Logo
FULL SITE MENU

1979 15hp johnson , runs out of fuel at high speed

Walmart has a new tank for $65.00 with free shipping...they also sell these tanks and fuel lines, connectors etc within the store.
 
antlers said:
This motor ran fine up until last season, When it would not run at high speed. It runs fine now if you feed it fuel. The fuel pump is only pumping enough fuel for trolling speed. Proven by fuel pressure gauge. Looking at the old fuel pump removed, Does not look like there was any thing wrong with it. If its not lack of pulse from the port. I do not know what to try next.
Click to expand...

I wouldn't trust a visual inspection of the fuel pump... I'd spend $38 in a new one to get that out of the way: http://www.ebay.com/itm/Fuel-Pump-R...ash=item3ad33bcfcb:g:DUoAAOSwmgJY6vot&vxp=mtr

Strangest things have happened with parts that look perfect but don't perform for some mysterious reason.
 
As per my 76' manual..Max lift 30"...1lbs@600 [email protected]@4500rpm. No flow rate given.

It seems that model has more complaints on fuel delivery than others is my observation. If things are not close to perfect hi speed starvation occurs.

I'll say again..the needle seat port size is too small..its on the edge.

That max suction lift of 30" is with no restrictions like primer bulb springs and back flow checks and so forth.

Just having an old stiff pulse diaphragm that looks fine will make the pump insufficient. Not regarding to dead head pressure but flow rate. If you are getting a true 3psi at the carb while running under load there is a restriction between the carb inlet nipple and the needle. Again..that needle seat port is too small for other than ideal conditions.
 
Last edited:
I agree its worth trying another new fuel pump at this point. Never had any problems with the carb before and while motor was running strong. I have contacted a Evinrude, Johnson shop of the problem. If the next fuel pump does not fix the thing .Its going to the shop. And important to let everyone what the problem really was. This may take some time, as this shop is out of our state, but I know the mechanic. Thanks for all the threads and help.
 
johnnygjr said:
Good luck and keep us posted
Click to expand...

Before I close just want to say that if you suspect a poor fuel delivery/starvation, whether it is tank, line, or pump, you raise up the fuel tank.....perhaps put it up on the seat or cooler.....then you can notice an improvement. Otherwise it is carb related. In your case I would suspect a slight closure in the high speed jet. You may have to physically clean the jet with the correct size drill bit or tip cleaner. Ethanol is a real culprit to create a semi transparent deposit within the jet itself. Many pros even will pass this by as okay if they can see and/or blow through the jets and passages. The above mentioned problem will most often occur after the off season, when the owner/operator first fires it up. You can try a "witches brew" of SeaFoam and Amsoil PI @ double concentration. This is an incredibly productive brew and will dissolve the scum that makes your motor starve for fuel. This deposit that is caused by deteriorating gasoline, especially ethanol will restrict needle/jet openings ever so slightly. On certain carbs that are engineered on the verge of starvation. This is how I support my family and why my outboard repair business is successful. Many motors don't need to be dismantled but just cleaned. Let's support ethanol for use in most modern applications but not in anything seasonal or containing fuel delivery components of rubber composition. When you get non oxy at a gas station where the pump has only one hose, be sure to pump that first gallon in your car or truck. Of course if the pumps have dedicated hoses, you don't have to worry.
 
Last edited:
Just to let everyone know. I took the motor to the shop. The problem was faulty seals,thus low pulse to the fuel pump.IT FOOLED me until I did fuel pressure test...So don't rule this out even if it might be rare. Thanks.
 
antlers said:
Just to let everyone know. I took the motor to the shop. The problem was faulty seals,thus low pulse to the fuel pump.IT FOOLED me until I did fuel pressure test...So don't rule this out even if it might be rare. Thanks.
Click to expand...
Thanks for the update.... do you happen to know which seals were replaced? Are we talking about the crankcase here?... if so, you must have had a serious bill on labor cost I imagine?... (Just curious here)
 
Yes we are talking crank case. I know the mechanic, so I sold the motor for $100.00 for whatever they want to do with it. parts no doubt from what he said.
 
antlers said:
OK, here is what happens when I turn on full throttle. Just about the time it tries to plane the boat it runs out of fuel, pumping the bulb will help but never will reach full speed. If I do not pump the bulb it just goes flat, and motor stops. Then I can prime the bulb and the motor will start right up and run fine at slow speed. Have checked the carb. again, it is spotless inside, high speed jet is clean, float level is correct. The fuel pump is new. The bulb with line and connectors are all new. Only thing I can come up with now is the pick up tube in the tank. See no way in to it. Maybe try to blow it out with air. Untill I can find another tank to try??? any other ideas welcome. Wanted to add. This will not happen with motor on test stand. It will run full speed. It has to be in the water pushing the boat under load.
Click to expand...
Sounds like your fuel pump diaphragm is weak or bad
 
Fixed doesn't mean it still can't go bad these gaskets have tendency to get weak in a matter of years 3-5 of deteriorating. And also to your primer bulb the one-way valves on them can go bad.
 
If the engine idle is fine goes into gear but at high speed or going into full throttle it dies it's in your fuel pump. There's one other thing to check to your oh I forget what they call it it's like a timing position if it's not in the right position it'll die too That's about the only three things that can be fuel pump diaphragm primer bulb one-way valve and that timing position
 
Back
Top