25XD fuel starvation at full throttle

[killforfood]

I have an 84/85 25XD Merc that runs out of fuel at full throttle. If I?m quick (before it dies) I can chop it down to ? or ? throttle. The fuel bowl will slowly refill and I can floor board it again till it runs low.

I suspected leaky fuel lines and have tried new lines, new bulbs, new fittings and a few different tanks but no change. I also inspected the fuel screen and fuel pump flapper gasket and they both appeared to be in good condition.

I?ve developed a starting procedure that is required to start or re-start the engine. I made a catch can with a motor fuel fitting to connect and purge the fuel line into. Once I?m getting a solid stream of fuel, I connect it to the engine and pump the fuel bowl full, then start.
If I don?t purge first, starting and keeping it running (even after vigorous bulb squeezing) is very difficult.

If it dies at full throttle, I have to purge the fuel line again before it will restart.
If I anchor for an hour, I have to purge before it will start or stay running.
Once it gets a good prime, it will run all day at less than full throttle.

I know this is typically very much a leaky fuel line issue but I?ve tried everything that I know to address the problem with no results. Now my Son is beating me up to go Crabbing and Salmon fishing at the mouth of the Columbia. I?ve been out here enough times to know the MIGHTY COLUMBIA is no place to be with engine problems.

What am I missing here? Any ideas?

Not enough engine signal pulse?
Leak on engine side?

Thanks, Joel.

 

[will941s]

Re: 25XD fuel starvation at full throttle

If you replaced the following: New lines (outside, and engine), primer, tank, and tank to motor connections...and inspected all the fittings and connections for the slightest leak; try this. Remove the carb, take it apart and rebuild it. The kit is pretty cheap and it could have clogged passages. Also it's a great chance to change all the gaskets in the carb that could possibly be leaking, as well as inspect the carb for cracks. While you have the carb off, take a peak into the intake manifold with a flashlight and inspect the reeds. Make sure they are closed all the way, not cracked or chipped, and the seal in the middle of the reed block is intact. Let us know what happens.

 

[killforfood]

Re: 25XD fuel starvation at full throttle

Thanks for the advice will941s.

Well, I guess I better order a carb parts kit. While I'm at it I should probably do the impellar and change the lower unit oil also.

Could bad reeds reduce the signal pulse to the fuel pump?
I play with sprint karts and we pulse the fuel pumps off of the intake manifold. The motors I race are all 4 stroke so this 2 stroke reed valve stuff is kind of new to me.

Thanks, Joel.

 

[killforfood]

Re: 25XD fuel starvation at full throttle

I finally had a chance to get the boat out after rebuilding the carb.
It starts easy and runs smooth, with good power except I still have fuel delivery issues. Getting on plane sucks the filter bowl down pretty quickly but if I back it down to cruise speed quick enough the pump will catch up in time to keep the engine from dying. The other option is to give the bulb a few squeezes while at full throttle. This has been an ongoing problem for years with this engine. I?ve tried new tanks, hoses, carb rebuilds and even took it to a shop a couple times. No cure?
Any ideas???


PS Reeds and center seal looked good.