Thanks for the post!

One or more of the components may not be installed correctly, this is my first thought. Not to say that you don't know what you're doing, but I would first confirm that the piston ring doesn't have a nick or fold around the perimeter of the ring and that it has a tight seal inside the cylinder. Also make sure that, when you turn the crank by hand, that the piston is not coming up past the top of the cylinder at TDC (Top Dead Center), as it should be flush.

Do you have the Type 1 or Type 2 model? The type 1 is older and used the single valve plate with the "3-fingered" valve. This has been replaced by the AB-9429999 double valve plate assy...is this what you installed? If so, make sure the smaller slots on the valve plate are on the Intake (air filter) side of the head. Below is a parts diagram for your reference:

www.mastertoolrepair.com/portable-oil-fr...h1506f-p-747266.html

If all components are installed correct as far as you can tell, the in-tank Check Valve may be stuck closed or partially closed...this has been known to happen with this model. If this is the case, you can unscrew (I believe) the valve cover and clean up the ball and spring valve. It's a good idea to coat the valve with a light coating of Vaseline.

I hope this helps!

- MTR

I believe you're referring to the "quick-connect" fittings on either end of the plastic tube going from the tank to the manifold, correct? On the breakdown below this fitting is reference #513.

The link below is to the "Type 1" version of your H1506FWH model, which is yours I believe; I originally sent you the link to the wrong version of this model:

www.mastertoolrepair.com/portable-oil-fr...7265.html?cpID=20557

The tubes you're referring to are reference numbers 127a and 127b.

I believe the nylon tubes are metric in size, not your typical 1/8" or 1/4" sizes. I'll confirm this with a rep, however.

- MTR

By the way, the size of the two plastic tubes are below:

Part# 9270006: 4mm inside dimensions, 6mm outside dimensions

Part# 9270026: 6mm inside dimensions, 8mm outside dimensions

- MTR