Quadrajet, high idle with warm engine

[kikkegek]

Originally Posted by MadManAndrew

I personally gauruntee you that if you turn that choke on your problems will dissapear. The high idle of the electric choke will only go off when the choke has power and is functioming correctly.
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I checked the choke mechanism and it is not keeping the idle on high. I lifted the fast idle cam by hand and then it will keep the idle in the high position. But since the choke is not functional at all, it is not activacted,thus couldnt cause any high idle...

I wanna check tomorrow, but I even think they took out the choke-plate.

I'll take some more pics tomorrow.

I'll be back...

[ray_mcavoy]

Originally Posted by kikkegek

hi thanks for the reply.
I contacted ignitionman, maybe he can help me with the teflon mad...I dont really understand it.

Do you have any pics of how you did it?

I don't have any pics of the ones I've done so far, but I do have another Q-Jet with this problem that's on my to-do list. I'll take some pics of that one while I have it apart. Might be another week or two before I get around to it though.

Basically, what it involves is cutting a sheet of .014" or .015" thick teflon into little rectangles about 5/16" or so wide by about 1" long and rolling them into loops to form home-made "bushings". From the factory, the Q-Jet baseplate already has a stepped bore in the throttle shaft holes that provides the necessary clearance for these "bushings" (no drilling necessary). That is of course, assuming that your carb hasn't been rebuilt already by a shop that installed metal bushings. The hardest part of the whole procedure is getting those factory staked throttle plate screws out. And you need some somewhat hard to find #3-48 machine screws to replace them.

[kikkegek]

@ Ray: that would be great. pics would be greatly appreciated.

I took the top of the carb 2day, bt like I said. The carb linkage is absolutely fine when it is cold and the engine off.

here are some pics...didnt have time to take the whole carb of.




I also reconnected the Choke, but I dont think this will solve anything.

I did found out something more today. The linkage is also fine when the engine is at operating temperature, but not running.

I drove it a while today, turned it off and checked the linkage. And it moves just fine. When I then turn it on, the linkage last bit again feels harder to move, preventing it to go to full idle just with the springs.

This must be caused by the low pressure from the engine.

I did notice there it some movement in the linkage. I just dont know if you'd call it a lot or acceptable. Since I have no reference.

I am absolutely still in the dark what is causing the friction...cause that what it seems to bee...maybe the linkage has worn and theis causes the valves to rub the inside of the carb when the engine is running and sucking in air and gas?

[ray_mcavoy]

Originally Posted by kikkegek

@ Ray: that would be great. pics would be greatly appreciated.

Hi kikkegek,

Here are some pics and info on the home-made teflon bushing installation.

Photo #1 is a before photo showing the throttle not completely closing against the adjustment screw when the accelerator pedal is released normally.


Photo #2 is for reference to show the fast idle mechanism. The choke is open so the fast idle cam (stamped with the letter "Y" on this carb) is in the down position ... not holding the throttle up on fast idle.


Photo #3 is the baseplate removed from the carb. The removal procedure can be found in most repair manuals. Also shown in this pic are the materials necessary for the repair. I couldn't find a source locally so I ordered mine from www.smallparts.com


Photo #4 shows a quick "before" measurement of the throttle shaft looseness. About .020" of play. Enough to feel noticibly loose when wiggling the throttle shaft lever.


The throttle opened and closed just fine by hand (no catching). But if I put a bit of side pressure on the throttle lever (to emulate the spring pull), I could see that the throttle plates were making contact with the bore before reaching the fully closed position. This is what was keeping them from closing normally.

Photo #5 shows a Dremel tool being used to carefully grind off the staked ends of the throttle plate screws. Attempting to remove the screws without doing this will usually result in the heads twisting off.


With the staked ends ground off, simply unscrew the screws to remove the throttle plates. Take note of their position for re-assembly time. You'll also have to remove the linkage connecting the primary & secondary throttle shafts as well as the fast idle tang on the end of the primary shaft. Again, check with a repair manual if you need more info on removing these pieces. With all that out of the way, the primary throttle shaft (with lever attached) will slide right out of the baseplate.

Photo #6 shows the "stepped bore" that's present on all Q-Jet baseplates from the factory. This is what allows the teflon "bushings" to be installed without any drilling. The shaft only rides on the inner (smaller) part, leaving the outer (larger) part unworn in all but the most extreme cases.


Photo #7 shows the shaft laying on the baseplate. The orange arrows are pointing out the worn areas of the shaft that were riding on the smaller stepped down parts of the bore. The white arrows are pointing out the unworn areas of the shaft that were in the larger stepped up parts of the bore (this is where the home-made "bushings" will go).


Photo #8 shows one of the home-made "bushings" partially installed in the baseplate. Another "bushing" is temporarily placed in position on the throttle shaft for reference. These "bushings" are made by simply cutting the teflon into approx 3/8" by 1" rectangles and rolling them into a loop.


Photo #9 shows the driver side bushing being installed. With the bushing partially inserted into the baseplate, carefully slide in the throttle shaft.


Photo #10 shows the passenger side bushing being installed. Carefully slide it in between the shaft and baseplate bore.


Photo #11 shows the bushing fully installed flush with the edge of the baseplate. The .015" thick teflon is a perfect fit in the factory stepped baseplate bore.


Photo #12 shows the throttle plates re-installed with the new 3-48 x 1/4" screws. Make sure the throttle plates are fitting properly in the bores before fully tightening the screws. Use Locktite on the threads and "stake" the ends. You don't want these screws backing out and going down inside your engine.


Photo #13 shows an "after" measurement taken in a similar manner as photo #4. The play is down to .004" and not even noticible when wiggling the throttle shaft lever.


With the carb re-installed on the truck, the throttle now returns to the idle position normally. This particular carb only needed bushings on the primary shaft, but the secondary shaft can be done using the same procedure if necessary.

[kikkegek]

WOW Ray, that is a really nice write-up!

thanks man! I absolutely consider doing this...

[ray_mcavoy]

Hi kikkegek,

You're welcome! I can't guarantee that it'll fix the problem. But based on your description of how the throttle feels, adding some of these bushings should do the trick.

[geezer#99]

Originally Posted by kikkegek

WOW Ray, that is a really nice write-up!

thanks man! I absolutely consider doing this...

A word to the wise.
Find another carb and tear it apart and fix it. Just for practice.
If you ruin the one you have then you'll be without a truck to drive.

Awesome pics Ray.

[kikkegek]

alrighty,

checked the choke unloader 2nite, to see if it was causing the problem. unplugged it...first put a hose on it and sucked on it, but the unloader doesnt move...probably broken? is that bad?

I then plugged the connection to the carb and drove it a bit. But no change.

Still got the annoying high idle when I dont kick the throttle...

I made two short films (As requested) hope you guys can see what I mean...

first one without engine running (sorry movie is upsidedown)

YouTube - Quadrajet throttle without...

second one with engine running (sorry again upsidedown)

YouTube - Quadrajet throttle with engine...

As you can see it is only a very little bit that the throttle stays open.

and it's almost like the little play there is in the linkage seems to be gone when the engine is running. I can not feel any play when the engine is running.

[kikkegek]

I finally found the cause why my carb will not return to full idle postion...

I installed new dual springs...like they are supposed to be. BIG and THIN spring combo. These are a lot stiffer and have no problem returning the lever to the idle position.

So my problem was caused by weak springs...the ones that were on before did almost not offer any force when near idle position. while these new springs do...

as you can see in idle postion they are allmost fully relaxed...so PROBLEM SOLVED...thanks guys for all the support!