Fast Idle

[Large Arbor]

I have the twin 600 Holley set up and was looking for some guidance on decreasing the idle rpms. Can someone point in pictoral detail of which screws I used to decrease idle speed?

I think I know, but want confirmation.

Phil

[Bernica]

Have you checked for vacuum leaks first?

[DanEC]

Phil - I don't have the best picture but if you look at this picture of mine you can see a bit of red there behind the vacuum secondary linkage. That is the fast idle cam and the screw is down at the very bottom of it and sits on the steps on the fast idle cam except when the choke comes completely off. The bad news is I don't know of any way to really get to the screw to adjust the fast idle without removing the carb or at least raising it up a couple inches to get a small screwdriver on it. The head of the screw is at the bottom with the screw facing up. I need to lower mine a little too and because of the difficulty in getting to it I haven't done it yet.

[DanEC]

By the way I'm assuming you meant fast idle since that was the title of the thread.

If you meant the curb idle speed, it's on the other side. If you look closely you can see the screw just above the 4-wire ignition wire retainer.

[Large Arbor]

Ok, I will give it a look. I may have to wait like Dan.

Phil

[Large Arbor]

I tried turning the idle speed down some, but it eventually just stalls.
I posted on the FE section as well.

Dan - in the one picture it looks like you are saying adjusting the mixture screw. Is that what you are saying with getting to the little screw?

Phil

[Bernica]

If you haven''t already, check last few posts on this thread. Same problem.
I have learned over the years that if I can't get noticeable changes by adjusting the four corners of the carb at idle, I have other problems.
Just my 2 cents...

Setting Timing

[DanEC]

Hi Phil - not sure what phase you are in. The first thing to do is set the idle mixture screws which are the screws on the side of the fuel bowl in the side of the metering plate. Since the carbs are mounted backwards, the metering plates are on the rear side of the carbs. A starting point is to usually lightly bottom all four of them (both carbs) and then turn each one out 1-1/2 turns.

Then back out the idle speed screws which are on the passenger side down just above the carb base plate. Back them out until you can see that they are just losing contact with the cam they bear on. Then screw them back in say 1 full turn - not sure where you will be with there but hopefully it will idle.

Depending on how you intend to adjust your idle mixture, hook up a vacuum gage or a dwell/tach unit if adjusting it based on rpm. Either one will work but I kind of like a tach.

Start the engine and if it's idling too high or low, adjust both idle speed screws equally until it's idling at an appropriate speed to proceed with. On the front carb turn one side's mixture screw in and out while watching the tach and adjust it for the highest rpm. Then go to the other side of the same carb and do the same. Then go back to the first mixture screw and play with it a little to make sure it's still set for the highest rpm. Basically you are just tweaking the mixture screws to achieve the highest rpm which is the most efficient setting.

Once done with the front carb, go to the back carb and repeat this, adjusting for the highest rpm. If the idle speed creeps up too high (say over 1000 rpm), turn both idle speed screws back an equal amount (CCW) slightly to lower it back down. Back down both screws the same amount so that both carbs are equally contributing to idle. Once you have the rear carb mixture screws adjusted for the highest rpm you can call it good or go back to the front carb and fine tune it a little further. It's sort of a back and forth process to optimize the mixture settings.

Once that is done it's just a matter of adjusting both idle speed screws equally to the idle speed you want. But always make equal adjustments to the idle speed screws on the two carbs.

This is basically the way ERAChas recommended setting up dual quads.

Good luck. Let us know how it goes.

[Large Arbor]

Thanks Dan, will give it a shot.

Phil

[Bernica]

DanEC is good! I forgot it's a dual-quad, but setting the primary "blades" or "butterflys" as some call it is a good one and right on and a great starting point...