My 87 has had a very confused changeover and fuel return system so I decided to swap out the known working parts from my 79. So I removed the changeover valve and installed the one from the 79 and set aside the valve from the 87. Then I noticed something very unusual. That valve is less than two years old and the previous owner sourced it from SNG Barratt. As you know the fuel hoses from the tanks up to the fuel pump are 1/2" (or 12mm). Looking in the fitting I noticed the hole through which the fuel flows is very small. It measures 3/16". So the area of that hole, and therefore the amount of fuel that can flow through it is only 15% of the 1/2" hose. Does it seem to you that is a very small hole? My lawn mower has a larger fuel hose.


Below is a photo. The fittings are machined aluminum. Both inlets have a 3/16" hole and the fitting that goes to the pump has a 5/15" hole. I wish I had noticed what the 79 valve had before I installed it; I don't really want to take it apart again just to look. Your thoughts?


Jeff

1/2" fitting with 3/16" hole

 

I would be a genius if I knew all the ins and outs of how these things are designed.
But I think the difference is to either reduce or augment the pressure of the fuel coming in through the hose from the pump.
Sorry I can't be of better help.

 

I've never taken a good look at an original valve so I'm not sure if the small hole is right or wrong

It isn't uncommon to have large diameter feed into a smaller diameter, so as to ensure the smaller diameter is always well fed, so to speak.

The pump outlet is only 5/16" as I recall....so a full 1/2" diameter is not needed to properly supply the engine.

Hopefully someone has an original valve to compare.

Cheers
DD