nevarmore

This is on my all-stock 85 GS. I have been half-heartedly fiddling with a high idle (sits at 2000) and finally did some real wokr today. After turning the idle screw all the way in the engine did not die. This leads me to belive that my idle issue is a fubar'd linkage or a vacuum leak. Used up about 4 feet of hose relpacing the lines on the right side of the carb.

Two questions:

1. I used a long run of vacuum line instead of reusing the old white/clear plastic hardlines. Is there any reason I should NOT have done this?

2. There is a whatsit on a few of my vacuum lines. It has green ends that the vacuum hoses slide over with a black center section. Is this a check valve? If so I have at least one that isn't letting anything flow in either direction.

nevarmore

I also forgot to mention that the idle dropped when I kicked on the A/C so I think that I can rule out the A/C compensator. I also capped off some exposed vacuum ports on the carb. There was one high and centered on the drivers side and two on the passenger side.

After rereading the idle adjustment instructions posted by Sterling (yes search does work), I was futzing with the idle MIXTURE screw not the SPEED screw. My Haynes said both were on the driver side and the mixture screw was capped. I saw only one screw and no cap. Since my idle is at 2000 it was metering off the main circuit. I could have turned that all I wanted and gotten no response.

Sterling

I agree with your assessment about the idle being drawn from the main because everything you did din'd make a difference.
Usually with a vacuum leak you'll find something that makes the engine want to die out, but never idle below what you're getting (around 2K rpm.
But since you have replaced everything and I'm sure checked everything thrice, then I'd have to say that you should look at the possibility ofsomething binding your linkage.

Try turning the idle SPEED screw out (counter clockwise) a few turns, and peak don the primaries.
If there's still a gap in the primary valves, then it's got to be a linkage problem.
But if they are fully closed, and the secondaries are also, then you have a leak.
(The secondaries are set so they close enough to slide a piece of paper through. but if it's much more than that, I would check both ends of that shaft for binding.)

The green thing- I believe that is a check valve you are talking about.
And replacing the hardlines with hoses...You still have the idle comp on? (That's fine) Just make sure everything is TIGHTLY Sealed!
Try troubleshooting that section by capping the nipple over the idle screw where that white hardline used to go, and vice gripping the hose that goes to the idle comp valve.

The idle comp valve is a very sensative unit that incorporates an accordian typ cylinder filled with inert gas. It is subject to barometric pressure, and operates a very fine valve that lets air into the idle circuit. If it is comprimised, you'll have this idle problem.

My guess as to the reason they used hardlines for the idle comp valve is because the rubber is flexible and when it gets hot, it becomes slightly elastic. This could cause inconsistant idle that varies with underhood temps.

Unless you do alot of altitude change driving, you could eliminate the altitude idle comp valve all together. But I like to suggest you get it working properly for a stock carb.
With performance carbs, the task of rejetting to compensate for altitude is the norm. The altitude idle comp valve attempts to correct the main circuit operation, as well, via the emulsion system.

http://www.sterlingmetalworks.com/al...omp_valve.html

nevarmore

Thanks Sterling. You know your **** and are able to share it, thats a real gift.

I've got to go by AutoZone to get more vacuum hose, sine the car will be warmed up I'll check the idle comp vavle. I also re-read the 84/85 supplement to my Haynes and saw a pic of the idle speed screw. Damned ******* called it a throttle adjustment screw instead.

I think I wil be retaining the altitude compensator, I do some rallying in western and southern Ohio. Its not like driving in Colorado, but there are some significant climbs on those courses.

Which way should I install the new check valve? At present it is not flowing at all, but installing a new one backwards wouldn't get me anywhere.

nevarmore

I found the idle screw. I just love Mazda, because theres nothing else I wanted to do except burn my hands and try to find the correct combonation of extensions to get to the idle speed screw.

Which way do I turn this bugger to lower the idle, clockwise or counter-clockwise?

Sterling

Counter clockwise lowers the idle.