SOS 351 engine question

[mabbore]

So I am out yesterday doing some wake board runs with my friends on my Sunsport. When I take a hard turn under power and the boat all of a sudden starts to run rough. Not terribly so, but enough that I have to add about 300 rpms to the throttle plate to keep it at idle. The engine seems to more noticeably vibrate, and not absurdly, but more than usual, and this seems apparent from idle to 2000 rpms. I did not take it over 2k rpms for fear I might damage something. just some back story on this boat, I have had her for 2 years and have put almost ~250 trouble free hours on her. I change my fluids every 50 hours, my plugs and fuel filter every 100. I upgraded to electronic ignition about 50 hours ago (great investment by the way).

2 things that I recently happened that might have affected the engine. I put a bottle of carb cleaner in the gas tank, i figured it would be good just so I could avoid cleaning the carb as long as possible. I recenly broke off and lost my gas cap and had to replace it with one of those cheap perko ones that uese a key ring to keep it held in place. Well my buddy was filling up the tank and jammed the funnel in there and the key ring fell into the tank. But its pretty big, so I did not think it would be an issue. I am thinking that this issue could be 1 of 3 things; my coil is original and might need replacing (does anyone know the resistance specs on it), that key ring might have jarred loose some krud in my gas tank with help from the carb cleaner and clogged my fuel filter, the Carb might have clogged circuit.

1987 Sunsport, 351, BW71c

[chris young]

If you don't already have one, get a vacuum gauge. They can tell you a lot in very short order. Holley has a good video here,http://www.youtube.com/watch?v=NrnzD7PgoHI and I think it's the 3rd or 4th reading in they talk about ignition problems, which at first glance is what I'd suspect. To me it seems like you're missing a cylinder, but that's purely a guess based on very little info. The fact that it happened with the boat turning hard under power kind of leans more in the direction of some crud in the gas tank making it to the fuel intake though.

A vacuum gauge will take a lot of the guesswork out.

Good luck, keep us posted.

[Cusefan78]

I would check all your wires, cap and rotor first if they are old they might have popped free or aren't making good contact. Sounds kind of like one of the cylinders isn't firing properly or it's a fuel issue with the carb and its not dropping enough fuel. Also make sure the distributor isn't loose. Might have bumped the timing.

[DAFF]

I'm leaning towards water suckage.....Carb gulped some water from the tank and giving the shutter and bad drivability.

[inair]

I'm leaning towards water suckage.....

Yah, I'm leaning toward "suckage" too :)

[Cusefan78]

Oh didnt catch that part. Water would do it

[mabbore]

I don't think its water, just because I had been running it at least an hour that day with no issue at all. But I will do a; vacuum , compression and resistance check on it this weekend.

[haugy]

Well water is more dense than gasoline, so if you did get some water in tank from the fill cap it would go straight to the bottom where the pickup is.

[mabbore]

Any other ideas? Im heading to the dock tonight with a compression gauge, meter, new fuel filter and some carb cleaner.

[Torque]

Check your grounds, and for fun, look at your valve springs and rocker arms. A sudden, abrupt change can be a multitude of things. a bad ground will get you every time though. Good luck!

[mabbore]

Check your grounds, and for fun, look at your valve springs and rocker arms. A sudden, abrupt change can be a multitude of things. a bad ground will get you every time though. Good luck!

You know, I didnt even think of the ground issue. I will clean up some of the contact areas. What should I look for on the valve spring/rocker arms?

[chris young]

If you have a vacuum gauge it will tell you if the valve train is working correctly, I know I sound like a broken record, but watch the videos or just read the charts. No need to pull the valve covers. Still though, I'm with the others on the fuel issue, Coming out of a hard turn and sudden bad running really sounds like something made it to the fuel pickup in the tank.

[Torque]

You know, I didnt even think of the ground issue. I will clean up some of the contact areas. What should I look for on the valve spring/rocker arms?

Unless you know what your looking at, I.E. the pre-issue vacuum level vs the current level, it won't help you. If you were intimately close to your engines characteristics, ( if you were a racer, or monitored it regularly) you would see it on a vacuum gauge. If you did break a spring, you would hear it clatter. If it dropped the valve attached to the spring, there would be no question regarding the sound going on in there. I would check for a ground issue or water in the fuel. Last recourse, pull a valve cover and look at the springs.

You can pull the lower float bowl bolt to drain the fuel into a cup. Just pull one of the lower bowl bolts. The fuel will run out of that bolt hole so you don't have to replace the bowl gasket.

I was a dragboat racer for years, so I've tossed pistons into the bilge and ingested plenty of water over the years, but the simple ground will get you every time.

Good Luck!

[mabbore]

first I want to thank everyone for all their help. I have been coming to this forum for a couple years now and I cant say enough about the support I get here. So yesterday I head to the dock to start diagnosing my boat. First I start by checking timing chain slop, it looked great probably 2-3 degrees. Then I cleaned up couple of the grounds for the ignition and others. But its still running funky. Next I spray some carb cleaner around the base of the carb and manifold to help uncover any vacuum leaks, but nothing. After that I am still scratching my head. I decided to just take it out on the lake and rip on it since I was pretty sure it was a fuel issue. Sure enough after a short flogging on the water, SHE RAN GREAT! Im not sure if it was just some gunk clogging a jet or what, but either way she is back to normal. Thanks again everyone! Sorry for the fire drill, but you just never know.