Shuriken
Well-Known Member
TLDR: cylinders not firing until fuel is added into intake ports; pilot fuel jets and jet block passageways are clear; where is the problem?
Long version:
So on another set of carbs (02 model), I have a couple of cylinders that will not fire at idle. If I give a little puff of aerosol into the vacuum ports of the offending carbs, those cylinders will fire.
So.... I've checked, cleaned, and inspected the bowl internals, including the pilot jets inside the jet block. I have also checked dry float levels. I reassembled and still had the same issue, so disassembled again and thought I would have seen crud from the fuel tank and obstructed pilot jets in the jet block but everything looked good.
The cylinders fire when I present the additional aerosol fuel, so the pilot system on these 2 carbs is not working right, and the bike is too sloppy just off of idle. I can feel the cylinders activate while riding when I open the throttle butterfly valves slightly, and the bike has full power thereafter.
So... someone help me (re) understand our variant of CV carbs. Our idle mix screws are on the air/intake/non-fuel side of the carbs and are thus controlling fuel/air ratio by adding or subtracting air, correct? I can gently seat them (reduce air, increase fuel ratio) with no effect, and I can turn them out (increase air, reduce fuel ratio) with no effect. The mix screws are not broken, which would definitely make the screw turns ineffective. Adding aerosol fuel fires the cylinders, so where is the problem?
If I map the pilot fuel jet holes in the jet block where they mate to the carb body, I can find what I believe is the internal passageway from the pilot fuel in the jet block into the carb body. I assume this passageway will carry fuel up to the throttle butterfly, where it gets mixed with air from the idle mixture screw opening, and that if the pilot fuel circuit is clogged inside the carb body, this would explain the lack of fuel, and thus lack of combustion.
However, the internal pilot fuel passageway should be larger in diameter than the pilot fuel jet itself, and shouldn't get clogged.
On a properly running vmax, is it possible to misadjust the idle mix screws out so far that combustion stops? Can these idle screws deliver too much air? I'm just trying to figure out where the idle combustion problem is, in consideration that the pilot fuel jets themselves are clean (the bike has stock / oem jetting).
I can find generic circuit diagrams for CV carbs but the ones I've seen show the idle / pilot mixture screws operating on the fuel circuit, not the air circuit. I suspect idle mix screw issues or there is still a pilot fuel blockage I haven't been able yet to clear, or both.
Anyone else fixed this issue before?
Long version:
So on another set of carbs (02 model), I have a couple of cylinders that will not fire at idle. If I give a little puff of aerosol into the vacuum ports of the offending carbs, those cylinders will fire.
So.... I've checked, cleaned, and inspected the bowl internals, including the pilot jets inside the jet block. I have also checked dry float levels. I reassembled and still had the same issue, so disassembled again and thought I would have seen crud from the fuel tank and obstructed pilot jets in the jet block but everything looked good.
The cylinders fire when I present the additional aerosol fuel, so the pilot system on these 2 carbs is not working right, and the bike is too sloppy just off of idle. I can feel the cylinders activate while riding when I open the throttle butterfly valves slightly, and the bike has full power thereafter.
So... someone help me (re) understand our variant of CV carbs. Our idle mix screws are on the air/intake/non-fuel side of the carbs and are thus controlling fuel/air ratio by adding or subtracting air, correct? I can gently seat them (reduce air, increase fuel ratio) with no effect, and I can turn them out (increase air, reduce fuel ratio) with no effect. The mix screws are not broken, which would definitely make the screw turns ineffective. Adding aerosol fuel fires the cylinders, so where is the problem?
If I map the pilot fuel jet holes in the jet block where they mate to the carb body, I can find what I believe is the internal passageway from the pilot fuel in the jet block into the carb body. I assume this passageway will carry fuel up to the throttle butterfly, where it gets mixed with air from the idle mixture screw opening, and that if the pilot fuel circuit is clogged inside the carb body, this would explain the lack of fuel, and thus lack of combustion.
However, the internal pilot fuel passageway should be larger in diameter than the pilot fuel jet itself, and shouldn't get clogged.
On a properly running vmax, is it possible to misadjust the idle mix screws out so far that combustion stops? Can these idle screws deliver too much air? I'm just trying to figure out where the idle combustion problem is, in consideration that the pilot fuel jets themselves are clean (the bike has stock / oem jetting).
I can find generic circuit diagrams for CV carbs but the ones I've seen show the idle / pilot mixture screws operating on the fuel circuit, not the air circuit. I suspect idle mix screw issues or there is still a pilot fuel blockage I haven't been able yet to clear, or both.
Anyone else fixed this issue before?
