Rookie carb tuning

[Z-Driver]

What are some basic steps for setting up a carb after initial fire up? I'm new to everything and I just learn it as I go, but this has me stumped.

I've played with it for about a week now and nothing seems to be improving. It is running extremely rich. the butterflies don't move and fuel drips out of the secondary boosters.

I did the best I could to set the timing (about 12 btdc) but nothing I adjust makes much of a difference.

The carb is a Road Demon 725; basically a holley configuration.

[Tim240z]

Sounds like fuel it getting passed the needle and seat. Too much fuel pressure?, or some dirt in the bowls?

 

Tim

[datsunlover]

Yah, I had a similar problem in my 85 RX7 350sbc swap when I fired it up. That was a stock 'quadrabog' 4bbl, but it was the same symtems you are describing. I didnt have a fuel presure regulator, and I was forcing too much fuel into the carb. (about 30 psi from the stock fuel pump I think) It wouldn't idle below 1500 and smoked (mostly fuel.. some oil ) like a bugger!

[rustorbust]

take the bowls off and there will probably be dirt in them. take the needle and seat out and blow it out. And it is running rich because of the xtra fuel being dumped in it. Clean that out and if it doesnt help than you probably have to much fuel pressure depending on if your running a electric pump or not.

[A. G. Olphart]

Tim got it in one

 

If fuel is only dripping from the secondary boosters, that lessens somewhat the chance that excess fuel pressure is the cause.

 

One plan of attack:

1) Adjust the secondary float level.

2) If that doesn't stop the flow then I'd check the pressure.

3) If the pressure is OK or you don't have a guage, then pull the secondary bowl and check for crud in the needle valve.

 

With the bowl off one may check for needle valve sealing by blowing on the inlet gas line while holding the bowl and float assembly upside down...

NOT OSHA recommended as gasoline is a known carcinogen.

 

On an old carb one sometimes finds soggy plastic floats (which no longer float) and brass floats with leaks (same result). I've no idea what one finds on new carbs.

 

Good luck (if you get mad at your Demon, you could pass it on to me ).

 

Darn I'm slow- Two posts came in while I was writing!

[Guest Z-rific]

I'm not familiar with Demons, but if they operate the same as Holleys, then I can add some help.

 

First, get a small fuel pressure regulator and put it inline right before the carb. Then there will never be a question of how much pressure you have. And if in the future, your engine has problems firing or staying running, you can diagnose whether you're getting proper fuel.

 

Anything under 9 psi and you're probably fine.

 

If it's like a Holley, then you may need to come down on your jet sizes. 725 cfm is a lot. They are cheap and easy to swap out. Drop down a size, and drive it for a while. Then maybe another size later.

 

Adjust your float level. Again, it's easy to do.

 

Now, get a vacuum gauge from a local parts store. Plug it into the appropriate vacuum port (not sure on a Demon) and check your vacuum. Turn your idle screws in, which hopefully will increase vacuum a bit. This is leaning your mixture. I always get max vacuum about 1/2 turn before the engine wants to kill.

 

Clean your plugs before any work and chekc them afterward. Hopefully they will look like they are burning properly.

 

Follow the other posts advice on your drip.

 

Are they vacuum or mechanical secondaries? If vacuum, you may need to play with the secondary diaphragm springs to get the secondaries to open at the right time.

 

Step on the gas pedal (engine not running) and have a friend check to make sure the throttle is opening all the way. Too many times with hot rodders, the throttle doesnt max open, which hurts both primary and secondary operation.