1987 Force 125 pulsating when run at WOT

[jlaird72]

Ironically, this engine is absolutely spotless. Tested beautifully, as well. In an attempt to be thorough, had it tuned up, new plugs and carbs rebuilt, gas tank emptied/cleaned, and a fuel/water seperator installed. Then we get it on the water feeling very confident, and after running it at WOT for 20min it starts pulsating (for lack of better words). I back the throttle way off, and it idles (and starts) perfectly. Apparently, this is a common problem with these engines, but I haven't been able to find a consistent fix. Can anyone advise??

 

[jerryjerry05]

Welcome,
This isn't a common problem.
I've only heard about this twice???
Look at the flywheel and see if it has any wobble as it turns or if it turns smooth and straight.
Do a linc and sinc. Top questions in the forum.http://forums.iboats.com/showthread.php?t=431021
Rebuild the fuel pump, valves and diaphragm.
Pay particular attention to the float levels when you clean the carb.
Carbs off compare jets. Make sure they are the same size.
Carbs off. Check the reeds for broken/ missing reeds.
What's the compression readings?
On the side of the motor is 2 dog bone looking parts. Take em apart and clean the carbon from the reeds/ filters.
The filters/ screens will probably get ruined when removing. They aren't available any more, don't worry just don't replace unless you can find a piece of micro screen and make your own.
Check the tank vent line. Some times they get clogged and can cause fuel starvation.

This should keep you busy for a couple of hours.


Good luck.

 

[fisheymikey]

if possible do a short video post on youtube thats always good

 

[Jiggz]

I'm not sure where you got the word it is normal for these engines to pulsate at WOT. I've got a '89-125HP and never experienced such a thing.You need to isolate the source of the problem by identifying to see if it is fuel related, timing or other mechanical problem.

I'll start by checking the fuel-water separator to make sure it is plumbed accordingly by checking the flow arrows. If it is then install a clear fuel filter between the pump outlet and the carb's inlet. While running at WOT (with the upper cowl off) check the status of the clear filter to make sure it at least stays 1/2 full. If not then you have a fuel delivery problem, leaky fuel hose, restricted tank vent, faulty check valves on primer bulb, or even a restrictive separator. If it does, then you might have a carburetion problem or timing problem. If the pulsation stops with the cowl off, then you could have exhaust leak. If you suspect carburetion problem, check the float level setting to make sure they are correct.

 

[Nordin]

Check the fuelhoses, you must have 3/8 in or larger. At WOT the fuelpump is not able to deliver enought fuel with smaller hoses.

 

[jerryjerry05]

The Chrysler/ Forces came from the factory with 1/4in hose.
My twin 85's have 1/4in hose from the tank to the carbs.
The 1/4in. hose flows way more than enough fuel to run his motor.
When I changed to a single 225 the hose feeding it was 1/4in. and I had no problems.

If the old hoses are exposed to Ethanol they could be breaking down or melting.
They can delaminate and collapse inside, shutting off the fuel at high speed????

If the separator is plumed wrong it will still flow the same amount of fuel it just collects the dirt/crud on the wrong side of the element in the filter.

 

[Nordin]

jerryjerry I believe you, but I have had problems with lager Chryslers and other brands too (from 35Hp and up) with 1/4in hoses.
Have change to 3/8 and the problem disappeared.
Just my own experience.

 

[Jiggz]

"If the separator is plumed wrong it will still flow the same amount of fuel it just collects the dirt/crud on the wrong side of the element in the filter."

It wasn't too long ago when a member was complaining about losing speed at WOT and all it took was an inspection of the fuel/water separator being plumbed backwards. And yes, it is correct it will still allow fuel flow but as reality will tell you, it's not the same amount of fuel flow as when plumbed properly, hence the arrows.