Since rebuilding the head on my 53 with a 216, the truck has run near perfect. Fun to drive again. Was running well one day, then wham, starts to run like crap. I’ve probably put 200 miles on the head. It’s got dual Zenith’s and the distributor has been upgraded (no points). Idles great, took great pains to make sure both carbs are set the same. Float level spot on. Floats good. Takes off from a stop with good acceleration but starts to blubber around half way through RPM range. Checked compression᠁85-90. Valves were almost spot on as well. I bought it restored 10 years ago. Not familiar with that style of distributor and to be honest, not that knowledgeable in setting the timing or vacuum advance. Should you be able to twist the distributor or slide the vacuum advance ? I can’t get anything to move. Not sure which path to go down now. Any advice would be certainly appreciated.. Thanks in advance.
That "upgrade" to the distributor is probably the problem. The most common one out there that most everybody uses is notoriously unreliable. Can you post a picture of the internals of the distributor with the cap and rotor removed? Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
"Its never the carburetor". That is my mantra which I depend on to force myself to look everywhere else for problems before monkeying with the carburetor. Do that. Now having said that, in your case you have 2 carburetors. Twice the trouble theoretically. There are two quick and easy tests that you can try to see if it is a carburetor problem. 1) Pull a spark plug to look for black soot. 2) If the plug looks fine, as you approach the speed at which it blubbers, pull the choke knob out slowly to see if the blubbering goes away. If it does, one of the carburetors or both are running lean.
Last edited by 52Carl; 09/02/20222:03 AM.
1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission
Thanks for the reply. Yea, I lean towards something in the ignition. It happened so suddenly. I remember years ago changing cap, rotor, points but I don’t know how this “upgrade” works or how to test if possible. The carbs are so simple but gave me a reason to check and sync them. I will do the carb test and let you know᠁Thanks again for taking the time to respond.
That's not the electronic ignition I was expecting to see. I have no idea who manufactures that system, or any way to diagnose possible problems. If I had the engine in my shop, I'd probably source a conventional distributor and coil for troubleshooting purposes and run a series of baseline road tests to see if the performance improves. The distributor housing is supposed to rotate counterclockwise a few degrees as the vacuum advance functions, but that will only happen at light load and relatively constant throttle. The dual carb setup might be dropping the vacuum enough to prevent the advance from working as designed. Is there any vacuum on the distributor tubing at idle? If the distributor tube happens to be connected to full manifold vacuum, it might be holding the distributor in the "full advance" position all the time. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Jerry, that might be the latest version of the dreaded Pertronix but I don’t know for sure. It is triggered by the lobes on the distributor shaft not from a fitting over the shaft.
Martin '62 Chevy C-10 Stepside Shortbed (Restomod in progress) '47 Chevy 3100 5 Window (long term project) ‘65 Chevy Biscayne (Emily) ‘39 Dodge Business Coupe (Clarence) “I fought the law and the law won" now I are a retired one! Support those brave men/women who stand the "Thin Blue Line"! Hug a cop! USAF 1965-1969 Weather Observation Tech (I got paid to look at the clouds)
There are vacuum lines running to each carb. I have not performed any tests for vacuum. If in fact it were held in the full advance, would the symptoms be consistent with my problem? I wonder if I track down a possible manufacturer of the module ,they could help troubleshoot .
In trying to identify the type distributor, it was suggested to call Langdons Stovebolt in Michigan. He suggested checking fuel pressure at 50 MPH. Went to auto parts, rented gauge, purchased fittings, headed for home in the old truck. Halfway home, wham, it starts running perfectly. I was telling the young kid at the parts store my story and he mentioned that sometimes if you overfill the gas tank, it plugs a vent tube᠁᠁᠁.now that you mention it, this started shortly after I let the nozzle click off on its own which I normally don’t do. Is this 20 year kid on to something? ( The tank is now 3/4 full after all the messing around)᠁ Anyway, it runs great again, my valves are spot on, my carbs are adjusted, my compression is OK , I’m more familiar with the truck and “feel a little closer” to the old gal.. It does have the Pertronix distributor which I’ll be changing out soon.. Thanks for the heads up.. And again, thanks for the help. Hope this can possibly help someone else down the road even though it’s not entirely definitive . Take care
I'm working on a modification that will allow the more reliable and better-engineered General Motors reluctor and pickup coil to be installed into an original distributor housing, with the module mounted on a heat sink in a location that's not visible to a casual observer. That will allow purists to run a stock-appearing distributor with modern HEI internal parts. Best of both worlds! Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
I use a Deve modified tall cap distributor (uses a mid-70's Chrysler spiked wheel and pickup), a GM HEI module hidden inside an old voltage regulator cover and a Blaster 2 coil. It's been working well for many years.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12 '52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
Do you by chance have a new aftermarket gas cap? They come with a valve in them to make them ventless. You can remedy this by drilling a 1/8" hole in the plastic on the backside of the cap. This will make the cap vented just like the original. I do not believe that your 20 year old kid was correct about the vent tube being a problem for this design of gas tank. The small tube on these tanks is for allowing air out while filling the tank with gas. It does absolutely nothing once the gas cap is on.
1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission
The gas cap is the same one I’ve been using for years. I agree, the extra full tank was just a coincidence. May not ever know exactly what the problem was. Wish I knew but glad not to be stewing about it. I did drive it with cap loose at one point, had the same symptom.. Thanks again for the help.
