I have a standard stock style power valve 4.5. I tried 3.5, 6.5 and 5.5 it did the same. Just followed the power valve rating . Size...not sure need to check that yet. I'm pulling around 10-11 inches of vacuum at idle.

He should still have vacuum at 4k rpm. Maybe its not a carb issue. The blower might be tired.

Have you tired a "Boost Referenced" power valve? I don't mean like where it gets its signal, but a actual powevalve modified so that it opens at a certain boost level, rather than vacuum drop. With the blow thru, a standard style diaphragm powervalve can be tricky. Opening too early, therefore causing a bog. If you set it up to say open at 3psi of boost, you may find that helps.

Absolutely wish I went that way vs. The carb shop crap. If I'm going to invest anyore than $200 bucks into this I just going to pull the trigger on a Holley fuel rail EFI sefup.

I just purchased a 4 window #6 power valve. It really feels like a initial lean out condition when opens. Having to run the black accelerator pump cam seems a little extreme for a big head, 238/248 solid roller, 327 cu engine

http://www.theturboforums.com/smf/in...topic=110547.0

You can make your own

Also, are you running an AFR gauge?

The way C&S does it, is they change the PV opening rate by using little shims behind the spring. Adding a shim makes the PV open later, removing them makes it open sooner (more or less spring tension). Easier than playing with a bunch of springs.

I will say this. My buddy had some pro systems blow throughs on his boat engines. In my opinion, they sucked. Fuel curve sucked, idle sucked, low speed driveability sucked.

I convinced him to get some C&S aerosol carbs, Fixx here talked highly of them. With the new C&S carbs, the Fuel curve we dialed in with the help of roger on the phone, was perfect. In the boat, they idle like stock 500EFI's, 600RPM in gear. These are 522ci that made well over 1000hp on the pump.

With the way your hat is positioned, keep an eye on those #1 and #2 plugs. Those will probably be the lean ones

Thanks for the well detailed link. Lord knows I have enough PV's to destroy to make one good one. This theory makes perfect sense.

Yes I have AFR gauge. Currently I have idle set at 14. Cruise at low RPM's with constant petal is 12.2 to 12.5 max. Moving through the PV opening it briefly goes way lean then drops 11.5. If i'm too low in the RPM's I can see 10.5. WOT is 12.5 to 12.8. To me, the WOT is a little high and cruise is a little low. I have re-jetted recently from 74P86S to 76P88S and had almost no change on cruise but brought my WOT numbers down from a scary 13.6. (had a couple lean-out pop backs at high RPM's ) My assumption tell me that it's cruising on the idle circuit. Subsequently, I may need to look at fuel restrickers also. Especially since I can't get turns on idle mixture screws which is probably complicating enrichment circuit.

Interesting note: on a full exhaust I tried 2 locations for the O2 sensor. One at the collector and the other 3 feet further down in the H pipe. The collector readings were actually very similar. Maybe a tad richer.

Do you have 4 corner idle setup? Have you tried closing the secondary screws, and opening the primary screws a bit more? Should richen the transition a little. This may help the stumble. IMO 4 corner idle just isn't needed on a mild street engine. Big compression, big cammed large port race motor, sure. Sounds like a lean stumble. Or possibly a larger squirter.

CSU's boost ref pv is adjusted with a screw that puts more or less tension on the spring to open sooner or later when boost comes in. I don't know if Kevin (at CSU) would sell one by itself but its worth a try. I have one of his carbs on my turbo (street) car and it's fantastic. His tech support is second to none as well.

Tried squirters, overall best ones are in. Closing the secondaries more- the problem is when you do that theirs is a slight delay in fuel. Subsequently, put it back the way Carb Shop had it set. Going to install the power valve tonight. If that fails I'll either make one or contact CSU to see if they will sell one. I really believe the pressure is causing a delay or a weird disruption to the enrichment circuit. Plus, I need to get the very light load AFR's higher.

After typing all this I do remember trying closing the front idle mixture screws all the way (open rears more) and had almost no stumble at all. Ran really flat though.

MT-Next time you make a run to Racine let me know. I have the first round. Andy

Sounds like a plan Andy. The power valve mod just may do the trick. Conventional valves just aren't designed for that situation . Good luck with it .