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4/01/2014 3:56 PM  #1


Carb/ High idle when warm

Hello everyone!  Boy has it been a long time since ive been on here, glad to see you are all still going strong on here, this is a truly amazing site!  I had to put my mustang on the back burner for a while as I was getting married and moving.  Now im back at it, and getting the new garage set up and finaly got the car there.  I just got the alignment done with the new steering box/column and its night and day difference. 

Im having an issue with the Carb though.  a while back alomost a year or so I had the carb rebuilt and it was going great.  Now after sitting it starts and runs no problem, but the high idle does not kick off.  Ive never been that great with carbs and was wandering if i have to spray some carb cleaner in it or have to loosen the 3 screws on the electric choke and adjust it?  any help would be greatly appriciated. 

Thanks

 

4/01/2014 5:34 PM  #2


Re: Carb/ High idle when warm

Welcome back...
Need details...

What engine?

What kind of carb is it?

Electric choke heater, or heated from exhaust manifold, or not hooked up?


Money you enjoy wasting is NOT wasted money... unless your wife finds out.
 

4/02/2014 12:31 AM  #3


Re: Carb/ High idle when warm

sorry, its a 302 V8, 5 speed transmission with a holly 600 cfm carb.  It has an electric choke hooded up via a positive wire from the coil.  It used to work without an issue now it keeps the idle up at 1500 even when warmed up it wont kick off the high idle when I rev it up.  Also if I pull on the gas pedal with my foot while at a light for example it does bring the idle down.  I dont know if maybe my return spring is worn or if its a carb issue or anything else.

     Thread Starter
 

4/02/2014 9:24 AM  #4


Re: Carb/ High idle when warm

Dis-connect linkage from carb.
Leave the return spring in place on carb.
What does it do now?
If it idles down normal its the linkage thats binding somewhere.
If it still idles high its a faulty carb or the electric choke.
After warmed up......disconnect choke and see what happens.
If it calms down its the carb..if it doesn't adjust the choke or leave dis-connected.

I made a simple heim joint and threaded rod carb linkage for mine.
Real smooth operation and looks pretty trick too.
6sal6


Get busy Liv'in or get busy Die'n....Host of the 2020 Bash at the Beach/The only Bash that got cancelled  )8
 

4/02/2014 9:36 AM  #5


Re: Carb/ High idle when warm

Not sure that you should be running the choke off of the positive coil wire.  It may depend on your ignition setup if not stock but if the system is using the original resitor wire you are getting reduced voltage to the choke heater as well as dragging down your ignition circuit.  I believe that running the choke off of a separate full voltage ignition-on circuit is preferred.  I agree, though, disconnect the linkage and see if it behaves.  Other possibility is that the high speed choke cam in back of the choke heater is stuck.  If you pull real hard on the throttle, you can bend the throttle rod and get the idle down but you are damaging the carb.  With the linkage disconnected it should drop back on to the idle screw with no force.  Do some google searches on choke adjustments, etc.  Holley has some great youtube videos on adjustments and troubleshooting that are easier to follow than any written description.

 

4/02/2014 11:49 AM  #6


Re: Carb/ High idle when warm

Another idea is to look around for a vacuum leak, they too could create a high idle.


65 mustang coupe, 351W, C6-  2800 stall, B&M blower, 9inch- trac-loc 3.70 gears
 

4/02/2014 12:29 PM  #7


Re: Carb/ High idle when warm

First, find a full 12 volt source to connect it to, such as the terminal on the back of the alternator.  You may not be heating the electric choke enough to do the job.

Second,  see that little red part on the passenger side?  Push it with your thumb and hold it down as you blip the throttle slightly, with the engine idling.  If the idle drops down, then you have determined that your choke is not coming off the fast idle cam (that red thing) fast enough.  The red piece cannot be pushed to normal idles speed setting (downward) unless the throttle is open slightly.   If it is a fast idle speed cam problem, that can be caused by wrong choke heater element setting, not enough voltage to the choke heater, the fast idle screw is adjusted too far, or there is something broken/missing/dirty that is keeping the fast idle from working right. 

Moving along...
Assuming a fast idle cam issue.
1.  Loosen the three screws on the choke heater element and rotate it while holding the throttle open slightly (engine OFF this time).  If the choke butterfly moves in corelation to the rotation of the heater element, we can move on to the next step.  If it doesn't, remove the black heater element (3 screws) and reinstall, making sure the loop on the end of the internal spring is connected around the tang on the lever inside the mechanism.  Once you get that hooked up, reinstall the heater.  With the engine at room temperature, hold done the throttle slightly, then rotate the heater element until the choke is just closed tight.  Then tighten the three screws.  Retest to see if problem is fixed.  If not... here we go for step 2....

2.  OK, it must be assumed that if you held the red fast idle cam down, the carb would return to its normal idfle setting.  With the red cam all the way down, adjust the normal curb idle where you want it to idle.

3.  Next, remove the carb, drain the gas out of it, and turn it upside down.  This will let you see the fast idle cam.  The red cam has three steps on it.  Take a razor blade and remove all but the last, biggest step on the cam.  Make your cut smooth, and at about the height of the lowest part on the cam.  What you are doing is revising the cam so that when you first start the engine, the fast idle cam will be at its highest setting so the engine can idle when started cold without you having to hold your foot on the gas.  The cam is designed so that, over time as the engine warms up, it moves from the biggest step, to the middle step, and then finally the smallest step, then to no step.  Remove all but the highest step.  Then you can start the car, let it idle on fast idle for ten seconds or so, then blip the throttle and the fast idle cam will come completely off the cams so you are back at normal idle.  This works best in warm to moderate climates.  If you drive the car and it is 30 below all the time, leave the cam alone.  By removing those steps, it lets the fast idle go away quicker, and then you can adjust the choke settings as you like without having to worry about whether it is going to trip top the fast idle setting.

4.  Once you get the steps removed, close the choke butterfly so the fast idle speed screw is sitting raised up by that one step on the fast idle cam.  Adjust the screw so that you have 0.030" clearance between the curb idle speed screw (on driver side of carb) and the linkage that interfaces with the curb idle screw.  BAsically, you want the one last step on the fast idle cam to hold the throttle open 0.030" until the choke heater heats up and releases the linkage off the fast idle cam.

5.  Turn it over and bolt it back on.  Assuming all the linkage works freely and you have full 12 volts, it should work fine.

6.  If that fast idle is too fast or too slow to suit you, you can open the throttle 100% (engine OFF) and reach that fast idle screw by turning yourself upside down on the passenger fender and getting a 1/4" wrench (older Holleys used a slotted screw).  Tighten the screw to raise fast idle or loosen it to lower the fast idle.

All of that razor blade mod will allow the carb to come off fast idle much sooner, but still leave it working for initial starts, making the car much more liveable for the typical gearhead.


Money you enjoy wasting is NOT wasted money... unless your wife finds out.
 

Board footera


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