| Primary throttle plates and linkage slop [message #261275] |
Mon, 08 September 2014 06:35  |
budworks521
Messages: 137
Registered: October 2013
Location: Grand Rapids MI 1974 Pain...
Karma: 4
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I got my rebuilt carb back and installed. I noticed that once it is all together that the accelerator pump linkage/primary throttle plates to the gas pedal has some wear (rubber retainer and slip ring) which seems to keep the primaries slightly open at idle. If I push the throttle linkage forward the plates move a tad bit and the idle slows dramatically. I have slight popping in the carb at idle and if you throttle it it goes away. My intake had some carbon build up in the primary area and number 5 and 8 plugs had carbon on them. My question to the veterans out there is: will new parts (available from GMC place in California) cause more tension on the plates to close them tighter? They seemed tight when I got carb back and explained this to the rebuild guy. He said he worked on getting the plates tighter. Also, has anyone ever run into a scenario where the ignition module and coil pack on top of the distributor tested within parameters and still worked wrong. My vacuum is good and my compression testing was good. Thanks
1974 Painted Desert
455 upper half rebuild
constant project inexperienced mechanic
Grand Rapids Mi
Always trying to learn
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| Re: Primary throttle plates and linkage slop [message #261277 is a reply to message #261275] |
Mon, 08 September 2014 06:51  |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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The carb closing is forced by TWO carb return springs. One is inside the other and mounted from the carb linkage forward to the intake manifold. If one is missing or broken you will have the symptom that you describe. Replacement springs are available from Dorman and sold by most auto parts stores and Jim Kanomata.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Primary throttle plates and linkage slop [message #261347 is a reply to message #261275] |
Mon, 08 September 2014 23:09 |
Craig Lechowicz
Messages: 541
Registered: October 2006
Location: Waterford, MI
Karma: 0
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Along with the two springs which Ken Burton has mentioned, the other thing that seems to cause inconsistent idle speeds is near 40 year old rusty, stiff throttle cables. My friend Tim and I have both ended up replacing them on our coaches. Although his was damaged by a small electrical fire, and mine was so stiff it kept the cruise control from operating correctly, it can also effect idle speed repeatability.
Craig Lechowicz
'77 Kingsley, Waterford, MI
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| Re: Primary throttle plates and linkage slop [message #261367 is a reply to message #261275] |
Tue, 09 September 2014 07:00 |
budworks521
Messages: 137
Registered: October 2013
Location: Grand Rapids MI 1974 Pain...
Karma: 4
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I was beginning to wonder about my throttle cable as well, the rubber retainer is very worn and sloppy thou I did manage to stiffen it up. My tension seems to be fair and now I am leaning towards bad gas since it took forever to fire up my generator. Same thing with the 455 hard start when cold easy start when hot. I checked the wires for the plugs and saw equal numbers for plug wire lengths, I might try my new plugs but not sure if that would be it. Running out of ideas, either ignition, fuel, or timing and the timing is dialed in and ran great up till late June. Thanks for any help identifying my carb popping noise.
1974 Painted Desert
455 upper half rebuild
constant project inexperienced mechanic
Grand Rapids Mi
Always trying to learn
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| Re: [GMCnet] Primary throttle plates and linkage slop [message #261373 is a reply to message #261367] |
Tue, 09 September 2014 07:51 |
Jim at the Co-op
Messages: 291
Registered: May 2014
Location: Orlando Florida
Karma: 2
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This is one of the problems working with old iron. We are running into
issues then manufacturer never considered. There is use and then there is
time-- both are killers. I joke about having a hole in a metal plate worn
out but that is what you have here. A carb "rebuild" on an older carb has
to entail more than a carb kit and a good clean job. Tolerances in things
need to be considered. The company I use to refurbish my carbs does just
that. For $285 a carb will have been totally dismantled and every part
checked as it goes back together. The carb is run through a flow bench
then put on a big block motor for a 3 gas exhaust evaluation. It's fitted
with a new electric choke so you are ready for the exhaust crossover
blocking procedure. Unless there are plates replaced, the $285 covers the
job.
Not taking anything away from local rebuilders, they are simply not
prepared to do the things needed sometimes on our older parts. I have
found this process works well for me, whatever you do---- do not swap carbs
at a shop. Have them remanufacture your carb. You know it's trauma and
where it's been.
Definition: Carberator---- a controlled series of spring loaded air and
fuel leaks...
Jim bounds
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On Tue, Sep 9, 2014 at 8:00 AM, Lawrence Harrison
wrote:
> I was beginning to wonder about my throttle cable as well, the rubber
> retainer is very worn and sloppy thou I did manage to stiffen it up. My
> tension
> seems to be fair and now I am leaning towards bad gas since it took
> forever to fire up my generator. Same thing with the 455 hard start when
> cold easy
> start when hot. I checked the wires for the plugs and saw equal numbers
> for plug wire lengths, I might try my new plugs but not sure if that would
> be
> it. Running out of ideas, either ignition, fuel, or timing and the timing
> is dialed in and ran great up till late June. Thanks for any help
> identifying my carb popping noise.
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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| Re: Primary throttle plates and linkage slop [message #261403 is a reply to message #261275] |
Tue, 09 September 2014 14:23 |
budworks521
Messages: 137
Registered: October 2013
Location: Grand Rapids MI 1974 Pain...
Karma: 4
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Again I just went out to my 455 and pumped three times and "forced the primaries completely closed" i.e. pushed throttle arm forward tight and my engine started right up. IF I don't do that it takes many turns on the engine to get it running. I still have serious popping in the carb as if running lean and that means more air and less fuel. If my gas is bad I wonder if that would cause the noise. My carb rebuilder said that most quadra jets have some slop in the bushings and allowed for air intake with the primaries not completely closed back in the 70's. WHY does my engine only want to start easier with the primaries completely closed when starting??? I am going to drain the tank of my 7 month old 93 octane gas and try fresh gas and see if that is my problem. What a debacle...
1974 Painted Desert
455 upper half rebuild
constant project inexperienced mechanic
Grand Rapids Mi
Always trying to learn
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| Re: Primary throttle plates and linkage slop [message #261512 is a reply to message #261275] |
Wed, 10 September 2014 15:59 |
Chris Tyler
Messages: 458
Registered: September 2013
Location: Odessa FL
Karma: 7
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I assume this is with the choke off?
Air leaks at the throttle shaft are a common problem with older Q-jets. Bushings are not usually replaced on most rebuilds. The kits are availible but it is somewhat involved to do. First time I did one I bent the shaft.
Which leads me to the next question: With the linkage and external springs off, will the primary shaft spring back on its own? The spring on the shaft should do that.
Check for binding on the accel pump link. [Some rebuilds have a speed clip put on the link for easy removal] also, check to make sure the high idle cam on the choke isnt hanging up. This puts the idle stop higher when the choke is on and can be adjusted.
You can get higher tension return springs from summitt or jegs or what have you.
Older Qjets have exposed idle screws that you can easily adjust. later ones still have the screws, but they have plugs over them to keep people from tampering with them. You can pull the plugs with the carb off and rig some extentions to adjust the mixture for best idle
Quick way to check if you are too lean is to cup your hand over the air horn. If it smooths out, you are too lean. It is also possible you are too rich at idle if the float level is too high or if the wells are leaking.
Quick way to check the shaft for leaks is to spray with lthium grease, which will breifly seal it. You can also check for vac leaks with WD40 and a extention straw. do one spot at a time
Hope this helps.
76 Glenbrook
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| Re: Primary throttle plates and linkage slop [message #261671 is a reply to message #261275] |
Fri, 12 September 2014 05:41 |
budworks521
Messages: 137
Registered: October 2013
Location: Grand Rapids MI 1974 Pain...
Karma: 4
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Senior Member |
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My bushings had been replaced but still seem to be making my plates hang up. The rebuild guy said the shaft might need to be replaced? I did find that my accelerator cable had a lot of slack and I did fix that with the split shot sinker trick found in the forums. I have yet to test if it will keep the plates tighter at start up. I will still experience the popping noise though. I threw a shop towel over the air horn with it running at operating temp and the engine ran the same so I guess it isn't running lean in that regard. I also adjusted the idle screws a bit to lower the idle/rpm and it helped. I'll check out the items you mentioned over the weekend. As far as I can tell all the stuff you mentioned seems to be spot on. I want to test the vac break diaphragm and see if it is working right. I read reports that if it isn't it leads to flooding of the carb which I am experiencing with my gaskets being wet. Thanks for the input.
1974 Painted Desert
455 upper half rebuild
constant project inexperienced mechanic
Grand Rapids Mi
Always trying to learn
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