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Twin carb question

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Venturing into resetting my twin monoblocks after a complete strip down and I got to wondering why it has been necessary to remove the choke, blank off the choke cable adjuster and blank off the throttle stop on one carb. I have read on the forum that these steps are often taken with twin carb set ups but I would appreciate if someone could explain the reasoning behind it, when it seems so important to have both carburettors in perfect sync. 

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Does not make any  sense to me. But before spending cash on missing parts check the bodies for wear with a good slide.

Thankyou Robert, you seem to be homing in on why I asked the question in the first place. I have been having trouble restarting my bike and I narrowed the problem down to carburation. Whilst trying to sync the carbs I noticed that, although the slide operation was in unison, the nearside (no throttle stop) slide was open wider than the offside. Having in mind that both carbs shoul have the same settings I screwed the offside throttle stop in to line up the slides only to find the engine less responsive than before because the throttles were open too wide. I then backed off the offside throttle stop and she fired up on the first kick however there is a marked difference in the temperature of the exhaust systems which makes me wonder whether the nearside slide needs to be lowered to nearer match the offside. This brings me back full circle because ther is no way to adjust the throttle stop on the nearside.

I Had hoped that one of the carburation buffs might have thrown some light on the problem but it is looking as though I will be reinstating a throttle stop and going down the trial and error route.

Thanks for your interest. Regards Ron.

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My suspicion is that the Po could not get the motor to slow down to a tickover  and the throttle stop screw was so far out that it would not hang in there ,so better out and blocked the hole!!. All pretty daft, but then we are mostly -----aren't we??.

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If the motor refuses to slow to a tick-over, there is a problem with a sticky throttle cable, the carburetor slide(s) being excessively worn, or the ATD is holding too much advance.  Check, fix

I don't muck about with the balance of the carburetors for idle control.  What I do is put a pair of spacers of known exact size under the slides, say a pair of 1/8" drill bits  (use the shanks, not the flutes!), and adjust the cables so the slides lift at EXACTLY the same moment.  Then set the idle screws so that you get an even slowish idle and the slides lift off the stops at the same moment.  This assumes you have already set the pilot mixtures correctly

Paul

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Do you perhaps NOT have a mirror image pair (left plus right handed) of carburretors?  Are they non-standard concentrics, or original monoblocs?  In any case, they should each have the throttle stop screw on the outer facing side of the carb bodies.  Is yours blocked off with a solid screw (in which case you can replace it properly), or solid casting (in which case the screw might be inaccessible between the two carbs, or removed because of lack of space).

Many thanks for your input David, I do not have a matching pair and the throttle stop screw on the nearside carb has been replaced with a blanking screw, had it been there it would have been difficult to access but not as difficult as the air screw which is almost impossible to adjust without dropping the carb out.

Thanks Paul, heading for the shed to try the drill shank trick. My big problem with that procedure is that I am on the limit of my adjusters and I think that I am going to have to find some extended ferrules or spacers.

Timing seems to be fine it's definitely a fuel problem that I am battling

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Interesting theory from another forum. "Dommies can run very well as a single and it might be that you are firing up on one cylinder and the second carburettor is only coming into play when you tweak the throttle, this might explain the temperature differences on each exhaust" Straight out to the shed,started her up then removed the nearside HT lead resulting in very little change to the engine note. The theory seems to tick all the boxes and it would be great to hear if anyone on this forum has any experience or comments to add.

 

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