787 Carb Pop Off Help

[teamgreen737]

Just rebuilt carb with authentic Mikuni rebuild needle and seats And fuel pump check valves. My needle and seat will reach proper pop off however will not hold any pressure and all pressure is being lost out fuel in (blue line with fuel filter). Any suggestions?

 

[teamgreen737]

If I plug fuel line in (blue with filter) I still lose pressure (not as much) and spray down test doesn’t show any other leaks?

 

[RockwallRick]

I had the same problem with the Mag Carb on my GSX. In my case it was caused by a misplaced gasket in the fuel pump.

 

[mikidymac]

First get rid of that inline fuel filter as they are not needed and have been known to restrict fuel flow.
To test pop-off you have to plug any of the outlet fittings on the fuel pump side. On MAG carbs it is easy to loop a piece of hose on the return and outlet, on PTO carbs or single carbs just cover the return with your thumb.

Use WD-40 on the needle and seat every time you test the pop as it has to be wet to get an accurate reading.

It should pop fast, clean and reseal tight after popping and about 5-10 psi lower than it popped.

I just had a fuel pump cover leak this weekend on a rebuild as it would loose pressure. First fill the seat area with WD-40 and see if you have any air bubbles around the seat o-ring. Next spray the outside with soap and water. On mine it was the shaped o-ring on the fuel pump block, I inspected the cover, groove and o-ring and they looked fine and shifted the cover over a mm or 2 and it sealed perfectly fine after that.

Finally that blue fuel line looks nice but after a year or two it will get really hard and start to leak air so keep an eye on it.

 

[teamgreen737]

Thank you for the wealth of info MikeyD.

I have rebuilt these numerous times and use wd for popoff with a very nice homemade gauge i made. I have replaced everything at this point- check valves grommets all gaskets needle and seat.

My needle and seat are not leaking, if I thumb the fuel in while i do pop off test (line with the inline filter) I can get pop off test to work correctly. If I do not plug fuel in all the pressure from the Pop off test setup as shown is lost out the fuel in before pop off can be reached.

Hold on is my setup incorrect?!? Should i be putting air pressure into Fuel in (blue line with fuel filter?)?

 

[Pwnage1337]

You should plug the return line and provide air into the inlet line

 

[mikidymac]

So many hoses in that picture....
Nothing needs to be connected to the pulse line.
The fuel inlet is were you connect the pressure gauge, pop-off tool.
The return and/or outlet fittings need to be plugged.