Ultra XP850 Almost there!
it's starting to make sense to me. Except the Power valve stuff. At idle 1150RPM i'm only making 11 inches of vacuum. I have no idea where it is at cruise. Maybe I'll pick up a long piece of hose and bring the gauge in the car to check that.
Also, I'm usually over 2500 at cruise. 4.30 gears. I know 60 MPH is around 3100 RPM.
Anxious to try the smaller MAB's. Have to order those. Have 31's all the way up to 40.
.026 would be far better than .031 especially if your cruise rpm is that high.
For the power valve, the tuning lie (it now can no longer be considered an error because it’s been proven an error for so long that if guys are still teaching it wrong they are just lying but I digress) of using half idle vacuum is wrong.
It always was wrong and in a few very limited situations it’s always wrong.
The power valve can be wide open at idle and it will not flow any fuel. ZERO.
That’s because it feeds through the booster when it adds fuel under load. If the booster isn’t started, the power valve can be wide open and it won’t affect anything.
There are a couple of exceptions to that that come to mind.
One is the blown power valve. This was an issue from the days of when Colt industries bought Holley. They made some power valves on worn out tooling or something that caused them to fail like that.
It is rare now.
The other is the power valve hitting the back of the cavity it sits in.
This holds the metering block away from the main body and causes a leak. The power valve gets blamed but it’s really a casting issue.
Every carb should be checked for this. Simply take the gasket off the metering block and with the power valve installed normally set the metering block on the main body.
It should sit flush. You will know if the power valve is hitting with that test. If it is, simply grind some clearance in the bolt boss or whatever it’s hitting until it doesn’t hit.