Surging at 4000 rpm ?'s again

[Gorilla0178]

If its not one thing its another. Went out for another run today, the motor surges at about 4000 rpm. How can I tell if its the prop slipping or a power issue? I'm not sure it happened the first few times i took it out, but it happens now. I've worked out the fuel issues it had, the boat takes off great and will run great right up to about 4000 rpm if I give it more gas it surges between 4000-4500.I might get it to 5000 but eventually it starts to do it. I tried the prop at all heights and it still does it. If its in neutral it will rev quickly and crisply up to 6000+ no issues. Speed seems to fluctuate with the surging. The motor seems to be getting plenty of fuel, the primer bulb is always hard and the bowls seem full all the time. The speed when it happens is about 60 or so. It also stalls sometimes after letting off and making a turn arould. Not sure if thats part of it. The set up is a 17 action marine, 200 johnson, 5.5 jackplate, propshaft 4" below pad all the way down, level with pad all the way up, stock lower, 13.5 25pitch 4 blade bass boat prop. Any ideas where to start with this? I really want to get this worked out.

[spbutler]

I chased what I thought was fuel problems for a month and it was ignition, the power pack.
You shouldn't rev your engine up in neutral, you could blow the motor because of no load.
I used a inductive timing light to catch the problem, losing spark on 3 cylinders intermittently. In a separate issue I did have a prop that slipped but it was during take off.

[Gorilla0178]

I didnt rev it much, just gave it a good step on the gas. I dont think it is the prop, but i want to be sure. How did you catch it with a timing light?

[Forkin' Crazy]

What's it do when you push in the key?

[Brabender]

Does it get progressively worse as you run it?

[Gorilla0178]

Havent tried pushing in the key while running, didnt think of that. Would that rule out fuel?

It doesnt do it at all running under 4K, if I step on the gas it might get to 5K or so, then it drops to around 4K and if I give it gas from then on it revs between 4-4.5K back and forth. Kind of like hitting the limiter, but i know its alot higher than that. Runs good up to then. I think I do remember it from before, but it had to go awaw for a short time i think, I've run it higher than 4.5K but not much, If I've seen 5.5K I'de be suprised. But then speed and experance has something to do with that.

[Gorilla0178]

Any ideas, I really hate to spend hundreds of dollars to take it to the mechanic if i can figure it out. I'll put it in the water again this week and see what happens when I hit the primer. Not sure what else to check.
I'll check the plugs and wires too.

[Gorilla0178]

I was doing some research online, read someone else had similar prob. when he pushed the choke it took off, I'll test that this week, if that is the issue how do I fix it. Assuming its that simple to find.

[spbutler]

You need someone in the back with an inductive timing light (clamp on) on one of the wires while you drive and see if it goes out when problem happens and if light doesn't go out move it to a spark plug wire on the other side, still doesn't go out try the rest of the wires. At least you would know if your losing spark. Another test would be a spark tester at idle to see if your getting sufficient spark for each cylinder. They're cheap from any auto store.

[racer]

What year 200? with or without air box? what mains in the carbs?

[Gorilla0178]

1999 year, with airbox, not sure what mains, its a stock motor.

[Gorilla0178]

Well I bypassed the water seperator/fuel filter, to make sure its not restricting fuel. There should be no reason for it to be restricted now Its free and clear. I ran it for a bit on the hose and no prob. I dont know what the fuel press is, but I undid the fuel line to carb #1 and it squirts plenty of fuel, I couldnt pinch it off by hand. There's no leaks or anything, and all carbs are getting good fuel. I'll take it out for a run tomorrow, Keep you posted....

[Gorilla0178]

Ok here's what I found today. I bypassed the fuel filter for the test today. It fired up with a little hickup today, so be it. I warmed it up and slowly ran it up to about 50. Give it more gas runs up a little more then starts to surge, push the key in, no change. I stop make sure the primer ball is pumped, then take off hard, boat runs up to 5k still going, then starts surging. I stop again and check the primer ball, takes 3 squeezes to fill the carbs. Do the same thing over, running great for about 30 sec then surges, primer ball thakes 3 squeezes to fill. I did this a bunch of times and it was always the same. Runs great for 30sec or so then surges, if you let off the gas and then try to give it more it gets worse. So I'm guessing the fuel pump isn't keeping up with the demand??????? The good news is I feel like I was driving it the best so far, until the surging starts. Running real straight, and nice. I think the surging screws the handling up, today you could feel that everytime it surged, it would torque the
boat over to the left and screw up the handling. What do you think????

[JohnR]

Assuming the fuel pump is on the motor, I would say something is wrong between the bulb and the tank. The pump is sucking plenty of fuel and emptyying out the bulb because the fuel can't make it to the bulb. Maybe there is a restriction in the tank. I've heard that there is a check valve on the end of the pickup inside the tank and sometimes it gets stuck or somewhat stuck closed.

John

[Gorilla0178]

The fuel pump is on the motor, the tank is brand new, just had it made, it had tape over the holes when I got it. Dont have a antisiphon valve on the tank, then its just 10 or so feet of 3/8 hose, then the bulb to the motor where there is a small inline filter. I dont see where the restriction would be, thats why I bypassed the big filter, to be sure it was a straight path to the motor. Still did it. Would not having a antisiphon valve be it? I wouldnt think so.