elka uses an incredible amount of fuel. i notice that the inside of the tail pipe is black with a kind of soot,that blackens your finger when touched.my friend yesterday mentioned that she may be running too lean. what does he means?. isnt that that the carb needs adjustment?.i bought and installed a holley street dominator manifold, and a new holley 600 cfm carb. that was last year, but since i only drive elka very little, i never worried about the gas use.it just came out yesterday because my friend is looking for an older chevy to play with..if i am getting 8 miles to a gallon it is a lot..she runs good, no hesitation or backfiring, missfiring or smoke. how do i adjust that carb?.

Black soot in the tailpipe would indicate that it's running rich. Either way, a carb adjustment may be needed.

A rich idle mixture can be adjusted with the mixture screws on the carb. Your problem does not sound like a idle circuit problem though. If the main circuit is rich that is where you are using all that fuel and sooting up your exhaust. I do not claim to be a Holley wizz what so ever but I believe it can be corrected with changing jets or a power valve. Get a Holley pro on it.

What year elky is it? That seems really low, especially compared to my '84 Elky. I get around 15-16 MPG in it and I don't drive with fuel efficiency in mind (I could probably get 17-18)

What is the list number on the 600?
Some of the Holleys 600's cam with 66 primary jets, #8734? I think??
anyway you may look in to that.

Its been touched on a bit already but, lean means you are getting a mixture of Air/Fuel that doesn't have enough fuel. It creates excessive heat in the combustion chambers and while it does "seem" to give more performance it will burn the valves and other components of the engine up over time.

Rich is the opposite, as was mentioned. Too much fuel in the Air/Fuel mixture. Two of the signs you've mentioned, poor economy and soot in the tailpipe. However, it doesn't always mean you have the wrong jets. For instance if you have a Q-Jet and it has been on the car for ever (Factory) now it's sooting up the tailpipe and getting lousy economy, you could have a cracked base, it's a common condition and you may notice that you have to pump the accelerator pedal every stinking time you get in the vehicle when it has sat over night, may even smell gas.

Tightening the air cleaner wing nut too tight will cause the cracks and other problems. Sounds silly but it's true, you pull the all thread which is actually screwed to the bottom plate of the carburetor too hard and the plate will bend and give and even separate from the gasket, over time it causes cracks and a warped base plate.

Trash in the gas can impede the metering valves from functioning properly and create a too rich or too lean condition. That case a good cleaning and a new fuel filter is in order. This usually happens when you have the vehicle stored for a long time or change out a fuel pump and even replace the fuel filter. Gas will turn to varnish and plug or hamper proper operation of the carburetor. Those jets are generally very small and can get plugged or collect debris fast. Floats will stick open or just starve out.

So if the carb has been on the vehicle a while and had been operating well up to some point, probably a good cleaning and kit and it will be good as new. If not, just replacing jets is not always a good idea. You can actually go too far the other way, thinking it's getting better performance and you end up running lean. Six months down the road you may have other more serious conditions occur.

You need to set a fuel curve and to get it right or at it's best you really should use an Air/Fuel Ratio meter and I believe the ratio is something like 11 or a little over. Just slapping on a carburetor (Bigger/smaller) to change characteristics like economy or performance is just a stab in the dark - at best.

Anyway it's just a thought.

ok, i am kind of getting it. i am looking for an air/fuel tatio gauge to install, and i see all connect to the o2 sensor, and ecm.mine has none of that. is there something out there for me?. i will also install one of those vac/gauges to properly tune elka, and make it look racey in the procces. i have seen some engines with little gauges hooked op at the engine itself. what are those?.

There is a A/F ratio guage with sensor that could be added. They are not cheap and probably not needed in your case. Find someone localy that can tune your carb. Many times a carb will be great right out of the box, don't sound like yours is. Some minor work could straighten it out.

This is a little off subject, but should still apply. I spoke to the tech guys at Demon about a year ago and they indicated that every carb should be within 2 jet sizes of being right. If you think about it, this makes sense. A given amount of air will need a given amount of fuel. They should be jetted pretty close right from the assembly line. The question then becomes: What is right? 14.7:1 for fuel economy and emissions or approximatley 12:1 for performance?

Devin

The meters have to be added to older cars. Well, they don't "Have to be" it's an option but does help in tuning and troubleshooting. Yep they are a little pricy and you'll have to have the O2 sensor bung put on the exhaust.

If you go with the two jet sizes off then figure out what you have from the box and go buy one larger and one smaller..... Well, just one size smaller actually you already know you are too large right now. Really you need the "kit" it comes with more than just Jets.

The other option is to go to someone who has the equipment and have them do it for you. I'd go with a good 13 probably at highway speeds, since I'm mostly highway driving, and if it's a little rich on the local streets (Stop and go) that is good. But then that is just me.

A kit will have some other advantages, on Race Night, you can re-tune for racing and go to the local Track and do your times and even test what is the best for that evening. Our local track has what is called a "Test N Tune" night, Wednesdays where you just go make your runs and get the tune, tires and all that good for Friday or what ever.

Yep, as others stated, you have a rich condition most likely at cruising speed. Smaller primary jets and possibly a power valve change could be in order. A 65 power valve should be fine, that's what normally comes in those carbs,if it's bigger numerically than that it could be dumping fuel too soon. Go down at least 2 sizes on the mainjets and see what that gets you.

I used a cheap A/F meter and a vacuum gage and tuned my 454/700R4 to an average 14-15mpg. It took some time tweeking but it paid off in the end. :cool: