[Steve R (Rizrtse)]

I have a 70 rtse with a hp 383 magnum that I just rebuilt to stock specs. I put a Holley 4160 back on top and it just doesnt seem to tune up very well. Runs lean after all adjustments. Everyone is telling me to scrap Holley and go with an Edelbrock Performer that seems to take an adjustment well. Any opinions would be helpful. Steve

[Dave R (Roppa440)]

It doesn't really matter what carb you have fitted if you can't tune it Steve. A carb is just a chunk of metal. If it is going lean there is a reason for it. Maybe the jets are too small. When does it go lean exactly? How do you know when it is lean?

Myself I find it very difficult to tune a carb without a rich/lean indicator. Until I fitted one of those I never knew where I was with carbs except at idle. The idle settings are easy to set. But that has no effect on part or wide open throttle. You would be surprised how many people I know think that adusting the idle mixture will make their carb run richer or leaner when they are driving!

I have posted a large thread about tuning carbs. Try working through that. There is also a good book about tuning Holleys.

Also a rich/lean indicator is a lot cheaper than a new carb!

[Dave R (Roppa440)]

Just read this again during an idle moment at work. Let me try to list every possible reason I can bring to my (small) mind that might result in it going lean.

Jets too small.
Float level not correct.
Fuel pressure low.
Fuel filter blocked.
Fuel boiling due to heat in line or carb.
Power valve not opening because it is not matched to the vacuum signal.

That's all I can think of off the top of my head.
There can't be too much wrong with the system really. Half of these problems would still be there if you changed carbs so you really need to get to the bottom of it. Knowing when it is going lean and how you know it is lean might help me narrow this down a bit more for you.

[Hans (72challenger)]

A small mind but with a high C.R.!!

[Dave R (Roppa440)]

Yes. Crap Ratio!

[Christer (Christer)]

I have some experience of tuning motorcycles (like our cars a vehicle that rests during wintertime).

A problem that I have met, is that during wintertime the gasoline in the carburettors creates oxide and this causes starting problems in the spring. The tiny little channels gets blocked by this oxide, and the engine will not start or it runs badly. (In the book of instructions they recommend to empty the carburettors in the autumn, but not everyone does that, myself included)

How to get rid of this problem? There are some different ‘anti-oxide-solutions’ that can be mixed with the gasoline to clear the channels. This often works but not always. If the oxidation is severe, the only way to go, is to take the carburettors apart and clear the channels with compressed air. A rubber hose atop of the ‘air-pistol’ is a good idea (directing the air to the channel).

I have no idea if oxide also causes problems in four-barrel carburettor, but I do not think it is unlikely. To my knowledge, this is a increasing problem since they stopped mixing lead into the gasoline.

Another thing to keep in mind is that gasoline gets old and bad as time goes by. Gasoline not more than three months old has a noticeable decreased quality that may be noticed when running the engine. I know a guy who could not get his motorcycle running because of old gasoline. He had to fill up the tank with new gasoline to get it running.

[Steve R (Rizrtse)]

Dave/friends, I'm no mechanic but the few who have tried to get my car (after a major restoration) to run well have failed. My car has decent vacuum (15) and idles well at initial start. The ping issue went away when one mechanic recurved the distributor a bit. However, when it gets hot the engine wants to knock off at idle. Seems like the choke may be keeping the engine with enough gas until it gets hot and then it sputters. One mechanic says the 284 duration cam is causing some of the issues. I have a repro 4160 california emmissions carb that is about 600 cfm I believe. Another believes the CFM should be higher with the slightly modified cam. I know you have suggested trying to isolate the problem but these guys have failed to find anything significant. They feel its a "bad egg" carb from Holley and I should try at least to replace it. Someone suggested a 675CFM Street Avenger but I'm not thrilled setting up the fuel line on the other side of the engine. Can anybody suggest a good replacement carb for a 383 with a slightly modified cam bored .040 over? Also, what is the chances the fuel is boiling? What would produce such an occurrence when everything is new on this car? I'm going to post the entire engine rebuild specs later on.

[Dave-R (Roppa440)]

Your main problem is not just that you are not a mechanic but that the guys looking at your car for you are not very good mechanics either. They very obviously do not have a clue what they are talking about.

What measurement of the air/fuel mixture have they made when the engine was hot? Was it too rich?

While standing watching these idiots have you noticed yourself that the exhaust smells rich at idle?

The normal situation with a longer duration cam is that it needs more air and fuel at idle than a stock cam. These idiots should know this.

If you have to have the idle screws turned out a long way to get it to idle at all it could be that they are setting it very rich to keep it running. Also the choke when it is on will make it more rich.

It is probably something very basic and simple that needs doing like making the two holes in the primary throttle blades bigger to allow more air into the engine at idle.

Go find someone that knows how to tune a carb.

[Dave-R (Roppa440)]

Did that sound harsh? Sorry. I am having a bad week.

[Steve R (Rizrtse)]

A road test timing and some minor adjustments are it at this point. I'll give it to a speed shop. If you had to start over what carb would you fit that brings a bit of originality to the car?

[Dave-R (Roppa440)]

In other words nothing at all done that is of any use.

That would be a Carter AFB fitted originally.