Sprint - carb misbehaviour

[soe8m]

I never experienced it as a fiddly job. It's a few minutes you talk about. Setting it by opening angle doesn't give more power or whatever. It's not the choice between smooth take off or max power but a comfortable running engine as it should or a not correct adjusted linkage. I think you also don't have the throttle valve/shaft screws all in line. One "blocking" airflow having the bended widened slot inline with the shaft and the other slot inline with airflow allowing more air into the engine.

You concentrate on idle and the first few degrees opening because that's the most area you drive/cruise take off and can cause unwanted hesitations or vibrations. From around 25% opening to full the opening angle difference isn't an issue anymore.

Jeroen

[GrahamFountain]

Jeroen, for whatever reason, you're are seizing on an irrelevant point and failing to grasp the issue: Those arms have to be set after any significant rebuild of the carbs and or linkage. And messing with the linkage plate is not the solution to one or both being so wrong you can't set the idle. Exactly when in the process of setting up the carbs, and possibly how, is secondary to the point that they must be set.

As to the exact sequence, the starting point surely has to be the BL Repair Operations Manual, which says slacken, set, and tighten the arms after setting the idle. I think the ROM (apologies for using that TLA without expansion) is a bit more than a "book of adjusting carbs [...] written by a man with a vision". But it is an interesting critique.

And we both disagree with the sequence given in the ROM, holding that the clamps must be released before setting the idle. I then unscrew the idle screws, and set and clamp the arms before setting the idle. Whereas, you hold that the arms should be left slack while the idle is set, then set and clamped. I appreciate the point about one idle screw affecting the throttle position of the other carb if the arms are clamped at that point. But there's never any risk of that in my method.

Frankly, I doubt that there will be any significant difference in the offsets between the butterflies from setting the arms before or after setting the idle, and the only real (and still not big) difference anywhere will be in how much slack there is in the accelerator pedal. There would only be a significant difference in offset between the butterflies with the arms set after setting the idle if the two idle screws are in very different positions. And if they are, then there's some other problem that wants addressing. So I don't see the issue in worrying about it. Except, I don't want to have to set the arms again if, for some reason, I have to back the idle screws off much, like when changing between summer and winter mixture setting. In which case, if I've set the arms too close to the actuator tines of the forks on the butterfly spindles, the arms will limit how much I can withdraw the idle screws before they make no difference.

As to it not mattering if the butterflies are both fully open at full throttle: When I drive like a nun, I'll stop caring about maximizing how much mixture I can get into the engine. When I say like a nun, of course I exclude Sister t'racer.

As to the difficulties I have in setting the arms, I just find it very fiddly to get the butterflies to open at exactly the same point, to a value of "exactly" that satisfies me. I get them close enough and tighten the second clamp only to find that the little bugger has moved. Then I end up trying to estimate how far it will move as I tighten it, set it wrong by that amount, and see if that works - which it usually doesn't. So it's trial and too much error till I happen on a setting that's right or my exacting standards are moderated by how bored I've got. It may be that my technique is at fault in that. In which case, suggestions for how to do the task easily would be more help than simple dismissiveness of there being a problem.

Unless of course you're saying it's easy to set those arms because it doesn't matter that much if the butterflies open exactly together or not. In which case, what is your point?

Graham