Hey all,
Hoping someone can point me in the right direction to resolve an inconsistent idle. The car is definitely driveable but not as well mannered as I’d like it to be for my 21-year old daughter who drives it.

Here’s the deal: it starts easily and runs normal when cold, but once warm it tends to idle rough. Sounds like a faint miss and often wants to die at a stop sign. Sometimes it idles normal but more often acts as I’m describing. When I drive at road speed the performance is good, but when I slow down and stop it’s even harder to keep it from dying. After engine is switched off, re-start is almost instant if I try within several minutes after the car was turned off. But if I wait 5-10 minutes it will usually take a lot of pumping to start. In either case it doesn’t run so well at idle when hot.

The car is a ’68 Dart with a ’73 225 engine, A904 trans. Has a weber DGEV, it's a brand new carb as of several months ago. I don’t believe there are any vacuum leaks, at least a friend and I resolved all those a while back when we tuned the car on his engine analyzer. At that time we adjusted jets for optimal efficiency. The idle problem has become progressively more pronounced though I have not touched the carb or choke. Car has HEI electronic ignition, good plugs set at .045 gap. Excellent compression on all cylinders. Fairly new cap, rotor, and wires, hot coil, I am using the original (?) distributor - that’s about all I have not changed on the ignition system. PCV and breather are clear and working. Engine runs pretty well other than the poor idle when warm.

I am trying to figure out whether this is most likely a carb issue (that’s my first guess), or ignition, or??? Being a mechanic isn’t my day-job so any ideas on solving the puzzle are much appreciated! Thanks,
Bill

What's the line voltage (measured across the battery) with the engine hot and idling and the transmission in Drive?

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Have you adjusted the valves?

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

plus one on checking valves, although a 73 should have hardened seats, my 70 dart did exactly that. turned out i had burned through most of the seats on my car, hopefully yours just need an adjustment.

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-Christopher

"Gray Ghost"-1970 Dart.
"Frederick II"-1994 Geo Metro.

+2 on re-checking the valve lash... run them loose for the best idle quality and vacuum signal.
DD

I'm running a DGEV on my stock slant and finally got it running right. All of the previous suggestions should be looked at first. I had the same symptoms that you described and traced most of it to a too-small idle jet for the primary. The carb that I had was originally used on 2.2 and was tuned accordingly (out of the box). I couldn't get the warm idle from stumbling no matter what I did with the idle-mixture screw and timing. I found a good troubleshooting guide at http://www.webercarbsdirect.com/WeberCa ... _s/274.htm. The description on unstable idle is covered and pointed me in the right direction.
They sell different jets but I ended up progressively drilling the exsisting jet until I ended up with good results. The good thing is the jet is accessible from outside the carb. This solved the idle quality problem for me. Also, I found that it idles better when the distributor is hooked up to the timed port on the carb, not the manifold. Hope this is helpful.
-Rich

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1985 Dodge B250 Van

I would certainly hope so... you never hook the distributor vacuum advance hose to anything but ported or "timed" vacuum on the carb...

~THOR~

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1984 D100 Shorty Custom
Certified Auto Appraiser - RevItUp Classic Appraisals
President - Cherry City Bombers CC
Part of Tyrde-Browne Racing

Thanks for the suggestions! In reply,

1. Voltage across battery is 14.3
2. Valve lash is set - (sorry I forgot to mention it in my first post). I followed /6D's tutorial on this site and a friend double-checked it later. That was a couple of thousand miles ago so it could have changed but I doubt it.
3. I will experiment with bigger primary idle jet. Just wondering, did that change affect gas mileage or performance in any noticeable way - or just fix the rough idle when warm problem?
4. Vacum to dist is off the base of the carb.

Great tips guys - keep them coming!

At hot (slow) idle, in Drive? What kind of alternator are you running?

Probably a good idea to check operating voltage at the HEI module, too.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Hey Dan,
14.3 across battery at warm idle in drive, 13.9 at the HEI module. Is that about right?

It's excellent, but it's uncommonly high. What kind of alternator and regulator are you running, and what is your idle speed?

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Bill, answer to #3 is that it fixed the idle quality. It can now idle at 650-700 rpm without a hickup. Smooth idle in gear and settles down nicely when coming to a stop. I originally thought a valve job was in order (97000 work-truck miles) but that was not the issue. I don't believe that it effected fuel consumption in any measurable way. I haven't done a mileage observation yet but I plan on tanking it up in the next few days and get a figure. I suspect it will be in the 13-15 mpg range with the way I use it.

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1985 Dodge B250 Van

Hey Dan,
Alternator is stock, over the counter NAPA. Regulator is Echlin as recommended in your HEI article. My HEI set-up is a little different - as posted by gold duster 318 - but seems OK. I've run the same diagram on my '69 cuda for 7 years. Don't have a tach but idle speed was pretty low as I took those readings. My voltmeter is cheap so may not be precise. As you recall, I've had problems with voltage spikes on this car, so I'm all ears!
/'box,
Thanks for reply on fuel - that is encouraging and I will let you know what happens.

Take a picture!

What happens if you are running the engine and you disconnect the vacuum advance hose from the distributor?

There should be NO change in idle what-so-ever.

~THOR~

_________________
1984 D100 Shorty Custom
Certified Auto Appraiser - RevItUp Classic Appraisals
President - Cherry City Bombers CC
Part of Tyrde-Browne Racing

That's a good check, Thor. My carb is older and has only one vac hook-up that is ported. It was indicated in his post that his is carb is new and he may have different vac connections available. Bill, if there's more than one, make sure you're using the proper vac source. Direct manifold vacuum could cause idle issues and unstable timing. With the throttle closed you should have no vacuum to the dist. Also, you may have the idle adjustment set too high in order to keep it running in the current state of tune. In this case you will be uncovering the port inside the bore enough to send a vac signal to the dist. potentially compounding other issues.

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1985 Dodge B250 Van