Yamaha 115 2stroke fuel pump.

Hello,
I have Been tracking down a fuel problem on a 03 yamaha 115 tlrb. 2 stroke. Long story short I've narrowed it down to the fuel pump. When I pump the primer bulb and start the motor it will run until about 3000 rpm and up it will surge. Also if I accelerated to quickly it would act very sluggish. When I shut it off then start it up in a few minutes it will run for about 30 seconds and all have to pump the bulb again. My question is what should the crank case pressure/vacuum be where the fuel pump bolts on. There is 140 psi in all 4 cylinders. What do you think?? Thanks

 

They're not expensive to rebuild - the whole pump is only about 40 bucks, but they have a couple of non return valves which both have to work. They seem to generate crystals if gas is left in for any length of time (reaction with the aluminum) and these can occur after the filter, and will mess up the valve operation. Take it your setup looks like this;-

http://www.boats.net/parts/search/Yamaha/Outboard/2003/115TLRB/FUEL 1/parts.html

also check for air leaks in the suction side hoses.

but yes, your logic points to the pump - these are not like the mechanical gas pumps on cars - they rely on oscillating pressures and pump only a small amount with each cycle - if they are not 100% working there is not a lot of redundancy.

A good sanity check is to disconnect the fuel line and dribble gas into the intake - if the engine runs well - it's a fuel issue.

 

Yep that is the one. I just ordered one from Yamaha it was $43 to my door so I will update with the results thanks for your reply.

 

As a long-time Yamaha owner, I got in the habit long ago of not trusting their fuel pumps. For some reason, 5 or 6 years is all that many of them are good for. I keep several on hand and usually carry a spare on board.

 

Well I got the new fuel pump on. After all the air was bled out it took about two pumps on the bulb and we were good to go. she runs like a champ. thanks for every ones advice.