Weber carb swap performance
 

Currently I have the factory carb on an Offy dual plane intake. Its the Canadian carb so there is no garbage and it works fairly good. Low end power is as good as can be expected but top end is just non-existent, it really struggles over 4000RPM. Cruising power is again as good as could be expected. Overall drivablilty is great, just a bit of stumble cold if you instantly floor it from idle. Timing and compression good, valves and seats re-lapped with new springs and seals. In short the engine is in good shape. Maybe I got lucky with the stock carb, maybe the Canadian non-smog ones are better or maybe I don't know any better. So... I was thinking to re-machine the Offy manifold to take a Weber 32/36 (the stock carb if I recall is 32/40 and the CFM's are about the same as the Weber 32/36) So what I am getting at is this, will I get any real performance/top end gains doing a Weber swap? I get pretty good mileage about 25-26 MPG (Canadian Gallon) and like that. I did a crude back road 0 to 60 and it was around 15-16 seconds and can just about pin the speedo (You really know how scary the handling of a short wheel base, leaf spring, solid front axle rig is at that speed!) I've read lots of stuff about guys that swapped out a worn out factory smog carb and/or a rebuilt engine with good results but not seen any thing about swapping out a relatively good carb on a good engine. I know the DCOE's are just the cats meow but don't want to go that route.

Most of the people I've talked too that switched to a weber didn't necessarily do it for performance gains. Consequently most of the people I've talked to that noticed gains are people whose factory carburetors were not working very well.

In my opinion, if your factory carb is doing its job, don't fix whats not broke. I'm a fan of the factory carb myself. Never ran a weber on any of my r engines and never felt i'm missing out. If i was going to switch to a weber I would do it for sake of simplifying things- not expecting a bunch of performance gains.

Hope this helps!

cfm's are about equal except for factory 20r they had about half the cfm's (150 something) as 22r carbs. what kinduv power are you expecting above 4k? pretty sure you are on the downward curve @ that point. If your getting 25+ MPG sounds like you are doing great. My 32/36 only got about 18mpg with 4.30 gears and a 4 speed. my 38/38 gets 17mpg with 4.30 and 4 speed. And thats a US Gallon of 93 octane. just to be clear your getting over 300 miles on 12 gallons of gas?

i guess i was wrong horsepower peak supposedly is around 4500-4800 rpm, but I don't like going there. nor do I feel the pull @ those engine speeds. I'm basing my info off a 20r not 22r.

So I've concluded its as good as its going to get within what I've spent on it or want to spend on it. Now I believe that part of the lack of top end power is the Offy dual plane manifold doing exactly what its advertised to do...improve low to mid-range response and drivability...within the capability of the stock 22R engine and at the cost of top end...you just cant have both especially with a carb/manifold set-up. I seem to re-call that the stock intake did have better top end, which makes sense with its more open runners, but that was over 20 years ago and not driving it for 15 years until 2 years ago. I was looking just to improve its power above 4000 in third gear, currently I don't think it'll hit redline in third or it takes forever to get there, and I don't want to rev it that high for that long to find out. Briefly revving that high to pass or merge into traffic I'm O/K with. And as I said the drivability with what I've got/did is great for 'normal' driving and don't want to mess up. So as it was said by rowdy235 its not broke and unless someone else can give un-disputable info that I will get a measurable gain it stays as is.

I found some old carb data I had stashed away...The Weber 32/36 is 325CFM and the stock 22R is 326CFM. If you calculate out the CFM requirements for the engine it has ample with the stock carb (230CFM @100% VE (volumetric efficiency)). The 22R is likely in the range of 80 to 85%VE at best.

Unfortunately for some bizarre reason Americans and Canadians decided they couldn't measure things with the same system or even have a gallon which is the same size! So it gets about 21 to 22 miles to the US gallon or about 360KM's on 40 litres (that was the last fill-up rounded). The 'Canadian" gallon (the old Imperial gallon) is about 15% bigger. Thus the misunderstanding of 300 miles on 12 gallons.

I recently switched out my stock carb for a Weber Carb on my 20R Pickup. I expected to see some improvements, but WAS NOT prepared for just how much of an upgrade it was! My truck now fires up with vengeance and purrs. My fuel consumption and horse power has drastically improved. My stock carb was definitely a little dirty, but a rebuild still would have matched what I have now with the Weber. Im a serious fan of the conversion.