15hp yamaha 4 stroke PLEASE HELP!

floridaboating

Recruit
Joined
Jun 19, 2010
Messages
2
The motor will only start with the choke pulled. The second I push the choke in it stalls. I have completely disassembled the carb atleast ten times just to triple check eveything. I have soaked it in carb cleaner, pulled and cleaned the jet, checked the float......all seems to be fine. I have purchased new fuel lines, inline filter, hoses and gas tank just to make sure it was clean.
When the motor is running(with choke out) it seems that the inline fuel filter runs dry of fuel as if maybe the fuel pump is not working correctly and sucking fuel from the tank. I pulled the fuel line right after the fuel pump and turned it over. It pumps fuel, but is it possible that it is not pumping the right amount of pressure? I wanted to go ahead and replace the pump and diaphram just to eliminate them as the cause, but they are very expensive. Does anyone else think along the same lines as I am, or does anyone have any other advice on what to try. I am getting desperate as I have alot of hours on this thing with no good results.
 

rodbolt

Supreme Mariner
Joined
Sep 1, 2003
Messages
20,066
Re: 15hp yamaha 4 stroke PLEASE HELP!

pulling the choke forces the fuel mix rich, my guess is the carb circuits are still dirty.
if it runs with the choke out fuel is in the fuel bowl.
 

floridaboating

Recruit
Joined
Jun 19, 2010
Messages
2
Re: 15hp yamaha 4 stroke PLEASE HELP!

Do you have any other suggestions on cleaning the carb. I have soaked it in "gunk" carb and parts cleaner for 15 mins. at a time and then blow everything out with a air compressor. The only other thing I can think of that was tampered with. It looks like the air mixture screw was messed with. I set it at 2 1/2 turns out. Does that seem right for a 2003 15 ESHB motor?
 

rodbolt

Supreme Mariner
Joined
Sep 1, 2003
Messages
20,066
Re: 15hp yamaha 4 stroke PLEASE HELP!

no spec for the mixture screw, it was originally capped but 2.5 to 3 turns should make it run.
sounds like something is still blocking a passage.
 

LIsound

Recruit
Joined
Jun 9, 2010
Messages
2
Re: 15hp yamaha 4 stroke PLEASE HELP!

Make sure the pcv system is not clogged. A clogged pcv can cause the fuel pump diaphram to collapse while the engine is running, when the diaphragm collapses it stops the fuel flow to the carburetor.
 
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