My previous thread I had an accelerator pump issue on my Rochester BC. I tried everything that was suggested, and discovered the pump bore was too scored. I could start the truck by dumping gas down the carb and it would idle and drive no problem. Just no squirt to start it. I decided to replace it with a reman Rochester BV. No setup instructions as it’s “been set for a bolt on and run with no adjustments needed”. Well it wouldn’t idle, it was really low and would die. I turned the idle screw 1/2 turn and now it idles (though low/lower than my previous carb). I did notice faint puffs of black smoke at the tailpipe. And there’s hesitation/struggle as I’m going through the gears. I haven’t had time to pull a plug but they’re probably black. I really don’t want to start tearing into this “new” carb. Yes yes, things can be ***embled wrong, but hoping I can just make an external adjustment. If not, there’s a 12 mo warranty so I’ll probably just swap it. Thanks in advance. Ryan
heh...there's no such thing as "no adjustment needed". Play with the idle speed and idle mixture adjustments. Also tell us about the choke...what does it have? is it connected to anything? pictures will be really helpful here.
Squirrel, I figured as much. Choke isn’t hooked up as the truck/motor doesn’t have the rest of the divorced choke system. It isn’t closing though. Let me know if different photos would help. Thanks, Ryan
Have you tried adjusting mixture screw? You said you raised idle screw, back out mix screw a turn, post some info like vacuum readings, steady at idle? What is the idle rpm? Does it go up when you adjust mix ? Rebuild carb may need float level checked, if metering is different from old carb, a little timing advance may help, and yes check plug condition first, if fouled, clean or replace, and do your adjustments.
Probably is not going to run well without choke until the engine is totally at operating temperature. All adjustments should be made AFTER the engine is hot. Idle mixture screw should be at about 1 1/2 turns, and then adjust the idle speed with the throttle positioner screw. Jon
A working choke would really help matters, especially at cooler engine temps. It can take a while to heat up the intake manifold on an I-6 which helps with fuel atomization. Also check that the two screws that attach the throttle body to the bottom of the float bowl are snug.
So idle mixture was set at 2 1/2 out from all the way in. I set it to 1 1/2 per recommended above. Also 1/2 more on the throttle position screw. Still rich, and it looks like the gasket for the top portion to the bowl is now getting wet from the inside and is wet on the outside - not sure if the fuel level should be that high? Not sure on the vacuum and rpm as I done have those tools to measure. Going to reach out to the remanufacturer and see what they say (probably nothing), after that looks like I'll be opening it up and tearing it apart to check everything inside. Thanks again for all the replies. Ryan
Could have a high float level, which you can adjust relatively easily, although you'll need some instruction. And knowing what the carb fit originally would help too. Also pretty common for the zinc parts on old carbs to be warped, as zinc likes to move around when it's under load.
If you can, pick up a vacuum gauge. Very helpful tool for carburetor and tune up work in general. And most of them can also be used to check fuel pressure on mechanical fuel pumps. https://www.napaonline.com/en/p/BK_7000114 You might also check the tool section of any pawn shops you might have in your area for a vacuum gauge and a tach and dwell meter. Watch the prices though. Pawn shops around here can be a little too proud of their merchandise. I've seen the same stuff also show up at thrift stores at bargain prices though. A couple months ago I picked up a Craftsman vacuum tester and a MightVac hand vacuum pump kit off Craigslist for $10. Both still in the original boxes and in near-new condition. The sellers usually have no idea what they're used for. (You might also consider adding your location to your member information on your profile page. There could be a HAMBer in your area that might be willing to lend you a hand.)
Thanks for the replies. Looks like the auto part store loans vacuum gauges. Dumb question - what am I attaching the gauge to? Vac advance location? What am I looking for with this? I've replaced a lot carburetors on V8 motors and never tuned them using vacuum readings. Thanks again for all the input! Ryan
For tuning purposes you'll want the vac gauge connected to a source of full manifold vacuum. This can be to a fitting that threads directly into the intake manifold. Or it can also be connected at the carburetor, as long as the fitting picks up vacuum at a source below the throttle plates. That tends to be a fitting located somewhere down low on the throttle body. On your carb you may be able to connect the gauge where the choke pull-off hose is currently connected. A vacuum tee fitting might be helpful. Just make sure you're getting a good vacuum reading at a low curb idle speed. There may be other vacuum ports on a carb that supply vacuum only with the throttle at least partially opened. Avoid using these ports when trying to read true manifold vacuum. Here's a couple other links that may prove helpful. https://www.onallcylinders.com/2016/03/31/vac-visual-quick-guide-vacuum-gauge-readings/ https://studebaker-info.org/Tech/Vacuum/tvg.html
I called uremco and spoke to a person for about 20 minutes. Figured out the carb in a “new overseas” version and not a Rochester rebuild. He basically told me the same things everyone above did (not that I had any doubts!), and if I couldn’t get it running correctly after 1) the throttle position screw adjustment and 2) the fuel / air mixture screw adjustment, send it back on their dime. Pretty solid service in this day and age I think. So I removed the carb and checked the float level. The walker rebuild kit states 1 9/32. It was set to 1 10/32, so pretty close but a little conservative. Next I replaced the carb, brought truck up to temp and adjusted the mixture screw out. It came all the way out, and ran approx 3-5 seconds before dying. Replaced screw to 1 1/2 out from all the way in, and started. Let it run a minute and started screwing in. Went 1/2 (now 1 from all the way closed) and truck idle smoothed and rpm went up. No more puffs of black smoke. Drove and still hesitant going through gears. Turned screw 1/4 turn in (now 3/4 from all the way closed), drove, better still a little hesitation. Turn another 1/4 in and it wanted to die, back to 3/4 out. Haven’t sourced a vac gauge or dwell/rpm yet. Seems like a step in the right direction though. Thanks, Ryan
It sounds like you're gaining on it. If the idle mixture is a tad rich for now it won't hurt anything. It does little or nothing once the throttle is opened up a bit. If you think it's too rich going down the road drop the float level maybe an 1/8" (lower into the float bowl) and see how it responds. If you think it's too lean, raise it 1/8" (higher in the bowl). Maybe try driving it both with and without the air cleaner and see if there's any change. Make sure at idle that there's no fuel dripping from the main fuel nozzle. Temporarily wire the choke fully open, though it might make it kind of sluggish to star cold and won't drive as well until the engine and intake manifold are fully warmed up. If you want to experiment a little try pulling the hose off the choke pull-off and create a temporary vacuum leak. If it's too rich this will lean it out and may make it run better. If it's too lean the vacuum leak will make matters worse and may cause the engine to stall. This may help to at least determine if you're fighting a rich or lean mixture condition. Also think about giving us at least a general idea of your location. There may be some HAMB help nearby.
Ok, after driving it around a bit this is where I'm at: No choke and it takes a bit to keep it running after starting, idle is low and rough. Driving, there is hesitation / struggle accelerating and moving through gears. Once up to temp, the idle is higher and there is no issues accelerating and moving through the gears. I pulled (2) random plugs and they were both sooty. ClayMart - I'll try what you mentioned above. I've updated my profile, I'm in Vegas NV. THANKS again for everyone's help! Ryan
UPDATE - I picked up a dwell / rpm tool. Before starting the truck I pulled the forward plug and it was still black, the electrode area was lighter though. At temp the idle is at around 1000. I backed the throttle position screw out just p***ed a 1/4 turn from where it was, and it will idle around 700-800. If I back the screw out any more, it'll die. I looked down the carb while running and no fuel is dripping. I pulled the air cleaner off and the rpm decreased. I removed the vacuum line and the rpm decreased and it almost died. That being , said, it appears that it may be a bit lean BUT the plug is showing a rich condition? Next I might move back to the air mixture screw - richen it up and see if I can get it to idle lower and check the plugs. I'm close, just not quite there! Again, thanks for all the ***istance. Ryan
Good to hear that it's responding to some of your experimenting and troubleshooting. If it hasn't already been mentioned, try not to change more than one thing at a time. That way it's easier to keep track of what works and what doesn't. Are you using the large, original equipment air cleaner or some aftermarket "chrome-goody-go-faster" variation? Some of the little chrome jobs can actually create too much of an air flow restriction, even with a new, clean filter. Don't worry too much about getting a really low idle speed. For now something around 800 rpm should be a good baseline to work from. One dark spark plug doesn't necessarily mean a rich mixture. That would typically affect all cylinders. You might have a mis-fire condition in that one cylinder though, and there could be a number of causes. Try swapping that plug into another cylinder and see if it cleans up any after running a while. It would be more telling if you were able to actually put a few road miles on it instead of just running it at idle in the driveway. You might also try swapping the #1 plug wire to another cylinder (without disturbing the firing order) and see if the plug fouling problem moves to the new cylinder. Or put on a new set of wires if they're looking su****ious. Inspect the cap and rotor closely too while you're at it.
keep in mind that there are several different parts of a carburetor that will affect mixture, and they work at different operating conditions. So looking at a plug really won't tell you much about any specific operating condition mixture, unless it's only been run under those operating conditions. It could have turned black during cruise, and the idle is lean, and the plug really has nothing usefull to say about that. So you want to adjust the idle mixture screw, so it's rich enough that it won't die at idle. With the engine not running, gently turn in the screw till it just seats, don't force it! and count the number of turns. This gives you a baseline, so you can get back to, if you get lost. Then back it out the same number turns. Start the engine, turn the screw out half a turn, see what happens...but the idea is that you want to adjust the screw so it's idling well, which usually means as fast as it will idle with the idle speed screw not being changed. I do this by backing it out a turn, then slowly screw it in until idle speed starts to drop, then back the screw out 1/4 to 1/2 turn. If the idle speed is too high, then lower the idle speed, and go through the idle mixture adjustment again. And then you have to test drive it, see if it works under all operating conditions, and readjust as needed to make it work as best as possible under most conditions.
Have you checked your timing? Maybe a couple of degrees of initial advance at the distributor and go over your carb adjustment and give it a drive, clean the plugs if fouled.
Claymart-correct making 1 change at a time and writing everything down. It has a small (6 or 8 inch) K&N. Also, for clarification, I just pulled the forward plug NOT the other 5. squirrel-good points and definitely makes sense. I'll continue making these adjustments and see how it behaves under various conditions. Jagmech-haven't checked the timing. Might be worth a check though All-again the truck ran fine until the carb was replaced, so I'm not sure if items not related to the new carb (air cleaner, timing, etc.) would be a factor? Is every carb different, and therefore these items are important? Thanks so much for the input. Ryan
Ignition and carburetion work in tandem drivability wise, slightly different metering in the new carb may benefit from timing changes in your case.
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