Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

Ping when secondaries open up

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da_raabi:
Hi, I'm new here and fairly new to quadrajet carbs. I've rebuilt two of these in the past year or so. The first was from an old 1985 RV 454 I put in my Camaro, and that went well. The second was a similar carb that is on my 1986 Chevy C30 with the 454 (my daily driver). This one is giving me some trouble. I'll try to post up what I'm dealing with, any help that can be provided would be amazing. I'm at my wits end on this one!

The carb is the original for the truck. The serial is 17084226.

Before the rebuild the carb ran well. It's only issue was a bog when the secondaries opened up. It would fall on its face for about a half second, then take off like nothing happened. However, my primary reason for the rebuild was so that I could switch from 89 ethanol free gas to 87 or 89 regular (and save the 70 cent per gallon surcharge).

The engine is the original 1986 454 with no major modifications besides the removal of all emissions equipment.

During the rebuild I noticed one of the secondary emulsion tubes had fallen out and was plugged. I cleaned it out and tapped it back into place, along with tapping the three other tubes in as well as they were loose. I have no idea if they are over or under driven. I looked in Cliff's book but could not find any specification of how deep these should be inserted into the air horn. Specifically, I looked at page 85.

I did a quick rebuild, up-sized the main jets to 74s but left everything else alone.

I had trouble getting the choke back together as the arms had fallen off the choke shaft. Ultimately I appear to have gotten it right, and the choke now seems to function.

So now after the rebuild I have two issues:

The engine now pings heavily when the secondaries open (after being warmed up).
The fast idle does not like to disengage without manually doing it with your fingers (bumping the throttle does not do it).

I've adjusted the timing 20 ways to Sunday and tried both 87 and 89 octane ethanol fuel.

What could be causing this? Could this all be related to the choke linkages still being incorrect?

Thanks for all your help!

Cliff Ruggles:
"I had trouble getting the choke back together as the arms had fallen off the choke shaft."

Pretty rare for any of those parts to fall off the shaft but they must be correctly oriented and driven back on to the correct depth or the choke may hang-up like you are seeing.

Wouldn't have anything to do with the detonation issue provided the choke flap is wide open and engine fully warmed up when you are testing it.

A lean condition at full throttle or too much total timing would be the place to start.  It's typically not easy or common to get a later model low compression engine to ping on pump gas unless it's getting way too much timing (weak distributor springs will do this) or secondary metering rods not getting lifted high enough.

Did you use one of our kits and install a new plastic secondary cam/spring?........Cliff

da_raabi:

--- Quote from: Cliff Ruggles on January 24, 2019, 03:20:50 AM ---I had trouble getting the choke back together as the arms had fallen off the choke shaft.

Pretty rare for any of those parts to fall off the shaft but they must be correctly oriented and driven back on to the correct depth or the choke may hang-up like you are seeing.

Wouldn't have anything to do with the detonation issue provided the choke flap is wide open and engine fully warmed up when you are testing it.

A lean condition at full throttle or too much total timing would be the place to start.  It's typically not easy or common to get a later model low compression engine to ping on pump gas unless it's getting way too much timing (weak distributor springs will do this) or secondary metering rods not getting lifted high enough.

Did you use one of our kits and install a new plastic secondary cam/spring?........Cliff

--- End quote ---

Cliff,

Thanks for getting back to me on this. Let me see if I can answer some of your questions.

As to the choke arms, I was surprised as well. This did not happen on my first rebuild, and made for quite a lot of confusion this time around. For some reason, the arm that presses onto the splined portion of the shaft is very loose and keeps wanting to fall off. I know this is a redneck fix, but I put a very thin washer between it and the carb body to take up a little slop. The result is the choke works perfect, but I still have a sticking fast idle.

As to the ping issue, and first in answer to your question - unfortunately I did not use your kit. I did now know about your kits (or your book) until after I started researching my issues. Suffice it to say now I do!

I did not replace the plastic secondary cam, and in fact I totally forgot to remove it while cleaning the carb. Is it possible the carb cleaner could have destroyed the cam?

I'm pretty sure my issue is not timing, unless something happened while the carb was off the truck. It ran fine before the rebuild (although now I think on it, it did have a little tiny bit of ping under WoT conditions, barely enough to even notice). I also retarded the timing to the point of almost killing the engine, and it had no effect on the ping.

Cliff, thanks so much for your time. I don't know a whole lot about automotive carburetors, but I'm trying to learn!

-Adam

von:
This may not apply in your case but if your engine has an exhaust recirculation valve (EGR) it might. Any time I ever removed the vacuum line from one of those and plugged the line, the engine pinged horribly. Just a thought.

Cliff Ruggles:
"The result is the choke works perfect, but I still have a sticking fast idle."

I have PLENTY of those items in spare parts.  I've built over 10,000 later carbs with hot-air and electric chokes and have only ran into a couple where that part needed replaced, it's typically not a trouble spot with these units.

Shimming it will NOT work as it needs sufficient clearance to allow the fast idle cam to drop once the choke opens all the way.

If you didn't get the orientation right when you put the parts back together where they spline it will also cause choke problems.

If you didn't use out kit you didn't get a high flow N/S assembly and that could be part of the pinging issue as the carb fuel bowl gets sucked low when a small N/S assembly is used, leaning things out.

At a minimum I'd get one of our kits so you get the cam/spring, new retainer for the power piston, a much better accl pump, and the high flow N/S assembly.  I'll throw in the choke part at no cost so you can get rid of the washer deal and it will be indexed for correct choke function.......Cliff

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