Holley 600 Dual-stage PV

[R. Shackleford]

Hello all. I have a Holley 80454 600cfm that I bought from AllState Carbs (I know, should have checked here first but what ya gonna do). It's the factory upgrade for '65-'67 Mopars so I've read. This model has a dual-stage power valve (10.5-5.5). Apparently they are made of unattianuim and was wondering if anyone has swapped a dual-stage for a single? If yes then should I land somewhere in the middle like maybe an 7.5 or 8? Thanks for the read

 

[ckessel]

Haven't seen any mention of one of those for many years. General rule of thumb was to choose a valve that opened 1- 1.5" vacuum under what it idles at in gear, if auto. Most of their carbs just came with a 6.5 unit.

 

[R. Shackleford]

Yeah I saw the standard was 6.5 for Holleys but wanted to make sure cause I haven't found anything on goin from 2 stage to single and if there are any benefits to it. Carb runs pretty good except for a little flat spot off idle and the idle mixture screws are funky... The engine idles better and the manifold vacuum goes up as they tighten. I can run it with them all the way in even and its smooth so somethins up with the internals. I was running a 3/8 fuel line so went to 5/16 and that settled things a little. Floats are set perfect but unsure of what jets are in it or how good the passages are. Any ideas?
On a 318 poly with mild cam
14 BTDC
Automatic
Mechanical fuel pump (factory spec)

 

[R. Shackleford]

Ok UPDATE. Just heard back from AllState about the carb (3rd attempt) and they say it is a reverse idle carb where the idle mixture screws fattin as they tighten instead of leaning out. Didn't realize that so great information to have.

 

[ckessel]

Ok, I was thinking it was one of the Economaster versions with that 2 stage valve. Your main jets may have 3 instead of 2 digits on them. If so, those are close limit jets. They too can swap with normal. And yes the mixture screws are opposite normal on adjustments.

 

[steve340]

Those two stage power valves were typically fitted to carbs with an economy and emissions in mind.
They were in some performance carbs evidently. But these carbs would have had a special calibration of metering blocks and probably very small jets.
Holley state do not use these valves in a vehicle used on a drag strip.
The book states that your power valve is for high altitude.
If you swap to a single stage the engine might go very lean before the PV opens.
You need to be cautious playing around with that carb.

 

[R. Shackleford]

Those two stage power valves were typically fitted to carbs with an economy and emissions in mind.
They were in some performance carbs evidently. But these carbs would have had a special calibration of metering blocks and probably very small jets.
Holley state do not use these valves in a vehicle used on a drag strip.
The book states that your power valve is for high altitude.
If you swap to a single stage the engine might go very lean before the PV opens.
You need to be cautious playing around with that carb.

Ok well now that I know about the reverse idle I retuned it and she's runnin like a top. Still having a slight hesitation off idle at times. Depends on how fast I drop the peddle. No drag strip for this one just a cruiser

 

[R. Shackleford]

If I were to change out the PV for a single stage I take it I should up the jet size as well?

 

[ckessel]

One step at a time. But have like 4 sizes on either side of what you have currently. If the 1st two digits on the the jet say, 65 for instance, get 64/63/62/61 plus 66/67/68/69. Plus bowl gaskets, metering block gaskets and bowl screw gaskets. That way you're covered for oops. Only kicker is, the jets are expensive. Have any friends with a supply of jets?

 

[R. Shackleford]

One step at a time. But have like 4 sizes on either side of what you have currently. If the 1st two digits on the the jet say, 65 for instance, get 64/63/62/61 plus 66/67/68/69. Plus bowl gaskets, metering block gaskets and bowl screw gaskets. That way you're covered for oops. Only kicker is, the jets are expensive. Have any friends with a supply of jets?

Oh I'll ask around... Unless you're offering haha. I was looking at getting a refresh kit from Holley and some extra jets. Now to find out what size they are. Car runs fantastic aside from that little hesitation spot off idle. If I just step on it its not there, or if I slowly push its not there and only when I push at a medium pace does it show up (if that makes any sense)

 

[steve340]

Probably not worth playing around with that economy carb is you want to get more performance.
The metering block calibration will be that lean that I doubt you will get it right.
Just buy an Edelbrock, Summit VS or some other carb and get a good tuning guy to dial it in.

 

[ckessel]

I had a flat spot just off idle with my 3310. An adjustment to the accelerator pump screw/spring/nut took care of that.

 

[R. Shackleford]

Probably not worth playing around with that economy carb is you want to get more performance.
The metering block calibration will be that lean that I doubt you will get it right.
Just buy an Edelbrock, Summit VS or some other carb and get a good tuning guy to dial it in.

I appreciate the response/advice. Never liked Edelbrock/Carter personally but thats me. Also I like to do my own tuning on things which is how I learn. Not looking for a performance upgrade really for the carb just want to eliminate the flat spot is all. Carb gives plenty of power and the mileage isn't terrible for how its used. I know eventually the PV will give out completely so just wanted to see if anyones done the dual to single swap before cause ya can't find whats in it currently anywhere

 

[R. Shackleford]

I had a flat spot just off idle with my 3310. An adjustment to the accelerator pump screw/spring/nut took care of that.

Yeah I did a little adjustment before so I'll go back through now that the mixture screws are better set. Thank you sir!