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2024-03-21 Carb Sync Tips
Forums:
It's good to hear that all your work and frustration has been paying-off !
After 43 years I have simply become profecient with these carbs and don't have to think twice. It's totally about familiarity, which is an accumulated learned thing !
After 43 years I have simply become profecient with these carbs and don't have to think twice. It's totally about familiarity, which is an accumulated learned thing !
In no particular order:
I came to the conclusion years ago that the manuals instruction for setting the Fast-Idle is incorrect, in my opinion. . Much like the recommended 1.5 turns for the Pilot-screws. The manual indicates a gap of 0.54mm - 0.55 mm between the Idle adjusting screw and "the Lever". Illustration "E21"/page 50 (in my manual).
I have NEVER been able to achieve this TINY gap. On every set I've rebuilt (all road tested) including my original carbs, the gap is in the range of 2.0mm. This also applies to the set I recently rebuilt and are currently on my bike.I'm at a loss for words for a detailed "Set-up" explanation because other variables directly affect the idle and it becomes a "Rubik's Cube" scenario. Synchronizing, Pilot-Screw setting and final adjustment to the fast idle screw (Cam and roller) all play into the equation and "turning" something one way or another affects the other adjustments.
Choke plungers: They should start to lift at the same time and must close completely with no interference from the lifting forks. When fully closed the "Spools" must "Float". This ensures the plungers are fully closed and seated.
I have NEVER been able to achieve this TINY gap. On every set I've rebuilt (all road tested) including my original carbs, the gap is in the range of 2.0mm. This also applies to the set I recently rebuilt and are currently on my bike.I'm at a loss for words for a detailed "Set-up" explanation because other variables directly affect the idle and it becomes a "Rubik's Cube" scenario. Synchronizing, Pilot-Screw setting and final adjustment to the fast idle screw (Cam and roller) all play into the equation and "turning" something one way or another affects the other adjustments.
Choke plungers: They should start to lift at the same time and must close completely with no interference from the lifting forks. When fully closed the "Spools" must "Float". This ensures the plungers are fully closed and seated.
A vacuum leak anywhere will adversely affect the idle and will create idle consistency issues but generally not a choke applied "runaway" scenario.
I don't know if you've done the Choke Air mod. The original restriction size was an arbitrary decision .I had to start somewhere ! Those (few) that have reported on their own choke-air mod. indicate starting is much easier but the choke is "Finicky" until the engine warms. It works but is not perfect.Never walk away from the bike when it's warming-up on ANY amount of choke. The runaway can be SCARY! I think of this as the "Lazy Carb. Syndrome". Some idle circuits take their time to fully draw fuel equally and until they do the choke-applied idle will be rough but as each cylinder "comes on line" the RPM's will increase dramaticly !
The second set I am currently running allowed me to experiment with the Choke-Air restrictor size. I went from the initial restrictor size of 3/32" up to 1/8". I simply drilled them out. This has made the application of choke much more manageable and to some degree predictable, but I still will not walk away until the idle smooth's-out and the application of choke is minimal.
There are two "Gaps" that are critical. The aforementioned "2mm" between the Idle-screw and the lever AND the fast-Idle "Cam and Roller". With the Choke OFF, the "Roller" can not be touching the Cam ! The setting for this is easy. Simply back off the Adjusting screw "C" (per diagram) . There should be a few thou. gap between the roller and cam. This ensures that the idle is actually being maintained with the Idle Adjusting Screw. ( # 109 in the break-down diagram.)Throttle cable. I prefer to have the cable adjusted so that a few degress of rotation is required before the the throttles actually start to open. I like to see the "slightly" slack cable tighten as I roll the throttle those couple of degrees. This ensures the actuall idle setting is being controlled by the idle knob and not a tight cable.
There are two "Gaps" that are critical. The aforementioned "2mm" between the Idle-screw and the lever AND the fast-Idle "Cam and Roller". With the Choke OFF, the "Roller" can not be touching the Cam ! The setting for this is easy. Simply back off the Adjusting screw "C" (per diagram) . There should be a few thou. gap between the roller and cam. This ensures that the idle is actually being maintained with the Idle Adjusting Screw. ( # 109 in the break-down diagram.)Throttle cable. I prefer to have the cable adjusted so that a few degress of rotation is required before the the throttles actually start to open. I like to see the "slightly" slack cable tighten as I roll the throttle those couple of degrees. This ensures the actuall idle setting is being controlled by the idle knob and not a tight cable.
Ignition timing (if applicable) will have a very noticeable affect on the idle. Several degrees either way can make the difference between an "acceptable" idle and an Idle that will make you weep with joy !
If you've suffered through all this blah, blah I hope you got something from it and this in turn helps you with some of these points of concern.
I'm sure that after I submit this there will be something I have forgotten but in the meantime if questions arise - just ask !
I'm sure that after I submit this there will be something I have forgotten but in the meantime if questions arise - just ask !
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