My GMC 228 came to me 11 years ago with a not-stock Carter YF 964S. It has a 0.099" jet and (I think) a 0.075" rod. Runs good as far as I can tell. Gets around 14 MPG doing mostly rural 40-60 MPH driving. AC R45 spark plugs are a light brown color.
I decided I wanted to install a PCV system.
I found a valve cover from a larger GMC truck that had a hole in the center for PCV. I installed a Standard Motor Products V237 PCV valve (recommended by a 'Bolter) in the hole and connected the other end of the valve to manifold vacuum. To provide an outside air source, I cut the draft tube off of the oil-fill tube and blocked off the hole where the draft tube had attached. Then I replaced the oil fill cap with a Mr. Gasket breather designed to plug into a V8 valve cover.
I started the engine, but it did not want to idle. Not surprising as I had just installed a vacuum leak. I backed the idle mixture screw out 1.5 turns and the idle got a lot better. I set the idle speed to 600 RPM (A/C season here, 90F today) and found I could move the idle mixture back in a half turn with no change in idle. I'll crank the idle back down to 500 RPM late next fall.
My question is "What do I do about mixture driving down the road with the PCV valve installed?"
About 5 years ago I did a temporary install of a digital Air/Fuel ratio (O2 sensor) in an attempt to tweak the carb for better performance. The darn thing bounced around a lot. I finally just went back to the original carb jet and removed the instrument. Should I re-install it?
Or maybe just keep an eye on the spark plugs? If so, should I start with a new set of plugs so the current light brown color doesn't influence my opinion?
'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.
Light brown color isn't anything to worry about. Clean them up and gap them and reuse them.
1950 Chevrolet 3100 (Ol' Roy)
1939 Packard Standard Eight Coupe (The Phantom) | 1956 Cadillac Coupe de Ville (The Bismarck) | 1964 Ford Galaxie 500 coupe |1966 Ford Mustang (Little Red) | 1969 Pontiac GTO (The Dishpit) I 1979 Ford F-100 | 1976 Ford F-150 (Big Red) | 1995 Ford F-150 (Newt)
It would be interesting to reinstall the O2 sensor and see what you get, but the PCV isn't just air, it's hydrocarbons from the crankcase. But if it runs and drives well, and the plugs stay the right color, then I'd say leave R be.
Have you considered adding what some call an A/C "idle-up" solenoid? You set your idle at 500 (475 or whatever) and then when the A/C is on the solenoid pops out and once you increase the throttle, your idle stays at whatever the solenoid is adjusted for as long as the A/C is on. When it cycles off, naturally the idle drops back to 500 or whatever. I've found setting my idle at 475 or so makes my timing work better and my idle is fine as long as I don't try to run it too rich. Because of the PCV I richen it just a wee bit but not much.
~ Jon 1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
I've thought about it Jon, but don't think I'd like to go to the effort.
The first 1/2" or so of the pull on the manual choke knob in the cab bumps the throttle up without moving the choke butterfly on the carb. I sometimes use this to control idle speed. Works well to keep the truck at walking speed when doing parade duty (Christmas and 4th).
'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.
I understand, Bill. I bought 30 NOS idle up solenoids from a dealership where they had been sitting since the 70s and offered them here for what I paid and after waiting a year only had a couple of takers (think they were $15 each, shipping included). So I put them on eBay for $25 each plus cost of shipping and in a few days all were sold. It was easy to install. Just cut off part of a common angle brace, drilled one hole so it sits flush with the throttle body, bent at the angle I needed and painted it black.
~ Jon 1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
'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.
Monitoring fuel mixture by looking at spark plug insulator color is a practice that went obsolete over 40 years ago. Unless you're running leaded gasoline, which gave the "tan to chocolate brown" color we looked for on Fred Flintstone's car, plugs go from white to sooty black without giving any useful information about fuel mixture. Go ahead and look for it, but it's going to be like finding a chicken with lips! 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!
How should those of us without milling machines and lathes check mixture then Jerry? Is an Air/Fuel ratio meter the only answer? (see my previous complaint about A/F meters)
Wouldn't a tail pipe sniffer require running under load, such as on a dynamometer, to get good readings?
Last edited by Bill Hanlon; 05/08/20245:12 PM. Reason: additional info
'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.
