I need another lesson from carb gurus!!

Recap: high idle (1.5k) and wanted to adjust the air fuel mixture screw. Thankfully I was advised not to by you guys.

Ok, upon investigating the idle adjusting screw, it turns out that was the issue, except it does not end there. Upon looking closer I noticed the vacuum hose to the idle throttle control diaphram is removed and taped up (the prev. owner told me he didnt mess with anything). Obviously there is a reason he did this and I hooked it back up to find out, especially since it was definitely sucking, indicating a vacuum (dont know whether thats high or low). Guess what...the car wont idle at all with that hose hooked up. I dont know why and I need somebody to help me understand.

I'd appreciate it if somebody walks me through when (rpms) that line is supposed to have high or low vacuum, what are the ramifications of the diaphram arm pull that link due to a vacuum, and what conditions would cause the care not to idle. How does this interact with the idle screw and the throttle stop screw (aside: now that I think of this at this moment I backed out the stop screw trying to lower rpms and never brought it back to touch the lever since the rpms were high anyways). :stick:

Put my ass in the know!!

The Vacuum diaphragm on the passenger side of the carb controls Idle by using the force of a spring to increase idle (open the throttle) and the force of high vacuum to decrease idle (close the throttle).

High vacuum retracts the diaphragm arm and pulls the idle adjustment screw off the trottle, thus decreasing idle.

Low - 0 vacuum releases the diaphragm arm and the spring pushes the screw on the trottle, thus increasing idle.

Low vacuum or vacuum leak to the idle diaphragm will cause the idle to raise to 2,000 rpm or more depending on how the idle screw was adjusted.


THROTTLE STOP SCREW
This screw sets the lowest idle your car will run smoothly at durring normal operation (after the car has warmed up)

Think of it as a fail safe device for idle... but you need to adjust this screw before setting the idle diaphragm screw.

Anyways the procedure is to run the car till it's warmed up fan has come on at least once. then turn the idle diaphragm screw out untill you feel your car might stall. then start turning in the throttle stop screw to take up any gap. the idle should be between 550 650 rpm ( or 800 - 1000 ). (this is your lowest idle with no lights or a/c, fans running) then turn on your lights and fans to maximum and set the idle diaphragm screw to raise the idle to 650-750 rpm ( or 1000 - 1200 in neutral or 800 - 1000 in gear - Automatics -).

with a/c on adjust the a/c idl;e boost screw on the driversside of the carb to maintain the idle between 650-750 rpm ( or 800 - 1000 ). the a/c idle boost screw should not be used to increse idle above the idle diaphragm setting... only stablize it when the engine is under extra load.

I think what may be happening in your case is the idle stop screw is set too low so when you hook up the vacuum line the diaphragm is killing the idle because there is not a high enough stop point.

mindlos>>> Upon looking closer I noticed the vacuum hose to the idle throttle control diaphragm is removed and taped up.. "
Would u identify which "idle throttle control diaphragm" on Doug's PIC here:
http://87accord.com/carbpage.html
As I know on MT there is no such a thing, only a Throttle Control Diaphragm (Dashpot System) or u meant the A/C idle bust diaphragm..

I guess I stuck the "idle" there inadvertently. I was talking about the Dashpot System (K in the first picture) and not the A/C idle boost. Today I hooked the hose back up after resetting the throttle stop screw to a decent level. With the vacuum hooked up it turns out the idle adjustment screw was just not screwed in enough for the spring to counteract the diaphram, which killed idle. I screwed it in good and I must say the car idles to my satisfaction. Keeps consistent idle even under load.

It also behaves much better when I shift since the rpms dont drop down as fast. I no longer get the delayed jerk I complained about in the provious thread where letting off and on the gas pedal would be accompanied something like a fuel ripple 1-2 seconds afterwards. Nasty on gears 1 and 2 (slower speeds) unless I ride the clutch a lot. Now I only feel a slight jerk 2-3 seconds after I let it coast in gear sometimes on 4 and its almost unoticable when it happens.

Points to ponder for me is why this was unhooked. I hope there are no other problem that will manifest itself at the most inopportune time. At least I know where to start if I start having idle anomalies that wouldnt manifest themselves in the 15-min driving I did after adjustments.

BTW, sometimes I wanna throw the Haynes manual out the window, sometimes it helps. You guys rock though.

Thanks.

mindlos>>> ..Today I hooked the hose back up after resetting the throttle stop screw to a decent level. With the vacuum hooked up it turns out the idle adjustment screw was just not screwed in enough for the spring to counteract the diaphragm, which killed idle.
Ok, there are 2 adjusting screws, not sure which one u've used for idle.
Idle Stop Screw (firewall side). With engine warm and at idle, the throttle valve should rest on it, and only on it.
Throttle Controller (TC) adjusting screw, on the lever pulled by TC diaphragm rod. At idle this screw should not touch the throttle valve at all. The dashpot system on MT is not used to control the idle (as opposed to AT where TC is controlled by some solenoids as A20A1 explained). Correct adjustment of TC screw is with engine warm, pull #6 off and plug it, engine speed should slowly increase to 1400..2000rpm (basically what u had as false idle).
IMHO ur car may have a idle problem, previous owner found a quick fix by pulling #6 off, bingo got idle, too high though but what a hack.
Question is, could u adjust idle only with the Stop Screw ? Make sure throttle valve is free of TC screw or fast idle cam! Idle speed should be a little under 1000rpm.

Idle is fine with just the Throttle stop screw. but the only problem is you will hottice the drop in RPMs when you have the heater on and the head lights on.

DanG86LX, I just wasnt verbose. I actually did final adjustment with the throttle stop screw. I mentioned starting with it so that the engine wouldnt die. Here's what I did with the car all warmed up in order:
1. screwed in throttle stop till idle went up.
2. hooked up vacuum and screwed throttle control to idle went up
3. unscrewed throttle stop
4. unscrewed throttle control until the engine was really puttering like it was gonna die.
5. screwed throttle stop until desired rpms. Its hard to say exactly below 1k but I would say 800. Lower than that shook the car a bit.
- with brights and fans idle was still about the same (except the instant I just turned on the lights then it recovered) so I did not mess with the boost at all.

Bottom line is I went from throttle controller screw set to throttle stop screw set normal idle. That's okay right!? As you say, I do think there is an issue. From the amount of screwing I did on the "TC" is seems it would idle way way higher than 2K. If I thought about it further I would have unhooked it just to see.

Thanks for pointing out that the TC diaphram is vestigial in MTs. From following A20A1s instructions, it makes some sense now. Couldn't they have just taken it out and saved more on their bottom line? Unless I'm missing something.

The idle diaphragm is just too keep the car running smoothe under load... when the car was first made Keihin developed the carb for honda... I guess with all the optional equiptmet and the fact that automatics stay in gear... they needed something to keep the car sounding healthy... a stumble in idle certainly puts a fronw on my face everytime it happens. It's the little things that make the difference... I have to admit... despite all the jumble of vacuum lines honda did a good job keeping the emissions low and gas milage high... durring the time the car was still fresh off the assembly line.