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Old 08-08-2009, 11:45 PM
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intermitent high idle

Ok reak quick heres the deal: new intake manafold-car ran ok, but problems starting, rebuilt the carb, car starts fing, but idles high only after it goes to wot. i can drive all day at heavy part throttle and it stays at a good idle, but as soon as i push it to wot the idle jumps way up, and its like i can feel it in the gas pedal when i floor it-its smooth all the way through till right before it hits the floor board. its like pushing a toothpick through a watermellon. but only the first time, after i do it, the idle jumps and its smooth all the way through. and if i shut her off for 15 min or more its fine-until i hit wot again. any one got any ideas?

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Old 08-09-2009, 12:13 AM
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Quote:
Originally Posted by 85_Olds
Ok reak quick heres the deal: new intake manafold-car ran ok, but problems starting, rebuilt the carb, car starts fing, but idles high only after it goes to wot. i can drive all day at heavy part throttle and it stays at a good idle, but as soon as i push it to wot the idle jumps way up, and its like i can feel it in the gas pedal when i floor it-its smooth all the way through till right before it hits the floor board. its like pushing a toothpick through a watermellon. but only the first time, after i do it, the idle jumps and its smooth all the way through. and if i shut her off for 15 min or more its fine-until i hit wot again. any one got any ideas?

maybe something is sticking in the carb. check the linkage maybe its hanging up on something or the accl pump is sticking. just some ideas.
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Old 08-09-2009, 01:09 AM
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It would help if we knew what brand, size, and type of carb you have.
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Old 08-09-2009, 02:56 PM
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Originally Posted by ericnova72
It would help if we knew what brand, size, and type of carb you have.
its the stock q-jet (i believe it is an M4MC and aprox 750 cfm) installed idle air bypass in the base plate at 0.63", also has a 4" manafold to carb spacer. i made sure that the throtle cable and kickdown cable move freely-they clear nicely and the cables themselfs move easily. and i converted it from a thermostatic choke to electronic choke. the idle adjust screwes are backed out aprox. 3 1/4 turns, and the apt screw is somewhere around 3 and 1/4-did alot of hiar turns so i dont know exactly how far it is backed out.
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Old 08-10-2009, 12:37 PM
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Leaking throttle shaft bores can make this happen. Also if there is some binding somewhere or a weak spring (the one that closes the secondaries) it might not be closing the secondaries all the way. Ive had that happen on some old weber 32/36 2 barrels.
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Old 08-10-2009, 09:17 PM
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Quote:
Originally Posted by Torque454
Leaking throttle shaft bores can make this happen. Also if there is some binding somewhere or a weak spring (the one that closes the secondaries) it might not be closing the secondaries all the way. Ive had that happen on some old weber 32/36 2 barrels.
I dont think its the throttle shafts; i installed throttle shaft bushings, and made sure that there was no play. i customized the primarys and secondarys to open to a full 90deg. and played with it a while to make sure that it worked well. i did a fairly thurough job of rebuilding it. even boiled it in white vinigar and blew out all the passages with carb cleaner and comp. air! i think ill spend the weekend playing with it to see if i can see anything visualy sticking or binding.
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Old 08-11-2009, 03:53 AM
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Quote:
Originally Posted by 85_Olds
i think ill spend the weekend playing with it to see if i can see anything visualy sticking or binding.
Good idea. You mentioned modifying the choke- You might start there when looking for anything causing the throttle blades to stick open some, the fast idle cam/linkage could be the culprit here.

I would have seen where the curb idle stop on the linkage was at, when the engine was in "fast idle mode", if the stop was OFF of the curb idle screw, you would know for certain there was something holding the throttle open some small amount.
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