I bought a Proform main body and (finally) put it on my 750VS. While the carb was apart, I went ahead and put in the Holley brand power valve protecter as well.
When I went to start my engine with the upgraded carb, I forgot to remove the bowl vent caps that come on the Proform kit. There was fuel pouring from the air bleeds with the fuel pump running and I eventually realized that those caps have to come off
So it was pretty badly flooded and when it turned over, it went POW! And there were flames coming from the carb.
So... it started after a while, and it's running smoothly, but it's blackening plugs.
What I'm thinking is, this seems like it could be a blown power valve, but with the PV protection that I put in, I'm wondering if it might be a jetting problem.
Has anyone had a blown PV with the Holley check ball kit installed?
Or are the Proform kits jetted super rich?
It seems like it has to be one or the other.

Thanks for any help with this

 

How long has it been running with this carb and plugs? The plugs won't change that fast, it usually takes a few days of normal driving or a few hard passes down the 1/4 to 'color' them properly.

 

New plugs when the carb swap was done, mebbe 20 mi.

 

if your power valve was blown it would have a very rough idle, thats if it idled at all. i would say its deff not the power valve. what are the motor specs?
how big is the cam and what size power valve? be carful choosing power valves, some will tell you to take manifold vacum and cut that in half, but thats not correct.

 

It's a 350 with a pretty small cam in it, a CC-252. It idles smooth, I think the PV is 6".
It's very possible it's jetting, the carb has had quite a bit of work done to it and I haven't had a chance to do anything with it tuning wise except for adjust the idle.
I'm mainly curious if anyone thinks that the PV protection may have failed and it blew the PV anyhow when it backfired, in spite of the protecter.

 

is not the power valve if it idles smooth. the problem is that you have too much carb!thats the carb i bought for my 6in rod 11.8 comp. pump gas standard bore with a .585-.620 lift 256 258 dur cam! my setup was going to make about 500hp with a vortech head. and i sold it and he ended up makeing 545hp and only runs 26 degrees total timing. now do you think that shoulb be the same carb for your 285hp-345hp motor? this is in a 3300lb 78 z28 with a 3600 converter, and it ran a 10.72 1/4! it made 430hp to the ground. i really hate to tell you its too big but i hope you bought it because you need it for a future build.

 

Thanks for giving me the benefit of the doubt here. Yes, I have more serious plans for this carb.
But if the power valve is blown, it doesn't matter what motor it's on.
So you're sure the power valve isn't blown, from what I've described?

 

The carb is not too big. Read the first sentence. It is a Vacuum Secondary carb. You cannot over carburate an engine with a VS carb. It's just plain non-sense if any one suggests that you can. I ran a 780VS on a mild 305 for Autocross and Hillclimbs before buidling my 355. Worked just fine, made tons of power. That's the benefit of VS carbs.

Getting back to the real problem.

StreetIron85: Did you put in fresh plugs After the flooding problem? Plugs drenched with that much fuel will not clean up. They will remain covered in carbon. BTW, what are you running for plugs? Heat range and mfg. Did they run clean previously?

What was the jetting in the carb before you changed to the Proform body? I believe that the Proform bodies come with main jets included? Is this correct and did you use them? What size were they?

If you used the same jets as previously then you may have to change the jetting ( leaner ). The Proform bodies do have replaceable air jets, and these will affect the fuel curve greatly if different from factory.

Have you reset the idle mixture? Proper method is to warm the car up thoroughly, then hook up a vacuum guage ( undamped ) to manifold vaccuum. Start out rich, then lean the mixture till the needle just starts to waver. This will be what is called " Best idle" . 1\4 to 1\2 turn leaner will be " Lean Best idle". Usually used for passing emissions. 1\4 to 1\2 turn richer will be " Rich best idel". This is what most engines will be happy with.

BTW...it wouldn't hurt to change the Power Valve. Cheap insurance, but I doubt that it's the problem. I'm thinking that it is a jetting issue from the Proform switch. Of course you've checked your float level right? Fuel level should be just sightly below or at the bottom threads ( No higher) of the site plug with the engine running.

 

Chickenman
This carb is using a powerplate like your carb.
I was going to PM you about some baseline jetting for that after I got it up and running, but so far there hasn't been much road time. I have to take the cam out and get a new one cause some of the lifters aren't spinning (flat tappet hyd)
But if you could give me some baseline jetting tips that might help.
All I can say about how it's running at this point is that it smells rich and the plugs are black.
I can give you more info later tonight in a PM when I have some free time to look at my carb to see what I've got.
It's a 750VS with the proform main body and a powerplate, that's the only info for now tho.

Thanks

 

K...actually send me an e-mail. PM has too many restrictions on attachments and length of reply. Send me all the details of what Emulsion tubes, main fuel jets, main air jets, Idle jet and idle jet holder that you have in the Powerplate now.

Edit. Hey StreetIron85....clean out your PM BOX. It's full!! Can't send you my e-mail address.

 

now tell me why it would matter if it is a vs? does a vs sense airflow requirments? dont they just open the secondaries at a tunable vacum level?!?! do they partialy open the secodaries so that you dont over fuel/air the motor? i dont think so.....i think they open the secondaries according to vacum ,and when that vacum level is reached they open.not when that airflow requirement is reached. a dp on the other hand does this mechanicly. hey tell me if i wrong but explain.

 

Chickenman
I've been having problems with my PM inbox. It's empty but I can't recieve PMs for some reason.
I just learned of this today.

Vejtabul
Yeah VS carbs are versatile that way.
On a smaller engine or one that would othaewise be over-carbed the secondaries can be set up to open later (or not at all) if you want. All in accordance with your engine's demands.
How can you have such a fast car and not know how VS carbs work?

More:
If you've ever looked closely at a VS carb, you'll notice that the vaccum source for the vac diaphragm isn't the manifold vaccum, it's from a small tube that feeds from the pri venturi.
Thataway the airflow speed/volume through the pri venturi is what determines the sec opening. And that can be further adjusted with spring changes.

 

StreetIron85: rboyk@telus.net


On your PM, did you select the option to show PM from the very beginning ? Don't forget to check and claer the Send Box from the very beginning as well. I got caught out by that previously. Thought my PM box was clear...then checked from the very beginning and found like 250 messages!! LOL.

 

I'll look into that right away.

 

The answer to your questions : It does matter. Yes. No. Yes...Sorry, but you're wrong.

Vacuum Secondaries and ANY air valve carb, such as a Q-jet or Edelbrock do sense airflow requirements. That is the whole principle on how they work. They go about it different ways but essentially they all sense airflow requirements of the engine. That is why you ( generally ) cannot over carb with a VS or Airvalve carb

Read some basic material on it to get a better understanding. Here is a link to a basic diagram at Holley's tech site. Note: Diagram s not completely accurate as it does not show the " bleed " circuit....but it does give a basic view of how a VS carb works. Note: that engine vacuum has NOTHING to do with how a VS carb works. It all depends on rate of airflow through the Primary then Secondary Venturies.

http://www.holley.com/HiOctn/TechSer...fo/TI-223.html

Basically, you have a vacuum feed passage ( Pitot tube ) taken from the Primary side of the carb venturi. When airflow reaches a certain point this creates a vacuum at the Pitot orifice. This vacuum is then transferred to the vacuum Diaphram which depending on the Spring strenth will start to open the Secondary throttle. Holleys have quite a complex circuitry which includes another Pitot tube at the Secondary Venturi. This boosts the vacuum signal to the Secondary Diaphram when sufficeint flow has developed on the Secondary side. Thre is also an air Bleed linked to the Primary and Secondary vacuum sources, to ensure prompt closure of the Secondary throttle when you back off. This also controls the opening of the Secondary side so that you get a smooth progression.

One of the problems with Demon VS carburators is that the vacuum circuitry to the Secondary Diaphram is not as sophisticated. This results in the Demon VS carb having a Secondary action that is mor like an On\Off switch.

Hope this helps.

 

you are right. i was wrong.


but you were wrong about the edelbrock carb....take a closer look, they have mechanical secondaries.

they have that stupid air door above the secondaries, but i belive thats to smooth the transition.

 

Though the Edelbrock/Carter carbs and the Qjets both have secondaries that are linked directly to the primaries, they're not considered mechanical sec carbs in the same sense that a DP is, because of that air valve above the secondary bore.
Sure... I guess you could say the air valve smooths out the transition, but that's actually understating it quite a bit. Cause the air valve isn't just like a choke plate that covers the secondaries. It's got linkages that connect it to the secondary metering, and a very precise spring loading that controls the opening rate.
What that boils down to is that you could put an Edelbrock (or Qjet or VS Holley) on a truck pulling a 40 ft trailer... and floor it at 2000rpm (or maybe lower) and it wouldn't bog.
Which is why Edelbrocks or Qjets are considered VS carbs, to most people. Even though the linkage is directly connected to the primaries.

 

whoah! your talking about the new edelbrock carb. i was talking about the original edel. performer series carb.

 

Sorry...you're fighting a losing battle here.....


The early Edelbrock carbs use the same air valve method as the later versions. In fact Edelbrock bought the rights to Carter...which manufactured the AFB carb all the way back to the early sixties. These also used the weighted Air Valve flap. Carter also produced an Performance version called the " AVS" series ( " Air Valve Secondary" ).


Carter Four barrels, Edelbrock and Q-jets all are what are called Air valve or Air Flap secondaries. Air flow is contolled by either a spring loaded Air Flap such as on the Q-jet or by a counter weighted flap as used on the Edelbrocks ( all years ) and Carters.

Holley chose to go with a Vacuum controlled Secondary, which was also the favored method of control by Japanese mfg's such as Hitachi and Niki. Both VS carbs and Air Valve Secondary controlled carbs all sense and regulate airflow according to the demands of the engine.

Pick up some books on Rochester carbs by Doug Roe or how to build horsepower Volumes 1 and 2 by David Vizard. These have lots of info on how Vacuum Secondary and Air Valve carbs work...and once you understand the principles involved you can see why most Mfg's decided to go to these designs for the street.

The Holley DP series is a great design, but it was originally designed as a Race carburator only.

 

im just gonna shut up now. im never wrong....except this whole thread

 

Vejtabul
It sounds like you're just more familiar with double pumpers.
And... Hey!
By the sound of it your car's running too, I wish mine was.

 

Hey! I brought this from the dead to ask a question on the quote above...

I know the standard Edelbrock Performer carb has the counter-weighted air valves for the secondarys....but are they adjustable?? Or is there any case in which someone would need to adjust them?

I seem to remember that on the Holley's you can change the spring that acts on the diaphragm to open the secondary air flaps quicker/later. Depending on what tension spring you use.

So - is there an adjustment?

 

Well, does anyone here know?? No one owns any Edelbrock carbs on this board?

 

AFAIK they are not adjustable!

 

The Edelbrock Thunder series ( Rename for AVS series ) is adjustable. These use a spring operated Secondary Air Valve that can be adjusted like a Q-jet.

http://www.edelbrock.com/automotive_.../thunder.shtml

Nothing I could find indicates that you can get different counter weights for the regular Performer series though. You can " Hot Rod " the carb of course. Get out a Die grinder and remove some material from the counter weights....but you'd better have a spare set available. Phone Edelbrock Tech to see if you can order the counter weights separate. When Carter made these carbs ( Original AFB series ) the did have tuning kits with different weight Counter-Weights. Rare and hard to find.

The real question is if you " really " need to alter the opening rate of the secondary. If this is a street car or "Weekend Warrior" I'd say leave it alone. Too often people misunderstand how to adjust velocity controlled Secondaries and end up slowing the car down. Biggest mistake is opening the Secondaries too quick. If you can feel the Secondaries " kick" in, then what you are " feeling" is the car picking up.....after it has bogged on the initial Secondary " Tip-in".

For a max effort car...then there may be some gains to be had by very carefull and meticulous Secondary Air Valve tuning. If you're going this far....the best option, IMHO, is to sell the Performer Series carb and buy a Thunder series carb

 

Thanks alot for replying Chickenman35 and onebad82z!

As I said above, I used to own a 600 Performer years ago on a Dodge I had, and a shop ended up using a die grinder and cutting slots on the secondary flaps in order to case the air flaps to open later....but it still never ran right and they made 300 bucks from me.

But here I am again entertaining the idea of buying another one.

Only reason I am is because I'd really like to put my dual snorkle air cleaner back on so it will look original, and also because I run "collector" plates on the car now which means (in my state) that I need to keep the car in "original configuration" - or at least appear that way on the surface -even though it isn't close! lol.

Called Edelbrocks tech line 6 times so far - busy signal every time.

I looked at the "application chart" on thier website, and the duration on my cam (230-236 at .050) and 110 LSA. This puts me on the outer limits to run a 750 cfm - or- I could run a 800 cfm. I wanted to see what they'd recommend for the setup in my sig.

But i'm open to suggestions from you guys too!

 

Since you drive it on the street I'd definately recommend the smaller carb. Even for the strip...I'd go with the 750. More than adequate for your combo.

Another option is to modify the base of the Twin Snorkle Air Cleaner to fit the Demon. It's not really that big of a job. I've see it done. Certainly cheaper than switching carbs.

 

It's more than I have now. The Demon carb I have is only a 650 cfm DP which runs rich at idle.....I know there's more power in this engine just waiting to get out...just not sure whether it's in the intake side (which I doubt), or on the exhaust side (most likely).

As far as modifying the stock air cleaner, well - I guess it can be done, but it's not even close as is.