vacuum help

[80turbomonte]

have a serious vacuum leak going on 2 weeks now
it is a crb set-up with only three things needing vacuum
1.pvc
2.dist
3.brakes
this is a new motor 5 miles on it everything rebuilt including carb
i have 3 turbo carbs this is the third i have tried(kitted also)
tonight i resealed the turbo on carb side(gasket and o-ring)
didnt help with idle screw all the way out idles on 1150. i cant figure this thing out also on the road (might be related) runs great untill boost comes in then notta falls on its face boost go up rather quick to around 15 psi but does not pull hard at all. dont get any knock at all. starts falling off around 3000 rpms or so might be lean because of vacuum leak??that i cant find

 

[80turbomonte]

oh yea felpro intake gasket, runs 17" of vacuum at idle

 

[80turbomonte]

do ya think i have threee bad carbs?

 

[b4black]

Do you have the power valve plumbed to the intake? Is the PECV in place?

 

[80turbomonte]

power valve plummed? this is a stock turbo carb educate me please

 

[b4black]

The power valve is inside the carb. When under vacuum, it is sucked closed. Under no vacuum (WOT), it opens and richens the fuel mixture.

Normally it's sourced internally to intake vacuum though the throttle body, but on a turbo car, this pre-turbo vacuum isn't what you want. It can be under vacuum, while post turbo is under boost. This would cause a lean condition, when rich is needed.

So the power valve gets routed externally and connected to the intake manifold after the turbo. A check valve, or PECV is needed to keep boost pressure off the power valve.

This has been discussed before and there's probaly a lot if you search on "power valve". Also my website has some vacuum diagrams which may help. On my links page, look for the before black webring and find Pete's website -lots of good info there about the PECV.