Outboard stalls and quites

[Nicholson58]

Originally Posted by TrailerCruiser

I'll see about the idle adjustment. I'm going to get a new hose and inline fuel filter. As for the fuel pump why would it work fine when I first leave the mother-ship after startup, but not when I return after running at 3/4 speed for 20 minutes or so. Back to the hose, my hose is black rubber. I'm guessing this hose might not be compatible with ethanol, so I'm wondering if this hose might the culprit.

I had to replace all fuel hoses with NAPA gas hose rated for ethanol. That was only one of four ethanol caused failures. Runs much better now that we are in the Caribbean. Mercury 15 2-stroke mariner.

Does your motor have automatic choke, advance etc? Settings may be OK cold but strangle it when warm.

BTW, swapping out the aluminum factory prop for a Solas exact replacement in Stainless was like getting a 10% power boost. About $110 on line, not bad and the old prop is a spare.

[Cheechako]

It sounds to me like it's starving for fuel. (runs when choked/cold)
Check fuel filter, tank vent, last is gunk in a jet in the carb.

[Nicholson58]

For what it worth, I keep a one gallon NAPA carburetor cleaner with dip basket. This has fixed a lot of accumulated crud. Steel can, keep it in a plastic safety can and plastic bag.

[waterman46]

It runs well when cold, so many of the suggestions I've seen don't address the problem. Like water in the fuel, etc. If it will idle and run cold, that's a big clue. Does it take a load when cold? If so, how long before it quits?

I have never seen a small engine with an automatic choke, but maybe your has one. If it has an automatic choke, then it may be running fine on the rich mixture when cold, but when choke opens it stalls from mixture being too lean. Fuel starvation most likely cause, or a block in main jet if it will only idle but not take a load.

If it has a manual choke, after warming up will it run with the choke partially closed?

As long as you are getting a spark, sometimes the easiest fix is to just buy a new carburetor. If that works, then you have time to clean out the old carb for a spare.

[CarlF]

If this is a 4 stroke with a carburetor (vs EFI) and had ethanol gas sit in it for over a month - the odds are overwhelming that the problem is the carburetor has corrosion and varnish from the ethanol.

Buying new fuel will not fix it.

People in Florida always suggest carb cleaners because it works for them -- because their fuel doesn't have ethanol. Carb cleaners will not touch ethanol damage.

It's worth replacing the hose because that's cheap and easy. Might work.

But if not you have two choices

a) remove the carburetor and take it to an outboard shop to be disassembled and put in an ultrasonic cleaning tank overnight.

b) buy a new carburetor. In many cases this option only costs a little bit more the outboard shop and you can do it yourself. Iboats.com has new carbs for most outboards. Tohatsu Outboard Parts - iboats.com

[Q Xopa]

Im thinking the opposite of most of these sugguestions.

It sounds too 'rich' to me.

It needs to be rich when cold when fuel is not vaporising too well. So in your case its runs fine when cold.

If it runs fine when you open the throttle it needs more air, ie its too rich.

Is it carb or EFI?

If carb maybe flooding needle and seat.

Just a thought.

[rbk]

Pretty sure the 9.9 is the same line as the 15 & 20hp and would be MFI. The 9.8 is the same line as the 8 & 6 and would be carbed

[Jetx]

Originally Posted by Flatswing

Check the hose from tank. Black hoses are famous for delamination blocking fuel flow. If yours is black, 1st thing (& least expensive )I would do is switch to a gray fuel hose.

I agree delaminated / collapsing fuel hose is a possible cause, but hose color may not be a definitive clue. In my case, it was a (newish) gray hose that delaminated, collapsed internally, and caused stalling after the OB had been run hard. Replaced with a black, non-laminated hose and have had no trouble since.

[Nicholson58]

Originally Posted by Jetx

I agree delaminated / collapsing fuel hose is a possible cause, but hose color may not be a definitive clue. In my case, it was a (newish) gray hose that delaminated, collapsed internally, and caused stalling after the OB had been run hard. Replaced with a black, non-laminated hose and have had no trouble since.

Good possibility this could be the cause. Happened to me twice, two different engines. Go to NAPA one eq. and get E85 rated hose.

My gas tank dip tube fell off once. - also ethanol related.

On the Mercury Mariner there is a rubber coated bellows designed to squirt a bit of extra fuel when the choke is activated. Ethanol eats this coating in a couple months. Then the fuel leaks into the motor housing resulting in a super rich air mix. The motor will only start of you remove the housing.