Engine RPMs climbing/throttle sticking when engine is hot

[Barn Brewer]

I’ve been having an annoying problem that only seems to happen when the engine is hot. After driving for a while and when the engine is hot the engine RPMs will start to climb at idle. I’ve adjusted the idle after the engine is warm to around 1000 but once it’s good and hot they start to climb to 1200-1300 or so. After that, the throttle will get stuck when shifting or engaging the clutch, revving up to 2000+. If I give the accelerator a quick tap the throttle becomes unstuck and goes back to 1200 or so but will get stuck and climb again most times that I shift or press the clutch in. This only happens after driving for a while when the engine is hot. Never happens when cool or even warm.

I just installed two new Solex 40/44 carbs due to a separate issue but this was happening even with the old carbs on there so I don’t think it’s related to the carbs themselves since this happened with both old and new carbs on there. Maybe the linkage though? I’ve ordered the Buttys Bits throttle kit and will install that when it comes in but I’m not convinced that’s the problem. It seems like the issue is coming more from somewhere in the engine compartment since it’s happening only when the engine is hot. Any other thoughts on what I should look at?

[richparker]

Im not a type 4 guy. But, I’d pull the accelerator cable, spray out the tube with compressed air and lube the cable. Then I’d turn to the linkage. Make sure it is lubed and moving freely, maybe it is binding when it expands. Lastly, what type of return spring do you have? Maybe the spring isn’t strong enough to pull the linkage back.
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’71 Westy build
Adventure thread
’65 Deluxe Build
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[lil-jinx]

have you had eyes on the carb/linkage ,while it was in the stuck position,seems odd ,there is not much in the linkage that would bind due to heat,maybe a linkage pivot at the carbs,but they should not heat much.
check your engine ground ,if it has failed,it may be grounding thru the throttle cable and heating up enough to ‘weld’ the cable to the conduit.
it could be a vacuum leak at high temp,some gap opening up,

just throwing thing out there,
what year and engine type might help.
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https://www.thesamba.com/vw/forum/viewtopic.php?t=620186
https://www.thesamba.com/vw/forum/viewtopic.php?t=668799
1974 Bay Westfalia. she likes to be called Ethel.
1968 Dune Buggy sold dec 2024

1974 parts bus
A smart man learns from his mistakes,a very smart man learns from other's mistakes.

[Barn Brewer]

[Barn Brewer]

[timvw7476]

The vertical pivot bolt in the image, the one with the sleeve, can use greasing along the entire length.
The rest back there you leave clean to avoid attracting dirt.
And the Bit you mentioned will help. The VW push rod under the pedal does end up off-center after the first thirty years & ends up jamming up in surprising ways limiting full travel .

[Nitramrebrab72]

It's normal the metal in tension springs start loosing tension from 175°f and on top of that they expand in length reducing the initial tension setting weakening the springs overall force considerably ...

[lil-jinx]

that return spring looks to be a little too long,it should have tension on it.
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https://www.thesamba.com/vw/forum/viewtopic.php?t=620186
https://www.thesamba.com/vw/forum/viewtopic.php?t=668799
1974 Bay Westfalia. she likes to be called Ethel.
1968 Dune Buggy sold dec 2024

1974 parts bus
A smart man learns from his mistakes,a very smart man learns from other's mistakes.

[SGKent]

I can't see how your setup works, but it appears when you pull the cable, the long bar moves towards the right side of the photo. Then the spring pulls it back. There is no tension on the spring, and that looks like a heavy spring too. My instinct says you need a slightly shorter and 20% ish lighter spring.
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Skills@EuroCarsPlus:
"never time to do it right but always time to do it twice"

[Barn Brewer]

UPDATE:
I installed a new linkage spring hoping that the old one was getting worn out but that didn’t fix the problem. I ordered and installed a Buttys Bits throttle kit after that. During the install I noticed that there is also supposed to be a return spring at the front end of the throttle cable and mine was missing. The new BB kit plus adding a return spring at the front end fixed the problem! Good as new. Thanks to everyone for their help!