Port Check?

I would replace it with a shim type. If yours leaks you could run rich at idle. The normal is 20 lbs or look at your fuel pressure at idle and make sure it is above that.

 

I have done several customers with roots fuel systems from Randy Anderson with port checks set to 8 lbs (8 intake nozzles). It could very well be the spring has went a little weak. I agree 5 is low but I wouldn't just bump it to 20 lbs unless you had documentation it was originally set up that way.

Also unless you are measuring fuel pressure behind the barrel valve, pressure at the pump at idle will be different than what the port check see's.

 

All you care about is not having it open at idle so 20 lbs works just fine. As soon as the motor rpm comes up at launch it is going to immediately go above 20 lbs and open the poppet.

 

All I'm saying is if you start from scratch with 20, have everything around it, whatever, that's your tune up. I just don't like the idea of jumping from 5-8 to 20. I have a 481x deal with a roots I am tuning and I have to keep the port check pretty low to keep the rear cylinders cool.

Obviously a 20 lb check will flow less than a 5-8 lb check.

There are many different theories and set ups to a fuel system. I just caution anyone from making that big of a jump. It may be fine to make that jump. Then again, like my 481x car, it may have hot cylinders in the back that depend on that low check to keep the egt's down at idle. If the nozzling is based on the egt being 'x' at idle, if you raise that a couple hundred degrees, could be trouble down track.

 

Will, if you read the original post he never said what it was meant to be set at. He said it started to leak at 5 lbs. surely if it was set at 5 lbs it would be open at idle and the motor would be real rich