engine dying when slamming into waves

Hey all, I'm new to this forum, have a 1983 25 hp long shaft, just bought it, replaced the power pack to get it running, runs dang good with the remaining old parts on it, plugs, coils, etc. Plan on replacing pump impeller, plugs, carb kit as the weeks stretch on. While running it out on the river to just see how it does, and and what I need to address, I noticed that flat out, it's great... but if I hit rough water, and start slamming hard into waves, the motor will "die" on every slam, and comeback good between them...after about 15 hits, it will stall, but start right up again and run great...... this is fairly rapid, normal rough water type thing..... is it possible the needle in the carb is getting stuck on every bounce, cutting fuel for a split second? runs steady and good all other times, only runs bad when slammed hard. Thanx, y'all

It is not caused by the needle getting stuck in the carburetor.

Check all your ignition wiring for having a loose wire some place.

Extremely unusual situation you have there. All anybody can do from here is guess. Probably better chances of success at the lottery.

The problem is float level is off, when you hit the waves raw fuel is thrown up the emulsion tube which fouls the plugs for a millisecond. Common problem in race motors but they have slosh kits installed to prevent this.

faztbullet said:

The problem is float level is off, when you hit the waves raw fuel is thrown up the emulsion tube which fouls the plugs for a millisecond. Common problem in race motors but they have slosh kits installed to prevent this.

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Right, I was thinking float/needle/seat..... I've not done the carb yet, but I have been over the wiring and ignition system... all looks good... I'll put a kit in it, then test again.... process of elimination, but that motor sat for like 13 years, so it could use it anyway.... thanks for the insight!

When underway, the prop is under a load... BUT... rushing thru the water. Slamming into a wave normally causes a boat to drop rpms instantly. If your definition of "die" means the rpm suddenly dropped rather then stop running altogether.... then I would suspect the engine has met still water would increase the load factor on the prop forcing a rpm drop

I agree with what joe said, except the OP said it will stall. if I hit rough water, and start slamming hard into waves, the motor will "die" on every slam, and comeback good between them...after about 15 hits, it will stall, but start right up again and run great.

Maybe it is a float problem. Beats me.

fdrgator said:

I agree with what joe said, except the OP said it will stall. if I hit rough water, and start slamming hard into waves, the motor will "die" on every slam, and comeback good between them...after about 15 hits, it will stall, but start right up again and run great.

Maybe it is a float problem. Beats me.

Click to expand...

Actually, I mean "die" in the way on each hit, it's like you cut the throttle abruptly, then it revs back up, and after about 15 times of this, it'll stall out. It doesn't just change revs a little, that's normal. My first thought was fuel, not ignition, and the float thing seems to make perfect sense. If it's momentarily flooding out, it can only take so much of that til it says "screw it", lol. Ignition wiring might give me sputters and misses, this is just like fuel is being manipulated... I mean it's not just standard issue hard hits while running full out, I'm talking the slams that rattle your teeth and gives you back problems.. heh. Anyway, carb kit will be in by next week, I'll post results after rebuild.

Run with a timing light hooked up.----See how spark behaves when you hit those waves.

Heh, wear your life preserver too. And have your kill switch lanyard connected.

Water that rough!...... Cure = Bigger boat!

Ok gentlemen, resurrecting the thread, and what I've done...... rebuilt carb, still would bog and die on wot. As soon as throttle plate would just start to move... boom.. daid meat. Worse than before. Took Carb back off .. whoops, forgot that lil gasket that separates the tube in the bowl from the bottom of carb... i took it out when I set the float so I wouldn't lose it... well, I forgot to put it back in... but that's ok, I'm a trained professional. Anyway, took it back on the river... same thing... dies at wot after a few surges. Rinse and repeat... looked at main jet... oops... a lil bit clogged up. cleaned, reinstalled. Now, back on the river... ran great, got 25 mph out of her... could cruise wot 1/2 mile or so numerous times for like an hour.... then, it did it again.... only like 1/10th as much as it used to do... took the cowl off, and when it started to happen, i had a spray bottle with 50:1 in it, and gave it a shot or two.... it kept it from dying out, not great, but better...... hard to finesse that sorta thing while under way with a lil bit of rough seas, ya know?.....so I'm considering this a win at this point. Got back to dock.... put engine on idle, just a few hundred rpm above "stall point"... had a can of brake cleaner... gave it tiny little pssts around gaskets, carb, etc....seemed ok but if I got even CLOSE to the lower crank seal, boom.... stall, die, what-eva. So, I'm thinking a leaking seal, sucking air (or leaking mixture out) at high rpms?, but it idles like a dream.... low speed needle about 1/2 turn out from seated....I'm sure I'll have to change that after I put a seal in..... gonna order a seal tonight..... any of you guys think I'm on the right track here?

How did you manage to spray the lower crank seal? Just wondering.

shot it from the engine side, down deep in the center where it goes thru into the leg. Sucked it right in and stalled it a few times.