Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
Heavier throttle (mostly) issues
MP81:
Updates from today - stopped just before putting the air horn back on just in case there is any feedback that requires me to access the components that would be under it.
Cleaned up the main casting and throttle plate a bit:
Main casting and throttle plate reassembled:
New needle and seat installed
New float installed:
Mixture control solenoid, metering rods and power piston reinstalled:
New accelerator pump installed and TPS reinstalled:
I also reinstalled the choke housing and linkage.
tayto:
--- Quote from: MP81 on September 12, 2019, 02:04:14 PM ---1. I found the needle still stuck to the old float via a clip. I believe I have read this clip is not necessary (I see the new one does not have one), which makes sense to be, but I figure I'd be sure, as I can probably put the old one on the new one if it's of any help to the carb.
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If you are running a stock mechanical fuel pump I would opt to keep
it. I rebuilt a qjet for friends stock 1980 Firebird about 4 years ago and discarded the clip. Upon attempting to start the car would only run if I dumped fuel down the throat. Removed airhorn and found the needle sealed so well the original pump could not break it free. Installed clip, fired up immediately and ran great after setting idle speed, mixture, etc. Now could the pump have just been tired? Quite possible, I know Cliff runs an e-pump and has diacarded the clip.
--- Quote ---2. The needle seat in the kit looks to have no slots near the threaded base, whereas the one I removed from the carb does. What is the purpose of those slots in the old one - was that the incorrect one that someone put into this carb in the first place?
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Most likely an aftermarket replacement, it's clear that someone has rebuilt the unit before. Install the correct one supplied in the kit and move on.
--- Quote ---3. The secondary cam - this looks to go up top in the air horn? The screws I imagine are for the secondary air plates? Remove those, remove the shaft and install the new cam/spring?
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make sure to grind the tips of the screws off if it hasn't been done already. they are staked from the factory and there is a good chance they will snap off upon removal. i reinstall new screws with blue loctite once i get the flaps where i want them.
--- Quote ---4. Because I am (probably) an idiot, I did not count the number of turns of the lean mix screw before I removed it. I can see a distinct change in color that shows me, roughly, how far down it was originally, so that helps, but is there a good way to set that? The plug in the air horn above is removed, so I should be able to adjust it, on car, I believe - I may have to make a tool, though (I bought a flexible Lisle one for the lower two screws, if needed - rather have it and not need it, than need it and not have it). This may lead into the next question...
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I believe Cliff's generic starting point is 5.5 turns out from seated for the APT and 2.5 turns out from seated for the idle mixture screws
--- Quote ---5. Dwell meter - do I need one?
Hopefully less chaotic of a (long) list than my 453,000 posts before.
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I have an automotive DMM that has dwell and rpm settings. My digital timing light also has one. If you have access to a DMM that can measure duty cycle you can convert to dwell with this formula:
Dwell = (360 divided by # of cylinders) x (%DC divided by 100%)
Have you verified that the throttle shaft has been bushed? I have not come across a single unit that doesn't need bushings.
MP81:
Hot damn - thanks for the replies to all my (too many) questions!
The clip looks easy enough to remove, and I don't have to do too much work to get back down to that point, so I can pop that on. It just goes through one of those slotted holes on the end of the float, yeah?
I'll have to check the screws up top and see, but thanks for that advice - something I likely would have missed. So those four screws are for the throttle blades - remove those, pull the shaft out, and replace the cam/spring in the center?
Regarding the lean mix adustment screw, which also holds the mixture control solenoid down, it seems like when I removed it, it was basically tightened to "tight" - I'm not sure it should be any other way, because otherwise the solenoid would be pretty loose. I'm tightening by hand though - I get the double-D "socket" today, so it'll be easier to do than using my fingers. I tightened it back to the same "point" - and angle of the Double D - as what I removed. But that'll come out when I put the clip on the needle.
Looking at getting this, as it measures Dwell Angle...and has Prime Same Day: https://smile.amazon.com/INNOVA-3340-Automotive-Digital-Multimeter/dp/B000KIMHRQ/ref=sr_1_1?keywords=Automotive+DMM&qid=1568374886&s=gateway&sr=8-1
As far as the throttle shaft - I do not think I saw any bushings, but I have to look again. With the primaries open, there was probably 1/16"-1/8" end play or so, but as the blades closed, they centered themselves. The shaft rotates nice and freely, without any play around the shaft itself, just end play.
At this point, I don't have time to do the bushings, since the carb needs to be back on the car (and tuned) tonight. But it seems to spin freely, which is good.
MP81:
Cool, my buddy has a timing light with the dwell function, so I'm just going to borrow that from him today.
I've noticed various O-rings in a bag (where a new check ball was) as well as a small thicker round gasket (maybe an inch diameter) and then a very thin white plastic ring of a similar diameter - can't figure out where any of these go.
MP81:
Looking at the CCC instructions, it seems they recommend 3.5 turns back from bottomed out:
https://cliffshighperformance.com/wp-content/uploads/2018/10/1981-up-ccc.pdf
I will start with that, I'm thinking.
I'm going to see if I have something thin that'll fit down the boss of the air horn in the event I need to tweak from above - the tool I bought does not have a small enough DD for the LMS - it does fit the two idle mix screws on the bottom though.
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