Should I keep it or trade it?

[cmg96]

Well I just got back in from a nice ride. When you give it gas you it sputters and sounds like a low toned whoopee cushion.

[cknfrmr]

maybe you could go to your local drag strip and talk with someone that runs a setup like that and they could help you out getting it tuned right. Or maybe point you in the right direction. Most racers have worked out just the perfect tune. good luck with it. KEEP IT.

[72 Copper C-10]

IMO I would certainly consider projectking's advice. I agree that it seems like a carburetor issue.

[cmg96]

I am considering just starting with a new carb my question is do I buy for what I have or what I want? I am not familiar with carbs outside of holley. I want it all black so the avenger comes in black. I don't really like chrome.

[cknfrmr]

chrome carb lives matter.

[cmg96]

Hah I want minimal chrome my SC is chrome. Heck it can be pick if it would just run tip top.

[67 chevelle]

find out what the words 'boost referenced' mean , you need that , and make sure there is oil in the front resivior of the blower , bost gauge is advisable also , to be sure its working , should top out around 7 psi

I had one in my 49 , the teflon strips wore on it and no boost

[jjzepplin]

Good point. Might be boosting nothing. I thought about this too but assumed there was already a boost gauge.

[67 chevelle]

boost refrance has to do with the way the carb is set up , the vacume refrance for the carb power valves to engage must come from the manifold below the blower , not where the carb mounts , there are specific cabs for this , or a natural asperated carb can be modified . throwing a regular carb on a blower moter will result in an engine that allways runns rich , do some research , the blower is a pain , but once setup corectly , a blast and worth keeping , everyone wants one

[cmg96]

I am already reading an awesome I found on blowers and specific carb setups etc. I am thinking this is going to fun. I believe I am going to take your advice and get a supercharger carb like a 4150 and start from scratch.

worst case I can sell this double pumper locally and offset it a little.
it has been identified as either a 4778 0r 4779.

[BugzC10]

What's the latest on your SC adventure

[cmg96]

Howdy y'all - It has been a bit but I have been busy learning and working.
I am leaving the supercharger where it is right now. I have had everything tuned and it feels like it is working. Hit the gas and it goes and seems to go faster than normal so that is good. I will be tinkering with it to learn more after this project.

I am knee deep in suspension work. I ordered a complete moog kit. I am doing ball joints, tie rods, ULC & LCA and whatever else I find as I am going through it.

I am going to focus back on the motor shortly but I am trying to get it sound before I turn it up.

I am considering a lift Atlas® BP-8000 or maybe the maxjax. The question is should I just get nice jack stands and a jack like everyone before me and have more cash for the truck or get the lift and have to stall my project?

[Starballs-135]

I've read this forum off and on for quiet a few years. You've inspired me to actually sign up. I enjoy fighting tuning nightmares, I'm not far from you so if you ever need help send me a message.

[nonstop]

Originally Posted by cmg96

Howdy y'all - It has been a bit but I have been busy learning and working.
I am leaving the supercharger where it is right now. I have had everything tuned and it feels like it is working. Hit the gas and it goes and seems to go faster than normal so that is good. I will be tinkering with it to learn more after this project.

I am knee deep in suspension work. I ordered a complete moog kit. I am doing ball joints, tie rods, ULC & LCA and whatever else I find as I am going through it.

I am going to focus back on the motor shortly but I am trying to get it sound before I turn it up.

I am considering a lift Atlas® BP-8000 or maybe the maxjax. The question is should I just get nice jack stands and a jack like everyone before me and have more cash for the truck or get the lift and have to stall my project?

If you can swing it - get the lift! Lifts are what a lot of us WISH we had! I don't have the cash or room, so I do everything with jacks and stands. In the long run, it will pay off!

[cmg96]

I am looking at the atlas bp8000 I have no experience buying lifts. I have 10ft ceilings and have looked into portable lifts like triumph 7000c and maxjax but they are more than a baseplate lift. I have been saving my pennies for quite a bit of time to have the cash for this lift. That is why truck doesn't have anything new or shiny. I do have space but I am concerned with stationary pillars for all the space they take. My shop is 900-950 sqft.

[BigCountryx]

I am considering replacing my Holley in my blazer with a FITech TBI setup. They make a forced induction version too. Check them out, might be just what the dr ordered and not much more (if any depending on the carb) than a new carb.

[cmg96]

What kit are you looking at? I have never considered EFI on this truck.

[Stepside Jim]

I just put 2500 miles on my truck with similar set up as you have.
The blower is a fantasic way to get all around power.
As mentioned, Boost referencing a carb is the way to get past your problems. The power valve on your setup will never open to richen the mixture when you are under load. The suction (vacuum) from the blower is constant, meaning the vacuum is always keeping the valve closed.

There are simple ways to convert your existing carb to work with the blower, if interested, I'll post the information of how to convert your carb.

When converted, the vaccum source for the power valve will come from the under side of the blower, then by a vacuum line the vacuum signal will get to the power valve by way of an outside source vs from under the base plate that it does now.

In my picture you'll see a vacuum line with a tee fitting on the carb. On your carb, you now have a black rubber cap on the vacuum fitting, this fitting will now become the source of which will signal the power valve. Don't worry about my tee fitting I'm using it for the vacuum modualaor on the transmission.


Good luck, Jim

[BugzC10]

Stepside....please post the power valve conversion. I'm sure there are others following this thread considering a Supercharger like I am.
Thanks

[cmg96]

You beat me to the request. I have been on the fence about putting a built BBC and selling my sc 350

[Stepside Jim]

Ok, I took some pictures to help tell the story.

There are a couple of ways to convert a normal carb to be Blower referenced. Simply Google "how to" and you'll find some different ways to do it.

I searched and found this particular way to work for me. One thing I try to get across to anybody doing something new is.... Know the theory.

Know why we have to convert a Holley carb for a Blower. Know the changes that have to be made to the carb. Know how the changes are going to alter the normal function of the carb.

As I mentioned before, we are going to use an existing "Ported" vacuum port off the passenger side, as marked by the arrow.


Once the metering block is removed we can see there is a path in the metering block for air to pass through. Also notice is ending close to the power valve itself. We will not be altering this metering block, but it is nice to see how close the vacuum passage gets to the power valve.


Here's a pic using a used gasket, the impression takes us to the hole we will be altering soon. Notice also the large cavity in the middle of the carb, this is the cavity that we need to get to from the vacuum hose fitting from outside the carb.


We need to get from the end of the vacuum passage to the large cavity. This is the time I get a little nervous, drilling a perfectly fine carb, but here goes. The drill is a 3/32, get a new one to make a clean begin to the drilling. Start at an angle heading toward the large cavity.


In the above picture I made two arrows. The one on the left is the new hole that will transfer the vacuum signal from the intake side of the Blower to the power valve. We now have a way for the Power valve to function properly at idle and cruising, closed valve. We now have a way to lose the vacuum signal that is keeping your power valve closed in your situation. The new passage will now have a varying vacuum signal that will change as you depress the gas pedal so the power valve can richen the fuel mixture as needed.

The arrow on the right is the passage that originally supplied vacuum to the power valve, we will block this passage later.

One other way to get from the vacuum passage to the large cavity is to machine a groove into the surface from the vacuum passage to the large cavity. I drew a line where the groove would be made.


It is up to you to either tee into a vacuum port in the intake, perhaps where there is a gauge line already threaded into the intake. My intake did not have any threaded openings and I had to drill and tap to have the outlets for the vacuum source for the carb and for the Boost gauge in the cab. If you have to drill for a vacuum outlet, the intake has to come off to keep the drilling debri from falling into the engine.

Ok, we now have a way to control the Power valve, but we have to close the passage ways that 1) supplied vacuum from the carb base to the power valve and 2) supplied vaccum to the vacuum port we are using outside the carb.

Remove the base plate from the carb, you will find these two vacuum ports. The one the right in the picture supplies vacuum to the power valve. The one on the left in the picture is the one that goes to the vacuum port outside the carb. I put wire in each hole to mark and identify them better. We need to close these two ports, one simple way is to use JB Weld, mix up some and fill the holes.


Don't make a mess, the surface around these holes need to be clean for the gasket to seal when you reassemble the carb base plate. Let the epoxy dry overnight, it'll even settle a bit when it dries.


Ok, we've created a new vacuum path to signal the Power valve and we closed the old passage ways. We have lost a ported vacuum port which most never use anyway, such as the carb already on the truck with the rubber vacuum cap on it.

One alternative way to close the existing holes is to tap the holes and install a allen head set screw, like the pics below. I already tapped the hole.




I am sure others will chime in with the quick fix of upping the main jets 2 or 3 or 4 sizes larger to overcome the lean fuel issue on acceleration. For me, it's not option, for instance, I drove my truck 300 miles on Thankgiving day, dumping all the extra fuel for 5 hours at 70 miles an hour seems a waste.

As an experiment I rerouted my vacuum lines to run full vacuum to the power valve by running the vacuum line to above the blower vs below the blower. Where it worked great with below the blower vacuum, it pinged and predetonated with the vacuum from above the blower, such as yours is now.

Once you get the carb "Blower referenced", you maybe able to go with smaller main jets and get better mileage when this is all done.

Hopefully this will shed some light on an otherwise dark subject, good luck on all your projects. Jim

['63GENIII]

Originally Posted by BigCountryx

I am considering replacing my Holley in my blazer with a FITech TBI setup. They make a forced induction version too. Check them out, might be just what the dr ordered and not much more (if any depending on the carb) than a new carb.

Hehe... Blown injected. Doesn't get much better! Wish I had the $$$ to get a blower on the 7.4. It's getting to be a sickness!

In your case you're 75% there with the SC already. FI would just make it better if you could tune or had someone to tune for you. Pretty much set and forget. Turn key fun!

[jjzepplin]

Good write up! WOW! How about some pics of the intake where you tapped it for the vacuum?
Pics or it never happened we say here. HAHA!
Just want to know as this may be my Christmas present to myself.
Oh and what would be an ideal compression for this?
Would my 9.5-1 406ci work or should I build the 383ci for this.
Not gonna race or nothing just want some cool shiz in my garage.
Again-very nice write up! Pics are beautiful and now I understand for sure.
OP-Nice truck!