The green is for typical bone stock automotive engine in a car/truck.

Performance motors will have less idle vacuum. How much less depends on camshaft vs cids vs initial timing vs idle rpm….etc

I’ve had non marine performance engines idle with 3-4” at 1000rpm. Braap ! :)

You’re 15” is more typical of a mild marine performance engine. Again, forget the color, just look at the #.

A 65 powervalve is one rated at 6.5”hg
A 45 pv is one rated at 4.5”hg

I ran a similar spec'd 800cfm on my 425hp/454. It was a little rich, but worked fine after I started using Rapid Fire spark plugs. They wouldn't foul out like stock MR43's

6.5 Pri power valves are pretty standard.

When your intake vacuum drops to 6.5" hg, it opens, and flows extra fuel. It's tunable on the metering block for the jetting and air bleeds.

As an example, different props will load the engine differently. Lower pitch will be easier on the engine at the same rpm, and have higher intake vacuum. The engine is not working as hard, and less throttle is used etc.

The DV book is well laid out and easy to read. He wanted to put more info in there than the publisher wanted. I think he has some good YT vids on carbs too.

Any effort you put into research will exponentially help you out. It will also enable the folks here to get you dialed in even better.

If you want to feel better about your situation, go check out my thread on dealing with carb tuning. Has been a journey!

I'm not impressed at all with anything Holley says on the phone - call with the same question three different times and you'll get three different answers. Putting the carbs back to stock with what SB listed and trying again is the right direction.

Keep us posted.

Hey Tom, I have read through some of your carburetor woes. I'm hoping to skip to the end where it runs perfect after one more change :D
I have a few questions for you guys while I wait for Vizzards book to show up.
1) Do I check vacuum in gear?
2) Thinking about the idle mixture screws, they are only out 1/2 turn. I saw a guy talking about this very thing and he said you DON'T want them just cracked open. IF he is correct, do air bleeds affect the idle circuit? If I installed larger air bleeds it would require more fuel at idle? I could turn the screws out to make the entire "circuit" run more efficiently??
3) I posted that my vacuum is around 15 out of gear which would indicate that I need a larger power valve than the 6.5 that comes with the carb? If the power valve is improperly sized, is it possible that it is dribbling fuel at idle which is why my adjustment screws are only out 1/2 turn? The power valves are adding fuel when they shouldn't be?? Or would it be more likely to dribble fuel if I installed a larger (7.5) power valve??
Again, I ordered the carb book and I'm looking forward to being less dangerous and more educated on this subject.
Thanks for your help.

This guys has a pretty good video on tuning the holleys...helped me out earlier this year when i was dialing in a carb for a guy here at work that has a 71 mustang

Power Valves are spring loaded in the open position.

When the engine fires and pulls vacuum, they close up. A 6.5" PV only opens when the engine is throttled up and cruising at speed. When the vacuum reaches 6 5" of course.
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​​​ Power Valves can leak and have ruptured diaphragms. But if the carbs are new, they should be gtg.

It's nice to have a vacuum guage in the instrument cluster. It can also be used as an engine health meter.

Just an update for this thread. I have been working with a guy at Holley and he sent over a different spec sheet for the M-800 which I believe is the correct info. I had asked my engine guy to richen up the carbs and when I first pulled the carbs apart there were 77's in the primaries and I think 86's in the secondary's. The other sheet shows 78's in the primary so this can't be correct based on my scenario. Anyway I put the carbs back to completely stock spec's including the main jets back to 74's and 84's.
TomZ has been helping me and he ran across a thread (car site) where a guy says that there is a hole in the baseplate that is connected to the transfer slot in the secondary's that shouldn't be there. It allows unmetered fuel to flow rendering your idle screws almost useless which was what I was experiencing. He used JB Weld and filled them in and then everything worked fine. I was thinking about replacing these carbs with actual Holley's so if this didn't work I was prepared to replace them. I took a look and my carbs did have this hole he was referencing. I filled them in and my afr readings are way better from idle which is now mid to upper 12's to wot which is in the mid to upper 11's. Idle used to be in the low 10's and even some 9's. Soot on the transom etc. Idle screws are now out 3/4 of a turn instead of only a 1/2 and it is pulling almost an inch more vacuum at idle. Thanks again to TomZ for his efforts.
Fix that Rich Running Quick Fuel - Club Cobra

i have a 4360 cubic inch radial 28 cylinder you should see the size of the carb on that!

crazy ! And thanks for telling us.
Thanks to tomz , of course too.
:thumbs