Pop off pressure

[matempl]

I am rebuilding my carb using the carb rebuild thread. I am at the point of checking pop off and I can’t get pressure. I must have a leak somewhere. It’s a single carb 717. I am holding my finger over the return line but just can’t get the carb to pressurize. I can get pressure from the pump when blocking the outlet hose. Any thoughts?

 

[mikidymac]

Your post is a little confusing.

On the single carb models you have 3 ports on the carb.
1. The aluminum pulse fitting that is on the pump cover, you don't do anything with it.
2. The bottom brass fitting that is the fuel inlet, this should have your gauge and pump on it.
3. The top brass fitting, this is the return that you put your finger over to plug.

 

[matempl]

Yes that is what I am doing. The pulse line I am not touching, the line with the arrow in has my pump on it the arrow out has my finger on it.

 

[mikidymac]

Then you have a leak. Typically the fuel pump cover or the o-ring on the needle seat. Soapy water will help find it.

 

[NickCawks]

Your post is a little confusing.

On the single carb models you have 3 ports on the carb.
1. The aluminum pulse fitting that is on the pump cover, you don't do anything with it.
2. The bottom brass fitting that is the fuel inlet, this should have your gauge and pump on it.
3. The top brass fitting, this is the return that you put your finger over to plug.

Maybe try to run some hose from 1 to 2. Could be that your finger is oily and though it seems like your getting a seal with it a slight amount of air may be passing through still.

Just a shot in the dark! Miki always knows best!

 

[matempl]

So my leak was caused by the new stainless Allen screws that came with the osd kit. They didn’t have washers and the washers from the original screws don’t come off so the new screws bottom out without sealing the metering block. Put the old screws back in and works great. 34 psi pop off. Carb is holding 10 psi for over 5 minutes.

 

[mikidymac]

Awesome. I haven’t used the Allan screws, I’m cheap and save the $3.

 

[NickCawks]

Sweet, glad to hear you got the problem taken care of!