Old Yamaha giving me trouble... any ideas?

[chrismele]

I have a 1991 Parker 2510 with the orginal yamaha 250 that I want to keep running for as long as possable. I'm having an odd problem. Motor will run well and then won't.

This Saturday, ran the boat from LBI - Barnegat Light NJ to Tices shoal with the kids (about 40 min). Boat ran great all the way there. She would run wide open and top out aroud 5300rpms or so. On the way back I could not get her over 4400 rpm and she would not hold a steady rpm. It was almost like someone was squeezing the fuel line with fluxtuating pressure. Boat ran good last summer but I had this same problem on the last ride of the season.

This spring I changed the fuel line from the tank to the fuel filter as well as the line from the filter to the ball. Ball and fuel fitler assembly (Raycor) is also new.

Had a local mechanic run the boat last week and ran fine. Had another mechanic tell me to change all the plugs, hoses and filters on the motor. Third guy I spoke to told me to pull the fuel tank sending unit and remove the screen on the bottom of the pickup.

Looking for more ideas and thougths about the recomendations others gave me. I think the next time I have time I will run it on a 6 gal tank but I'm interested to hear ideas from others.

Thanks,
Chris

 

[DaleH]

I agree with the 3rd guy, plus it is a simple check, so I was going to suggest that AND checking the anti-siphon valve on the tank boss where you just put new fuel line.

AS Valves can clog up too. But I have also seen clogged pickup screens do it too. I use two box wrenches, 90-degrees apart, to unthread the square 'box' on top of the tank that the fuel barbs connect to. However, your tank may have a different fastening system for the fuel pickups.

If you want to keep her running well, please check the Yamaha recommended maximum RPMs for that motor as if it is indeed a 6,000 RPM motor then you are WAY too low in RPMs and need to change your prop. If that were my motor, I'd want to be running no less than 5800 RPMs on a clean bottom, cool air (NOT hot & muggy, as that can rob the motor of 100-200 RPMs), 1/3rd to 1/2 fuel, 2 people and all gear typically carried.

FWIW my bro's GW runs 1987 Yam 150s that we also do a 'Dunk decarb' to (do a search) every 50-hours and they're still running strong. He too is pitched to wind up only 100-200 RPMs off the max rating. Running too low is a sure way to kill a motor ...

 

[Brent]

Maybe the fuel pickup tube are nylon and cracked and need replacing
.. could be a loose clamp or fitting letting air in... Inspect the racor filter is tight

 

[chrismele]

Thanks for the replies. I think I will perform Dunk's decarb procedure and check the sending unit pickup.

Interesting comments about running her wide open (or close to wide open) being better for the motor then running at lower rpms. I've always tried to keep running her wide open to a minimum and kept her 1,000 or so below max rpm.

Thanks,
Chris

 

[DaleH]

Interesting comments about running her wide open (or close to wide open) being better for the motor then running at lower rpms. I've always tried to keep running her wide open to a minimum and kept her 1,000 or so below max rpms.

Chris:

You don't RUN her there all the time, but that is where you TEST and determine if your boat wears the right pitch prop ... which I don't think you are.

Your best all-around performance and economy will be between 3800 - 4200 RPMs, somewhere in that sweet spot.

 

[Brent]

How old is fuel.primer bulb?

 

[chrismele]

Bulb is new, all new fuel lines from the bulb back to the tank and new racor filter assumbly. Everything has double hose clamps...

 

[Brent]

Hopefully it is the ASV. Or tubes, screens

 

[BradH]

Yamaha or other engine manuf. bulb? The Yammys are the best, the aftermarket ones are junk.

 

[DaleH]

Yamaha or other engine manuf. bulb? The Yammys are the best, the aftermarket ones are junk.

Yamaha and Mercury bulbs are good, but from a dissection of all bramds the OMC/Bombardier bulbs are the best made as far as quality and robustness of parts. So much so that Mercury racing teams use them and that's all my local Merc dealer will sell and install. I insisted on one on my Suzi too.