Intake / Carb Questions

[strat1960s]

Ok, here goes. This morning, I went out and fired the car up. I had the motor running about 3 to 5 minutes and shut it off to adjust the idle speed screw to see if I could get the motor to idle on it's own. After adjusting the screw it would run very rough and would not idle up. I adjusted the idle screw all the way back, thinking it was something I could adjust another time. I went to start the motor up and again, it ran rough and would not idle up for me.
Here are my thoughts on this:
1. I have an electric choke on my carb, but have not hooked it up yet. I checked my Weber manual but it does not tell me how to hook it up. The whole time I have been running the motor and trying to start the motor has been with the choke closed.

2. I opened the butterflies and looked down into the intake. After all the smoke cleared, I saw that the entire bottom of the intake (the part with the little waves in it) full of fuel. Is this acceptable? Is this normal? Does this mean that I am running too rich or too lean?

The unfortunate thing about my being a mechanic in the Air Force is that I have only dealt with fuel injected diesels. I know for the most part gas and diesel motors are the same up to the fuel systems. I really don't know a lot about adjusting carbs.
Any suggestions?
I figured I would wait a couple of hours for the fuel to evaporate before going out and trying to fire it up again.
Thanks
Ted

 

[strat1960s]

Well Ya'll, I have the choke thing figured out. I have it hooked up to a power source and it worked. However, I have now picked up a nice little back-fire in the carb.

Any thoughts on this one?

 

[Anonymous]

You might want to check your float level and timing. Sounds like the float is too high and dumping into your manifold and the timing might be advanced a little too much or other related timing issue.
Also, wait till your engine warms up a bit before setting idle or at least until the flap is fully open on your choke.

Gary

 

[rbohm]

8) also when setting the idle mixture, generally the screw should be no more than 1 1/2 turns off the seat when starting the procedure. with the engine warm, turn the mixture screw one way untill the engine starts running rough, then go the other way untill you ge tthe same result, then back again. you should find the range narrowing each time you do this. you want to set the mixture to where you have the highest vacuum reading you can get with a smooth idle.

 

[strat1960s]

RB,

I have had the idle mixture screws set at 1 1/2 turns out. I haven't been able to keep the motor running unless I have the gas pedal pressed about 3/4s to the floor. See, my main problem is getting the car to idle. If I let the gas pedal off more that, it dies.
I think if I could get the idle taken care of, I would be able to better time and tune the motor.

Ted

 

[rbohm]

8) ok look for vacuum leaks, large ones like a missing plug or vacuum line. also what fuel pressure are you running? webers dont like more than 4 psi.

 

[strat1960s]

RB, I do not have a fuel pressure guage, so the pressure is whatever the stock fuel pump produces. I am thinking my float needs an adjustment. As far as vacuum leaks, i do not think that is the problem. I am leaning towards too much fuel (float needs to be adjusted).

Thanks
Ted

 

[66200i6]

What carb are you running?

 

[strat1960s]

66200i6,

I am running the Weber 38 DGAS.

 

[66200i6]

From your description it sounds like you are trying to idle off of the main circuit. Running the Weber 38 there should be more than enough venturi area to idle with the throttle plates in the proper position to activate the idle circuit. I would guess that if you used the choke to richen the mixture you could get the idle down. If that works you know that those idle jets need to be increased in size.

Like rbohm said the idle mixture screws should run at about 1.5 to 1.75 turns out. If you are trying to adjust beyond that point, it’s another indication that the idle jets need to be increased.

I thought for sure there were other Inliners out there that are running the 38. I’ll bet that they could give a clue to the final setting for the idle, main and air mixture jet sizes to use.

Hope that helps a little. Good luck, Ric.

 

[strat1960s]

RB / 20066I6,

You two were right on the money for suggesting the fuel pressure. I spoke to a Weber distributor yesterday and they told me the Weber 38 DGAS works best with only 2 to 3 PSI fuel pressure. I picked up a pressure regulator and a fuel pressure guage last night. I will try to install it this afternoon.
As soon as everything is put together and I get a chance to run the motor, I will let everyone know how the motor runs.
Thanks again guys, you've been a great help.
Ted

 

[strat1960s]

LOL,

Well, I added the fuel regulator and pressure guage to the fuels systema nd there was no change. I was told that the carb runs off engine vacuum and not off the fuel pressure generated by the mechanical fuel pump. After talking to a guy that builds race motors, he said that the "beefier" cam-shaft may be creating a larger than wanted vacuum inside the motor causing more fuel to flow through the carb. I guess my carb is getting mixed signals, LOL. Anyhow, I am going to call the machine shop that rebuilt my motorand get the specs, something I should have done right from the start. So, as of now, there is no real change in how my motor is running. Maybe this weekend, I will make some progress.
I'll keep you all posted, and thank you for all of your help.
Ted

 

[66200i6]

Actually that sounds backward. Increasing the lift usually causes a decrease in total manifold vacuum at idle. That is why a builder needs to increase the compression if the timing of the valves gets wider. The longer the exhaust and intake valves remain open together the more of that pressure in the cylinder you are going to lose.

The velocity at the venturi and the atmospheric pressure is what causes the fuel emulsion to be forced out of the idle circuit. The carb doesn’t know any difference if there are changes in engine setup. All it’s interested in is that velocity through the venturi.

If this engine has been changed to increase the volume of air it’s pumping through the original carb or you are using a different carb that was setup to meter that idle mixture with a lower volume, that carb needs to be adjusted accordingly. From your description you have both situations occurring here.

Try that tick that was mentioned earlier. Use the choke plates and anchor it in place to raise the vacuum level above the throttle plates. With this configuration see if you can get the idle screws into 1.5 to 2.0 turns out. If that works then you know you need to pull those idle jets and increase the inside diameter of the jet. By going back and forth you can decrease the use of the choke plate the more you increase the idle jet size (inside diameter).

It will take some time but you should be able to get that thing to idle.

Good luck, Ric.

 

[strat1960s]

Well, folks, this is what happens when you ask two different sources the same question, you wind of with different answers.
One source thinks it may be vacuum leaks and the other thinks that it needs a new power valve to compensate for the new cam-shaft. I have a guy stopping by this weekend to look into the carb theory. He's bringing a selection of jets and power valves. We'll see if we can't get this thing running. I'll keep you posted on what I find out.

Ted