comparison of cv carburators vs. mechanical slide carburators?

Question

doing a report on carburators and need a comparisons for cv and slide on the fuel ecomony, emissions and throttle response.

I have found some info on the www but mostly adds for businesses.

Thanks for your time

Answer 1

I agree with most of the other commentors, but I think the main benefit to a CV carb over a slide carb is the fact you can end up using a much bigger carb with a CV. Because of the constant velocity feature, the carb can replicate a smaller carb at lower rpm, but still open to a much larger throat size than would normally work well with the same engine.

They used to put larger carbs on old racing bikes, but the throttle response was terrible, the mixture couldn't ever be right for anything other than a small rpm range near redline. Accelerator pumps helped mask the response issue, but if you opened the throttle too abruptly, it still was too big a carb for lower rpm situations.

I had a 1966 Honda CB450 and it was the first CV carb use as standard equipment. The carbs were huge compared with what BSA's, Triumphs and other even larger twins were equipped with, and they worked well. They were also more adaptable for modifying the engine as well, without needing to replace the carbs with bigger one's. Straight thru, or megaphone exhaust, velocity stacks on the carb, higher compression etc, worked pretty well on that bike without even jetting changes. Although back then they weren't as leaned out as today's CV's for emissions control.

Answer 2

I can tell you about the throttle response. I'm sure you've learned that the fuel/air mixture enters the cylinder from the vacuum that the piston makes on it's down stroke. When the throttle cable pulls the slide up, the vacuum of the cyl pulls the fuel in, in a "HERE...GO!" attitude (quick response).
A cv carb (constant velocity) allows the fuel to enter the cyl at a steady velocity (smooth response). When the throttle cable opens the butterfly valve, the vacuum of the cyl pulls air through the venturi of the carb. The vacuum the cyl makes, enters a port in the carb which sucks the slide up, allowing more fuel into the mix. A more equal ratio of fuel/air enters the cyl.
I'm no scientist or engineer, but I would think that a cv carb would give better fuel economy because there's no excess of fuel entering the cyl. Also the emissions would be lower on a cv carb because the fuel/air mixture would burn more completely since they are balanced.

Answer 3

C.V carbs control the fuelling much better than slide carbs for the average street rider.
Slide carbs are controlled by the right wrist directly, so if you open the throttle too quickly, then you get a weak mixture momentarily until Mr. Bernoulli and his amazing venturi effect begin to work as advertised. This is because the relative density of air is much less than that of the petrol, so when you open the slide quickly, the air accelerates, yet the petrol lags behind due to inertia; hence the weak mixture.
Since CV carbs also operate more smoothly, these weak cuts, flat spots and glitches don't occur very often, so emissions and fuel economy are marginally better.

Throttle response is much better with a slide carb though, with wider throttle openings, at low throttle openings the CV wins.

Air mass flow is also better with a slide carb at wide throttle openings, because there is no throttle butterfly assembly obstructing the airflow. This is why race bikes used to use slide carbs, when the street equivalent machines used CV carbs.

Answer 4

Mechanical Slide

Answer 5

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