Help! Idle speed screw not working :(

[Chained_360]

I'm currently trying to un-f$#k the brand new Classic Holley 600 CFM 4 barrel on my Chrysler 360 V8.

So, first of all, I'm a complete newbie when it comes to tuning carbs. I know some basic ideas like idle mixture screws and idle speed screws, but I'm still not very good.

My current issue is that my AFR is really rich, so rich that I can clearly seek the smoke coming out of the tailpipes (with spastic, random backfires). My first concern is that the engine is idling a little high (in neutral), so I want to lower the idle speed. However, when I adjust the idle speed screw, nothing seems to happen.

 

[goldduster318]

well, first, look to see if the idle speed screw on the throttle linkage is actually touching anything. If it's on the fast idle cam, kick that off first. If it's not connected, you either have a vacuum leak or the secondary curb idle screw is holding the secondary blades too far open (it's on the passenger side of the carb):

Since it's too rich you should be turning the idle screws IN (there are on the side of the metering block).

I would also look for fuel dribbling out the boosters at idle. If that is occurring you'll need to lower the floats.

 

[Chained_360]

Thanks man, I'll try that out and see if it helps

 

[nm9stheham]

Yes, we just went through the same thing with a used carb. The secondary idle stop screw was CLOSED too far to the point that that secondary throttle plates were touching the sides of the bores. In that case, the carb is not allowing in enough air and the primary throttle was open too far to compensate. But when this happens, then the primaries are open too far, and the primary transition slots are exposed and that makes the carb too rich. The primary idle mixture screws become unable to compensate.

And if the secondary idle stop screw is too far OPEN, then you cannot bring the idle down properly.

1) Look at the secondary throttle plate position; they should be opened just a bit and exposing the bottom edge of the small vertical slots up in the sides of the throttle body. Adjust the small screw shown above to just expose the bottom of these slots.
2) Reinstall and readjust idle mixture with a vacuum gauge connected to the manifold vacuum for peak reading.
3) Adjust curb idle speed.

The choke has to be off and engine warmed up before the curb idle screw can be adjusted.

You may have to do a couple of iterations of adjusting on the secondary idles stop screw.

The backfires may be due to not being warmed up or timing may be off. Have you set the ignition timing to the 10-15 degree range when at lowest idle. That will get you in the ballpark to get started.

BTW, what engine, cam, etc.?

 

[70aarcuda]

and the age old question....

how much initial timing are you running?

 

[Chained_360]

I'll mess with the timing, but last time I looked I couldn't find the timing mark. Maybe I'll pull my head out of my *** this time

 

[AJ/FormS]

There is nothing comforting about having your head in that warm dark place, except perhaps, better there, than having it in someone elses dark,wa.........

Timing and T-port sync, and secondary cracking screw; but above all, a correct, stable, fuel level, and choke off.

 

[crackedback]

and the age old question....

how much initial timing are you running?

I'll mess with the timing, but last time I looked I couldn't find the timing mark. Maybe I'll pull my head out of my *** this time

LOL at the reply... If you don't know where the engine is timed, you can't do anything else constructive regarding the tune up.

Timing first. Stockish camshaft? Set it in the 10-15 range at idle and see if that helps.

 

[Chained_360]

So here's evidence of how bad I am with carburetors...

I just found the installation & tuning manual...

I get ahead of myself waaaaay too often.

 

[threewood]

Hey Chained, still having issues? Unhook the throttle cable to tune and see if that helps. Could be holding it back off the idle adjustment screw.

 

[pishta]

Don at FBO used top give out free Holley/Demon carb advice. read lots of his posts. he had 2 gripes: Always get your floats set correctly FIRST. your fuel level determines the 'pressure' the idle feeds are getting in addition to the vacuum that is pulling idle curcuit fuel. second was adjust the stops so that the idle slots are perfect squares, ie; they are exposed just as much as they are wide. Adjust accordingly and then start doin gthe rest of the adjustments. 90% of new carbs run fine out of the box. If you have a pipe cleaner, make sure your air bleeds are not plugged, all 4 on top should be clear.