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| BBD operation https://www.slantsix.org/forum/viewtopic.php?t=61857 |
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| Author: | gato [ Tue Jan 23, 2018 5:12 am ] |
| Post subject: | BBD operation |
looking down into my BBD to see the accelerator squirt. . . i get a good blast of fuel from both jets. i notice that it lasts about 25% of the time it takes to move the gas pedal close to the floor. is this normal? or is my blast being cut short? i am chasing a bog below 1500 RPM. trying to determine if i should first look into the BBD or the distributor. 
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| Author: | wjajr [ Tue Jan 23, 2018 6:20 am ] |
| Post subject: | Re: BBD operation |
At 1500 or lower rpm carb is running on idle and transition circuits for lack of a better term (i know these devices utilize rods and jets) and main has not kicked in, in other words it's probably already on lean side, and when intake see a lot of blue sky during large sudden throttle opening mixture goes real lean until main can get flowing. 1500 rpm is not moving much air through carb, so as you suspected, a longer duration accelerator pump shot is probably needed. Not being up on BDD's, just how one extends pump shoot, I can't say, but I'm sure someone will chime in on such a fix. |
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| Author: | SlantSixDan [ Tue Jan 23, 2018 11:21 am ] |
| Post subject: | Re: BBD operation |
You normally won't see a pump shot lasting the entire time it takes to open the throttle (unless you open it really fast). Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download, but the problem isn't necessarily coming from the carburetor. More detail about this "bog below 1500 rpm" will help you narrow in on it; that description isn't specific enough. What kind of car is this on, is it original or a transplant, what's the history of the carb, where'd it come from, what emission controls are (still) in place and operational, what ignition system are you running, what changed before the "bog" started happening, what exactly do you mean by "bog" and "below 1500 rpm", etc... |
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| Author: | Reed [ Tue Jan 23, 2018 11:56 am ] |
| Post subject: | Re: BBD operation |
Whenever diagnosing BBD issues, my first question is whether the metering rods are adjusted properly. The metering rod setting plays a big role in how a BBD performs. Check your metering rod adjustment. |
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| Author: | gato [ Thu Jan 25, 2018 5:27 am ] |
| Post subject: | Re: BBD operation |
Reed, i believe i have the meter rods set correctly. i have them at the longest stroke i can get. i have the correct /6 riser arm in place. that other adjustment at the top of the needle assembly is what i don't know about. the manuals say to leave that thing alone. i have no idea if it was ever messed with b4 me. Dan, this is a transplant BBD onto what is other wise a stock 225 in a 68 A108. the bog started when i first put the BBD on it many years ago. i just learned to deal with it because i mostly just use the van for long freeway cruises and it does real nice up at speed. a few months ago i realized i was running an 8 Cyl BBD while i had a 6 cyl version at my disposal. i don't recall where i got it. probly a swap meet or Ebay. u, and others here, helped me get the idle down where it should be by helping me realize i had the wrong throttle plates in place. the bog is identical between the 2 carbs, so either they r both perfectly out of adjustment in exactly the same way or it is something else? i tried advancing the distributor. it is currently set at 2-3* BTDC. if i bring up to about 10* the bog lessens. but then i get a lot of pinging under loads at higher speeds. i really suspect the distributor, but i want to try to get the BBD as close to spot on b4 i get into the dizzy. |
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| Author: | matv91 [ Mon Jan 29, 2018 2:18 am ] |
| Post subject: | Re: BBD operation |
http://www.slantsix.org/forum/viewtopic ... tering+rod |
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| Author: | gato [ Fri Feb 02, 2018 5:17 am ] |
| Post subject: | Re: BBD operation |
thang Q. i had not seen that b4. |
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| Author: | gato [ Sat Feb 24, 2018 4:35 pm ] |
| Post subject: | Re: BBD operation |
just a qwik "Thang Q" to all that offered ideas. the link to the metering rod set up was the key. i got in and set it to the .035 today and the old van woke right up. i think i'll be fiddlin with it a bit more, and after that i'll get into the distributor. itz almost ready for another run out to the 4 Corners Area. thanks again. D~~~! |
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| Author: | Slant Cecil [ Sun Feb 25, 2018 1:36 am ] |
| Post subject: | Re: BBD operation |
I'd put a kit in the BBD so I know I have a fresh pump (#25). Make SURE the metering rod arm (#22) and pump arm (#23) are properly adjusted. Only then I would adjust the step up piston (#11) if needed. 
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| Author: | gato [ Sun Feb 25, 2018 8:22 am ] |
| Post subject: | Re: BBD operation |
this was a carb i didn't realize i had. i don't recall where i got it. probly Ebay or a swapmeet. i did go thru it and freshen things up. and it ran just fine once i got up to speed. it just felt weak during acceleration. yesterday i did find the piston specs was very lean. a simple adjustment and it is much more normal. |
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| Author: | gato [ Wed Feb 28, 2018 7:04 pm ] |
| Post subject: | Re: BBD operation |
now that i am getting over the initial surprise in the difference in performance,. . . do the metering rods come in different sizes? r they stamped/marked as to what size they r? where? same questions for the jets the rods run thru? r there any data/charts somewhere detailing what rods-jet combinations should best be applied for different altitudes? still some adjusting to do. . . trying to think out all the variables. |
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| Author: | matv91 [ Thu Mar 01, 2018 3:03 am ] |
| Post subject: | Re: BBD operation |
http://www.slantsix.org/forum/viewtopic ... lit=spring |
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| Author: | matv91 [ Thu Mar 01, 2018 3:17 am ] |
| Post subject: | Re: BBD operation |
Meter rods different sizes yes, also different step-up spring. Sedans soft spring, heavy station wagons got stiffer spring.What numbers on your rods? |
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| Author: | gato [ Thu Mar 01, 2018 6:01 am ] |
| Post subject: | Re: BBD operation |
i did not notice any markings on them. that is why i asked. where r they marked? i will have to take them out to find which ones they r. maybe over the weekend. it would help to know where to look because i missed it so far. |
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| Author: | gato [ Thu Mar 01, 2018 6:19 pm ] |
| Post subject: | Re: BBD operation |
oh.. . my BBD lives in an A108 van. i would guess that means it should get the heavier spring? |
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