Quadrajet Questions

[OldsFan]

Ok, so I pulled the carb and figured a few things out.

1) You're 100% right.  The accelerator pump cup seal is getting hung up and causing issues.  Take a look at the pics to see what I mean.  That's how it came out of the bore, with the cup seal wrapped around the return spring.

2) I compared the original pump and the new one and it looks like they are the same.  Measured with a caliper, the inner plastic pieces are a couple thousandths off.  The outer seal on the original is obviously much smaller, but also pretty worn out.

I am going to come back on the dual-capacity solenoid stuff.  You may be right, but I am thinking of replacing the temp switch just in case.  Still, lemme get the carb right first, then we'll troubleshoot that...

Pick up a GM 1711591 pump kit.

Is there a good place to get these?  Do you think the Napa ones are no good?

Even small amounts of silicon will damage O2 sensors, making them ineffective.

No O2 sensors on my truck.  No CCC, just a knock sensor and electronic spark retarder.  Still, I get the picture and good you mentioned it.   Was thinking of putting in a wideband, so it is a good idea either way.

As far as the procedure for polishing up the bore, that sounds great.  I think I understand exactly what you are describing.  Just one question...  You mentioned that I should "Remove the valve and check in the base of the accelerator pump bore."  What did you mean by "check in the base" of the bore?  Were you talking about removing the check ball that is under the screw next to the pump bore?

[bd]

Enriched fuels take their toll on rubber compounds.  Some pump cup materials are more prone to swelling than others.  From the image you posted, it seems that applies to the Napa pumps.

Typo on the GM part number - it should have read 17110591. 

The 17110591 cup is made from Viton and has a distinctive red color.  I installed literally hundreds of these before the advent of factory injection to resolve pump cup distortion issues resulting from enriched fuels; and I enjoyed great success.  Likewise on burnishing the pump wells.  The pump kit "should" be available through any Chevy/GMC dealer or AC Delco retailer.  You can Google the P/N as well, with hits on Ebay, etc.  Tip: Spray the plastic cone in the kit with WD-40 to make installation onto the plunger assembly easier.  Then, install the cup and expander spring together in one step.

I mentioned silicon contamination of O₂ sensors, because of your earlier thread on the wideband installation.   

Remove the dual-capacity valve below the solenoid and remove the accelerator pump check ball under the screw retainer, because polishing the bore will produce fine abrasive particles that will find their way into the pump passages.  That way you can wash and blow the passages clean when your done, prior to reassembly.

If you measure the voltage drop across the DC Temp Switch with the circuit connected and ignition switched on, you should measure the same voltage as that supplied to the solenoid, until the engine heats to temperature and the switch closes.  At the point the switch closes, you should measure zero volt drop across the switch.  The switch is digital.  It's either open or closed.  Resistance through the switch should be infinite when cold, switching suddenly to zero as it closes when the engine heats sufficiently.

[OldsFan]

Ahhh...  The improved part number helps a lot.  I was wondering why I couldn't find it googling it before.  I'll order one tonight.

I mentioned silicon contamination of O2 sensors, because of your earlier thread on the wideband installation.   

Wow.  Your memory is better than mine!  I barely remember talking about that and once the carb started acting up, just put it out of my mind altogether.

Remove the dual-capacity valve below the solenoid.

Yeah, this is the one thing I haven't figured out how to do.  Looks like you could use a pair of screwdrivers to twist it out or maybe needle-nose pliers?  I think it is just threaded in there, right?

Oh yeah, are you sure on the 120 grit emery?  I picked up some, but it feels pretty rough, like it might tear up the bore.  I got some 1200 as well, just in case.

[bd]

Remove the dual-capacity valve below the solenoid.

Yeah, this is the one thing I haven't figured out how to do.  Looks like you could use a pair of screwdrivers to twist it out or maybe needle-nose pliers?  I think it is just threaded in there, right?

There is actually a "special tool" for that - lol  (It seems there are special tools for e/g - need to keep the tool companies happy I guess  ).  Get a large screwdriver that will fit the slot then notch it with a file or hack saw for plunger clearance.  It just threads in.  There are some select dash nut sockets that work, too.

[bd]

Oh yeah, are you sure on the 120 grit emery?  I picked up some, but it feels pretty rough, like it might tear up the bore.  I got some 1200 as well, just in case.

At 20,000 RPM, 120 should work just fine.  Remember, it's only a 1/4" arbor.  The paper will unwrap and  expand outward to polish the bore.  You will not be applying pressure to the bore with the arbor.  Perhaps, "polish" is the wrong word.  You're not trying to create a shiny bore - rather you are breaking any wear marks and smoothing the bore with a very fine crosshatch pattern.  The entire process generally takes only about 5 - 10 seconds with the hone to achieve a finished surface.  If you are uncomfortable using 120, go finer.  But, you're not wet sanding paint - 1200 will take a  l-o-n-g  time.

[OldsFan]

Ok, I understand.  I pulled the carb apart tonight and tried to "feel" it with my finger.  It isn't rough like sandpaper or anything, but clearly it isn't right.  The pump hangs up badly when it is dry.  The old one just drops right in there.  But I think it is original to the carb, so it may have just shrunken and dried out over the years.

I'm going to let things dry out a bit before I try to burnish the bore.  Even a small amount of gas and sparks sounds like a bad idea. 

I ordered the GM pump you recommended.  That'll take a couple days to get here.

In the meantime, two more questions related to this:
-Did they make multiple size accelerator pumps?  The original just looks so much smaller than its replacement.

-I noticed that driving around with the carb after the rebuild, it took more cranking to get it to start after sitting than it used to.  It isn't a lot more cranking.  Let me put it this way - before, if I let the truck sit for 6 hours, it would start instantly with two pumps of the pedal.  After the rebuild it was taking more like 5 seconds.  Could this be because the accelerator pump was messed up and the pumps of the pedal had basically no effect?

[bd]

Ok, I understand.  I pulled the carb apart tonight and tried to "feel" it with my finger.  It isn't rough like sandpaper or anything, but clearly it isn't right.  The pump hangs up badly when it is dry.  The old one just drops right in there.  But I think it is original to the carb, so it may have just shrunken and dried out over the years.

I'm going to let things dry out a bit before I try to burnish the bore.  Even a small amount of gas and sparks sounds like a bad idea. 

I ordered the GM pump you recommended.  That'll take a couple days to get here.

In the meantime, two more questions related to this:
-Did they make multiple size accelerator pumps?  The original just looks so much smaller than its replacement.

-I noticed that driving around with the carb after the rebuild, it took more cranking to get it to start after sitting than it used to.  It isn't a lot more cranking.  Let me put it this way - before, if I let the truck sit for 6 hours, it would start instantly with two pumps of the pedal.  After the rebuild it was taking more like 5 seconds.  Could this be because the accelerator pump was messed up and the pumps of the pedal had basically no effect?

Bore diameters have been fairly consistent for a long time.  However, pumps were manufactured in various lengths.  Compare the original pump to the service replacement.  Are they the same length?  With the duration spring removed, wiggle the upper shaft where it enters the lower plastic cup holder on both pumps and compare the amount of looseness.  Are they similar or notably different?  If the pumps are different lengths, use the original.  If the pumps are the same length, but the newer pump has less 'wiggle,' use the newer pump.  The 17110591 pump and expander spring will be slipped onto one of the two plungers.

As to differences in starting, before and after your rebuild... you installed a new float and set the float level (the old one was heavy), you replaced the accelerator pump (the old one was worn undersized, the new one stuck in its bore), you adjusted the idle mixture screws, perhaps you epoxied the various fuel well plugs (you didn't say), nearly all Qjets exhibit warped fuel bowl covers, etc, etc, etc.  Is there any wonder that fuel delivery changed?

Remember when you "fit" the new pump (lubricated with ATF or a sparse amount of silicon grease) into the bore, it should slide like silk while providing a positive seal and strong pump shot.  And, don't forget to reinstall the ball check, etc, after thoroughly cleaning the passageways.

[OldsFan]

Hey Rich - I finally had some time this weekend to do this.  It seems to have worked.  I was concerned about the 120, so I used 220 grit and just worked it a little longer.  It caused a lot of white dust to be spit back out and seems to have cleaned up the bore a lot.  I cleaned it thoroughly with Berrymans and let it dry out over night.  After that, I just dropped the check ball back into place and screwed it and everything else back down.

Initially, the pump was still coming back up somewhat slowly, but then I put some silicone dielectric grease on it just above the air horn.  That made all the difference!  I tried it out and there is now no stumble when cold or hot.  It actually seems to be a lot smoother than before.  The thing that has me concerned is just that the stupid seal is obviously gripping the pump shaft a bit too tightly.  I guess I'll have to re-apply the grease now and again. 

So, coming back to your other comments...
-Yeah, I ended up keeping the original pump but putting the new seal and garter spring on it.  The pumps were very, very similar, but I figured the original had worked for years and seemed "tight" enough after the test you mentioned.

-Starting is also greatly improved.  Two pumps and she fires up on the first crank.  I am thinking that the pump seal was so bad that it wasn't putting any fuel into the bore and so it was taking a long time to raise the mixture to an appropriate level without it.

-I tried something new on the well plugs this time.  I found some epoxy that was listed for being "gasoline resistant" and able to be used to fix fuel tanks.  I forget now what it was called, but I'll look it up.  I've always used JB-Weld in the past and had good luck with it, but I figured on trying something else out.  As long as it stays put, I should be ok... 

[bd]

Congrats!

Regarding the pump shaft seal in the bowl cover, I suspect that it was staked too tightly, causing it to compress slightly - hence expand inward, tightening around the shaft(?).

[OldsFan]

Ok, so assuming you are right about the shaft seal...  And it is altogether possible -
Do you think I should pull the air horn and replace the seal and try to just drop it back into place?  I had a lot of trouble replacing that seal and getting the washer-like backer to stake back into place, so I may have overdone it.



Also, can you tell me how you would test that temp switch for the dual capacity pump shot?  I mean, the truck is driveable (and runs quite happily again), but I don't think the temp switch is ever grounding.  Because of that, the pump shot does not get reduced when the engine reaches operating temperature.

If you think it doesn't really matter, I'll let it go - but my overall goal is to make it perform as well as it can.  To be fair, I am pretty sure this wasn't functioning before my rebuild either.  Take a look at the attached pic.  The crud in there is (obviously) from when I was tearing it down.  Don't worry, that's long gone now! 

[bd]

The accelerator pump shaft seal may relax with use and not require further attention, so I wouldn't pursue the seal unless it continues to bind the pump.  For future reference, the pump shaft seal rarely needs to be replaced during an overhaul.  Carburetor cleaner doesn't affect the seal and they almost never wear out.

You can check the dual capacity temperature switch with a voltmeter or an ohmmeter.  The temp switch is OFF-ON and either open (cold) or closed (warm). 

Voltmeter: Measuring the voltage drop across a cold dual capacity temperature switch with the circuit connected and ignition switched ON should register the same voltage as that supplied to the dual capacity solenoid.  Once the engine heats to operating temperature and the switch closes, you should measure "zero" volt drop across the switch. 

Ohmmeter: Resistance measured through the switch with the switch unplugged from its circuit should be infinite when cold, switching abruptly to "zero" ohms as it closes from engine heat.

As to whether you should "restore function" to the dual capacity pump (DCP), you stated that the engine presently accelerates well with no hesitation when cold or hot.  Well, the DCP is designed to decrease the pump shot when warm, which could introduce a warm hesitation.  Why not try this simple test.  Bring the engine to operating temperature, ground the temp switch wire to energize the solenoid, and then test drive it.  Determine what effect the DCP will have on drivability.  Then decide for yourself and post the results.