Question: Carb.... IdleAir Bleed and all that....

[VetteV8]

So, I have now my professionally painted car at home, and have made some trips with it; I am very pleased with it, and now wanted to do some verifications on the basics, but on the carb. till now nothing as I did not have a Dwellmeter.
I now acquired a dwell meter, so I am able to do some checking on the settings.

I have no complains about the running of the engine, although the fuel consumption, highway only, cruising is 14 MPG.
I set the base timing to 12 * [was 8* ]with the 4 lead plug disconnected. Reconnected this plug and connected the dwell meter, when the engine had been idling an radiator became hot.
it showed 21* on the 6 cyl.scale.

Then took it on a short drive, about 5 ml. and left it in Drive [which I had not done earlier ] and set the parkbrake; surprisingly, this easily held the car, while in Drive.
The RPM were spot on @ 500.
The dwellmeter however went out of scale completely !!
The cover of the Air Bleed Valve was already removed; turning the screw had no effect.

Let it rest for a short while, and went back to read the manual once more; yes I had done everything correctly....
So started the engine, and this time the dwell showed 21* again and was stable there; Drive and parkbrake engaged.
Adjusted the air bleed valve, but no change in the settings away from the 21*...........

So turned the ignition OFF, and back ON and saw that the dwell meter was at the end of the scale.

I then measured the voltage on the dwell wire, and saw 12 volt, with a system voltage of 12,5 Volt Ignition ON, Engine OFF.

What does all of this tell you, Mr. Experts??
I understand that one can expect the dwell angle to vary slightly, while running;
Also that adjusting the air bleed screw should see some change in the dwell setting, but I don't see that..

What is my next step? remove the carb and see if the idle mixture screws are accessible?
Or what?

Your input is most appreciated.
Cor

 

[VetteV8]

What happened? Nothing much.... all our knowledgeable forum members on vacation perhaps, or am I too impatient?
Would be nice weather to do some testing and wrenching today, as it is pooring rain.
Hence I want to do something useful, and work on the car.
So any comments are welcome!

Thanks,
Cor

 

[hotmtrsports]

My 1st thought is if you "have no complains about the running of the engine", why are you messing around with it?

Chuck M

 

[VetteV8]

Your thought falls in the same category as: "It it ain't broken, don't fix it!"
and I do not agree with that philosophy, many things can be better than they currently are, and I want to understand the system, so I am familiar with it, when something does go wrong.
And I do not call that "messing around with it", just trying to find the optimum.

Hoping to get constructive responses.
Thanks,
Cor

 

[Peer81]

Just don't ask such difficult questions during vacation time I think!

The first thing I would check, you can do this with the engine in park, but the outcome is slightly different then when in drive. Fully warm and check the dwell on the 6 scale. Look if the needle is tracing slightly (not steady but "idle" within 1 degrees + and - the number you get. If that is the case that give the engine some quick rev's. You should see the dwell meter change, same thing when you put your hand on the choke valve you should see the dwell meter go to the rich side (If i remember correctly above the 30 degrees.).

The problem with the idle system is that the system on it own (with stock carb) will always be on the lean side. The idle mixture holes are to small and the idle tube openings are to small. But you can always try to get it right without taking the carb apart and drill you're way in. Some other topics on this subject show that when turning the idle mixture screws out will still let the engine run lean except when the screws fall out then it's full rich

To give an example of mine. My idle mixture screws needed to be 5 to 6 turn's out with altered pre emissions idle mixture screw openings to get around 30 degrees. Now I also opened up the idle tubes just a little and with the original 3 1/3 turns it's " about right". Problem with mine is that I have my wideband o2 sensor running next to it and it says the engine is running lean when my dwell meter points to rich.... But it's a hobby

I hope this helps a little.

Greetings Peter