Sticking throttle

[38plymouth]

OK this is driving me crazy. The last few times I've driven my car the idle will stick a little high like maybe a thousand to 1500 RPMs and I have to tap the throttle to get it to drop. I've unhooked linkage and cables and everything is free. Nothing is sticking and I lubricated everything just in case. With the car off and everything unhooked the throttle moves nice and free with no binding. As soon as I start the car with all the linkage un hooked and just working the throttle by hand it gets stiff and will hang up a little. In fact sometimes the throttle will just take off and rev right right up. I tried a stiffer spring and that doesn't do much. It might have helped a little. I took the carburetor apart thinking the accelerator pump was sticking and it's not I can't find anything wrong in the carburetor. Any thoughts?

[JBNeal]

I had a similar problem with the '49 1-ton throttle hanging up especially in warmer weather...drove the truck for years occasionally toeing the throttle pedal to get the rpms down when rolling up to stop signs.  I did notice accumulation of dust around the throttle shaft after several years, so I'm guessing that the shaft bore is no longer cylindrical.  This would cause a very small leak in the charged air passage, where the shaft could get wedged or roll into a low spot during operation.  Considering how many resources it would take to correct this occasional higher-than-desired engine rpm condition vs. just toeing the throttle pedal every once in a while, I opted to live with it as the ol' buggy having another personality quirk

[Ivan_B]

Is the throttle physically sticking when the car is running (versus not running) or is the idle simply not returning back to normal, at times? 🤔

[38plymouth]

It only does it when it's running. I have to kick the pedal to get it to idle back down or physically push the throttle on the carburetor with my finger. If it's not running it doesn't do it at all. It doesn't matter if the linkage is on or off the carburetor when it's running the throttle will stick in like a high idle situation. It does it about every other time you press the throttle. I just took the carburetor apart again can't find anything wrong.

[Ivan_B]

Are you able to mark the 100% closed throttle lever position with a pencil, or something like that, to see what happens when you have to push it to get the idle back to normal? This is one issue if it is physically sticking open, and another one if the throttle is actually closing but something else is keeping the idle up, until you touch it. I don't see how the running versus not running engine will cause the throttle to get physically stuck, assuming the same temp. etc. 🙄

Also, if you had the carb apart, did you  remove the throttle from the shaft? I, once, had it not installed back very precisely, causing improper closing.

Moreover, I once saw a DIY accelerator pump repair, inside a carb, which caused the throttle not to close down 100%, but it was like this all the time, not intermittent.

 

Edited May 17 by Ivan_B

[38plymouth]

I know this doesn't make much sense and it's confusing the heck out of me. I'm sure I could get a very stiff spring that would solve the problem but then I'll have a very stiff throttle pedal. Nothing changed with the car when this started happening. It's never happened before and for the life of me I can't figure it out. I can work the throttle 50 times with the car off and it always closes against the idle speed screw. If the car is running at least every other time you touch the throttle it sticks open a little bit and will only come back if you kick the throttle down.

[Ivan_B]

I do not think that you need a different spring, etc. What's different when the car is running? We have some vacuum, etc., but that should probably only help to close the throttle, if anything 🤔 I assume that your choke is always all the way open? Do you have the same issue running without air filter?

Could this be vibration-related? I suspect you've already tried some WD40 at the throttle shaft holes/bushings?

Edited May 17 by Ivan_B

[soth122003]

Just a thought, but I think JBneal is onto the cause. Your area around the throttle shaft has a little bit of crud (not really visable to the eye) between the shaft and the bushing, that is being affected by the heat or vibration from a running engine. This is either causing it to become sticky when warm or expanding a little to keep the throttle from not closing all the way with out the snap from tapping the throttle. You might want to take the carb off and soak the throttle plate section (or the hole carb) in a carb cleaning solution for a few hours and then clean it off according to the instructions. Best result would be to completely disassemble the carb and soak it or use a sonic cleaning machine. My car does this occasionally and it can be annoying but is really a minor annoyance, and just tap the throttle to fix. When I need to pull the carb for major cleaning or repair, that will be addressed at that time.

 

Joe Lee

Edited May 17 by soth122003

[38plymouth]

Well the throttle works really smooth like butter without the car running. I have never had the throttle shaft out of the carburetor and all the years I've owned the car. I'm going to pull the carburetor and see if there's anything going on there but I just don't think that's it. I'm willing to try it though cuz I'm at a loss here. 

I'm actually ready to just buy a new carburetor. I've rebuilt this one so many times and I have so many strips screws I'm just kind of over this thing. I swear I've had it apart 30 times in the 25 years of on this car.

[38plymouth]

Well I'm shocked but feel like it's fixed. The throttle shaft has always been a little sloppy and probably leaks a bit. Anyway I pulled everything apart again and was thinking the throttle shaft is so loose and smooth there's no way there's anything wrong with it. I cleaned and lubricated it really good and put everything back together and was thinking that was a waste of time. But apparently that was it because so far I can't get the throttle to hang at all. I also finally stripped the fourth screw that holds the top of the carburetor on so now it just has three nuts and bolts. So I'm really ready to just buy a new carburetor if anyone knows of something that would would work with these engines. 

[desoto1939]

Where the linkage comes across over the top of the head look at the point where the linkage attaches to the bottom of the carb. There might be a rod that control the throttle speed and also a very small piece of metal called the throttle shaft dog. You mght have a groove in the shaft dog and it is sticking and keeping the idle high on your carb.  I had this very same issue with my 1939 Desoto.  The throttle shaft dogs are hard to find.  Might find a used  carb and it might still have this on the base.

In the picture it is the metal piece that is to the left of the throttle adjustment.

Rich Hartung

Desoto1939@aol.com

1939 40 41 42-54 Throttle dog.docx

[Ivan_B]

1 hour ago, 38plymouth said:

I'm going to pull the carburetor and see if there's anything going on there but I just don't think that's it.

Hold on. If the throttle is definitely closing when not running, but you can see that it is physically sticking a bit open when running, try lubricating the shaft bushings first

[soth122003]

I believe almost any of the Carter B&B carbs will fit your 38. Just look real close at the pics and make sure they match up close. The mount to the intake should be the same on all B&B's. Best bet is E-bay and try to find one that's been on a wrecked or sitting car that hasn't been used in years. They are easier to rebuild and you will probably be able to mix and match from your old carb.

 

Also, cleaning and lubeing the throttle shaft, your problem will come back. May be a few weeks or a few years. The wear on the shaft will always let dirt in and it will hang again at some point. Short of a professional rebuild to address bushing wear, that's about the best you can hope for.

 

1938 Carter models are: B6H1, B6J1, C6J1 and C6K1. Like I said check Ebay.

 

Joe Lee

[D35 Torpedo]

I had a similar issue and it turned out to be the accelerator pump spring, it was stretched to long. As far as throttle shaft leaks, I put an O-ring on either side to mitigate any possible vacuum leaks.

[Dan Hiebert]

I'm having the same issue right now.  I rebuilt the carb over the winter and re-installed the Sisson choke.  I had been running the car with a manual choke and the fast idle disconnected for over 30 years, but I don't think that has anything to do with the current sticking issue, and it wasn't sticking before.  BUT - I really haven't had time to look into it - and I think the OP's and a few suggested resolutions of simply lubricating the throttle shaft will be the answer...because I did not lubricate anything on the carb or throttle linkages when I put it back together...duh.  The service manual calls for it, and I just didn't do it.    

[Ivan_B]

2 hours ago, Dan Hiebert said:

The service manual calls for it, and I just didn't do it.

I admire your self-criticism 😅

Let us know how you fix the issue.

[FarmerJon]

I had a similar problem last year. I cleabed the carb, lubricated the linkage. No change.

Added a stronger spring, then a double spring. It quit sticking but pedal pressure was excessive, and yhe action was noticeable notchy.

One day while driving, the screws holding the gass pedal to the floor came out and the pedal fell off, only leaving the linkage shaft sticking through the floor. I was mid traffic,  so I just had to make do.

I noticed that the action was much smoother. 

Once home I removed the second throttle spring and found that now the sticking is gone. 

I have just been driving without the pedal ever since, but intend on diagnosing what is going on at the pedal hinge.

[Ivan_B]

TS mentioned that he tried disconnecting the linkage, so it must be the carb itself.

Do you have a pedal hinge on 48? I just have 2 "balls" that the rubber pedal is pivoted to.

[Dan Hiebert]

22 hours ago, Ivan_B said:

Let us know how you fix the issue.

Lubricating the throttle shaft, choke shaft, and the throttle linkage, and replacing the throttle return spring seems to have done the trick.  I don't know that the spring was a contributor, but I decided to replace it.  Mainly because the old (not original) one was ugly.  Took it out for spin and couldn't get it to replicate the sticking problem.  I just use engine oil applied with one of those sexy vintage "dinka-dinka" oil cans and wipe off the excess oil. 

[38plymouth]

Just an update I drove the car quite a bit yesterday and cleaning and lubricating the throttle shaft seems to have worked. The throttle never stuck once like it was doing. It is interesting trying to lubricate it while the carburetor was on the card did not work I had to actually take it off and disassemble it.

[Ivan_B]

Couldn't you just squirt some WD40 on the shaft ends, using an extra long tube, from the top?

[D35 Torpedo]

Wd40 is the wrong product..but I get where you're going. I use fluid film or move it.

[Sniper]

WD40 has it's uses.  I used it as a prewash after I get home from the range.  Does a decent job of washing carbon out of places.  As a cleaner, yeah, as a permanent lubricant, no.  A nice dry film lubricant comes to mind, you don't want something sticky catch grit and tearing things up. 

[38plymouth]

5 hours ago, Ivan_B said:

Couldn't you just squirt some WD40 on the shaft ends, using an extra long tube, from the top?

Tried that and didn't work. Literally had to pull the carburetor off disassemble it and have it on its side then I sprayed it with some silicone dry lube stuff I had and that fixed it.

[Ivan_B]

Well, that must mean that your throttle shaft is in good condition - no gaps, right?