Dies at idle

[Petros]

I have been having a problem that was intermittent, and today it just got to the point where every time I allow the rpm to drop below about 1000 rpm it would die (really annoying, but still drivable). Drives completely normal above 1000 rpm, lots of power and no missing.

In the past sometimes when the engine returned to idle, like when coming to a stop, the idle would either dip down to 400 rpm, or just die. This occurs only when it was warm, and over last six months, only occasionally, now all of a sudden this morning it does it all of the time.

About 3 weeks ago I had the carb off and cleaned it out, replaced the accelerator pump and the secondary throttle diaphramgn. It drives good otherwise, I checked the float level (good), and all vac lines (no issues found). I turned the idle speed up so it now idles about 1000 rpm, and seems to stay running so far. Any setting below this it will surge up and down, often stalling when it gets below 400 rpm.

Any ideas what would cause this?

[Lil Beast]

Something is wrong with your carb! I had that happening for a while, until I decided to throw in the weber! I've rebuilded mine as well, run great, good mileage and everything but would die under 1200 rpm or so! Sound similar! I suspect a bad float, worn out and does not keep adjustment! Every time I would adjust mine it ran fine for 2 mins and died! I had to reopen the carb adjust the float and again 2 mins and dies! Like the little flap you got to bend is too soft! But I'm not 100 percent sure on that one! And I've rebuilded many carbs, included the weber I'm running now with no problems at all!

[smokerx]

In the past sometimes when the engine returned to idle, like when coming to a stop, the idle would either dip down to 400 rpm, or just die. This occurs only when it was warm,

This part sounds like the dash pot screw (or whatever) on the carb. adjacent to the throttle not being screwed in enough from what I know of it. The difference when it's warm is the different idle. I also had that problem, and I think it was a crack on the base of the TVSV (or whatever) creating a vacuum leak there. I'd spray carb. cleaner at it to check for vacuum leaks, then try a turn on the dash pot screw. Finally I'd check the gas pump and see if it's sucking air somewhere like a rusty tank line. Then I'd make sure my warm idle wasn't tuned jankity reflecting any of these issues.

[Petros]

Actually I think the dash pot screw fixed the problem. As an afterthought, before I even read the last post, I turned it in a turn and a half, and than backed off the idle speed (it was really annoying at 1500 rpm), and I has not stalled out since. I am letting it idle at just under 1000 rpm, still a bit high but not as annoying as 1500.

I do not care for having the engine linger at higher rpms too long after I release the throttle so I backed the dash pot off so it just barely made contact with the throttle plate crank. It was working fine for a long time but recently started giving me trouble, perhaps some wear in the throttle shaft or something is causing it.

Oh well, car is drivable again. And I do not plan on replacing the carb, but that will hopefully go away soon when I do the 4age engine swap.

[Lil Beast]

With my experience if you can't adjust your carb properly after a rebuilt and you know all the vac lines and little adjustments are right! and can't find the right idling and mixture! Kinda like your problem will die at right rpm! But to have right mixture it's too high! It's the float adjustment that is wrong! Or just a bad float! It doesn't take long to adjist, a bit of PITA tho!

[Highlander]

Which Dashpot screw was out of adjustment? The only one that I know of is on the choke breaker.
The reason I ask is that I've been fighting a similar problem on the green car. Granted I haven't gone through all of the adjustment routine as I just got the carb reassembled- had to replace the choke breaker, the choke opener and the throttle positioner-some broken diaphragms, some lost and failed linkage bushings, etc. plus the last person into the carb cut the solenoid valve wires and spliced them back together so short that they were taut. They also had swapped the 1st and 2nd solenoids in the carb body. Now that all of that is working right, I've got this no-idle situation even though when I first restarted it, it ran and idled great. Different day, Different shit.

[Petros]

The dashpot is on the end of the primary throttle shaft opposite the main throttle cable bellcrank (towards the front of the car). It is a little vac operated device that catches the throttle plate to prevent it from slamming shut when you rapidly let off the throttle. It prevents an instant spike in vacuum that will cause a momentary richer mixture. If it is adjusted too far the engine runs longer at part throttle before it returns to idle, too little it slams shut too fast which can cause the idle undershoot.

You might also want to make sure the idle mixture adjustment is not all gummed up. To clean that out you have to remove the soft plug, back out the idle mixture and clean out the idle jet and passage. That means of course you have to adjust the idle mixture.

[Highlander]

Ah! The Throttle Positioner- Hadn't thought of that-
What tool (specifically) do you use to adjust the mixture? I always run into the problem of flat-blade screwdriver at an angle not engaging when the blade is vertical, due to the EGR system being in the way. Makes adjustment difficult to say the least, I've thought about making a special tool that's just the right length and diameter to fit and keep the blade perpendicular to the screw, I've just not gotten around to doing it.

[ARCHINSTL]

Tool - I took an extra-long L-Allen wrench (I think 6 or 7mm size and maybe 10" long) I had from the bike shop and ground one end flat. A screwdriver would have been better, but the ones I had that were long enough were also too fat.
Tom M.

[Highlander]

Exactly the problem, Tom, If the screwdrivers are the large enough, they are too large. I ground one of my small, long flat blades down and all it does is bugger up the mixture screw. I'll just keep thinking, after all, that's what I'm good at

[ARCHINSTL]

I just had a thought on this - how about reworking an old hacksaw blade? I'd think it would certainly be stiff enough - but maybe too "thin in the slot?" Worth a look, though.
Tom M.

[Highlander]

At first blush, it seems that a hacksaw blade would be too thin, but its worth a try. What I had in mind was a piece of hex stock turned to the ID of the mixture screw hole, and then milled to create a slotted screwdriver end. That way the blade is always concentric and perpendicular to the mixture screw. Then I was thinking of cutting it so that it would protrude ~ 3/8" and put a press fit knob onto the end so that you'd have infinite adjustability, and it wouldn't fall out when you let go- no more having to find the correct orientation every time you need to make a minute adjustment.
Waddaya think?
Obviously, you don't leave it on the carb once you're done. after rereading my post, it almost looks like that's what I was talking about.

[ARCHINSTL]

Not having the metal-working apparatus at my disposal (nor the skills, I must add ), I tend to take what we in the bicycle trade used to call the "blacksmith bike mechanic" approach. In the Army, we called it the "field expediency" approach.
Your solution sounds elegant.
Tom M.