Throttle sticking

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JDNightFox
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Throttle sticking

Post by JDNightFox »

Recently my engine has been sticking at 1500rpm and I need to rev it to get it back to idle

Is that a symptom of the choke sticking closed? I was thinking I need to grease all the fittings again
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Re: Throttle sticking

Post by xirdneh »

Grease ? Should be very light oil.
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BaileySims
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Re: Throttle sticking

Post by BaileySims »

I've developed the same thing awhile back. I just added a return spring to the bell crank and called it a day. I even had to do it to my truck as well. Maybe it's a weber thing?
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dlb
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Re: Throttle sticking

Post by dlb »

Check for carbon buildup at the throttle plate, and clean it with carb cleaner if you find any.
JDNightFox
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Re: Throttle sticking

Post by JDNightFox »

Okay so I oiled all the moving parts and then coated them with lithium grease, the movement was a bit gritty initially and now it’s smooth

I also sprayed down the whole carb with carb cleaner

It returns to idle now, but if I lightly step on the gas it will still rev up to 1500-2000rpm and hang there for a few seconds and then drop back to idle

This is annoying because when I’m shifting it will rev higher than when it was in gear and it’s making it clunk into the next gear

I saw that I have a broken diaphragm underneath the carb, I’m not sure what it goes to but it is attached to a paddle that can pull on the throttle
It looks like it’s part of the EGR or something
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Abletobecain
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Re: Throttle sticking

Post by Abletobecain »

Is your car A/C equipped? I think the part you're talking about ais the A/C actuator. Look at page AC-17 in the FSM. It bolts up kinda under the EGR and has a little ribbed diaphragm and the paddles on it hit the throttle positioner right? That ribbed diaphragm is torn on both of mine. I rebuilt the carb on my DD without messing with the diaphragm in question and it runs great without the issues you're describing. My A/C belt is disconnected though...dunno if that matters.

Actually, before I rebuilt the carb I had the opposite issue as you...as soon as I took my foot of the gas the RPMs would drop so fast it would stall out. I'm not sure what it was but the rebuild fixed it.
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Petros
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Re: Throttle sticking

Post by Petros »

You need to check something else: there is a small diaphragm on the front side (facing the front of the car) of the carb that is there to prevent the throttle from slamming shut (to reduce a spike in emissions). It has a linkage to the throttle shaft with a screw adjustment. It is a simple adjustment to set it correctly, see the FSM.

if set improperly the speed either drops off and sometimes stall out when it returned to idle, or it will not completely return to idle, or take a long time to return to idle. I like it to return to idle a bid faster the factory spec, but that is within the range where it behaves properly.
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JDNightFox
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Re: Throttle sticking

Post by JDNightFox »

Petros wrote: Wed Oct 30, 2019 4:14 pm You need to check something else: there is a small diaphragm on the front side (facing the front of the car) of the carb that is there to prevent the throttle from slamming shut (to reduce a spike in emissions). It has a linkage to the throttle shaft with a screw adjustment. It is a simple adjustment to set it correctly, see the FSM.

if set improperly the speed either drops off and sometimes stall out when it returned to idle, or it will not completely return to idle, or take a long time to return to idle. I like it to return to idle a bid faster the factory spec, but that is within the range where it behaves properly.
I know which screw you’re talking about, my one was unscrewed far enough that it wasn’t in contact with the other side at all so I don’t know if that was it or not
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Petros
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Re: Throttle sticking

Post by Petros »

JDNightFox wrote: Thu Oct 31, 2019 7:25 pm I know which screw you’re talking about, my one was unscrewed far enough that it wasn’t in contact with the other side at all so I don’t know if that was it or not

That adjusting screw should not make contact when at a normal idle, but only comes in contact right after you release the throttle after a high rpm run. So rather than the throttle plate slamming shut, the linkage slows the throttle return and brings it slowly back to normal idle. so it only makes contact during the transition from high speed to idle.

You would think it should not affect much, but if this screw adjustment is too slack, or too advanced, it will nearly be undrivable. you will have missed shifts, or the engine wanting to stall out between shifts, or when you come to a stop.
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JDNightFox
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Re: Throttle sticking

Post by JDNightFox »

Petros wrote: Thu Oct 31, 2019 11:41 pm
JDNightFox wrote: Thu Oct 31, 2019 7:25 pm I know which screw you’re talking about, my one was unscrewed far enough that it wasn’t in contact with the other side at all so I don’t know if that was it or not

That adjusting screw should not make contact when at a normal idle, but only comes in contact right after you release the throttle after a high rpm run. So rather than the throttle plate slamming shut, the linkage slows the throttle return and brings it slowly back to normal idle. so it only makes contact during the transition from high speed to idle.

You would think it should not affect much, but if this screw adjustment is too slack, or too advanced, it will nearly be undrivable. you will have missed shifts, or the engine wanting to stall out between shifts, or when you come to a stop.
So I touched the throttle a bit while watching the screw and I see what you mean now, so I went in there and adjusted it

I found a cracked vacuum line on my TVSV which may be where the sticking high rpm was coming from, since it was part of that line
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