Pinging at WOT second gear

[l.neidlinger]

Hello all,

I have a 1982 GMC C1500 that I have been slowly getting the carb dialed in after having to fix vacuum leak after vacuum leak and other problems the truck has had after sitting for 10 years.

I bought a rebuilt carburetor for it, but have been having problems with it pinging at WOT in 2nd gear, right around 65 MPH, about when you can hear the secondaries start to open. The balancer has, unfortunately, slipped and I cannot accurately set the timing. I run 89 octane gas, and have the base timing set to where it won't ping at WOT in 2nd anymore, but it seems that is set too retarded as it bogs and backfires up through the carb if you accelerate hard from a stop or low speed, and if you punch it at cruise, the engine stumbles for a second, then picks up. I checked the accelerator pump shot, and it seems ok.

I took the secondary rods/hanger out and found some interesting things the rebuilder did. The passenger side rod is a "CH" rod with a large witness mark ground into it, the driver side rod is a "DR" rod, the hanger is a K. Could there be some problem with the secondary rods being too lean, or the air door opening too late?

Here is a (admittedly blurry) picture of the "CH" hanger:

[l.neidlinger]

I should have specified - Truck has a bone stock 305.

I still have the stock quadrajet that came on it. I took the secondary rods out of that to compare. It has a J hanger with DR rods. The rods look very good, I may pop those in with the J hanger and see how that works out.

[l.neidlinger]

Threw in the DR rods and J hanger from the original carb and drove it to the store and back. The bog at WOT seems to be greatly reduced, but the weather has been colder today and this carb seems to love to run completely different if the temperature outside changes even just a little, so I will have to see when it decides to actually be spring around here.

I did notice, now, what sounds to me like "light" pinging at WOT at lower RPM's. I could just be crazy. A 305 couldn't be this thirsty.

[Cliff Ruggles]

The best thing you could ever do here is to completely and correctly rebuild the original carburetor and put it back in service........Cliff

[l.neidlinger]

Unfortunately someone tried replacing the mounting gasket on this truck some while ago and when they tightened the fitting for the brake booster too tight and cracked the throttle plate.

[l.neidlinger]

Well, thanks National Carburetor.

It must have sucked a gasket today. Suddenly surges like a vacuum leak at idle. Disconnected all vacuum lines, no change. If I put my hand over the choke, it pulls 20" and smooths out. Sprayed around the outside of the carb, no changes. Must be internal.

The inside of this carb is horrid. It looks like it was used as a saltwater boat anchor. The mating surface of the body and the air horn is the same. It looks like they tried to get one of the jets out, but it was stuck and they nearly rounded out the jet trying to get it out.

Lesson learned.

[Cliff Ruggles]

You found out why we don't work on commercially "remanufactured" carburetors here, they are PATHETIC!......Cliff

[blazer74]

Thankfully you still have the original carb and didn't give it up for a core.

[Cliff Ruggles]

I hate to beat a topic to death, but we STRONGLY advise folks to avoid anything commercially "remanufactured".  You just can't mention this enough as we continue to see folks buying over the counter q-jets and having extremely POOR results with them.

The companies that build these "remanufactured" units have even resorted to using front inlet carburetors to replace side inlet Chevy carburetors by installing a goofy 90 degree fitting into the front of them.  Just had a customer contact me a few days ago about having us build one for him (pic below).  It's an Oldsmobile center section with a Chevy bottom and choke linkage on the side of it.  The carb was originally "hot air" choke, so no telling what cobbling was done for that conversion, and it's NEVER going to work well no matter how much effort one were to put in it.

It's also EXTREMELY dangerous to have a bunch of rubber hose on the pressure side of the pump.  That line should be solid steel with the filter inside the carburetor. 

If/when you cut a metal line to install rubber hose and clamps, at a minimum put a bulge on the ends of the steel lines so the hose can't slip off if you hit a big bump or get into a collision........Cliff

[73ss]

The zip tie to the heater hose is a nice touch. That should keep the fuel nice and cool.

[429bbf]

you can if your a little crafty fix the throttle plate .take a die grinder and v out the cracks , fill the v notches  with marine tex and and let set a couple of days . retap the hole slowly and you will be able to reuse the base plate. hth