphon.

[83hurstguy]

Check the accelerator pump in the carb. WITHOUT the motor running, watch the accel pump squirters on the primary side and have somebody pump the throttle. Make sure you are getting a good solid stream of fuel from the squirter.

Make sure the springs in your distributor for the spark advance aren't broken.

[JimN]

Or, remove the throttle cable and pump it manually.

I'd like to know more about the history of the boat, as far as other engine problems. The unfogged cylinder is intriguing. Was it #1? Maybe it could have used more fogging oil and that's all but if the others were all well coated,....

[Maristar Toy]

It did overheat 3 summers ago when pump and thermostat went bad. I had it checked out at a Marina directly afterwards. They said no damage had been done. Plus it ran good last summer. The 'dry' plug was on driver side and it was one of the 2 middle cylinders. The Marina did a compression test this week and said it was ok.

[Maristar Toy]

Yeah, once the boat is planed out and you give it full throttle, it takes off.

Thanks, Greg

[Maristar Toy]

With engine off, I did verify fuel squirts in carb. I will advise mechanic about springs. Thanks.

[JimN]

Ask if they did the compression test with all plugs removed. If cylinders 2 and 3 lost the gasket between them, it sounds like the same symptom as the one I worked on. Unfortunately, it may have checked out OK immediately after the overheat but subsequent running may have caused the current problem.

How old are the plug wires?

[Maristar Toy]

Ask if they did the compression test with all plugs removed. If cylinders 2 and 3 lost the gasket between them, it sounds like the same symptom as the one I worked on. Unfortunately, it may have checked out OK immediately after the overheat but subsequent running may have caused the current problem.

How old are the plug wires?

Jim,

I've put about 220 hours on current wires over a period of 7 years. The engine has 330 total hours. I don't know if they are original or if they were replaced before I bought it. They're probably original since I bought it with 110 hours and 8 years old.

[GuitsBoy]

Jim,

I've put about 220 hours on current wires over a period of 7 years. The engine has 330 total hours. I don't know if they are original or if they were replaced before I bought it. They're probably original since I bought it with 110 hours and 8 years old.

Even without too many hours, at 7+ years, those wires may be suspect... Might as well invest in some new ones.

[JimN]

Wires get wet, the insulation stops insulating and then crossfire happens. I would definitely replace them when they're this old. There's no guarantee that this is the problem but they are awfully old.

[Maristar Toy]

Wires get wet, the insulation stops insulating and then crossfire happens. I would definitely replace them when they're this old. There's no guarantee that this is the problem but they are awfully old.

Sounds good. I will replace wires. Thanks, Jim.