The Dodge Challenger Message Board

Hello,

Trying to set the idle mixtue on my 440 (mild - 268 comp cams, 452 heads - stock, Edelbrock 750-1407, 1.6 Harland Roller Rockers, about 10:1 compression, 2300 stall converter, 727, TTI headers,1967 intake-nothing fancy-dual plane). Hooked up a vacuum gauge to the manifold. Timed the car at 34 - 35 at 3,000, and about 14 - 15 at idle. I can get the car to idle in park at about 850 - 900. Idle set screw is very twitchy. Car will almost stall, and with a quarter turn jumps to 1,300. I can get it back at 900 with a little work, and seems to idle pretty smooth.

In trying to read the vacuum at idle, it seems to be around 8-10, but bouncing to much to determine what adjustments to the idle mixture screws really does. At 1,700 or so, vacuum increases, and gauge reads fine. Dropping back down to idle and I can't get a solid reading to make adjustments.

I have the vacuum advance on the distributor attached to the timed port on the carb, just wanted to make sure this is right. The Edelbrock manual said to go the full vacuum port for non-emissions. I know you all are right on this, but just wanted to be certain.

Looked for any vacuum leaks on the intake, and retorqued all bolts to spec, including the carb. Carb is new.

Is there a "basic" setting on these carbs in terms of idle mixture? I read somewhere to bottom out, and open 1.5 turns, is this a good starting point?

Car bogs off idle up to about 1,600 rpm, then runs strong. No black smoke or anything, just not great response. Engine should be better off the line with the set up I have, I would think. I am not mashing the throttle as there are only about 50 miles on the new rebuild. Just doesn't feel as responsive.

Car seems to run hot too, idling for more than 10 to 15 minutes and it gets pretty hot, probably would overhead. May be adding an electric fan in the near future. Maybe the rebuild is still too new, and it will loosen up and cool a little better? Also, will header wraps make any impact on the under-hood temps?

Thanks as always for any help!

- Rich

One other thought...the fuel line from the pump to the filter to the carb seems to get pretty hot, could this impact things as well?

Thanks,

- Rich

The 1st thing I would address is the timing. You're probably going to need around 20 degrees or more initial. Thats what I have on my 440. Get it up to operating temp then add some initial by slightly twisting the dizzy until its difficult to start or kicks back on the starter, then back it down slightly till this goes away. This will be your initial timing. This will clean up the idle and make carb tuning easier. Dave or someone with more Carter carb knowledge can get you along further. I'm a Holley dude Great to see you're back on the road Rich, I know you have had your trials and tribulations with it. (Setting a higher initial timing WILL increase the total timing a like amount so you might have to take some mechanical timing out of it, I sent my MP Dizzy to Don@ www.4secondsflat.com for a re-curve now the car has a different personality,,I like it! I use his whole system) BTW, have you pulled a few sparkplugs plug to see what they look like?

2 plugs - #7 and 8.

I am no expert, but pretty black, too rich?

I adjusted the idle mixture screws in (leaning) to bottom out and then back out 1.5 turns (still not sure this is a good starting point). I must have made 3 - 4 full turns, so that may explain the richness and the darker plugs.

Thanks for the reply Eddie, I am going to advance the timing. Can I add stiffer springs to avoid too much advance at higher rpms? My distributor is just an MP bolt in electronic conversion kit. Can I limit the vacuum advance somehow?

Thanks for any comments on the plugs.

- rich

Thanks for the timing advice Eddie. It was more like 10 degrees at idle. I kept advancing the timing up to 20 degrees, then backing off the idle (by advancing it jumped to 1,500).

Finally, after about 4 adjustments (probably turned the idle screw down 1.5 to 2 turns), it was idling at 900, and reading about 16 lbs of vacuum, very solid.

If the timing is too retarded, will that cause the engine to run hotter?

Thanks again, love this site!

- rich

Yes. Too little advance makes the engine hotter.

Advance the distributor until the rpm increase levels off. That is the engine telling you how much advance it wants. Don't go above 25 degrees though.

But having done that you have a problem. Your distributor will now advance far too high over 3000rpm and you will damage the engine with detonation.

You can only run high initial timing if you restrict the total timing.

The only way to do that used to be to weld or epoxy the slots in the advance weights to limit their movement.
However I think companies like FBO make a plate or gizmo to do this.

You must read my instructions on how to set your timing VERY carefully.

In the end you probably will not need the vacuum advance at all.

BUT
There is another method to get more initial without all this. that is to use manifold vacuum for the vac advance. This gives you lots of advance without having too much over 3000rpm.

It is easy to do it this way but not as good for performance.

Just took for a short drive, wow, no more bog off idle, much better response. I only took it up to around 2,800 or so, no pinging or any drop in power suggesting too much advance. It did run cooler too.

Dave, I will take a look at the total timing (no second person to help me throttle it up today) and work one of the fixes you suggested. What is the max "safe" timing at 3,000?

A am thinking of installing an air/fuel mixute. Can someone send photos of where to locate the sensors?

Thanks again for the responses.

- Rich

oops, that should read air / fuel mixture gauge, not mixute

The sensor should be within a few inches of the manifold (or header collector)

You engine will need about 34-36 degrees total all in by 3000rpm.