Cascade Crew

Leejo2005 · Member Joined: 12 Jul 2009 Posts: 466 Location: Kennewick

I finally got my Firebird running again but am in need of help.

I just did a cam/intake/carb swap on my LG4. The engine idles fairly well even with this new cam but I did have to turn up the idle screw a bit to do it. I've read that this can cause the carb to act weird if you set it too far. Something about the idle circuitry. Anyways when I rev up the engine and let off the throttle it tends to get close to dying but recovers. While in gear doing the same thing usually results in the engine dying.

I've checked for vacuum leaks and haven't been able to find any. I currently have the iginition baseline timing set to 12adv. Any suggestions?

I've never messed with tuning a carb before.

Holley 4175 (Q-jet replacement)

Twilightoptics · Posted: Sun Jul 12, 2009 7:25 pm Post subject:

So you ditched the computer controlled carb in favor of a Holley style Q-Jet. With a cam and intake.

Did you replace the Computer Controlled Distributor with a mechanical unit?

Leejo2005 · Member Joined: 12 Jul 2009 Posts: 466 Location: Kennewick

Yes I replaced the distributor with a non computer controlled unit.

The carb and intake were just laying around so what the heck why not. There was definately something wrong with the Q-jet(too much to talk about) or else I would have kept it for now.

Twilightoptics · Posted: Mon Jul 13, 2009 6:22 am Post subject:

http://www.florida4x4.com/tech/quadrajet/qtune.pdf

Leejo2005 · Member Joined: 12 Jul 2009 Posts: 466 Location: Kennewick

Thanks for the info!

I've got it running a lot more stable now, just had to play with the timing and idle setting a little bit. I'm planning on using the M4ME on the 305 I've built for my Z/28 since the one it has is toast.

From what I can tell my problem is that I have to turn up the idle screw too far to keep the car idling so too much of the transition slots are exposed. I'll have to take a look at it later to see if that is the case.

chevymad · Posted: Mon Jul 13, 2009 5:07 pm Post subject:

If thats the case you need to open the secondary butterflys a little. Take the carb off, turn it upside down. On one side you'll see a small set screw that adjusts the secondary idle opening. I'm not sure of the exact setting on yours since its a spreadbore. But just open them some and see where you're at.

Leejo2005 · Member Joined: 12 Jul 2009 Posts: 466 Location: Kennewick

I'll try that tomorrow after work. I haven't had too much trouble with it today. Also, my secondaries wouldn't open at all so I removed the check ball from the vacuum actuator and now it works great.

HONDASLAYER · Posted: Wed Jul 15, 2009 2:56 pm Post subject:

Leejo2005 · Member Joined: 12 Jul 2009 Posts: 466 Location: Kennewick

If you remove the cover on the top of the vacuum actuator there is a passage with a check ball in it. I had pulled it out to temporarily give my car some balls.

I wouldn't really recommend doing this though. I have since put it back in and I got a different spring for it.

Also, after driving my car for a day it has become clear that I'm getting about 3.5 MPG. The car smells like a chevron station and drives like crap. I've checked for fuel leaks and vacuum leaks and all looks good there. I tore the carb down this evening and thoroughly cleaned it. I suspected the needle/seats were bad but they looked brand new. Anything else I should check for before I put it back together?

The carb is a Holley 4175 series 650 CFM P/N 80555C.

Any help would be greatly appreciated.

chevymad · Posted: Wed Jul 15, 2009 9:00 pm Post subject:

Does it have externally adjustable floats and sight plugs? Make sure the floats are properly adjusted if it does. If thats ok, you probably need a new powervalve. Try to buy an actual holley branded one. I quickly went through several echlins before buying a holley kit.

Leejo2005 · Member Joined: 12 Jul 2009 Posts: 466 Location: Kennewick

I have a kit on the way now. The power valve and the chamber towards the inside of the carb from it were really gunked up and corroded. I cleaned it up but I'm still waiting on my kit to get here. Also, the floats aren't externally adjustable but I busted out my little machinists ruler and set the heights while I still have the thing disassembled.

What power valve do you think the 305 would need with this? The kit comes with one but when I looked them up individually it looks like there are many variations based on what vacuum pressure they open at.

chevymad · Posted: Wed Jul 15, 2009 10:02 pm Post subject:

Kit one is probably fine. For finer tuning you need a vacuum gauge and go cruising. I forget the formula, but someone may chime in with it.

Leejo2005 · Member Joined: 12 Jul 2009 Posts: 466 Location: Kennewick

For power valve sizing i've heard to take the vacuum at idle and divide by two and that's your power valve size. I've given up on the Holley 4175 and since installed a Summit 600 cfm carb. I've gotten rid of all my carb problems and the car no longer smells like the inside of the gas tank but I'm having a hell of a time getting my ignition timing right. I have a few ideas at fixing it but it's going to have to wait until tomorrow I don't want to wake the neighbors.

chevymad · Posted: Sun Jul 19, 2009 9:40 am Post subject:

The holley guys don't seem to like that spread bore carb much either. A 600 will be plenty on your car. I run a 600 on the 350 in my truck and its just fine. What kind of timing issues are you having?

Leejo2005 · Member Joined: 12 Jul 2009 Posts: 466 Location: Kennewick

As far as my timing goes I think that I need to tweak the curve at which the advance happens. I'll experiment when I get home how much mechanical advance I get at different rpms and such. It just seems like I can get the timing right for low rpm and kill the mid/upper or the other way around.