Outboard issures

My brother has an older lund ’90-’94 with console. He has an older rebuilt 40hp motor on it with no power tilt/trim. I dont’ know much about boats at all and he hasn’t talk to a mechanic yet, so trying to get some feedback first. The motor works good, starts up fine and runs good ate low to medium throttle. But at full throttle it starts to jerk on and off. What would be the problem here? Is it the motor? The jerk sort of goes away when you reach max speed but comes back here and there. If you lower the throttle just under max its find again.

I also wanted to know if anybody has tried them power tilt/trim kits and if they are worth it. Thanks.

Sounds like you have a spark plug that is fouling out, had the same thing happen to me at the end of last year.

don’t know anything about the t&t, but I wouldn’t want to be lifting up a 40hp to many times a day!

It does sound like a spark issue. Plug or wires. Somethings loose

Could be clogged jets too, had a very similar problem with my 60 Yami from bad gas sitting in the carb over the winter. Varnish builds up and impedes fuel flow. Try the plug replacement first, then tear apart the carb and replace the jets.

Spark plugs or fuel filter!

Try the plug first but it could be a number of things. Check for fresh gas run some SeaFoam. If it is a slow die of power then I would say it`s fuel related. If it`s sharp and total cutout then I go for electrical.

It could be a weak coil. Being that it idles fine, as the trottle comes up it turns the coils around the flywheel to increase timing a loose wire or worn spot could cause the problem. Check connections. I am geussing it just may be the coil pack.

Good Luck

It’s very hard to trouble shoot something without seeing it or hear it run. But I would have say it sounds like a weak coil.

Ok…i will probably check the plugs first..maybe best if just replace. Next…what part is the coil? Confused with that part. I will also check the gas.

I’m not sure if I explained it well enough. I’ll try explain the problem a little better. The engine idles and starts up fine. When running it is still fine at low, medium, and even 3/4 throttle. Once the boat gets going and flats out from the tipping, and you knock it into full throttle it will still run fine. But every couple of seconds at full throttle it will have multiple jerks together. You can see the motor jerking, (lame analogy, but sounds kinda like when a pinball hits the rubberband part in a pinball machine, hitting it multiple times.)It doesn’t lose speed but its quite a strong jerk, which I don’t feel too confident about. Keeping it under full throttle will take that jerking away. I can see how a miss fire on a plug might result that jerking. You guys think anything else could be the problem?

One other possibility-
A small hole in the fuel line or bad connection that draws in unwanted air at higher RPMs, starving the fuel system.
Runs great at lower RPMs but wrong fuel/air mixture at higher RPMs.

When you explain the jerking and the motor is jumping it is not like the motor is jumping in and out of gear is it?
I had an older outboard with similiar issues and that problem was when a guy did the lower unit on it he did not get it set properly. Also if you pulled the wrong plug when draining the lower unit this same result can happen. When you pull the wrong bolt out it drops the shaft. Motor will still run and gears will engage but when trying to get full throttle out of it she started hoping and jerking kinda like you explained. But not seeing or hearing it for myself this is just another idea.. Hope it is not the problem I explained cause years ago it ran me 400.00 bucks and that is when shop costs were 45.00/hour.

The aftermarket tilt/trim systems are really nice. CMC makes one for 35hp and up motors and I think Panther makes one too. One of the nice features of these aftermarket models is the ability to have the motor mounted higher due to the 6 inch setback that the tilt/trim unit provides and they allow the motor to kickback freely compared to a factory tilt/trim. I have a small CMC made unit on my flatbottom with a 25 hp merc and I put the larger model on a friends boat with a 40hp- he had problems with his older boat with factory tilt and trim- lost the skeg a couple times

Definetly change gas before u spend money on anything else.
U said older outboard, how old? A friend of mines will only run w-f-o when he uses non-oxygenated gas, which is recomended in some older engines, but also sometimes hard to find.