Outboard Mechanics 101 - Fuel Starvation

[Captain Bill]

TexSail has probably got it. A small air leak downstream of the carb will cause this problem. It seems you have the carb pretty well covered though it is possible you will need to have the carb put in an ultrasonic cleaner to be sure. I once had a similar problem and nothing I could do with compressed air and solvent could get those really small idle ports clean. I finally took it to the local shop and he put it in an ultrasonic cleaner for a couple of hours and that took care of it. Fortunately the local shop is very good and only charged me $75 including reassembly and testing.

[perchance]

There is very little vacuum at wide open throttle. Vacuum is greatest when the throttle plate is closed.

[Therapy]

Originally Posted by starfish62

How would I check for bad reed valves? Can they be cleaned like the ports? Or must they be replaced?

I don't remember. Dimensions and clearance measurements I think.

[Therapy]

Originally Posted by TexSail

Check the gaskets and fasteners on the carburetor and any intake manifolds. I had an old Johnson with exactly the same symptoms of which you speak. There was a bad seal from carburetor to block. At full throttle, the high vacuum would suck the carburetor closer to the block and seal the leak and the motor would run great, but let off the gas and the leak opened up allowing air in leaning out the mixture and necessitating choking the engine to run. Any loose fitting on an intake manifold could cause the same problem.

Dang, I forgot that one.

Gettin' old...........

[TexSail]

Check any vacuum lines too. An old line will sometimes develop an air leak which will close at higher RPMS. IMHO, it is instructive that the motor seems to be running lean at low RPMS but OK at full throttle.

[starfish62]

Update and THANKS ALL!!! Sat down yesterday and completely dismantled the carb and fuel pump and soaked everything in brake cleaner--NAPA happened to have it on sale for next to nothing so I saved a few bucks--blew compressed air through EVERY port, replaced the float bowl and intake gaskets and then put it all back together. Engine now starts effortlessly without choke and idles smoothly. The whistling sound also seems to have disappeared. My only issue is that, once started, the dinghy seemed to go directly to the Tiki bar on Saturday nite; though it did, several hours later, unerringly return to the big boat which is a puzzle as I have no recollection of driving back! Again, thanks to everybody for helping brainstorm the problem. Now if anyone has any ideas as to how to prevent the dinghy from going to the Tiki bar I would be all ears.

[Therapy]

Originally Posted by starfish62

Now if anyone has any ideas as to how to prevent the dinghy from going to the Tiki bar I would be all ears.

That one I have never been able to figure out.

[Stillraining]

Hide wallet on return...Dingy wont remember where

[onestepcsy37]

i had an experience similar to 'phillsboat'.

motor would run very roughly if at all, and i couldn't find the problem. sadly, even the local yamaha dealer couldn't fix it for a more than a few minutes. kept telling me stories about ethanol in gasoline and how the problem could take many visits to fix (cost me two visits and two hundred bucks).

then, on a hunch, i rebuilt the fuel pump - about twenty bucks for gaskets/membranes.

end of problem.

[mangomuffins]

Thanks Starfish!!!

Just lo0gged on to see if I could find my "particular" problem and there you have it... hope the solutions work too

Hope you guys are well... maybe you should get over here and see OUR beaches before BP arrives they are stiil clean!!!


cheers all

mm

[starfish62]

Hi MM, good to hear from you. Let's hope the oil is taken by the ocean currents to the place where it is least destructive.

If you rebuild the carb, put a little something tacky--like some permatex--on the idle jet plug as it has a little pressure on it and needs to stay in place.

Originally Posted by mangomuffins

Thanks Starfish!!!

Just lo0gged on to see if I could find my "particular" problem and there you have it... hope the solutions work too

Hope you guys are well... maybe you should get over here and see OUR beaches before BP arrives they are stiil clean!!!


cheers all

mm

[Sunspot Baby]

Did you replace the hose from the fuel tank to the engine? Mine wants a new one every year or two.

George