Adjusting SU air fuel mixture, just don't get it

[LeonV]

Sounds like a vacuum leak.

[Bruce Palmer]

Bruce, if it requires 4 to 5 turns down to run the best, where would you focus your attention? I have adjusted the float level multiple times and still am looking at 4 to 5 turns down for both carbs to run the best. Plugs look light brown. Crazy ...

Why so many float level adjustments? Floats should be set to the correct level and left alone and everything else adjusted around them at that setting.

Are these our carbs?

Anyway, let the car idle, shut it off and pull the domes and pistons and look down into the nozzle orifice and see where the static fuel level is with the nozzles set where you have them set. Report back on this.

[Duffman]

Bruce, was thinking that the fuel level in the bowls was too low and have adjusted to fill more, thus raising the level in the nozzle and requiring less turns to gain the correct mixture of fuel and air. That was my intent. Will do as you say and reset floats to the 9/16 mark and report back on level in nozzle. These are borrowed carbs, mine have major vacuum leaks and waiting to send in for rebuild.

[Gary in NJ]

Photo's are always helpful. If you can get a photo looking down at the needle, and advise how many turns you're at, we may get some good info.

[Duffman]

Ok, sorry it took so long, but reset the floats to the 9/16" level, per Ztherapy video, and ran the car for a while at idle, with adjustment at 4 1/2 turns down. Looked into the nozzle to determine the fuel level and had difficulty seeing it. Pictures would not come out clear enough, but it looks like the fuel level is another 1/2" below the top of the nozzle (rough guess) at 4 1/2 turns down. Now, I am thinking 2 areas of concern would be the fuel pressure and the float bowl valves. The fuel pressure is running right around 3 psi, but starts at closer to 4 and can fall off to around 2 psi. Is it normal for the variation? I realize it is a mechanical fuel pump, but would have thought a more level consistency. Also, the float bowl valves could be sticking. They have been cleaned up but the rubber tips are just fair in quality. What else am I missing?

Thanks!!

Edited October 24, 2011 by duffman

[Duffman]

Bump, any other thoughts on this?

[Bruce Palmer]

Yes, sorry....

If at your current float settings you are having trouble seeing the fuel down in the nozzles you need to raise the float levels. Setting them like the video shows will give you a low setting, a level way down the nozzle tube and a lean condition...... Hanging the lid vertically while blowing into the tube will give you your current setting without worrying about over powering the tiny spring inside the needle and seat.

Steve and I are having talks about how all this should shake out. I want him to determine where the fuel level will fall in "2 1/2 turn" nozzles with the float level set spot on at .55" which he certainly can do.

That float level setting is a "given" in the trade and everything should adjust around that. As the only hard and fast number this setting needs to be established correctly.

My assumption is this: If the properly set float level yields a fuel level in the "2 1/2 turn" nozzles somewhere near the top of the nozzle then proper adjustment of the nozzles to get the correct mixture setting should be close at hand. Like, I'd say, a turn one way or the other.

This should establish a good starting point and from there it's needles, damper oil, perhaps dome spring tensions and the big unknown unseen item.... air flow which would include vacuum leaks, which will determine how your carbs will perform.

Again my feeling is this, with a used unknown set of carbs, this float level / nozzle level issue should be the first to be attacked. Get that right and life ought to become much easier.

Will report back after we get this level thing established.

[Duffman]

Thanks, Bruce, will be interested to hear what you come back with!

[Johnny wick]

I guess ill have to double check with the 1/16 above the nozzle method a 2.5 turns. I already adjusted both floats at 9/16 and have the turn both carbs ton4 turns clockwise to get the car running fine. Plugs still look lean to me. Can you explain this 1/16 above the nozzle method at 2.5 turns method better?

[Mark Maras]

 Let me start with a correction. The fuel level is supposed to be 1/16" BELOW the tops of the nozzles. The reference point you're looking for is the smallest hole in the fuel nozzle. The small hole that the jet needle slides into. The optimum setting is to have the fuel level about 1/16" below the tops of the nozzles, with the nozzles at 2 1/2 turns down. The fuel,1/16" below the nozzle tops, will allow the nozzles to be lowered a bit to richen the mixture without the fuel puddling over the nozzle tops. You may need a flashlight to see the reflection of the fuel surface in the nozzles.

[Johnny wick]

So i should start by closing the fuel mixture knob from 4 turns to 2.5 turns clockwise, crank the engine for 1 minute with the choke on as the car is cold and remove the domes and pistons. If i dont see the 1/16" below the nozzle top then the floats are still not set to 9/16 or .55 inches? do i measure this with the digital caliper? At least i know we are getting close.

My mechanic advise me on  not touching the float levels any longer and drive the car at 4 turns clockwise as it was set.  I just dont feel it should be this way.

Please advise me.

 

 

[Mark Maras]

 Ignore your mechanic. He couldn't get it right. When you get the carbs set and the engine is running good, he'll be asking you questions about tuning. Turn the mixture knobs until the nozzles are at the top. Then turn them both 2 1/2 turns down. Start the car, use the choke if you have to BUT be sure the choke is off before checking the fuel level in the nozzles. The choke physically pulls the nozzles down. let the engine run for a minute and pull the domes and pistons. The fuel level should be 1 /16" BELOW the nozzle tops. If it needs adjusting, you could try a thicker (5/8") or thinner (1/2") gauge (depending on which way it needs to go) or just bend the tangs a bit and try it again. Either way it's going to be trial and error until the fuel level is correct.

 A note on choke cables. Be sure the cables are adjusted so the nozzles fully return to the top when the choke is off.