68 383 with 750 carb. Runs rich

[Mattax]

Mine Holley was rich as well, changing the power valve mad a great difference. From Holley Power Valve Tuning - Holley Blog:


"High Performance Engine Power Valve Selection:
High performance engines with modified cylinder heads, long duration camshafts and single plane intake manifolds may require a change to the power valve. To find out which power valve your high-performance engine needs, you can perform the following procedure:

1) Hook a vacuum gauge to an intake manifold vacuum port.


2) Warm up the engine and note the vacuum reading at idle. Automatic transmission vehicles need to be in the Drive position, while manual transmission vehicles can be in Neutral.

3) Divide the vacuum reading in half. The number will determine the correct power valve.


Each power valve is stamped with a number that indicates the correct vacuum opening point. For example a power valve with the number #65 stamped on it, will open at 6.5 inches of engine vacuum. As an example, a vacuum reading at idle of 13-inches, is divided by two and results in a 6.5 inches of vacuum. Therefore, you should have a #65 Holley Power Valve installed in the carburetor.


If you divide the vacuum reading and it falls on an even number, you should select he next lowest power valve number. For example a vacuum reading of 8-inches, divided by 2 and you come up with a number of 4. In this case you would use a #35 power valve.

Finally, if your engine produces 13 inches of vacuum or more, the stock power valve that the carburetor is equipped with from the factory, is sufficient.


Holley power valves come in a range of orifice sizes. The higher the number the more fuel is added."

Ugh. The last sentence of that blog advice indicates Holley is really losing it in terms of technically knowledgeable people. Its too bad.

As for the rest, Holley has suggested using 1/2 of idle vacuum in their aftermarket publications years, although occassionally instead they suggest a PV rating half of highway driving vacuum.
Its one of the few bits of guidance from them that has no connection to engineering or science. Given no other option, maybe its better than nothing.

Why do say this? Because the power valve's job is to richen the main circuits when the load on the engine gets high. In other words as the engine approaches wide open throttle either to accelerate or go up steep hill the mixture needs to go richer. There is no direct correlation between this situation and an engine's vacuum at idle.
Working from high cruising vacuum at least is reasonable because at cruise it definately doesn't need enrichment. We also know that at light part throttle it shouldn't need enrichment - in fact it will want leaner mix. So taking half of cruising vacuum would at least be a logical possibility. The truth is some engines will make good power on a lean mixture up to 80 or 90% throttle (ie low vacuum) and others will need enrichment at only 60 % throttle (relatively high vacuum). And the only way to find that out is testing.

There is one other consideration in PV opening. It must stay open through the top of a WOT run. If an engine is somewhat restricted, or for any reason is less efficient in the run the manifold vacuum will go up. In this situation a really low PV opening (as suggested in the example) will be a disaster.

Getting back to the OP's 3310.
If it hasn't been molested, the PV should have no effect on idle. However there are situations where it does. If you're sure that's whats happening, it can be dealt with if its a problem.

 

[DJC]

Ugh. The last sentence of that blog advice indicates Holley is really losing it in terms of technically knowledgeable people. Its too bad.

As for the rest, Holley has suggested using 1/2 of idle vacuum in their aftermarket publications years, although occassionally instead they suggest a PV rating half of highway driving vacuum.
Its one of the few bits of guidance from them that has no connection to engineering or science. Given no other option, maybe its better than nothing. ....

Well, thats really good info, thanks for that. Sometimes its hard to know what to listen to when you don't have the experience. We assume manufacturers would know the product best, but obviously thats misguided sometimes. And the anectdotal info from some "helpful" people can be no better. Info like yours is clear and makes sense. My apologies to possibly steering the OP astray.

Dave

 

[yellow rose]

Mine Holley was rich as well, changing the power valve mad a great difference. From Holley Power Valve Tuning - Holley Blog:


"High Performance Engine Power Valve Selection:
High performance engines with modified cylinder heads, long duration camshafts and single plane intake manifolds may require a change to the power valve. To find out which power valve your high-performance engine needs, you can perform the following procedure:

1) Hook a vacuum gauge to an intake manifold vacuum port.


2) Warm up the engine and note the vacuum reading at idle. Automatic transmission vehicles need to be in the Drive position, while manual transmission vehicles can be in Neutral.

3) Divide the vacuum reading in half. The number will determine the correct power valve.


Each power valve is stamped with a number that indicates the correct vacuum opening point. For example a power valve with the number #65 stamped on it, will open at 6.5 inches of engine vacuum. As an example, a vacuum reading at idle of 13-inches, is divided by two and results in a 6.5 inches of vacuum. Therefore, you should have a #65 Holley Power Valve installed in the carburetor.


If you divide the vacuum reading and it falls on an even number, you should select he next lowest power valve number. For example a vacuum reading of 8-inches, divided by 2 and you come up with a number of 4. In this case you would use a #35 power valve.

Finally, if your engine produces 13 inches of vacuum or more, the stock power valve that the carburetor is equipped with from the factory, is sufficient.


Holley power valves come in a range of orifice sizes. The higher the number the more fuel is added."

I hate to keep saying this but Holley is DEAD WRONG and has been DEAD WRONG and will continue to be DEAD WRONG about how to select a power valve opening.

I can't believe they still publish junk tech like this. It's shitty to keep screwing the public with ignorant crap like that.

The power valve can be wide open at idle and IT DOES NOT MATTER. This has been proven more than once. Mark Whitner made a YouTube video on this because of this stupid method continuing to be promoted.

Don't do it like that.

The correct way to select power valve opening is to drive the car with a vacuum gauge hooked up and read your vacuum at a cruise. Whatever that number is, select a power that opens 2 numbers lower than your cruise vacuum.

That's how you need to do it.

Why Holley still pedals this crap is beyond me. It's stupid and it needs to be corrected.

 

[yellow rose]

Note: I should have read the entire thread before making my post. I see it was already covered.

 

[AJ/FormS]

YR's assessment sounds pretty good.
My engine cruised at 15. And with the PV plugged, it would go flat lean at 10.5 on the gauge. The closest PV I had to that was a 12.5, and it works pretty good. Been in there since year 2000.
Using Holleys method, I wouldda had a 5.0 in there. Or a 4.5

 

[Mattax]

can't believe they still publish junk tech like this. It's shitty to keep screwing the public with ignorant crap like that.

YR. I appreciate the second. stated a little different. Why? I think we know why. The tech writers aren't techs anymore. The website people sure as the sun come up never studied the fluid circuits in a carb.

Well, thats really good info, thanks for that. Sometimes its hard to know what to listen to when you don't have the experience. We assume manufacturers would know the product best, but obviously thats misguided sometimes. And the anectdotal info from some "helpful" people can be no better. Info like yours is clear and makes sense. My apologies to possibly steering the OP astray.

Dave

Dave - You're a class act for feeling that way and saying so, especially when its no fault of your own. Its perfectly logical to assume the manufacturer's know their product. More so when its from a company that made 100 of thousands if not millions of carbs for production vehicles. There's just a disconnect because the 99.9% of the tech people at these companies are not the same as the guys and gals who designed them and worked with the automobile makers. Its worse now because no one has had to make carbs for production cars since 80s.

Someone really interested in fine tuning PV opening without expensive test equipment* can run time trials over a consistant stretch of track with a stop watch or equivalent. The first run at steady speed, and each run after crowding [holding] the vacuum at 2" lower and lower from the first run. Each run should get faster (shorter time). If it goes flat or surges early, that tell us its too lean for that load and it needs a higher PV opening point. This is one of the last things to test for. All the steady state, including WOT and highway cruise, needs to be tuned first. Or you may just find that the engine seems to go flat at part throttle. I was having that with a carb for a long time. I tried some crowds with the datalogger showing rpm, AFR, MAP and acceleration. Its not easy crowding a vacuum. In the end it turned out to be timing related not fuel ratio.

There's been some carb guys, like Mark Whitener that Yellow Rose mentioned, who have been sharing some good testing and experience. More than that, they've shared all of the research papers and engineering books on the subject they've come across. Until the AFR curve was explained by one of those guys, I thought the carb's job was to provide increasingly richer mixtures as the throttle opened. Not only did they explain, they cited the books and even posted scans of the graphs. I reposted some of that here
Wideband O2 Sensor location advise

*If you happened to be so lucky as to know a place with NOx gas measurement and a load dyno then it can be done by observing the combustion.
"The purpose of the power valve selection is to enrichen the mixture prior to the combustion temperatures going too high. To set a powervalve correctly requires a NOx sensor. Different engine combinations need fuel enrichment at different power levels."
Bruce "Shrinker" Robertson. post #4 "Another Power Valve Question" archived Innovate Motorsports forum

 

[gdbuick]

Ok, I have a lot of ideas and suggestions to go through I appreciate everyone’s help as I’m new to the mopar world. I added a few pics to my 69 skylark that I used to own /work on and a link to the last engine I installed for anyone interested. I have business trip so I won’t get back to this for a week. If anyone has a similar setup to mine and can send some pics of their breather and pvc setups that would be helpful. Part numbers too helpful in the event I need something that the local auto store doesn’t have. I do have the service manual but with my current setup I don’t think it will help much.
Good running engine taken out for a 627hp pump gas motor install.

 

[gdbuick]

New motor

 

[gdbuick]

If you search You tube that’s my former car after 27 years it was time for a change
Buick 455 Stage 2 with a 308 solid cam

 

[gdbuick]

Just a little update Business trip then vacation now manifold is off due to a major oil leak that sprung up thread in Big Block A body tech "383 intake gasket and valve cover choice". Getting new valve covers, PCV installed and a new intake gasket. I wonder if part of my issue getting this thing to run right was oil getting into the intake/exhaust ports and a vacuum leak, time will tell.

 

[7milesout]

I'm new to all this. But during replacement of my exhaust system, I had a bung welded into each header collector. And added an AFR sensor and gauge. Now I can tune like a ****. I don't know how anyone having tuning issues can live without an AFR gauge. The ole Scamp, while not a big monster power machine, runs like a top. A cool local auto / hot rod type of shop did an alignment on the ole Scamp. When I got it back they said, "that ole Scamp sure runs good." They had to drive it to confirm the alignment.

Prior to the AFR gauge and new exhaust, I always thought I was flooding the 360 when starting. Turns out, I was never giving it any fuel. It would take me forever to get it to start, it could be very frustrating. I would rarely pump the throttle after an initial pump or 2 because I assumed I was flooding it (this was with the rusted out previous exhaust system). It acted and smelled just like it was flooded.

After being able to see what's going on with the AFR gauge, I wasn't flooding it at all. I was starving it. And now I can tell that the first few pumps (after sitting for a few days) are not really doing anything but priming the pump well area of the carb.

There's one thing I can tell ya … an LA 360 likes fuel. I didn't read all the replies but I realize you're running a 383. But if it is at all possible, get an AFR gauge running on your set up … you will NEVER regret it. I believe you when you say it is rich. But how rich? How do you know it's good, when it's "good?"

One of the cool things is that WOT is easier to tune, than is just cruising and normal accelerating. I've got the ole Scamp hitting and hovering right at 12.2 AFR at WOT. So, even though it's not a power king, it's doing all it can do when it's at WOT. All I can get out of it, and safe. I can't express how awesome an AFR gauge is.


7milesout

 

[mopar head]

I`ll add my 2cents, Your manual choke is not hooked up, is it flapping around freely? If so that might have something to do with richness. I too like the color of your car and also like those years of Buicks. Good luck.

 

[gdbuick]

I'm new to all this. But during replacement of my exhaust system, I had a bung welded into each header collector. And added an AFR sensor and gauge. Now I can tune like a ****. I don't know how anyone having tuning issues can live without an AFR gauge. The ole Scamp, while not a big monster power machine, runs like a top. A cool local auto / hot rod type of shop did an alignment on the ole Scamp. When I got it back they said, "that ole Scamp sure runs good." They had to drive it to confirm the alignment.

Prior to the AFR gauge and new exhaust, I always thought I was flooding the 360 when starting. Turns out, I was never giving it any fuel. It would take me forever to get it to start, it could be very frustrating. I would rarely pump the throttle after an initial pump or 2 because I assumed I was flooding it (this was with the rusted out previous exhaust system). It acted and smelled just like it was flooded.

After being able to see what's going on with the AFR gauge, I wasn't flooding it at all. I was starving it. And now I can tell that the first few pumps (after sitting for a few days) are not really doing anything but priming the pump well area of the carb.

There's one thing I can tell ya … an LA 360 likes fuel. I didn't read all the replies but I realize you're running a 383. But if it is at all possible, get an AFR gauge running on your set up … you will NEVER regret it. I believe you when you say it is rich. But how rich? How do you know it's good, when it's "good?"

One of the cool things is that WOT is easier to tune, than is just cruising and normal accelerating. I've got the ole Scamp hitting and hovering right at 12.2 AFR at WOT. So, even though it's not a power king, it's doing all it can do when it's at WOT. All I can get out of it, and safe. I can't express how awesome an AFR gauge is.


7milesout

I agree that’s certainly a good idea to have a bung in the headers for that. Like being on a dyno when you want.

 

[gdbuick]

I`ll add my 2cents, Your manual choke is not hooked up, is it flapping around freely? If so that might have something to do with richness. I too like the color of your car and also like those years of Buicks. Good luck.

That choke is locked in pretty solid and not moving. Thks