2007 9.9HT fuel starvation issue - any ideas?

[RichPrice]

Fuel line primes and engine starts like a dream. Generally runs for between 20-30 mins before stalling. Sometimes goes longer and can’t pin it to a certain rev range but it is often when it’s at a constant rev (medium thrust) as opposed to when you are reducing to idle or accelerating. Primer bulb is always soft and after a quick pump the engine starts immediately.

10L fuel tank has been cleaned out and fuel line (inc bulb) replaced with Yamaha parts. Arrow is pointing upwards although we do seem to have a fair bit of excess fuel line. Am I doing anything stupid with the fuel line in terms of configuration? Where do I start in terms of diagnosis? Any help/guidance massively appreciated.

[boscoe99]

Full model of the motor would be helpful. There have been many T9.9 four stroke models offered.

It is normal for a a primer ball to be soft when the motor is running.

When was the last time the fuel pump was serviced? That is the first place I would focus on.

The use of longer fuel hose means there is more restriction to fuel flow that the fuel pump has to work against. If the primer ball can be pumped so as to keep the motor running that is somewhat indicative that the fuel pump is not doing its intended job.

[panasonic]

Primer ball seems to be awful close to fuel inlet fitting on the engine. The little bit of fuel line between the ball and inlet fitting would have to make quite a sharp turn if I am looking at your picture right...

Perhaps this tight radius in the line is causing a restriction there? Maybe when you turn the engine a certain way it could be kinking the fuel line somewhat.

Is there a reason you have the primer ball so close to the engine? Again I am only going by the picture you provided...maybe it is not as close as it looks.

[zenoahphobic]

I'm with Panasonic, could be that your attention to the " bulb being vertical " has caused a kinking of the hose near the engine fitting. 20 to 30 minutes running suggests this.

And I'm with boscoe good to pump the bulb say after 15 mins running time and see if the running time has extended by that much, but that could confirm either hose restriction or a weak pump.

I would reposition that bulb further back leaving 6 inches to a foot to the inlet fitting. This bulb needing to be vertical has been debated before. I personally believe it not critical as many outboards are connected to their separate tank in all manner of positions without problems. It is only needed to be held vertical when pumping, the fuel in the line helping seal the valve when compressing, people say.

[cleddau1]

Agree, move the primer bulb, check fitting at engine or tank is not letting in air, keep fuel line as short as possible, and, er, remember to undo the vent screw on the tank.... What is the difference in height between tank and engine? Diaphragms in fuel pump may have perished, easy to replace.....

[pstephens46]

Will my boat sink if primer is horizontal?

[walleye1]

Yamaha fuel line kinks real easy.

[boscoe99]

Will my boat sink if primer is horizontal?

Not necessarily. However, if the primer ball is upside down then the boat will turn over so as to right the primer ball. Sorta like a smart phone

[panasonic]

Yamaha fuel line kinks real easy.

Yamaha fuel lines are nice and last a long time....but as you say if they are curved into to tight a radius for whatever reason they will collapse.

[pstephens46]

Yamaha fuel line kinks real easy.

Walleye - have you been fishing? Is there a season for Walleye?