I have a 1952 3100 that I call spot because every time I start it up it leaves a black spot under the tail pipe. The back story on this truck is that I bought someone else's failed project. There were enough good features to make it worthwhile. The engine is a rebuilt 1958 235 mated to a 1958 powerglide (cast iron). I originally tried to run on the two Rochesters on a Offenhouser manifold but that was even more of a problem. It has a 12V negative ground system with electronic ignition. The truck also came with the original intake manifold so i went back to a single Rochester since I had two that looked new. I have to either settle for a bad idle/low speed operation or advance the timing which smooths it out mostly but then it has a flat spot around 40MPH. Here are some of the things I know already: 1) Without lead in the gas I am not going to get that nice grey tailpipe and sparkplugs. 2) The 235/Powerglide combo is not ideal for anything that wants to travel faster than a piece of East German strip mining equipment, but it is what came with the project and it fit without altering the floor. 3) Rochesters are not my friend but again I tried to use what I had. 4) I jetted the carbs down from the original 58s to as small as a 47 with no appreciable difference. 5) The Power Jet is open and the gasket is not in the way. With what I have described does anyone see any main "Red Flags" The engine has 700 miles on it and seems to have no problems other than It seems to run rich. My next solution is to pave my concrete driveway with blacktop and forget about it. I do have a power brake booster added that works great but with it and the vacuum from the transmission as well as the distributor advance am I skimming too much off this intake? Any help would be appreciated. Tom
Cast iron Powerglides do not have a modulator, so there will be no vacuum loss there. Once the brake booster charges up on startup there will be no vacuum loss until you apply the brake. If you're not dancing a jig on the brake pedal, no problem there. Are you sure the vacuum piston is raising and letting the power valve close? There should be a slot in the carb base gasket that allows vacuum to get to the power piston- - - -some aftermarket gaskets don't have that slot. The OEM gasket has four slots, so it's idiot-proof- - - -no way to install it wrong. 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!
You might have to get the motor and carb back to stock and start from there if you have not already done that. Put the stock main jet in, double check the pesky power piston is free and moving, and double check the float level. Accelerator pumps are problematic. This new fuel plays havoc with them. See if yours is messed up and replace if needed. From there, I would check to see that the vacuum advance is working. By that I mean it is moving with the change in throttle blade position, and that the rubber diaphragm inside the advance can is not leaking or ruptured. I have a little piece of stub flared line and a rubber hose to test mine. Apply a little vacuum, or just suck on the hose, you will know instantly of the diaphragm is good or not. If the advance is good, make sure no vacuum leaks at the steel line from the base of the carb to the vacuum advance. Adjust the idle mixture and idle speed screws.
From there, double check you have the timing set at tdc, just for starters, so the powerglide adapter plate pointer is pointing at TDC. When I get home from work tonight, I will post a photo of a Sun Tune up card for the 58 Pass. 235. This will help you with that if you don't have any materials to reference.
If the timing is set properly, then you might consider taking the top part of the distributor apart, and remove the distributor plate, and take a peek at the mechanical advance. It needs to be clean, both springs need to be intact and the advance weights should be free and moving. If not, you will need to clean out the junk (there are two drain holes on the bottom of the distributor housing so you can use a little carb spray and a small soft brush to clean it up a bit.) As HRL noted, use the correct base gasket on the carb.
