• Hello there guest and Welcome to The #1 Classic Mustang forum!
    To gain full access you must Register. Registration is free and it takes only a few moments to complete.
    Already a member? Login here then!

65 Autolite 4100 secondaries not closing, causing high idle.

C

Coupe

Member
So I have my car done and I am desperate to drive the damed thing but every-time I go around the block the secondaries hang up and I cant get it to stop doing that.

I changed out that white plastic choke stop with a screw because it was bent after decades of use just in case that could be an issue
This is the mod I am talking about,
Untitled.jpg

But whats interesting is that new screw does not touch the linkage for the rears like it is in the pic that gave me the idea, should it be in contact all of the time?

From what I have learned that plastic stop (now a screw) was just to prevent the secondaries from opening while the choke is engaged and not for pushing the rears closed. So that "Mod" may have been a waste of time based on erroneous information.


----------------------
Initially I thought it could be the diaphragm lever or the rear throttle shaft needing some attention, but I took the rod off of the diaphragm and both the rear shaft and the lever work smoothly, the rear throttle shaft opens and closes without any drag at all.

I started to think it must be a vacuum issue but when I google about the 4100 and secondaries most of the hits are about them "not working",so mine may be working to well or to early etc..?

Then I started to hear all of the conflicting stories about that check ball in the secondary diaphragm "5th hole" and now I am getting confused.
I did not use a ball in mine, but after considering my issue of hanging once the rear bore is activated and factoring in how soon they come in, maybe I need one?

The carb is a 65 but I cant remember the exact foot stamp number, but it is definitely a 65 because the fuel line threads directly into the body with no filter, I remember it being for a 289 car when I looked it up initially.

Here is my diaphragm body, do you know if this type should have a check ball? If so what size?

IMAG0896.jpg


Here are some other pics of the carb.

IMAG0897.jpg


IMAG0898.jpg
 
Well, in an old thread I found that a 1/8 ball is what should go in that hole, so I tried it with no change.

Its weird, with the car off I get no stiction and can move the secondary with no issue (provided I move the main throttle linkage first), but with it running if I open the throttle a small bit and engage the secondaries a little bit with my other hand, it sticks like a bad shaft or something.

It must be goofey vacuum holding it open?
 
Vacuum should not hold them open. If so...when you stop the engine, the secondaries would close provided nothing else moved in the primary system. I would pull the carb and go over it real carefully. Check the position of the throttle plates inside the secondaries.
 
I don't know but pony carburators ...wouldn't that be a good source for some info ????
I have one from a 66 A-code . Need some pics from it ????
 
Well, when the motor is off the issue cannot be replicated, and when I remove the actuator rod noting binds on the lever or the throttle shaft, so I have ruled out mechanical drag as the culprit.

AZpete, the carb is fresh and I rebuilt it myself, It sat in the tank overnight and then had a bout with the wifes dishwasher and then an air hose. I even re-bushed the main throttle shaft to eliminate air leaks. The car runs great overall, but if you activate the rears you will be stuck at what sounds like a 3k idle.

B67FSTB, Any pics of that side of a 4100 would help me out at this point.
 
AZpete, those links are great, the book seems to show a ball in the 5th hole.


Well, I went back out and bent the rod from the actuator to look like it should, it was a bit off and I did not want it to be so long that it held things open and whatnot, but no change.

At this point the diaphragm may be damaged because I took the top off and double checked my lid gasket and did not hear any air movement from the hole on top of the body near the center bolt, but it still hangs when I open the rears by hand.

I did take more time just now looking while the idle was high and it honestly felt like the rear shaft was tight in its bore, like it needed to be honed to fit or something, but then the motor died and it would spin like it was a new one? Excessive vacuum under the carb holding things open?
 
"AzPete" said:
Can you force the secondaries closed once opened and allowed to idle at the faster speed?
Click to expand...

Yes, I can push them shut, but I can feel friction in the throttle shaft, but only while running. Once it dies it flops around freely.

I guess the best thing I can do now is pull it off and double check the rear throttle plate alignment.
 
Well, the plates look right. I went ahead and pulled the diaphragm out again and I must have destroyed it the last time I checked it and installed the ball. So, the vacuum in that cannot be the issue.

But, since this is a 4100 mounted on a performer intake I used a steel spacer plate under my factory PCV spacer,(gasket, steel spacer, gasket, then factory spacer, gasket, carb) no big deal everything sealed up great but I did use an open style gasket between the carb and factory spacer, and that would allow front vacuum to enter into the secondary throttle area increasing pressure? (I know,im reaching but it sounds good)

But, the aftermarket intake is open between the front and rear throttles anyway, but maybe they need to seal up better closer to the carb?
 
What I haven't heard you do yet is to see if there is the possibility of the secondary throttle plate hanging up on the carb spacer or the intake manifold once the secondaries open up. Since the plates turn free off the engine and turn freely when closed on the car, that makes me suspect the plates are hanging up on something on the engine.
 
"Midlife" said:
What I haven't heard you do yet is to see if there is the possibility of the secondary throttle plate hanging up on the carb spacer or the intake manifold once the secondaries open up. Since the plates turn free off the engine and turn freely when closed on the car, that makes me suspect the plates are hanging up on something on the engine.
Click to expand...

Good idea, but the thing is if that were the case they would hang up even when the motor is off, and they dont. The rear shaft feels entirely different when the engine is running. That and I dont think they are sticking open far enough to get past the carb body, much less into the OEM aluminum spacer, were talking a small amount, just a bit off of that tiny, upside down set/stop screw.
 
Is the choke open all the way? It might be setting a chain of events???? See, we all can reach.....

I thought the same as Midlife did...also, how does the gasket fit the inside near the throttle plates?
 
Well, as thick as the carbs base is, the butterfly's dont even need to get into where the gasket is to make the idle much higher than normal, I doubt the plates were even far enough down to get out of the body.

I went ahead and re-centered the shaft, re-centered the plates and made the pin that pushed the secondary shaft closed much thicker with a bushing so it acts like a roller "pushing" the rears closed when I dump the throttle. This way it can compensate for a weak spring or other issues ( I need to find a new spring also). If this works I may make one out of brass or even rollerize one.

Bushing.jpg


Also, I still think my base gasket being the clover leaf was wrong and I will use the one with 4 holes instead.

I will post updates tomorrow, I need to pick up a new $22 rebuild kit just to get a new diaphragm for the secondary. I wonder if NAPA sells just that part? EDIT: Yes, $12 with a new lever.
 
Last edited by a moderator:
Coupe - did you ever get the issue of your secondaries resolved? I am having the same issue....secondaries work free when car is off, but act like vacuum is holding them closed when running. I also used the hipo gasket (1 large oval + 2 circular holes) since I have a hipo 289. Also my engine only pulls 10 or 11 in/mg of vacuum when idling, so don't know if that has to do with it.

I can overcome the vacuum and force them open by hand when the engine is running, but they definitely want to stay closed.

Thanks
 
You must log in or register to reply here.
Back
Top