Aisin carburetor idle circuit routing (1 Viewer)
- Thread starter cbmontgo
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Will do this tomorrow. I was thinking about that episode, and now I wonder if I threw a kink into the accelerator cable back in the cab at the pedal. I say that because there’s no kink in the cable under the hood.
Pighead, I just looked and there is no kink or obstruction in the accelerator cable either in the cab at the pedal or at the carburetor. I’m gonna include photos of both ends. In one of the pics you can see my bright shiny new Idle Speed Screw, too. Does it look wrong?
With the engine off, there is actually a slight bit of slack in the accelerator cable (that you may be able to see). As I move the linkage to simulate the accelerator, yes I feel a positive clunk when the throttle plate closes.
Any ideas? Next steps?
Did you try removing the ball joint linkage from the bellcrank to the carb throttle lever? It might be extended a bit, and it is adjustable.?
Yes that’s what I tried first. But at full limit the Idle Speed Screw just didn’t have the stroke to make the adjustment needed. So I opted for the longer ISS.
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You're going backwards!
The only reason you would ever feel a need for a longer screw is is because you cant get the idle speed UP enough on the standard screw. And what would make the engine run below the recommended idle speed? Poor vacuum/ retarded timing. And you've already said that your timing is retarded.
If you get a screw long enough to open the primary more, the idle vacuum will only go down. Also, the additional volume of air allowed by the wider opening is guaranteed to engage the primary nozzle to start spraying gas, further ensuring your idle mixture screw will have no effect.
Do you understand this concept?
Just looking at the pic's, it seems to be there is a lot of wear in some of the pivot points on the linkages that will mean slop and that the rotation will be canted. Things rotated out of plane don't produce their original effect. I have seen stepped washer that will bush the holes back to true but will stay in place due to the step. Or you could like braze them shut then ree-drill them to the proper size.
I understand the concept that engaging the primary circuit can keep the engine running instead of the idle circuit, and this is bad.
But to keep the engine running without using the choke, I needed to speed it up, so I used the Idle Speed Screw.
But now I seem trapped in a cycle where I can’t increase idle speed with the Idle Mixture Screw. Only the ISS works.
From what I have read, this is most often caused by (1) a vacuum leak, or (2) a blocked idle circuit passage in the carburetor. I’ve not found either of these 2 problems, and I’ve gone through a can of carb cleaner, sprayed thru the little plastic straw they give you, to every vacuum source I know of. I’ve cleaned the carb 3 times, and I can’t imagine a blocked passage after that!
So, back to your scenario: yes my reliance on the ISS to maintain idle has prevented me from lowering idle to 650 (my goal). And everything I’ve read says that I’ve got to achieve 650 rpm before I can set my timing.
The only reason why I know that timing is about 3-4 degrees btdc is that, out of desperation, I tweaked the ISS to allow the engine to run without choke, and it ran at about 800-900 rpm. Twisting the carb closer to “the bb” (7 degrees btdc) bogged the engine down until it died. And I couldn’t start it again until I moved back to 3-4 degrees.
What do I do first to start “all over again”? I’ve seen instructions online to back the IMS out from seated 1.5 turns, and as much as 5 turns.
Your experience, please!?
I forgot one key point. My whole goal here is to try to perform the “lean drop” tuning method.
There isn't a hang-up on this linkage, is there. The SOR carb identifier shows the linkage being connected thru the other hole on the 1st idle adjusting lever. A photograph, not top-down, of this area would be helpful. Also, there is a return spring on the bellcrank?
No sir, there’s no hang up. It moves freely. You have got some sharp eyes there! I will move that piece of linkage to the first hole!!
I took a couple of pics from the direction of the firewall that I will attach.
Also I’m not sure what a “bell crank” is, but I have a return spring on the forward end of the carb. I’ll get a pic of that also.
I really do thank you for your insights. I had about run out of ideas!!
Grayscale
I’m getting my hopes up. When I moved the linkage to the correct hole as you discovered, the carburetor innards shifted a bit. Unfortunately, I have my distributor pulled so I can’t fire it up right now but I’m encouraged!! Just wanted you to know.
thebigredrocker
SILVER Star
when you reseat the distributor, make sure it's fully seated so the blade engages the oil pump slot.
thanks for the reminder! The bolt that clamps the dizzy in place was as brittle as a toothpick. I flailed around trying to find an identical replacement bolt at ACE Hdwe, and then discovered I could buy the whole clamp from City Racer for less than 10 bucks! I ordered it and now I wait.
Grayscale,
I’ve finally got back under the hood! After moving the carburetor linkage to the correct hole like you suggested, I got sidetracked on a parallel project: the clamping bolt on my distributor broke! After some failed attempts to find a replacement bolt (it’s a weird one) I ordered a new clamp from CityRacer. It was supposed to fit, but was different to mine, having just one mounting bolt hole and being made to accept a dizzy of smaller diameter. So, I finally got an acceptable new bolt installed, but I installed it wrong! Duh!! I performed an install after watching an Aussie step thru it on YouTube. Good video.
Anyhow, I’ve got it running again, but still idling poorly.
I attempted the Lean Drop tuning method, but it just won’t idle at rpm’s as low as 650-800. I only have 15 in Hg vacuum, at 1000 rpm the timing is way “left” of the BB.
I’m not even sure that I’m running in the Idle circuit of my carburetor, because when I look down the barrel with a flashlight, there is a ring of fuel spray in the area of the emulsifier on the Passenger side only. None on the Drivers side.
Thats all the symptoms I can think of, other than telling you that the thick rich smell of exhaust is not making my wife happy!!
Thanks in advance for any ideas on how to proceed.
One more thing. I drove it around a little before parking it. It kicks and bucks like a bronco in the low rpm’s. In the high rpm’s it does fine. Weird.
Vac leaks have a major effect at idle compared to fuller throttle, Look inside the dizzy cap for evidence of arcing/hairline cracks, clean the terminals inside and out.
I’ve looked and listened with the aid of some carb cleaner. So far, I haven’t found it.
I’m thinking about disconnecting all vac lines and plugging them to see if that changes things.
