surging issue

[racerone]

???----4500 RPM or more ?-----Can you get 5500 RPM on this motor ?

 

[saltchuckmatt]

not specifically because the 12 gallon tank is full right now...BUT the motor starts and idles perfect... and when I take off initially with the boat and can get up to 30 mph and run about 4500 or more rpms for almost 1 minute...THEN the surging starts.... would the water in the tank PREVENT that?

Here is something it could be. I had that exact same thing happen many years ago. My tank ended up being the issue and this is how we found out.

Same symptoms. We finally hooked it up to a portable tank and it ran fine. So I pulled the intake pipe from the main tank and notice it had a screen on the end. Knowing that I had a big spin on filter I figured I didn't really need it. I pulled it off and hooked everything back up and problem solved.

I figured older tank or I pickup up some crap from a station but it fixed my problem. Motor would run fine, then at high speed screen would clog and then motor would surge. Stop and motor would run fine again. Usually your primer ball will collapse in this condition.

Try the portable tank.

 

[dingbat]

I would put a timing light or spark tester on each cylinder at rpm to confirm you’re not dropping a cylinder.
Drops have a very distinct sound, that I’m not hearing, but it would rule out electronics as a cause.

Being repeatable, cyclic in nature, and tied to a specific time and rpm, the problem shouldn’t be too hard to find.

 

[oldboat1]

Siphon from the bottom of the tank, and let it settle out in a glass jar. Any water will be visible at the bottom. HEET or a similar product may allow you to burn out the gas in the tank.

 

[Flyhog85]

I would put a timing light or spark tester on each cylinder at rpm to confirm you’re not dropping a cylinder.
Drops have a very distinct sound, that I’m not hearing, but it would rule out electronics as a cause.

Being repeatable, cyclic in nature, and tied to a specific time and rpm, the problem shouldn’t be too hard to find.

What the the sound sound like. I’m experiencing the same issue on my 93 Evinrude 60hp. I’m pretty sure I got junk in my carbs as my plugs are dry. My compression on each cylinder is 115,115, and 115. Spark jumps the gap perfectly and timing checks out. Replaced the fuel pump and it seemed to be doing better out the gate then it just dropped. I cruise at 5500 rpm’s and 34 mph in the boat and then it just drops down to 4,000-4500 and 25 mph. No rattle or clank etc.

I keep wondering if it’s related to fuel delivery in the carbs (recently replaced all hoses, and installed an inline filter).

Also getting good flow at the tell tale. Need to replicate it per the service bulletin though.

 

[Willyclay]

...and installed an inline filter).

OEM?

 

[Flyhog85]

The pump is an OMC pump but not factory original as this was initially an oil injected fuel pump. I try to use oem whenever possible

 

[airshot]

I have saw fresh fuel have water and otger crap in it. There are certain stations I wont buy gas at because they have a reputation of poor gas. Just a reminder...never get gas when the delivery truck is dropping off, or has just dropped off a load as it stirs up any crap on the bottom of the storage tank !!!

 

[Keyboardman]

I had similar issue on a 75hp Stinger. The fuel line was the double wall type and the inside liner was collapsing and restricting fuel flow.