The Stovebolt Site Forums The Shop Area Engine Shop Rochester 1 bbl preliminary fuel mixture setting?

What is the preliminary setting for the fuel mixture screw on a Rochester 1 bbl carb (1956)?

Thanks.

Try 1 1/2 turns

what ever happened with your overheating problem?

I think I got it fixed. I replaced the water pump and put a 7 lb. radiator cap on (still have the 180 degree thermostat on it). I also rodded out the block while I had the pump off, and I had the radiator checked at a radiator shop.

The engine won't idle unless I keep the choke pulled out. Does that mean I have the carb too lean?

Now I seem to have a terrible clunking noise coming from the bottom of the engine after it's been running for a few minutes. I hope it's not a bearing going bad.

I checked the fan for clearance again since I did all this monkeying on the engine because I thought maybe the noise was the fan hitting the radiator tank. I pulled back two of the blades that looked too close. I'll try it again tomorrow.

Something is too lean...
Try a couple of these and report back.
1) turn the fuel/air mixture screw in until it "just" bottoms out then turn it out 1-1/2 turns.

2) turn your idle speed screw up a turn or two then start it up and see if it will idle after it warms up alittle. It's not unusual to have to have partial choke when warming up.
If it does idle, adjust your speed down to where it will idle then start adjusting the fuel/air mixture screw to smooth it out.
Then adjust the idle speed adj to get the idle down where it should be.

If it won't idle it's sucking air from an open vaccum line, loose carb to manifold connection, loose manifold to engine connection or the passages in the carb are restricted/plugged up.

I agree with Volfandt's third suggestion: a vacuum leak (I'd bet on intake manifold to head, but all of Volfandt's suggestions are good).

I did have the fuel mixture screw turned out 1 1/2 turns from all the way in. I think the timing is probably off a little, too, but it's hard for me to get it idling good enough to set this without the engine dying when I turn the distributor.

I think I'll try turning up the idle speed a tad so maybe I can time it better then; problem is when you turn up the idle speed it changes the timing, doesn't it? Don't know which problem to tackle first, idle or timing.

I have new gaskets on the intake to head connection so I doubt there is a leak there. I had to enlarge the mounting holes a smidgen at the base of the Rochester carb to get it to fit the 216 intake, but I don;t see how it could be sucking air thru the larger holes. I can't think of anywhere else it could have a leak unless there is an extra vacuum port somewhere that I need to plug.

Today I didn't get to run it like I had planned because the original heater shut-off valve was leaking. I think I'm just going to replace it with an inline valve since there isn't anything new available that looks like the original shut-off valve.

There are a lot of places it could have a vacum leak. Lets get this truck running, first open the mixture another 1/2 turn, it won't hurt anything the 1 1/2 turns is just a base line setting. You probably do have a vacum leak, On the intake manifold there is a vacum fitting for the windshield wipers, it is under the carb, make sure it is not leaking.Check the hose to the wipers, maybe even plug the fitting till we get thinks running right. The gaskets on the intake, you said you put new ones on, did you use the manifold allignment rings( small metal ring that goes between the manifold and the head), these rings must be staight are it will cause a vacum leak, ASK ME HOW I KNOW. Also check the vacum advance on the distributor, it may be leaking, just unhook from carb and temporarily plug the line.
Good luck, keep us informed on the outcome.

A trick I use to hunt air leaks is to use some carb cleaner spray.
1st get your engine to idle at the lwest setting it can without dieing. Use the idle speed screw to set it.
Plug all vaccum ports to eliminate a leaky vaccum advance and winshield wiper motor. If the idle picks up once they're plugged you've found your leak.
If no change, take the carb cleaner and spray short burst of spray directed at all sealing joints one at a time.
Where the carb bolts to the manifold, where each intake manifold runner bolts to the head and around the throttle shaft on the carb. If the idle changes at any location you've found a leak.
Remeber to take short bursts while paying very close attention to the engne speed and sound. There should be no change if theres no leak.
I've used this method successfully on other engines and should on a stovebolt 6.
Good luck
Dave

After all the work I put into the Rochester carb and all the hope I had for it, I had to switch back to the Carter W-1 carb because I want to use the original manifold mounted horn and the inlet for the Rochester carb is directly in line with where the horn goes. The Carter has its inlet offset toward then engine, no doubt to allow space for the horn. Another hard lesson learned. Now I hope I can get it running properly with that old carb.

I decided to take a break from the engine stuff for a few days to try to get the brake system working.

You should be able to use a 90 degree fitting on the Rochester.