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1967 CB450K0 Black Bomber Rebuild - By Royhall
royhall:
No. I took the side panel off again and had a close look with a mirror on a stick and a good light. It appears that there is a passage for air all around the filter, it just doesn't look like it without a really close look. Once warmed up I gave it a bit of throttle to about 7000rpm and it ran cleanly with zero hesitation. Got to be careful as 4 years on it's not run in.
The engine sounds good with no rattles or knocks, so far no oil or petrol leaks either. I now need to get a few hundred miles on it then see what the oils like. Last time I drained the oil it was way above the max mark and smelled of stale petrol, it also ran out of the drain plug like water. Severe petrol bore washing.
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K2-K6:
I think you're on the right track Roy, with the removal of restrictive paper filter element, if I understand correctly.
At risk of teaching people to suck eggs :) the CV carb works by negative pressure between the throttle plate and the main jet positioning under the most restricted part of air slide.
Opening the plate cause a drop in the chamber above the airline greater than that underneath the slide, this then lifts the airslide as those two are unequal, until they reach parity at that same throttle plate opening, the jetting calibrated around this balance.
Now if the intake air path is restricted at air filter, the above and below vacuum (both coming from the same inlet tract airbox side) will not allow that relative separation as it shouldn't be restricted there. Without that, the air slide won't move upward against it's spring. This gives an odd /opposite affect to fuel metering though. With overall vacuum climbing and airslide not rising, it then starts to pull more fuel out of main jet even though the needle has not lifted, sending it significantly rich by that action. It's one reason, I believe that CV carbs aren't generally "choked "with a plate on airbox side.
It seems imperative that intake from outer end down to carb venturi (incorporating the entrance to above airslide intake must be as free as practically possible for the whole thing to work.
royhall:
I think that explanation is spot on, and may explain some of the reluctance to return to tick over issues as well. In this case the CV carbs do have a choke plate mechanism on the intake side. I find it's only required for initial cold start, and as soon as the engine fires it needs to go fully off. For some reason these carbs have a tendency to go rich at the slightest provocation. If it doesn't work this time I am going to buy a Mikuni conversion kit with cranked pod filters. Apparently it's like a magic bullet for Bombers.
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AshimotoK0:
If you sadly do decide to go the Mikuni route Roy, at least you will have a half decent set of Keihin 14C carbs to pass onto anyone if you ever sell the bike.
I did hear that some people have fitted Suzuki T500 carbs.
royhall:
Don't think T500 carbs are easy to get. I had a T500 some years ago that had snowmobile carbs fitted. I decided to fit the correct carbs but couldn't find any decent ones. Strangely, it ran great with the snowmobile carbs fitted it was just the airbox didn't fit correctly. As I was still in engineering then I made up some spacers, that sorted the problem. Wish I hadn't sold that bike, they are worth strong money now.
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