Throttle sticking after carb rebuild

[Notmikeb]

Anyone seen this before? It seems like my throttle doesn't want to fully close on its own after I rebuilt my carb. It starts off at 3k rpms and I can manually push it back down so that it is about the right idle speed but as soon as I turn the throttle again it sticks back at that 3k point.

Video for clarification linked below (forgive the vertical video)

https://youtu.be/T6Ua6qaeng4

[Notmikeb]

The throttle cable is also now has slack when it didn't have any before.

[ARCHINSTL]

Since you rebuilt the carb, my first thought would be that the nuts holding the throttle shaft on either side of the carb are too tight and the big return spring cannot pull it back down (is the spring present?). I encountered this last year when I installed shaft bearings on my Weber.
The idle speeds for an AT car should be 800 w/o PS and 900 w/PS.
There should be some slack in the cable - not a lot, but more than one might expect.
Another possible cause is a lack of lubrication in the throttle cable. Remove it, raise it high and dribble silicone fluid through it until it exits at the accelerator pedal - obviously put down some paper towels or similar under the pedal.
Tom M.

[Notmikeb]

I'm hoping it's something with the linkage. I think I can at least partially disassemble it without removing the carb again so I'll try that.

It's not the cable as it does the same thing with the cable disconnected.

[Notmikeb]

I had a thought, is it possible to have the throttle shaft 180 degrees off and still be able to install all the linkage correctly?

[Notmikeb]

Ok well I've fixed the high idle. I pulled the carb off again, removed the throttle linkage and throttle positioner linkage and reinstalled. I'm not sure what was hanging up but it is now fully closing just fine.

There is still an erratic loping at idle. I can feel it while driving too when coasting (surges).

Aside from the erratic idle speed, it is amazing how much more power I have now. Super thrilled with how the acceleration feels.

[Petros]

cycling speed at idle is indication of a vacuum leak. check all your vac lines are good (check very carefully), and they are all routed properly (a misrouted vac line can act like a vac leak, it is sucking air from somewhere that it is not supposed to be sucking air). If all okay, check gaskets and that all fasteners, including intake manifold, are snug. As a last resort, go through the test procedures from the FSM for each of the vac operated equipment, if one is bad it would also act like a vac leak. Usually these are very easy fixes, it is finding the problem that takes time. Forthrightly it is not that bad if you do your system checks in an organized manner (IOW, do not randomly pull or replace things without knowing what they do). there are good trouble shooting procedures in the FSM, just follow them in an orderly manner and you will find and fix the problem.

Always diagnose the problem BEFORE you try and fix it. Or you waste time and get very frustrated.

good luck.

[dlb]

agreed with peter, the cycling you're experiencing is probably a vacuum leak. check every device by sucking on the hose to it, making sure you cannot suck air through. if you can't suck on it (like the charcoal can), plug the hose that goes to it and try driving like that. do this one device at a time until you find the culprit

[Notmikeb]

I definitely have a vacuum leak somewhere and a bad one. I can feel a lack of power braking assistance when stopping. Will go through all systems tonight and see what I come up with. Do the carburetor base gaskets need sealant? I just installed them dry.

[dlb]

no, the carb base gaskets do not require sealant.

[marlinh]

Is the connector for the solenoids plugged in?

[Notmikeb]

The solenoids both had their wires cut when I removed them but have been spliced back together (soldered and heat shrinked) and the plug is reconnected so I doubt that is the issue. With the idle as rough as it is I have to think it's either a incorrectly connected vacuum line or a large leak somewhere. I'll go through every system tonight but I really wonder if something is not sitting flush with the carburetor mounting area. I did notice that the air cleaner didn't seem to want to sit as flat as usual but thought it was just my imagination. inwonder if I somehow pinched a line or the wires for the carb spacer/heater underneath the carb. That would account for the leak despite all the mounting nuts being tight.

This is all speculation at this point. Hopefully I'll have a fix reported tonight.

[dlb]

if it's a leak at the base, that will be easy to determine. let the engine run and spray carb cleaner at the base. if the idles rise a few hundred rpm for a second or two, there is a leak in that area.

[Notmikeb]

I'll try that. Thanks.

[Petros]

That is acting like a vac leak (rough idle, flat spot, weak power, etc). Inspect all the lines and obvious possible leak sources, verify the correct routing of vac lines from the diagram (misrouted vac lines can also act like a leak), and than use the carb cleaner method that DLB describes to look for leaks.

I have noticed that some brands of carb cleaner will slow the engine down when you spray it down the carb, and some will speed it up (Gumout brand I noticed speeds it up, likely have to do with the carrier fluid each brand uses). You can use either one to look for a vac leak, just test it by spraying a puff down the carb while it is running, it will either speed up or slow down. Knowing how it acts with your brand of carb spray, you than spray a puff of carb cleaner at various places around the induction system, vac lines, and various vac operated equipment to see if any are the cause of the leak. Direct spray at the base of the carb to see if it is the base gasket (it does not need sealant), if you get an RPM change, tighten the bolts a little (not too tight), to make sure it is the gasket. If it still acts like a leak, check vac hoses at the base area, and check the throttle shaft bore (sometimes it is worn and sloppy it will also act like a leak). If it did not act this way before the carb rebuild, it is not likely the throttle shaft, but something that you changed or forgot to install (hose, line, cap, screw, etc). so look for that first.

spray it at the various vac lines, manifolds, the TVSV (those can leak too) and at the intake manifold to head gasket joint. Again, short puffs directed at the area in question, watch for rpm change after each puff. when you find an area that changes, move closer and try and isolate the area and inspect it very carefully. some forum members have even found cracked intake manifolds (very rare, it was installed improperly by the PO and put stress on it that eventually crack it).

once you find it, the fix will be easy and quick, it is locating it that can be a PIA and takes all the time. That is why it is important to do it systematically. You will be happy once you find and fix it, it will run well again. it will happen, do not get discouraged, just keep at it until you isolate the problem and fix it.

Good luck.