fuel system pressure / vac test

[MH Hawker]

I have a minor 200 RPM fluctuation at WOT, I have twin 6 gal portable tanks and it is common to both tanks so i am doing some testing in the off season just to eliminate things.

I am thinking that I may have a air leak in my fuel system so I thought I would run a pressure / vacuum test and was wondering what the values should run. As a pure guess 20 lb pressure and 15 vacuum.

What i want to test is the line from the tank pick up through the clip on fittings to the last one on the motor.

 

[MH Hawker]

Re: fuel system pressure / vac test

Well it passed fine, I used 20 psi for 10 minutes and 15 pounds for 10 minutes with no sign of a leak down. So off the the next thing.

 

[wired247]

Re: fuel system pressure / vac test

what motor?

 

[MH Hawker]

Re: fuel system pressure / vac test

Just a small 15 hp mariner on a pontoon

 

[oldman570]

Re: fuel system pressure / vac test

Have you checked the level of the LU in the water when running at WOT to see if it could be getting air to the prop from the water flow? The prop just might be cavitating because of it and causing the RPM variation. You might need to lower the motor some and see if that helps. JMO
Oldman570

 

[MH Hawker]

Re: fuel system pressure / vac test

I hadn't thought about that, but the motor is set all the way down, good idea though. I have been sort of thinking my way through this for awhile, and i suspect it may be a float setting but while its home and not on the slip i have been looking into things. The fuel pump is vacuum driven so that needs a inspection to. Its a brand new carb so I would think thats ok and it really isnt much of a problem I just back it off a bit and run.

 

[Gibbles]

Re: fuel system pressure / vac test

on that note; the prop could be spinning on the hub.

I have that issue on my 650, one prop will rev funny at wot, signs of damage to the rubber bushing/insert thing...

Swap props and I don't have an issue.