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Old 01-13-2003, 04:23 PM
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Post engine run-on

i have a stock 350 and just changed the carb from a q-jet to an edelbrock 600. After I did that my engine will knock and ping after i cut the ignition off. i have checked my timing, have adjsuted my IMS with a gas analyzer, and finally checked for any vaccum leaks. this only happens when its hot....any ideas?

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Old 01-13-2003, 04:34 PM
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lean mixture, low octain fuel, slow idle down until you can throw that eld/ away put your qj back on good luck
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Old 01-13-2003, 04:35 PM
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so, lean my mixture out?
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Old 01-13-2003, 04:40 PM
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not trying to grt nasty, but lean mixture and low octain fuel ,the only reason for run on eld. famous for lean idle .didny mean to pi88 in your corn flakes
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Old 01-13-2003, 05:25 PM
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I know that if you have an auto trans if you dont put it in park before shutting it off it can somtimes help.
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Old 01-13-2003, 05:39 PM
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Engine run on is caused by pre-ignition and the failure of the carb to cut off air/fuel flow.

You may have to add a anti/diesel solenoid. They are available from EDELBROCK and HOLLEY.
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Old 01-13-2003, 05:47 PM
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Richen your idle mixture and try advancing your timing which will raise the idle speed allowing you to turn down your idle screw closing up your throttle plates more. I also run nothing but premium gas, it's worth the extra money.

[ January 13, 2003: Message edited by: dmorris1200 ]</p>
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Old 01-13-2003, 08:16 PM
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Get that idle speed down first. What kultulz says is correct. Set idle speed to 450 - 500 rpm with the solinoid disconnected or at the lowest possible rpm w/out dying, then normal idle speed w/ solinoid on. Most of the time that will solve the problem.
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Old 01-14-2003, 02:29 AM
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[quote]Get that idle speed down first. What kultulz says is correct. <hr></blockquote>
KULTULZ never said that the idle was the problem. He said you need to cut-off the air/fuel flow which is not the same thing. If his idle is already set within specs (according to his post looks like everything set to specs) how do you close the throttle plates more? You advance the timing (raises rpm) and then compensate by turning out idle screw. Your idle ends up exactly the same in the long run but throttle plates close more and with the timing advanced a bit and she'll run better. Car's rarely ever run best when set to specs, except late model FI cars. By richening up the fuel mixture that will also help to reduce combustion temperatures which helps.

[ January 14, 2003: Message edited by: dmorris1200 ]</p>
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Old 01-14-2003, 04:51 AM
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[quote]KULTULZ never said that the idle was the problem. He said you need to cut-off the air/fuel flow which is not the same thing.<hr></blockquote>

[quote]...failure of the carb to cut off air/fuel flow<hr></blockquote>

Well...in all actuality...it is the same thing. When emissions dictated that carbs go lean, this saw the introduction of the idle kick-up solenoids. The fuel mixture ratio was so lean that it led to bad idle and stumbling on tip-in. They raised the curb idle to remedy this. But it caused run-on due to the throttle plates not being able to close properly and fuel mixture still being drawn into the hot combustion chambers.

You can most certainly enrichen the fuel mixture/advance timing to correct the problem. But what if the initial ignition advance causes pre-ignition on load or hard starting? What if the idle circuit enrichment causes excessive exhaust fumes and fouling of the plugs? Remember the early days (70's) of the first emission systems?

If he does these adjustments and they cause more problems than they cure, the idle solenoid will allow the idle to be set where desired with the engine in whatever state of tune desired. Once the ignition voltage is removed, it will allow the throttle plates to slam shut, eliminating the problem.

Now, he could also be experiencing throttle plate/linkage bind, not allowing the throttle plates to close entirely also.

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Old 01-14-2003, 08:13 AM
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Again correct kultulz. Remove the carb from the engine, turn it over, back off the idle screw until it clears the throttle linkage. Check the throttle plates by holding a flash light at the opposite end of the throttle plates. If you can see light around the edge of the plates you may have to adjust them. Loosen the 2 throttle plate screws on each plate and tap them w/ the handle end of the screw driver while holding the throttle shaft shut. They will self adjust. Retighten the plate screws then adjust the throttle stop screw till the plates just start to open, this will prevent throttle plate sticking from the closed plate position and prevent excessive air from bleeding around the plates. That, in turn, will shut off air/fuel flow and stop run on (dieseling). Check the secondaries to make sure they are closing completely also. Make sure the linkage isnt holding them open.

[ January 14, 2003: Message edited by: 2-manytoyzs ]</p>
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Old 01-14-2003, 02:18 PM
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[quote]Well...in all actuality...it is the same thing. <hr></blockquote>
No it is not the same thing, if I can close the throttle plate further without changing the idle saying "cutting off the air/fuel flow" and "lowering idle" are not the same.
[quote]When emissions dictated that carbs go lean, this saw the introduction of the idle kick-up solenoids. The fuel mixture ratio was so lean that it led to bad idle and stumbling on tip-in. They raised the curb idle to remedy this. <hr></blockquote>
This all assumes he has a stock set-up for post-emissions with a idle solenoid. He stated he installed an aftermarket carb. He may not even have an idle-up solenoid. The only reason you should need a idle-up solenoid on a aftermarket carb is for air conditioning load. Otherwise the carb should be jetted rich enough without any factory M/C solenoids, etc. to not require a idle-up solenoid. I have been doing carb swaps for over twenty years and have never used (needed) an idle-up solenoid except to provide a idle increase to handle A/C load. Also doing state inspections for many years one of the first things I learned is as soon as any old car(pre-fuel injection) passes emissions testing to bump up the idle a bit and richen the fuel mixture. Also anyone else in the field that I have ever worked with has agreed that the settings needed to pass emissions are definately not the settings you want to make the engine run it's best. They kill the poor things just to reduce emissions. You can see right in the pictures of my carb that there is no idle solenoid. Why, cause I don't need it because like you said it was just a crutch from the car manufactures to compensate for all the detuning they did for emissions. And since I've had my license and been working on street rods I have never once found a car that I couldn't run with more advance than factory spec and couldn't richen up to run better. Richer mixtures lower combustion temperatures, reduce pinging, and can actually if not done to far can reduce gas mileage (have read testing on the mileage issue). Stock is one thing, but once you can all the factory emissions garbage it's a whole different ballgame. Maybe before you tell him to lower his idle till he stalls out stopping you should ask him if he retained any emissions hardware and if he has a idle-up solenoid. Like I said originally and this was all I said, lowering the idle and stopping the air/fuel ARE NOT THE SAME as I can prove that I can close the throttle plates more without lowering the idle. That is all, whether you agree with that method is a diferent issue but I know what's been working on the many, many carbed cars that I've been running on the streets and racing 1/4 mile since I've been driving and doing this for a living. Heck I used to have friends that would regularly come to my job so I could lean out there carb and retard the timing enough to pass inspection tests and then as soon as they're passed I'd bump the timing back up and reset the carb and away they would go till the next year. Now I would think if this wasn't working I would have a lot of pissed off customers with fouled spark plugs.
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Old 01-14-2003, 02:32 PM
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EW-W-W-W-W-W-W-W-W

...sheesh...

Retaining water this week? I will just leave it alone...
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Old 01-14-2003, 03:09 PM
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Sometimes choke problems can do this.. at least it did on my car when the choke didn't work too well... make sure the choke isn't staying closed
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Old 01-14-2003, 05:52 PM
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Correct again kultulz!
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