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JFairman JFairman is offline
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Join Date: Jul 2006
Location: S. Florida
Posts: 7,265
Originally Posted by T77911S View Post
enjoyed the thread. learned some things,

back to the FD.
I think you should replace that metal shim. It looks bent/dimpled in the pic
I think the problem is where the valve seals to the shim it can dimple and not seal properly

no sealant.

took mine apart too before sending it flowcontrol.
mine was clean also. I was a little disappointed. was hoping to find it bad.
talk with larry about the shim. great guy.

also balancing the flow out of the head is important along with max flow at WOT.
I think factory setting is 20% of the max flow the head is capable of.
larry can set it up for what ever you need.
Regarding the stainless steel diaphragm you're calling a "metal shim" for some reason.
I've rebuilt 4 of these crappy old cast iron things now. The original Bosch stainless steel diaphragms are polished glass smooth on both sides and they are installed dry. The replacement Salvox stainless steel diaphragms have a satin machined surface on them and Salvox says to use sealant so I always did.
I don't know why but maybe it's because the surface finish of the Salvox diaphragms is not polished glass smooth like the Bosch ones and because of that they suggest using sealant.

If you only smear a real thin coat of sealant on the two halves of the fuel head and no sealant next to the control pressure pinhole in the metal diaphram then nothing can go wrong using sealant.

This is the pinhole fuel supply orifice in the metal diaphragm that creates the control pressure circuit in the top half of the fuel head. The control pressure regulator returns fuel from the control pressure circuit faster or slower than it can be supplied through this pin hole by system fuel pressure on the bottom side and thats how control pressure is varied up and down to change the air fuel ratio.
It's just a pin hole so you have to be careful to keep sealant away from it or it could be clogged up by squeezed out sealant when bolting the fuel head back together. I'd rather use a little sealant than risk having to take all this stuff back apart if it leaks after not using sealant.

I drew a red arrow pointing at the control pressure fuel supply pin hole in a metal diaphragm. The rubber diaphragms in the aluminum lambda fuel heads don't have this pinhole and they use a different orifice for control pressure fuel supply.
Old 03-10-2017, 11:56 AM
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