Starting to try to get my engine running like a "shaved ape". Need help from the tuning gurus.

What is the proper order to do stuff in as far as timing, idle mixture, idle stop screw.

Here is where I am at now...will start and idle pretty well- need to rev it for the first min 1-2 to keep it running or it dies.- need to have the idle stop screw turned in to keep her running but not too much. I think I have the choke working pretty good. I did not actually time the engine since the rebuild. Idle mixture screws are at about 2.5 turns out. Car seems to run pretty good, smooth, no aparent problems, but does not have the ummph that I thought it would. Have not run it out past 3500ish rpms yet thought. I have no idea how the carb is set up. (would be willing to get a new one, if that would make life easier) Do have a Lars dist. setup.

Please give me a good order to work on things, as well as the most thoery behind it you can. It really helps to understand why I am doing things. With so many variables, I am not sure where to start. :confused:

 

Lars has some great tuning papers on http://www.corvettefaq.com


you wanna adjust mixture for maximum vacuum......(break out the vacuum guage.....)

id get my timing ballpark 1st (like ~12 initial....) , you say you already have your distributor curve set up with a lars kit....

then adjust mixture accordingly.... get idle speed to where you like it...i like mine rather low ~600 rpm...

and you need to adjust fast idle and choke......

 

Well you need talk to Lars, first off, gotta know what he set your initial at, should have given you a sheet on that...
so maintain the engine at whatever that idle speed is....hook or crook, and set the initial...without vacuum advance connected...may be easier if the vacuum hose is plugged, depending...
this is done depending on the cam, if it's wild, you need set for about 800-1000 rpm idle speed, if milder...600-800 rpm's is fine,,, this might change as you go throug the set up back and forth....
so once the initial advance is set, you gotta 'unrig' things to see what idle speed want to be....better be the same...or you gotta screw or unscrew the driver's side hot idle screw on the carb linkage...moves idle up and down...
this is assuming the choke is wide open and NOT springing closed period....

after that is set, you connect a vacuum gauge, to the manifold vacuum direct, don't matter where, just the manifold direct source, and tune the two brass looking idle mix screws in front for max vac reading 12-15 is ok....
now when doing this you have to be slow and careful...look and observe as you go...turning them in far enough will cause a stumble...back it off about 1.5-2 turns, go tothe other one, same thing...now adjust slow and careful for max vac reading....back anf forth untill no further improvement...
now assuming things are normal....that's about IT....

Now is MY opinion born of observations over the years....it never seems to last for very long in that 'sweet spot' when running a carb....
that is some of the reasons the EPA, and DOT got onto electronic engine management...more precise controll...

GENE

 

Adjust dwell(points) then timing, then idle mixture, then recheck timing since idle speed can have an effect on initial timing. All of these things need to be shuffled around since changing the timing and the mixture effects the idle speed and so forth. set ,check, recheck, and so on

 

Dolla -
I think you got the right answers above, but here's the correct sequence summary:

1. Get the distributor set up. Hook up a dwell meter, start the engine, and get the dwell set to 30-31 degrees. You set the dwell first, because every degree change in dwell changes the timing one degree. Once dwell is set, it's set - nothing will change or affect the dwell once it's done. With the dwell set, disconnect the vacuum advance on the distributor and set yout TOTAL timing to 36 degrees using an adjustable timing light as outlined in my distributor instructions (rev the engine until timing does not advance any farther and nail the timing down at this point at 36). Once total timing is set, you don't need to re-check timing - it's done and set and will not be altered by carb adjustments. Hook the vacuum advance up (I prefer the ported vacuum port on the carb - driver's side front of the carb).

Now set up your idle speed and adjust idle mixture. Good starting point is for both screws to be 2 turns out from fully seated. Turn both equal amounts to achieve best idle vacuum or best idle quality. Then re-set final idle speed.

The car should not die when you first start it up. If it does, it's indicative of your choke pulloff pulling the choke too far open and/or your fast idle speed screw being incorrectly set. The fast idle screw is located on the passenger side of the carb and is independent of your idle speed screw. When the engine first starts up cold, the choke pulloff should crack the choke open 1/4" as measured from the forward lower edge of the choke plate to the airhorn wall. If it's opening your choke more than this, you need to bend the choke pulloff linkage to get it to 1/4". With the pulloff correctly set and the fast idle screw cranked in to the proper fast idle rpm (about 1200) the car should start and run perfectly without the need to "keep it running."

Contact me if you need any help.


[Modified by lars, 10:04 PM 7/25/2002]

 

thanks guys! I should be able to try some adjustments this weekend and then Im sure Ill be back with more questions! :cheers: