Fuel flow issue

[ssiredfish]

Thanks in advance for any insight you might provide, here goes:

2007 Yamaha F150TXR 4-stroke

Problem: Engine is starving for fuel at high speed around 4100rpms. Does not over-rev and does not sputter. Matter of fact it acts as if something is sitting behind the throttle and you can only push the throttle so far. But after it hits 4100 you can throw it all the way down and she doesn't answer.

Fuel flow: Engine----->Fuel econ computer(FEC)----->Canister Fuel filter------>Fuel pickup tube------>Gas tank

Diagnostic: Replaced fuel filter(canister). No change. Cleaned the H2O/Fuel seperator. No change. Took a gas can down the other day and ran it into the H2O/Fuel seperator directly, ran like a champ(actually the best performance to date). Reconnected fittings at engine and plugged into fuel flow before the FEC from the gas can. Ran like it typically does, 5100rpms. Reconnected that back up and plugged into fuel flow before the canister filter from the gas can. Typical performance, 5100rpms.

At this point it is lookin like a bad main fuel hose from the tank, dirty pickup tube, or bad bulb because everything off the can is optimal......

I reconnected my main fuel line back up to the canister filter and the bulb wouldn't pump. Oh god tell me thats all it is. So I changed the bulb and re-pumped till tight and got runnin with the system set up the way it has always been. After 3mins she starts dropping rpms. Now I can pump the bulb while runnin and she will pick back up to optimum speed but as soon as you stop pumping, she starts dumping speed.

Ok, so lets go back to the gas can again and plug in before the filter then we will go to the tank after that. Never made it. As soon as I start pullin gas from the can before the filter, she bogs down again and won't recover.

I am thoroughly confused......Ran fine off the gas can, crappy off the tank and then crappy off the gas can for the first time Im gettin ticked

I am goin to replace fuel hoses today and inspect/clean the pickup tube. Any other ideas? Do you think I have completly ruled out a problem at the engine? I guess I should have ran direct from the can into the H20/Fuel sep. when she bogged down the last time to see if it improved but I was gettin pretty mad and had to get home for daddy duty

[99yam40]

Hook up a fuel pressure/vacuum gauge in different spots to see what you get.
It is better to test things, that way you know what is going on

[ssiredfish]

Since this appears to be a high-speed issue would it make sense or is it possible to run those gauges in during WOT???

[99yam40]

yes need to test at problem RPM

[rodbolt17]

you need to test fuel inlet vacum at the lift pumps and the VST fuel pressure at the problem RPM.
typically its going to be a resriction or a VST filter issue.
you can also monitor lift pump and VST output pressures.
both MUST be do simultaneously AND at the problem RM and load.

[ssiredfish]

you need to test fuel inlet vacum at the lift pumps and the VST fuel pressure at the problem RPM.
typically its going to be a resriction or a VST filter issue.
you can also monitor lift pump and VST output pressures.
both MUST be do simultaneously AND at the problem RM and load.

Ok. We have discussed getting to that VST filter. I was just a little hesitant to pull the Mani. I wanted to rule out other potential problems first.

Funny thing is I have ran it the last two days. 15mi and close to 10gals ran through it without the first problem. Not making it easy to diagnose the problem.......

[99yam40]

Still would not hurt to pick up the testing equipment and run some tests to make sure all is in spec,
you will have some info and experience at the testing with your new equipment when it rears it head again

Only need to get into the VST if pressures indicate it is needed

[ssiredfish]

Still would not hurt to pick up the testing equipment and run some tests to make sure all is in spec,
you will have some info and experience at the testing with your new equipment when it rears it head again

Only need to get into the VST if pressures indicate it is needed

No doubt it would!!!

Thanks again for all of your help. Hopefully I will be a stranger to these boards

[rodbolt17]

nobody loves me, until the outboard is dead.
pull the manifold,pull the vst.
straight fwd and not difficult.
if you dont bend the manifold gasket its typically reusable, the later style with orings, the orings are typically reusable.
the vst gasket,if not damaged is typically reusable.
1.5 hour job, unless bush ice is involved ):.

[ssiredfish]

UPDATE: Problem Solved!!!

Cleaned the fuel injectors and got the best performance to date for it. At WOT I was getting 5400rpms/45mph and 2.7mpg. At cruise, 4500rpm I was getting 35mph and 3.8mpg......Pretty dang impressive.

I just wanted to thank you guys for your help - Henry

[rodbolt17]

5400 is to low, reprop it so it can turn 5800-6000.
but once they get fuel in the cylinders they are sweet.

[99yam40]

UPDATE: Problem Solved!!!

Cleaned the fuel injectors and got the best performance to date for it. At WOT I was getting 5400rpms/45mph and 2.7mpg. At cruise, 4500rpm I was getting 35mph and 3.8mpg......Pretty dang impressive.

I just wanted to thank you guys for your help - Henry

Did you ever get some fuel pressure readings to make sure they are in spec?

[ssiredfish]

5400 is to low, reprop it so it can turn 5800-6000.
but once they get fuel in the cylinders they are sweet.

I know that's the craziest thing about gas engines right!!?!?!?!?!

I was told spec for that engine is 5000-5500. 6000 sounds awfully high but Im not an expert my any means. I called Yamaha with my performance report and they told me that was pretty much right on. I think currently Im using a 14.5 x 17 with a full load weight of approx 3100lbs

[ssiredfish]

Did you ever get some fuel pressure readings to make sure they are in spec?

My mech tested it and said they were functioning correctly.

I got two little "green worms" out when I cleaned the injectors. About 1.5mm long and squiggly. I have no idea what they were but they seemed to be the culprit

[99yam40]

Performance Bulletins | Yamaha Outboards

check out a rig like yours on this site to see what prop they used and the performance it gave.
I believe the 4 strokes usually run 6k , 2 strokes are 5500

Rodbolt is an expert and he even runs a F150 himself, so pay attention to him