Carburetor/engine idle concerns

[deejay1272]

I'm having some issues with my engine idle that seems to idle in the range of 1,500 - 1,600 RPM rather than the suggested 800 RPM. To trouble shoot my problem I'm using my spare AISAN carb to help me pinpoint the culprit (the photo below is of my spare rebuild project carb that has never been installed on my T4WD because I haven't started to rebuild it yet).

After consulting the FSM, fiddling with all the usual idle screws (blue circles below) and using carb cleaner to ensure that the throttle open/close action is smooth and reliable (spraying liberlly - with emphasis on the points indicated with arrows), I'm still experiencing problems achieving a reasonable idle speed. I know this much: I can blip my throttle and wait for the high idle condition to occur (which it does every time). To correct for this, I can simply hand guide my throttle lever (the curved bit with the knob at the bottom left of the photo) backwards to achieve 800 RPM. The difference in throttle position between ~1,500 RPM and 800 RPM is frustratingly small! Furthermore, no amount of movement of the idle screws will help the throttle position return that extra 1,000th of an inch where 800 RPM occurs.

I'm thinking that my butterfly valves at the very base of my carb are at fault here because while the throttle snaps shut with adequate force/reliability, there's still that extra 1,000th of an inch of throttle position return that is needed to return the system to proper idle conditions. If this is the case, then a simple removal and cleaning is probably in order. Does this theory sound feasible to anyone? Does anyone have experience with this, or an alternate theory?

Ps - I know the Weber would eliminate all of my fuel delivery woes, but I'm just not ready to drop $300 on one part at this point, so that's off the table for now. *Thanks!*

[ARCHINSTL]

Others have encountered this - among other threads, you might check the looong thread on RPM Cycling +... in Repair Guides. While it was about my specific problem, others commented on their situations similar to yours.
A possible, yet overlooked item: Do you have enough slack on the throttle cable? Remove the cable, snap the bellcrank a few times, note the resting position, and reattach the cable and compare. This fooled me for a while when I first hooked up my Weber (although it is not peculiar to a Weber setup).
Tom M.

[takza]

I added an extra throttle spring INSIDE the OEM spring. Also the fast idle adjustment on the front of the carb...if set according to specs can cause a fast idle.

[IHblarp]

deejay. Oddly enough my car does the exact same thing, only I have just rebuilt the carb. so I don't think that a rebuild is going to fix it but I could be wrong. On mine, I found that while driving, I could pull back on the bottom of the accelerator pedal with my toe to get it back down to idle. So based on that I would say that archinstl is probably on the right track. I ended up pulling my throttle cable off yesterday to see if it just needed lube but it moved freely in both directions. I guess I'll try messing with it again to get more slack out of it or using a stronger spring seems like it might do the job. Either way, good luck and report back if you figure anything out. I'll try to do the same.

[marquiess]

I also had this problem. On the front side of the carb there is another adjustment screw that stops the car from stalling on de-celeration. I adjusted this screw a tiny bit and the idle came down. Maybe this is it?

[ARCHINSTL]

Depending on the strength of the Aisan return spring in the carb, the bellcranks will return at varying rates and I'm fairly sure these springs are not included in rebuild kits (true ?).
I found that, even with a visible amount of slack, there just had to be more slack. This was true with the Weber, but also with the OE Aisan I had first on the car. It just needs more slack than you'd think. A stronger spring would help, too - and probably easier than takza's method (sorry). These springs are 25 +/- years old...
Lubing the cable will also help; elevate it and dribble lube through (but put a catch rag on the inside of the car!).

Check the FSM on the Throttle Positioner that takza and marquiess mentioned. This uses vac hoses - 'nuff said.

As detailed in the RPM Cycling thread I mentioned, I noticed that this was also not uncommon for carbed Toy 22R motors of the era (truck and others, I believe). Could not find much info on my prob but others had the same prob you do - some cable related and some not.
Tom M.

[IHblarp]

The rebuild kit I got (autozone) didn't come with any internal springs. my problem is most definitely related to the throttle cable, but I'm just not sure how to go about fixing it. I was hoping that I could just bent the tang that houses the cable assembly to get a bit more slack, (my cable adjustment is backed all the way out) but the tang is actually a pretty sturdy piece. I'm about to go fiddle with it so I'll let you guys know if I come up with anything that works

[Petros]

look for a vac leak first, no matter the throttle adjustment, if you have a vac leak you will never get it to idle down. Than check the linkage, etc. Sometimes there is wear in the barrel at the plate, and it allows air to slip past. ON these high mile engines wear is a very real possibility. There is nothing you can do about a worn out throttle plate/shaft or barrel except replace the carb.

[ARCHINSTL]

As far as cable length is concerned...
...check to see that there is nothing between the accelerator pedal's vertical shaft and the firewall that would block full movement
...I had to put a spacer in the cable at the pedal to shorten it almost 1/2" (it was that stretched), so I'd think your cable should be long enough; check to see if someone put a spacer in at the pedal
...you could (in effect) lengthen the cable by VERY CAREFULLY using an old bicycle shop trick when dealing with ancient Raleigh brake cables which, like these, had permanent stops on each end; use a cutting wheel in a Dremel tool to cut 3/8" or so of the casing - then it can be unwound around the cable itself, or cut lengthwise. This must be done very carefully, obviously. Note that I did not say this was EZ...
...you could ovalize the tang's mounting holes a bit to move it away from the block a bit
...this might be easier - go to a motorcycle shop and have a longer cable inserted with a new barrel end attached

Frankly, I just can't imagine having to do any of this with a 25-year old stretched cable.
Tom M.

[IHblarp]

WOW!!! I feel extremely stupid! apparently this whole time I had the throttle cable adjusted to it's shortest length, but thought it was at its longest. problem fixed. sometimes I'm the biggest problem with this dang car!

well, I'm glad it idles where it should. I just got to remind myself to think about stuff before i go about trying to fix something that's not broke!

[ARCHINSTL]

Sometimes the funnest times are had when one fixes those "ain't broke" things.
Kudos to your admission instead of just saying "I fixed it."
Tom M.

[deejay1272]

I like all the ideas presented here! Although none of the fixes are quite as simple as I would have liked to see. I guess you'll have that.

I think I'm partial to the idea that there isn't enough slack in the throttle cable. If exploring this option doesn't yield any results, then I'll try the additional spring option. I'll bet the combination of these two things will help me stay at that 800 RPM level!

Ps - It's really stressful for me to work on the engine when it's idling at ~1,600 RPM! When I physically turn the throttle lever backwards, then I find that my nerves are much more stable

[takza]

As far as the spring inside the OEM spring...I just happened to have one that would fit and work....from where else? Harbor Freight's spring assortment. Because of the air cleaner...it's difficult to add another spring elsewhere.

[IHblarp]

Ps - It's really stressful for me to work on the engine when it's idling at ~1,600 RPM! When I physically turn the throttle lever backwards, then I find that my nerves are much more stable

HA! I know what you mean!! It's kind of weird but for some reason when the engine is racing, my heart wants to keep up.

I ended up with mine around 900 (smoothest) but I also haven't timed mine yet, I imagine once its timed right it will come down a bit. If I set it below 900 rpm is seems to want to wander a bit so I guess I've probably got other problems too. I guess I'll browse the RPM cycling thread for some input

[ARCHINSTL]

HA! I know what you mean!! It's kind of weird but for some reason when the engine is racing, my heart wants to keep up.

What scares me is when the idle starts dropping - and dropping - and dropping - and dr