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| Too lean or too rich? https://slantsix.org/forum/viewtopic.php?t=51996 |
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| Author: | Otateral [ Tue May 07, 2013 9:04 pm ] |
| Post subject: | Too lean or too rich? |
After upgrading to super six, having a few issues and I'm fairly sure it's fuel related. When driving, there is sometimes a half-second hesitation when pressing on the gas. And if I really gun it, at around 30-40 mph there's more of a hesitation, but this lasts about 2-3 seconds at times. Sometimes, when slowing to a stop the engine will die. Also, sometimes when stopped at a light, the engine will stumble for a bit like it's going to die. But if I press the gas a little, it evens out. I'm also getting black soot out of the tailpipe when idling for a while in one place. My first inclination is that it's too rich, but turning the mixture screws in hasn't really helped. And the stumble at idle/dying when slowing sounds like too lean to me. I just don't know. The spark plugs are blackened, but they were that way before I did the upgrade. (I had a Holley 1920 set too rich before this) Do you think the blackened spark plugs could cause this? I have a rebuilt carter bbd. I rebuilt it myself, and this was my first attempt at it. The float was new, and I'm fairly certain I set it in the right place. HEI ignition. Getting plenty of spark. Any ideas? |
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| Author: | ceej [ Tue May 07, 2013 9:33 pm ] |
| Post subject: | |
The important part of learning about a carburetor is to understand that there are different circuits for different states. At idle, the carburetor is running in the idle circuit. If it is running too rich, the idle screws need to be turned in to limit fuel flow. To start, turn the screws with your finger tips in to the seat. Do not tighten them. This will damage the tapered idle screw and seat. Do not use a screwdriver unless you know the feel. It's really light. The idle mixture can start around 1-1/2 to 2-1/2 turns out. Once idling, turn one screw at a time in until the engine starts to stumble. Turn out, CCW, until it cleans up. Then open an additional 1/4 turn. Repeat on the other idle screw. Now, do it again. mixture from one barrel will impact the other. Two or three adjustments may be necessary. Your acceleration issue is related to the transfer slots, as you come off idle, and the accelerator pump. It doesn't sound like your accelerator pump is working. Time for a tear down to repair what ails it. Look HEREfor all the data you could wish for! Courtesy of SlantSixDan. He might poke his nose up here eventually. CJ |
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| Author: | DusterIdiot [ Tue May 07, 2013 9:36 pm ] |
| Post subject: | Couple of items |
Quote: When driving, there is sometimes a half-second hesitation when pressing on the gas. And if I really gun it, at around 30-40 mph there's more of a hesitation, but this lasts about 2-3 seconds at times.
I would check your carb settings for the accelerator pump, failure to 'inject' a shot of gas in the throat will cause this conditions. make sure your linkage is correct per the rebuild data, did you do anything special when you seated the pump piston in the bore?Quote: I'm also getting black soot out of the tailpipe when idling for a while in one place.
This is a different circuit from above, and changing the screws won't immediately change results. Sooted up plugs will not fire well no matter how much juice you pack through them (got a full magneto setup?)....I think if you take a moment to warm the car up to operating temp, set the idle to about 2000 rpm, then slowly mist some water into the carb throat (don't drop more than a tablespoon full at a time) over a few minutes will somewhat clean out your deposits (make sure tailpipe is not pointed at your garage door...) Shut off car, pull the plugs and if they are still sooty clean them out and reinstall them....if the car is older and leaking oil past the valve seals, you may need to replace them, and you may need to go to a spark plug that is a little hotter (next step up) to burn the deposits off the plugs to keep them clean. -D.Idiot |
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| Author: | olafla [ Thu May 09, 2013 7:54 pm ] |
| Post subject: | |
Whenever my Aspen produces a telltale black oval on the asphalt behind the exhaust outlet when idling, I know it's time for a checkup! (if there are droplets of water also, you'll know that the combustion process is incomplete, and actually produces water molecules instead of power!) A vaccum gauge should always be used, then you'll immediately see if there are any diferences from last time you adjusted the engine. Check for loose vacuum connections and hoses. One thing I recommend you should check before doing any serious carburetor work, is to confirm that the choke pulloff is adjusted correctly, and that the choke really pull off the choke completely. The second thing is your fuel float setting. I have found it important to do the final float level adjustment after all fuel pipes are connected, any fiddling with the fuel intake may also affect the fuel level on the BBD. Check for leaky floats. The metering rods can be adjusted a litlle up or down with the screw, and may remove the hesitation you experience. It's a time consuming task to adjust and test drive several times, but can be very rewarding. The metering rods have steps, and what you feel may be the transition from one rod diameter to the next, and that point will change if your vacuum reading is out of range. An old and faulty ignition coil may also produce those 'hiccups' before it collapses entirely. I presume that your valve lash is (almost) perfect, and that you have checked your ignition timing. BTW, I have found that my BBD require a good cleanout from time to time, no matter how good the fuel filter is. Olaf |
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| Author: | WagonsRcool [ Thu May 09, 2013 8:25 pm ] |
| Post subject: | |
Quote: (if there are droplets of water also, you'll know that the combustion process is incomplete, and actually produces water molecules instead of power!)
I know chemistry class was a long time ago BUT: HC + O2 = CO2 + H2O ! Water is a result of combustion. Most of the time you don't notice it because the exhaust system (& exhaust gases) stay hot enough to keep the H2O as vapor. If the car idles for awhile the exhaust cools so the H20 condenses out as droplets. @ Otateral, others have given good tips to follow (I'd stab new plugs in- just because). Here's a way to check the accel pump. With the engine off, hold the choke butterfly open & watch down the barrels as you slowly open the throttle- 2-3 seconds to full. There should be a steady stream from each pump squirter port(not a "dribble") into each bore. Do it again but much faster- now it should spray harder/further into the bores. You also want to double check timing, & that the mechanical AND vacuum advance work. |
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| Author: | olafla [ Thu May 09, 2013 9:23 pm ] |
| Post subject: | |
Quote: If the car idles for awhile the exhaust cools so the H20 condenses out as droplets.
Yes, but when you get the typical black patch indicating incomplete combustion, the droplets are present very soon, and in greater quantity. This is a visual observation done many times over many years.Olaf. |
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| Author: | DusterIdiot [ Thu May 09, 2013 9:59 pm ] |
| Post subject: | But... |
Quote: Yes, but when you get the typical black patch indicating incomplete combustion
I've gotten black patch from having run rich then changing to stoich correct and the water/vapor is cleaning out the deposits in the tailpipe...(takes a while to get that to go away...worse if you had oil in the exhaust...)-D.Idiot |
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| Author: | Otateral [ Thu May 09, 2013 10:16 pm ] |
| Post subject: | |
Really appreciate the tips guys. I got the fuel mixture setting right this time, and the water mist trick cleaned up the spark plugs really good. Still getting the bog while accelerating, so will follow your advice checking the accelerator pump and possibly pulling the carb and checking everything out. Taking lots of pictures as I go, too. I really don't know how the metering rods are supposed to be. I had a hard time getting them seated, but pretty sure I got it right. With the accelerator pump, what should I be looking for? I'm certain both check balls are present where they need to be, and 90% sure the right sized ones are in the right spot. I've got the electric choke conversion installed, and have had a hard time getting that right. It's been warm here lately so haven't had much problem letting it stay at or near full-open. |
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| Author: | wjajr [ Fri May 10, 2013 5:58 am ] |
| Post subject: | |
The accelerator pump is a rubber diaphragm or leather plunger sub assembly that is articulated when throttle plates are initially opened providing a measured extra shot of fuel over what fuel is flowing through the other circuits; idle, transition, main, and enrichment if equipped (Holley type power valve that yours won’t have). That plunger or diaphragm device becomes compromised over time and use and becomes incapable of delivering a full shot of fuel. All rebuild kits address refurbishing the accelerator pump. I may be mistaken but I think your carburetor has a leather plunger that displaces fuel in a cylindrical tube much like that hand water pump Hoss Cartwight would have used to fill a horse watering trough. That leather will dry out when a carburetor sits on a dusty shelf for a long time before it is sold, or just gets worn to a point where it is incapable of a good seal and won’t pump a full shot of fuel in a high millage car. |
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| Author: | Otateral [ Fri May 10, 2013 7:33 am ] |
| Post subject: | |
I did replace the pump when rebuiding the carter bbd with a new plunger that came in the rebuild kit. |
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| Author: | wjajr [ Fri May 10, 2013 10:15 am ] |
| Post subject: | |
Otateral: Quote: I did replace the pump when rebuiding the carter bbd with a new plunger that came in the rebuild kit.
Ok good! Make sure accelerator pump activates as soon as throttle shaft moves, in other words there has to be no, zero, zip free rotation of shaft before pump is activated. This adjustment if not correct will cause a flat spot or bog. Next is to make sure when engine is idling it is consuming only air fuel emulsion delivered via idle circuit, and not dipping into transition circuit. The theory is when throttle plates are opened too wide when setting curb idle carburetor will deliver A/F mix via both idle & transition circuits making a rich condition and non-responsive idle mixture screws, and when sudden throttle opening takes place the total mixture goes lean causing a big flat spot than car takes off. Someone better versed in rod type carbs can better explain how this adjustment is made, it has been over forty years since I played with one. A static or base timing adjustment will change idle rpm and allow carburetor to deliver fuel only via idle circuit. Increasing timing will increase rpm, and retarding will slow rpm. Slowly turning distributor by hand one way or the other will yield an rpm change. Hopefully you have good non electron leaking plug wires, or this may be a shocking experience… LOL Make sure throttle plates are closed by turning curb idle rpm adjustment screw out. Slowly advance base timing until correct rpm is achieved. Than you will have to bounce back and forth between idle mixture screws, curb idle screw and timing until carb responds to idle mixture screw setting in the 2 to 1.5 turns out position. Keep fiddling back and forth until highest vacuum reading and best idle is found. Go for a test drive, and report back. Fine print discloser: Don’t take offence to some of my lengthy explanations as they are mostly aimed at folks just getting acquainted with different systems one has to maintain on their old car. And we don’t have a handle on new to the board folk’s level of automotive acumen. Bill |
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| Author: | Otateral [ Fri May 10, 2013 10:38 am ] |
| Post subject: | |
No, I appreciate all the details. A year ago I had never even changed my own oil, but im learning quick. Before I get to the next step, I have to report today's events. I pulled into a parking lot and it stalled. As I parked I could hear what sounded like bubbling. I got out, took off the air cleaner and there was fuel pouring out from the top of the carb. Not the air horn, but the part with the thin piece of metal held on with 3 screws. Not sure if the bubbling I was hearing was fuel boiling in the carb or fuel boiling on the intake manifold. Either way, I figure fuel flooding into the top of the carb and out is not a good thing. |
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| Author: | Aggressive Ted [ Fri May 10, 2013 11:04 am ] |
| Post subject: | |
Quote: Not sure if the bubbling I was hearing was fuel boiling in the carb or fuel boiling on the intake manifold. Either way, I figure fuel flooding into the top of the carb and out is not a good thing.
So, that is a needle and seat problem.......not shutting off the fuel. Sounds like your float level is off or sunk.....the float should hold the needle into the seat to shut off the fuel after shut off. You need to have good surfaces to seal, so a new needle and seat. Any imperfections will not seal and stop the fuel.On mine I can watch the pressure gauge go up from 6 pounds from running to 16 pounds after shut off during heat soak .....and no fuel leaks! A nice heat deflector under the carb sure helps too! A fuel line mod might be in order to help minimize the boiling too. You can look at one of mine by clicking on the red link. |
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| Author: | Otateral [ Fri May 10, 2013 4:15 pm ] |
| Post subject: | |
The needle and seat and float are new. Pulled the top of the carb off to see if anything looked out of the ordinary and took a couple pics. http://imageshack.us/a/img541/5452/20130510101318.jpg http://imageshack.us/a/img22/6594/20130510153932.jpg I didn't notice anything immediately out of the ordinary. There is some fine grains in the float bowl, but not a lot. Considering this is a recent rebuild and a new filter, is that bad? Also, some googling turned up the idea that old fuel hose can cause the needle to stick. Do you think this is likely? |
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| Author: | Aggressive Ted [ Fri May 10, 2013 4:44 pm ] |
| Post subject: | |
Maybe some small debris got stuck between the needle and seat...some of those brass flecks or chunks of rubber from the fuel eating the old fuel line. Plus the manifold getting too hot....or float set a smidge too high. |
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