Thread: Idle circuit, Timing Related??

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Cayne, thanks for the diagnosis of my ears. I think they work well enough. In conjunction with my "time by ear" process, I also use a vacuum gauge. Perhaps if my engine were fresh, and operating at peak performance, your methods would be ideal. For now, I am just trying to make this tired old beast run as good as it possibly can. (which is still pretty good )

Thanks Denny, I'll give that a try. I appreciate the advice.

Originally Posted by DennyW

In that case, warm up the engine to operating temp. Get the highest and steadiest read on the vacuum gauge you can by adjusting the idle mixture. Then, turn the distributor (with any vacuum advance dis-connected) until you reach the highest reading, and back down 2" of vacuum. This is about the best spot for the overall breathing of the engine.

I don't mind being wrong but you need to tell me what is wrong.

So basicly you are doing the same thing with a vaccum guage as I do with a tach. 2" on the lean side for you or 20 rpm to the lean per side for me. If its because I don't set each screw the same, its because each needle and seat are different. If you use a tach you will see it. This was how I was taught at automotive school. We didn't use a vaccum guage but I can understand how it works. What I'm after is the proper adjustment of the throttle plates and the idle mixture screw. After that any adjustment of the timing that effects the engines rpm can be compensated for by a small adjustment to the throttle plates. No need to adjust the idle mixture screws.

If you start overly rich, you will see the rpm's increase as it leans out. If you go from lean to rich this will not happen. You will going overly rich then have to come back. I stand by the what said about the needles not being the same also. No needle and seat are the same. We are talking small differences here. The full turn was just an example.
I believe you're mistaken about the idle circuit. It draws fuel all the time. That is why it is important to get it right before you adjust the primary and secondary circuits.
There is always more than one way to do things. If you don't have a vaccum guage, you can use just a tach.

Originally Posted by Mike

I believe you're mistaken about the idle circuit. It draws fuel all the time. That is why it is important to get it right before you adjust the primary and secondary circuits.
There is always more than one way to do things. If you don't have a vaccum guage, you can use just a tach.

Just a little exsperiment for ya ,crank the idle speed up to about1000 -1300 rpm with the screw on the throttle linkage and crank the idle screws all the way in and see what happens
Things were a little different 20 years ago than now ,people used to really have to make do and I was one of those people.I cant count the junk carbs I have used when the previouse owner said they were junk or found them in a pile of junk,bolted them right up and proceeded to drive many miles with it ,to the previouse owners disbelief,sure the idle passages were blocked ,easy fix ,dont idle,sure the accelerator pump was shot,big bog for a sec when you accelerated it ,you just learned to feather the gas or punch it to the floor,sure the filter hold down was busted ,easy fix ,no filter.sure 1 of the four barrels was clogged ,no biggy ,let the other 3 work harder,now ya got a 3 barrel.!!If they were really messed up you had to use the choke about 3/4 of the way on to help increase vaccume to pull fuel thru the partially clogged ports we wont get into the 3 bolts holdin the tranny on or the block of wood with washers and wood screws holdin the starter on from just the top bolt,had to get the philips screw driver out and tighten that up quite often or carry a hammer to beat on the starter to get them last starts out of it before pay day or drivin cars with no reverse,after all you go forwards most of the time anyway I am just a young greenhorn,I cant imagine some of the stories the other fellas have. Your just talking about playin with the screws on the outside of the carb,not the stuff inside you have to peel plugs out to get to If Denny says them idle circuts aint runnin when the throttle blades are opened up,them circuts aint working then,besides that he was carb mechanic ,I think he just might know whats happening inside that fairly simple device ...... Best bet for learning is when you think someones mistaken ,do some research on the internet and find out whats really goin on.I would venture to say there is atleast 10,000 articles on carb tunning on the internet ,just google a few thousand up and start reading ,it will all be clear then. This is a perfect chance for learning .

Lets just say for argument's sake, one was working on a Rodchester Quadrajet (please don't tell me they are a quadrajunk, either you like them or you don't. I happen to like them.) Anyway, on the idle mixture screws, which way is rich/lean, in/out?

Out is rich.