Carbs

[wade]

Hey guys i have a 72 bronco with a 302 just rebiult, i put a 600 edlbrock on it ,when i rev it when the engine is cool its is snappy, but when its at operating temp and i rev it its floody and black smoke comes out of tail pipes whats up.

 

[BigNasty]

Sounds like a classic case of running too rich /emoticons/[email protected] 2x" width="20" height="20" />

Have you pulled your plugs and read them yet?

Check out these two sites for some good plug read photos and tech stuff.

Spark plug reading

Plug tech article

These can give a lot of insight as to where you are in set-up, especially on carbed motors.

 

[wade]

But why dose it run great when engine is cool.

 

[BigNasty]

Running great when cool is normal for being too rich.

Once it warms up.. it will run worse.

The easiest way I can explain it is air density.

When incoming air is cool, it is more dense and will give a better air/fuel ratio and will in effect, give more power, run better etc as there is adequate oxygen to burn the fuel being supplied. (phenolic spacer plates can keep the carb cooled, routing fuel lines thru an ice box etc.. all kinds of things can be done to help the incoming air and fuel ratio <- old & new race tricks /emoticons/[email protected] 2x" width="20" height="20" /> cool air intake set ups etc althogh your best solution is to get it running properly with what you have now.)

When the engine warms up, the incoming air will be warmed up also, making it less dense and actually decreasing the available oxygen to the engine, YET the carb keeps the fuel supply at the same rate, increasing the fuel ratio in the air/fuel mix.

When setting the idle mix, it's best to adjust as the engine is at normal operating temperatures just to ensure you don't go too rich or too lean.

As for the air density, even higher elevations will affect the air/fuel ratio also as the higher you go (mountains) the richer your engine will be as the air is thinner up there.

 

[wade]

thanks but what do to solve my problem

 

[BigNasty]

Hehe, I did forget about that part /emoticons/[email protected] 2x" width="20" height="20" />

Sorry /emoticons/[email protected] 2x" width="20" height="20" />

Pull the plugs and look at their tips.

They will have very dry puffy looking soot on them if it is running rich.

(If you can afford a couple of sets (plugs) or just want to scrub them clean for the rest of the checks, I reccomend it.)

Find the two idle adjustment screws on the carb. (Usually you start with the screws run all the way in (gently!!!) and backed out 1 1/2 turns.

Verify that is where the screws are and if not, get them like that, in gently, then 1 1/2 turns out.

If they already were like that, then turn them in (both screws the same amount) about 1/8 a turn, reinstall the clean plugs and start the engine, letting it get to normal temperature again. ( in is leaner, out is richer)

You guessed it, pull the plugs again and look at them /emoticons/[email protected] 2x" width="20" height="20" />

If they are looking more normal, then you are very close and can make the final adjustments to the idle screws with the engine running (idle) just remember that too far in or out will make the engine stumble, if you do that, just back them both out till it runs smooth again.

As long as the jets are not too large for the engine, you can correct the problem like this.

If you can't get the problem corrected with the idle screws adjustments, then you'll need to pull the carb apart and make sure the floats are adjusted properly and evenly for both floats(edles go from 1" to 1.25" from the carb upper to the top of the floats, if I recall correctly..) and pull the jets to see what size they are and quite possibly getting several sets of smaller jets so you can get the size correct. (might take a few jet changes if this is the case)

A 302 and a 600 cfm is a great combination, very strong when set up properly, so the big issue is just fine tuning the carb. (I had a 65 stang with a 289 and a 600 cfm holley, when I got it set up properly I scalded every vette in Va Beach with it /emoticons/[email protected] 2x" width="20" height="20" /> )