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| BBD Metering System https://slantsix.org/forum/viewtopic.php?t=27449 |
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| Author: | RMDV [ Mon Feb 25, 2008 8:27 pm ] |
| Post subject: | BBD Metering System |
Greetings, I have a 63 Valiant with a rebuilt BBD carb, intake and exhaust manifold from a 77 Volare. The carb seems to be running a little rich. Initial startups produce a lot of particulate carbon on the drive way until the engine warms up to normal operating temperature. When the engine first starts it goes into a fast idle. ~1200rpm then can be stepped down to ~1000 then to ~600 rpm in neutral. In the fast idle portions it soon loads up and stumbles requiring some help with the accelator pedal to keep it running relatively smooth until the engine starts warming. I replaced the old exhaust pipe with a complete new system of 2-1/4" ID. I am familiar with rejetting a Holly carb to change the fuel/air ratio and am assuming this might be needed in this case, but have not much experience with the BBD. I thought I'd ask for some ideas as to how get this carb to perform a little better. After the engine is at normal temp with the choke full open, it seems to run great except for a slight hesitation under full throttle that I attribute to a check valve not seating properly in the accelator pump circuit. I get typically 24 mpg on the highway at about 60 mph. Thank you in advance for your help and consideration. RMDV |
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| Author: | LUCKY13 [ Mon Feb 25, 2008 8:50 pm ] |
| Post subject: | |
To here your describtion I would have said it sounded lean, except for the carbon you speak off. When cold you have to tickle the peddle to help it run, this should be because it is lean. Each time you move the peddle it sqirts a bit more fuel in and that is what should be helping it run. Next time you start it, do it with the air cleaner off. Have a helper to start it for you and when it is running try slightly closing the choke flap a little, if it helps then you know its lean and you need to ajust the choke to where it is a little tighter. If it hurts then try opening the flap a little, then you know it is rich. One way or the other it should start and not die when cold. The hesitation could very well be the accel pump not working properly. But it could also be from being a little bit lean on the main circuit. You can ajust the metering rods up in the top of the carb and get it to richin up a little quicker, or to lean it down some. What it will do is delay, or bring the inrichment circuit in quicker, or latter. Raise them, it richens up quicker, lower them and it take more throttle befor it richens up. This can help ajusting these, but only so much. If its lean then going to a little bigger main jet will be needed. Maybe the carbon is coming out because you have it breathing better and its blowing out old build up carbon. If so it should clear up as time goes by. You might also make sure your timing is doing what its should be. Many carb problems can be simply from the timing not working as it should. Between timing and vaccum leaks ( check for those to) a many carb has been replaced. Jess |
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| Author: | SlantSixDan [ Mon Feb 25, 2008 9:44 pm ] |
| Post subject: | |
Carter BBD operation and repair manual (pdf) |
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| Author: | Reed [ Mon Feb 25, 2008 10:27 pm ] |
| Post subject: | |
Make sure the choke pulloff diaphragm is working and adjusted properly. As soon as engine vacuum is applied it should open about 1/4 inch. Also, the factory choke pullof coil is designed to work with an electric assist. If you are using just the exhaust manifold heat to heat the bimetallic spring which pulls the choke open it is staying on too long. You need to connect an electic feed to the coil. Next, check the metering rod setting: 
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| Author: | dank10fenny [ Tue Feb 26, 2008 12:39 pm ] |
| Post subject: | |
bbd have prolly the easiest adjustments around. pop that lil cover on the top. you got those two flathead screws, facing it the one on right is the metering adjustment, left is accel pump. my valiant would stumble a tad on accel even when warm, so i increased the accel pump sweep to get a lil more gas. you could have someone watch your tailpipe as you takeoff to make sure your not smokin it up wit richness, if your ghetto |
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