All sorted now.
I hadn’t adjusted it right. I’d been only holding the piston down and the cam, and not holding the shaft back as well. 
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| BBD Step up piston adjustment https://slantsix.org/forum/viewtopic.php?t=54862 |
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| Author: | nzpete [ Fri Mar 14, 2014 4:38 pm ] |
| Post subject: | BBD Step up piston adjustment |
Please can someone clarify the adjustment on the step up piston. I’ve been trying to adjust mine by holding it down, and rotating the cam lifter till it touches with the throttle lever backed off. However I find when you open the throttle there is some slack in the links and the throttle opens quite a bit until it starts to lift the piston if you are holding piston down. I’m having some trouble with a lean light throttle situation. Should it actually be adjusted so that the piston if held down will start to lift as soon as the throttle is opened? |
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| Author: | oldskoolracer [ Sat Mar 15, 2014 9:02 am ] |
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Are you asking about when you make the adjustment and it lifts a little when you let your finger off? If so thats fine, as the throttle opens (engine off) it will continue to lift itself because of the spring pushing it up. With the engine running, vacuum seats it into position, then the cam will lift it as the throttle is open and vacuum decreases. Other than that Ive wondered about any other adjustments myself but havnt wanted to mess with anything and make the issue worse. Most info I get says it not adjustable? Been fighting that part throttle issue myself for over a year and a half and still cant figure it out. |
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| Author: | nzpete [ Sat Mar 15, 2014 1:15 pm ] |
| Post subject: | |
Quote: Are you asking about when you make the adjustment and it lifts a little when you let your finger off?
No, it's the slack in the linkage from the throttle lever to the shaft running through that has the lifter cams on it. I've adjusted the step up piston as per manual, but notice when finished that if you hold the step up piston down, and then move the throttle lever, it takes about 1 cm of accelerator cable travel before it starts the step up piston lift. Therefore the throttle plates will be opening before the step up piston is mechanically lifted. Just wondering if this should be adjusted so it is happening simultaneously? I know that the older non solid fuel Carter's just relied on vacuum to control the step up piston. Why does the solid fuel one need this mechanical lifter cam mechanism as well as the vacuum system? |
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| Author: | oldskoolracer [ Sat Mar 15, 2014 2:25 pm ] |
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You can try to bend the rod slightly to take out the slack between the to linkages... A very small amount of "slack" is good, it allows things to move freely without binding... However when everything is installed and set correctly there should be no slack because the throttle screw should be turned in just a little... If you screw the curb-idle screw in 2 turns as if youre going to set the accel pump, is there still the slack in the linkage your seeing? I think (dont know for sure) that the cam lifts the piston up higher and opening the jets more than relying on the spring only. |
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| Author: | nzpete [ Sat Mar 15, 2014 4:26 pm ] |
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Quote: If you screw the curb-idle screw in 2 turns as if youre going to set the accel pump, is there still the slack in the linkage your seeing? |
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| Author: | oldskoolracer [ Sat Mar 15, 2014 4:38 pm ] |
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Any way you can upload a pic or two of what you are dealing with? If there is that much play even after beggining to open the throttle there may be something more wrong with it... If you do want to try and adjust that rod, do it with the throttle completely closed, and only adjust it to the least amount of slack as possible. You dont want any real tension between the linkages until the throttle is being opened... Hope that makes sense to you, and definately get a pic or two up if you can, if not no biggy, Ill still try and help you figure it out through simple discussion. |
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| Author: | nzpete [ Sat Mar 15, 2014 5:58 pm ] |
| Post subject: | |
Can’t do photo at the moment sorry. Thanks for the help. I think it’s my linkage that needs bending. Didn’t want to get carried away bending if it wasn’t this at all, but sounds like it is. Already have messed with step up piston adjustment which reduced the problem but ended up with black spark plugs in the process. It’s a new old stock carb that I’ve had stashed away for years, so I thought it was going to be fit and forget… Thanks for your help. |
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| Author: | nzpete [ Sun Mar 16, 2014 6:34 pm ] |
| Post subject: | |
All sorted now. I hadn’t adjusted it right. I’d been only holding the piston down and the cam, and not holding the shaft back as well.
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| Author: | oldskoolracer [ Mon Mar 17, 2014 8:53 am ] |
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Your very welcome! Glad to hear you got it pretty much sorted out  Ive been through two BBD carbs now on mine and am beggining to know this thing like the back of my hand lol 
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| Author: | olafla [ Thu Mar 20, 2014 10:30 am ] |
| Post subject: | |
The manuals for all Carter carburetors are linked in the FAQ in the engine section. Olaf |
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| Author: | nzpete [ Fri Mar 21, 2014 2:16 am ] |
| Post subject: | |
Thanks Olaf. It was these manuals which I had been looking at. In the manual it says to loosen the adjustment screw, hold the piston down and the cam down onto it and tighten the screw. This is what I done without thinking, and I checked the movement between the cam and the piston and all seemed good, however after chasing a flat spot for too long, I ended up back here, discovering the slack, and it seems that the slack was the cause of it. I haven’t done anymore thinking about it as the flat spot is gone, but with mine I needed to hold the shaft as well as the cam and piston to take the slack out of it. WIthout holding the shaft as well I ended up with slack every time. Maybe it might be something for others to check that may have fallen into the same trap as myself. |
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| Author: | oldskoolracer [ Fri Mar 21, 2014 9:33 am ] |
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Im actually gonna double check mine as well just for kicks, like I said mines been here for a long while and we've pretty much just learned to deal with it, but maybe there is still hope lol. And yea, Ive studied those manuals front to back multiple times. Got so bad I was having dreams about Carter BBDs at night!
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