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2bbl swap progress report
https://slantsix.org/forum/viewtopic.php?t=35942		 Page 1 of 1
Author:  LWS1967 [ Sun Jun 21, 2009 5:17 pm ]
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Just wanted to post an update on my conversion project here. Got everything mounted up and running. No really big problems with the actual modifications or installation. Biggest issue I ran across is the fact that if I had wanted to cut the throttle shafts and use the 1 bbl arm like stated in the article, it would never have worked. Not only was there no way to bolt it all up based on how the article is written (no way to insert the throttle shaft once assembled...maybe I missed something?) but the throttle shaft on my 1 bbl was thinner than the BBD...so I'm glad I went with the linkage fabrication and traditional mounting of a carb route as my first option. Took a little time to figure out the kickdown linkage, but did measuring and fab'd a couple of soft aluminum bellcranks to get the geometry sorted. Got the thing idling good at 550 rpm with 18 in Hg vac reading. My only remaining "sorting" is the accelerator pump. From the box, it was pumping too much shot, to the point of drowning the engine....much black smoke and stumbling. A couple of times on the road from a start I could'nt get rolling as it would drown the engine. Arm was in the closest hole to the pivot. Switched it to the outer hole (there's only two) and it's alot better, minimal stumble, but still some black cloud. I'm thinking maybe fab a little extension for the pump arm so that the linkage can connect even further away from the pivot so as to further slow the amount of shot? Idle ok, cruising initially seems in the ballpark....just want to sort the pump and move to the next thing. Any tips or advice on this is greatly appreciated! :D

Pulls alot stronger for sure...2 1/4" exhaust will be next along with further tinkering!


Lorin

Image
Author:  SlantSixDan [ Sun Jun 21, 2009 5:22 pm ]
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On both the throttle lever and the accelerator pump arm, the innermost holes give the shortest accel pump stroke. Outer holes give longer shot (more gasoline).
Author:  LWS1967 [ Sun Jun 21, 2009 5:49 pm ]
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That's my understanding. The outer hole gives a slower prolonged shot vs. the inner holes quick shot. It carburates off idle better in the outer hole, and short of smaller accelerator pump nozzles, I guess that maybe an even loner arm may slow it down further? Geometry is not my specialty so what do you think? :?:
Author:  SlantSixDan [ Sun Jun 21, 2009 6:02 pm ]
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Well, I'm confused by what you've written: You're trying to have less fuel injected when you step on the accelerator, but you're making the pump shot longer…do I understand you correctly?

It's essentially impossible for the accelerator pump to provide enough fuel to cause the engine to gag and blow black smoke. If that's what's happening, the carburetor probably has other problems.
Author:  LWS1967 [ Sun Jun 21, 2009 7:35 pm ]
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From what I can tell, the very first bit of pump shot is a bit too much, looking down in the venturi's there is a strong shot going in with just the first bit of pump actuation. I'm thinking that there's just a bit too much fuel being pumped in initially. I'm thinking it ought to be a little bit leaner...like smaller nozzles, more so than linkage adjustments. There's nothing wrong with the carb so far as I can tell from my minimal time running it...... I have'nt spent enough time with it to start thinking that it has problems, other than it is setup for a 70 318. Idle, low/mid/high speed, various rpm acceleration, and full throttle acceleration runs "seems" fine. I'll have to open it up and see what jets, rods, etc are in there for sure...should have done that to begin with! :oops: This is all improvisation, so trial and error it will be. Plenty of time now to play around with it. I know better than to expect a carb out of the box to perform perfectly from the get-go. I'll get it figured out, believe me, and let you know what I came up with, good or bad......focused on good of course 8)
Author:  LWS1967 [ Mon Jun 22, 2009 5:58 pm ]
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Well after a bit of test driving and thinking/looking things over (as well as doing some measuring) I've concluded that I was on the right track in regards to moving the linkage (from the throttle arm to the pump arm) further away from its (the pump) pivot point.... there is less fuel being pumped in over the entire application of throttle. The pump plunger travels less in its bore using the outer hole vs. the inner hole. BUT, there's still a little too much black smoke when I gas it at a stand still. Guess I'll just have to look at leaning things out...perhaps the step-up rods? Can you get different sized rods, piston, springs still? (like you can for the AFB's) Maybe that's where I need to look/tinker further? But HOT DAMN! the thing runs great, especially on the interstate. I can run 60-70mph+ and pass at will, pulls strong like never before. Sweet! :D
Author:  Old6rodder [ Mon Jun 22, 2009 7:30 pm ]
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Civilised cobbling.

You're right, inner hole on the base lever combined with outer hole on the pump lever'll give you the shortest total stroke.
However, too long a stroke shouldn't really be giving you the problem you describe, that'd be more the rate than the volume I'd think.

In that vein, one thing you could address is the pump spring strength, as that's what makes the rate.
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