Its been awhile..The whole 2 barrel set up inc screws, nuts, gaskets & hose clamp are neatly boxed, marked & ready for more fun. Since boxing it up I have found a 2 barrel from an 85 that has 1" venturis down from 1-3/16". This carb also has a choke butterfly & lever so will be easier to start than stuffing a rag in. Ive run it with a test wheel in a barrel & its better than the bigger one there which says little of how it will work on water. Ive got it on the boat now ready to test. Theres still a bit of a chill & the wind is up for a couple days so hopefully soon, I have run the boat last week exactly as is with a 1 barrel & noted rpms so I have a benchmark in case it goes well.
A fair amount less volume of air will pass these openings so hopefully the missing velocity will be found & it runs thru its range better. Ive got to make up a spray shield but have a plan thats easy to start with.
It is my opinion that you will get MORE air through the 1" carbs; why? Because you will get higher velocity , therefore more air. And, that's because your motor cant suck air with the same velocity that it can with optimum sized carbs.An example I saw ,about 30 years ago , here in Napa(calif) was a moded 60" six cylinder Merc,had 3 japanese motorcycle carbs installed . Looked beautiful. Started right up, then when he cracked the throttle, it would die, every time. problem? 39 M.M. carbs ! way too big . NO velocity when throttle opened. I believe if those were about 31 or 32 M.M. it might have run GOOD !
Drag racers regularly over-carburate as well, using a 800 to 1,000 CFM carb on a mild 350 SB Chevy. The Nationwide NASCAR racers, by rule, use a tiny 360 CFM four barrel carb on their 350-sized motors and make over 500 hp.
Jeff
Its because carbs work by vacuum. If your carb is too big, there will be no vacuum and no fuel mixed with all that air the large hole lets in.
That is what sets the practical limit on carb size
Since 1925, about 150 different racing outboards have been made.
That was the problem with the larger carb, it would idle & if you could get it thru the mid range it would catch & go the rest of the way up. Keep in mind the single barrel that works best is 1-3/16" at the v & 1-3/8" at the maniflod end, exactly the same as the bigger 2 barrel. The manifold is separated so 1 barrel feeds 1 cyl. & the new carb is 1" at the v, 1-3/8" at the manifold so in effect the cyls are drawing thru a smaller hole than the single & the only common aspects are the float chamber & the open common carb entry chamber. It still might get more air but im hoping with good result.
accelerator pump
The 350's are one of the best & most versatile engines made in its size class. Many unwitting rod'rs spent cash on the wrong stuff for years. Nowadays system matched kits are available & the guess-work is no longer. The big carbs would be kinda messy on a restrictor plate so that makes sense. Its the camshaft advance that really brings it up. Some newer cars have variable cam timing & are wildly quick.
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