701 Raider Pop Off pressure

[Tman701]

Hey guys,

To start off I have downloaded and read every document I could find related to tuning carbs. Here is where I need help.

I just rebuilt my 2 Mikuni 38's.
My current settings are as follows:

Carb1:
NV 1.5
Jet Low: 67.5
Jet High: 120
spring: dull silver

Carb 2 (PTO):
NV 1.5
Jet Low 67.5
Jet High 130
spring: dull silver

My issue is that the pop off pressure on both carbs with the dull silver spring is around 22psi. I tried the shiny silver spring and the pop off pressure jumps to 42psi.
There is no leak and the pressure holds fine. I checked the NV to make sure the tip wasnt messed up.

What is puzzling me is that the shiny silver spring is supposed to be 65 g and the dull silver 95 g. Also the shiny silver spring is longer than the dull silver.
How come with a lower gram spring my pop off pressure is higher? shouldnt it be lower?
Left spring is the dull silver and right spring is the shiny silver.

This engine is totally stock except for FA's.

Thanks,

Tman

[Technical Support]

Re: 701 Raider Pop Off pressure

Something doesn't sound correct. 65 gram spring with a 1.5 needle and seat will read 32 psi, the 95 gram dull silver spring will read 43 psi

[Tman701]

Re: 701 Raider Pop Off pressure

Thanks for the reply,

Its a weird one. I compared the ones I replaced on the carb and they are the dull ones also. So I put those back in and sure enough the pop-off is the same, right around 24 to be exact.
The pressure holds so there isnt a leak around the needle and seat. I even tried swapping them around from one carb to the other and get the same readings.
The shiny silver which is supposed to be the 65 gram spring reads 42 PSI, the dull spring reads 24 psi. This is on both carbs. I tested both thru the fuel inlet with the pump cover on and then I tried it with the pump cover off holding the hose nipple on the fuel filter port on the carb.
My carbs are pretty spotless with no corrosion inside or out. The NV's arent pitted or show any sign of wear on the tips, even if they did it would not hold pressure.
I thought about the pop-off pressure gauge being bad, but I have no way of checking it. I added wd-40 to the hose leading to the carb just to make sure.

The other thing that puzzles me is the color of the springs and the difference in pressure and size. Does anyone have any extra springs laying around that they could compare?

Thanks,
Tman