Still playing with this. Got all the timing and stuff square, but don't know what the correct idle speed is. I've read from 425 to 900. HELP!!! engine is a 1955 235ci Chevy installed in a 1951 3100 pick up with a 4 on the floor. What is the idle speed supposed to be? Thanks in advance for the help. Last thing I need to set before I take it for a ride and 425 just seems crazy low. It bogs out at 550.
I don't know what it is "correct", but I would set it to what feels right. Somewhere between 700-1000 rpm. Good luck!
She's sitting about 820 right now, but that seems high to me. She sounds funny. This is my first Stovebolt though, and I really don't know what it's supposed to sound like. I also don't feel like blowing it up. LOL. Want to eventually make it as pretty as the one in your avatar Stovebolt-54, but if she dies, there's a SBC waiting .....
Factory idle adjustment was recommended at 450 rpm for stick shift. The low rpm helps shifting into first gear without crushing gears on the stock non-synchro transmission. If your carb idle adjustment is dialed in using a vacuum gauge to get max reading and least vibration and your timing is right, it should not bog down below 550 rpm, like you describe.
On old cars, I always liked the idle up a bit, around 650-700 or so. Especially in winter or on those real damp days. Bob
Can't go wrong with idling high enough that the generator is charging at idle. This is good for getting stuck in traffic and not having a dead battery at the end of the day.
My as original 1955 pickup idled best @ 550 rpm. Smooth & steady. If your 235 is anything but smooth at idle or "sounds funny" - check the valve lash. This is assuming you know the rest of the tune is right - good plugs / wires/ cap/ rotor - points set right & a fresh condensor. B
If it blows up at 820 don't try driving it. If it is an auto set it @ 700 if it is a standard set it closer to 600 if it will idle that way. Donot idle it real slow as that is hard on the lower end.
To all that have replied, thanks! The carb on the truck is a Rochester Model B with manual choke. I haven't tried driving it because the idle was high. I was looking at the carb and realized, I don't know how to adjust the idle on this thing. It has what looks like two adjustments on it. One at the throttle body which I assume is the air/fuel mix, and another on the linkage which looks like it would be used to set up the fast idle seeing as it's on the same linkage as the choke. Am I wrong on this? Or, is the one on the choke the idle adjustment and you set the choke differently? Trying to get this sorted out today since I actually have a day off to mess with it. I'll post pics of what I'm talking about as soon as I can figure out how to resize them on my POS computer.
One more thing, I set the timing as per a few posts I found here. I zero'd the plate at the bottom of the dizzy, used a timing light to center the BB in the flywheel to the pointer, then used the plate and set it between 6 and 8 on the advance scale. I checked the dwell and she's sitting pretty right at 30. Plugs, points, condenser, cap, rotor and wires are all new. Did all this because it was running like crap, and the PO did tell me he wasn't quite sure what he was doing with it and pretty much just got it running so I could see that it would run. Been sitting in the driveway since, and I need it on the road.
The idle speed is the one that moves the throttle linkage. The idle mixture is the one in the base of the carb, that adjusts fuel flow in the idle circuit. Yeah, it would help if you know how to adjust it! First look at the choke linkage and make sure it's all working. The choke needs to be closed to start the engine, then opened as the engine warms up. You want to adjust the idle after the engine is warmed up. Turn the idle speed screw out to lower the idle speed to around 500-600 rpm. Then adjust the idle mixture, turn the mixture screw in until the idle speed starts to drop, then out until it stops increasing idle speed. This will get you close, but you might still need to turn it out a little bit if the engine hesitates or tries to die when you're starting to drive. After adjusting the mixture, reset the speed, try to get it down around 500 if you can. You will have to play with it for a while and see what happens when you try different settings. Us older guys who've been playing with cars for a while learned about this stuff when we were kids, working on go karts, lawn mowers, mini bikes, and the neighbors cars.....
Squirrel, since the choke on this thing is manual should I just check to make sure it's free and operating properly and open it as the engine warms up? I've never actually used the choke on it, and will usually sit there for a minute or two and feather the gas until she warms up a bit. As far as using a vacuum gauge for setting it up, do you do this at idle or do you have to increase RPM? I assume you just disconnect the line going to the vacuum advance on the dizzy and plug the gauge in, right?
you probably want to find a different vacuum source, such as the hose that goes to the windshield wipers, or else the plug where it goes on the manifold, if the vehicle has electric wipers. I don't use a vacuum gage for setting idle mixture, though. I use the "lean drop" method...find the point where the rpm drops when you turn the screw in, but does not increase when you turn it out. Then I'll turn it in or out just a little bit depending on what kind of car it is, what condition it's in, etc. This is the part where experience and playing with it will help you set the mixture just right.
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