Strange idling behavior?

[Si|v3r72]

I've noticed some wierd idling behavior lately in my 240. If I start the car, let it get fully warmed up, let out the choke, and let the car idle, it idles right where it sohuld - 700-750 rpm. Bit after I drive the car, then idle, it idles at 1100 or so - it won't go any lower than 1000.

Can someone explain why this is happening? Is it a problem? Should I adjust my idle speed based on idling after driving? The carbs could probably use a tune, but even as is, the car runs VERY well. One other thing that has concerned me since I bought the car was gas consumption - I average 15mpg.

Thoughts and help are always appreciated.

[2ManyZs]

It's possible that your linkage may be the problem. Check to make sure it is returning to the stops. Might be the springs are stretched a little bit too.

You might want to invest in the ZTherapy video for tuning your carbs, much simpler than trying to read it in a book.

Another slight possibility is that your timing might be set a degree or two too far advanced. If you have not checked it you might want to see what it is, and check your vacuum advance at the same time.

[Dan]

2ManyZs made a good point about the springs, if they're stretched out your throttle shafts won't return to where they're supposed to be and so you'll get a little more rpm. Also check the idle speed screw at the top of your linkage. It's really only used to flow test your carbs at high rpm, something like 4000 rpm or whatever your normal driving conditions are. Back it of if it's tight. Yes visit the ZTherepy site and get a video called Just SU Carbs it will make you an SU expert in about two hours. After you get that video gat yourself a unisyl flow meter and make sure that your SU's are flowing exactly the same, if one is flowing more than the other it's hard to get anything right with your engine. A little off the subject but worth mentioning, i replaced the old points in my distributor with a crane electronic ignition that uses an LED sensor to time the spark pulse, and that made my car just purr.

[Si|v3r72]

Ok I've been thinking about getting the ZTherapy SU video for a while now. I would really like ot be able to tune my carbs by myself instead of having to depend on someone else for it. Good call, I'll get it ASAP.

[dhayes5]

I have the Z-Therapy video's and they are pretty good. Another Item that I recently purchased is a colortune (can get them from Eastwood ~$60). This thing temporarily replaces a sparkplug and allows you to see the color of the flame in the combustion chamber. Takes the art out of setting your fuel mixture. You change the mixture until the flame is a bunsen blue. Works great!! Between this device and a Unisyn, carb tuning is very easy. Good Luck

[jcdozier]

I know I may be preaching to the choir here, but IMHO the throttle linkage should undergo an annual cleaning and re-lube. It's not good to just re-lube the moving parts - they should be cleaned off first. As we drive we get all kinds of crap, crud and corruption flying around under the hood, and over time the moving parts of the linkage collect a lot of it. I use a lithium-based high temperature grease, the same "stuff" as used to pack wheel bearings.

With so many moving parts and connectors on the linkage, there are abundant opportunities for friction and even binding. One often overlooked potential source of trouble is the alignment of the plastic "cups" at the ends of the several linkage shafts (the ones the plastic balls pop into - I know here's a "proper" name for them but I forget the nomenclature). They are adjustable, and if they aren't aligned right they can produce extra friction. I had a misaligned one pop apart on me - suddenly having a "floppy" accelerator and no engine control is a sure attention-getter.

[Si|v3r72]

I ordered the SU video from ZTherapy and the syncrotester from MSA. Is there anything else this newb needs to get my carbs right (assuming they're not far out)?

[Dan]

I think that's all your gonna need. You will be really glad that you bought it, i think i have watched it about five times just to make sure i know what he's talking about.

[Marty Rogan]

Silver Z,

I have had the same problem. I have changed vacuum hoses, Z Therapy carbs, checked the timing. Still have the problem. If you figure it out, let me know what the problem was.

Thanks,

Marty