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81 spada nt carburation

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danmiluk View Drop Down
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    Posted: 10 Jan 2017 at 20:13
Hi guys, i went balance the carbs on the bike. My books tells me to screw in the air mix screw then out by 1 1/2 turns would this be correct, i can remember readings some place that the left cyclinder 2 1/2 and the right 2 3/4.
what has prompted me to look at the carbs the right plug was super sooted, could anyone enlighten me.
cheers
danny
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Brian UK View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 10 Jan 2017 at 20:33
If one plug is very black, check the choke cables are loose when off, and the choke plunger is seating properly. Sometimes the neoprene seal on the bottom of the plunger gets distorted and won't seal the jet.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ken-Guzzibear Quote  Post ReplyReply Direct Link To This Post Posted: 10 Jan 2017 at 20:48
I start 2.5 to 2.75 you can hear it as much as anything  1.5 turns is the starting point make sure the engine is well warm or once set then when warm the tickover will race to say the least and yeh left and right are different Brian is correct tho the choke does need to be checked the end and the ring seal on the top edge do fail
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Dave P. View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dave P. Quote  Post ReplyReply Direct Link To This Post Posted: 10 Jan 2017 at 21:56
I noticed you refer to the "air mixture screw" On the older guzzi's with VHB's or PHF's that's a fuel metering screw. I just thought I'd mention it incase you are more used to Amal's which do have air screws and work in the opposite direction to Dellorto's.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 10 Jan 2017 at 22:35
Of course the Dellorto "choke" works the opposite way to Amals too, it adds extra fuel rather than reducing the air.
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Dave P. View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dave P. Quote  Post ReplyReply Direct Link To This Post Posted: 10 Jan 2017 at 22:47
True true,unless the Amal's a mark two.
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Mike H View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike H Quote  Post ReplyReply Direct Link To This Post Posted: 11 Jan 2017 at 15:23
The 1.5 turns out often leads to confusion, what it's actually saying is, when setting up carb settings start with 1.5 turns out, from fully screwed in; you then try getting the bike to idle and normally need to unscrew them a bit more so it idles without stalling. 2.5 turns as a final is common.

Note carbs must be clean, properly jetted, working perfectly, ignition timing perfect, etcetera. Else flogging a dead horse.

Your sooty plug is not likely to be just cos a carb has "gone off tune a bit". Indicates a bit more to it.

Start by complete carburettor stripdowns, clean, overhaul kits, new choke plungers, etc. EDIT: don't forget to also check needles for wear and correct number and position, state of needle jet, etc.

Modern petrol wreaks havoc on carbs internals these days I'm afraid, with sometimes massive deposits of rock-hard crud literally bunging thing up, last time I had to have all new jets.

NB: after doing so, the ideal idle screw position was indeed 1.5 turns, moreover the choke had to be left alone completely unless weather was really cold for starting, or it just flooded, so that's how much the original jets were partially blocked.


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Edited by Mike H - 11 Jan 2017 at 15:26
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