The Stovebolt Site Forums The Parking Lot Big Bolts Requesting input - is it the oddball carburetor?

Still periodically trying to get the '55 GMC 503 started. Most things appear to be fine: good spark, decent compression, but possibly a fuel issue? I posted earlier about the unusual Holley 885-JJG carb with governor - rebuilt it following the manual (looked clean and correct, best I could tell). Fuel is getting to the carb as seen thru visible filter just before it. But no pop, backfire, dampness on plugs, nothing. Also no response to a few squirts of starting fluid. It's not a carb that you can look inside to see accelerator pump action; and I'm not sure, due to the unique design, if starting fluid has a direct path to manifold as in most carbs. I wonder if somehow the vacuum controlled butterfly is not open or opening correctly. The mechanical response when applying the gas pedal is directly to the accelerator pump but not directly connected to the butterflies. BUT I'm not 100% sure it's a fuel issue. Murphy has taught me that what seems like one thing may actually be something quite unrelated. Your ideas?

If the engine won't run for a few seconds by pouring a little gasoline down the carburetor throat, you've got an ignition or valve timing problem. Just having a good spark isn't enough- - - -it has to happen at the right time, when the piston is at or very near the top of the compression stroke. Are you sure you have the spark plug firing order set correctly? I seem to remember the 503 I worked with having a distributor that rotated CCW, possibly, or maybe it had a non-standard firing order? Have someone tap the starter with the distributor cap removed while you watch for the direction of rotation of the rotor.

Thanks....it does have an unusual firing order, and I have determined that it rotates clockwise. But I haven't checked to see if the wires are in the correct clock position. I'll find #1 TDC and check that.

jaycoop, Just in case it may be helpful, here is a Holley 885JJG tech document that could be useful in future work on the carb. Here's another one from one of our very reliable sources.

Great, thank you! I'll check these out. I have found a lot more info on the rebuilding and adjusting of these carbs, as opposed to troubleshooting.

Got it running! It had several issues. One was the manifold was flooded- it was just hard to see in there to be sure at first, due to the design of the carb. The second problem was that even with a good battery, it wasn't winging over quite fast enough, so put 2 strong batteries in parallel, and it was much improved. I checked the firing order and the distributor clock positions and it was good, but I doublechecked the points gap and found that I had to fatten the gap a bit. It fired up fairly quickly after these things were addressed.