D40 Throttle Sticking question (Video)

[Spike Strip]

Resurrecting my 1968 FJ40 - It sat for about 10 years, covered. Carb was rebuilt (not by me, PO had it done), before mothballed. Engine is a 78 2F, if that matters.

As the video shows, RPMs stay up around 1100 or so and drop down to a normal 700-ish when I push on the throttle linkage.

Is this just a weak return spring or could there be issues with the throttle shaft? Throttle springs are discontinued, so does anyone know a good substitute so I don't have to buy 10 different ones to see which is best

How to test ?

Cheers.

 

[charliemeyer007]

I can't see what you are pushing on - it looks like some sort of adjustment screw: idle or mixture. Use a good rubber band to add some spring power and see if that helps.

 

[Spike Strip]

Yes, it's the idle-speed adjustment screw.

 

[bhsdriller]

I'd pull it off and cycle it by hand to make sure it's smooth and throttle blades don't hang up. If it's good then something is stopping it once installed.

I've even seen a gasket that was slightly too big between carb base and plate stop the throttle blade from moving freely

 

[JohnnyC]

you could just take the extension spring off and move the hooks to hold closer to the spring body

 

[mattressking]

1. How much vacuum at idle?
2. Smooth throttle shaft actuation, any resistance with/without spring? Shouldn't have any resistance other than spring tension, so I'd double check with spring removed. It should snap back closed without throttle cable installed. Does it snap back with spring installed?
3. Is the throttle cable clean and slide smoothly without resistance? With and without carb/pedal connected.

 

[Spike Strip]

With everything detached, including the throttle return spring and the throttle cable and choke cable, the throttle plate still hangs up just a smidge. So it seems like it's either a mis-aligned throttle plate or the shaft itself has issues.

 

[65swb45]

Alf, one of the things that I have never seen mentioned in the 20+ years that I’ve been on the forums is that sometimes the accelerator pump plunger and/or shaft in the D40/SD40 can hangup. While it’s possible to disconnect the little boomerang linkage that holds the bronze plunger shaft to the throttle shaft to test them separately, I’d much prefer to pull the six screws it takes for a look-see. It also makes it much easier to rconnect the little boomerang when you’re done.

 

[Spike Strip]

Mark A for the win !! @65swb45

Thanks everybody for the help and suggestions!

 

[JohnnyC]

Mark is the carb whisper

And as mark would say:
“As always, if you click the like button, then I’ll know you stopped by” and liked my answer (I added the last part)

 

[65swb45]

Sounds like you need a valve adjustment.

 

[Spike Strip]

Sounds like you need a valve adjustment.

Yes. That's on the To Do list when I swap out the stamped valve cover for the appropriate Aluminum flavor.