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Discussion Starter #1
The bike has a flat spot right off the bottom, particularly when I hit the throttle when changing down, it will coff like its too lean.
I am running Thruxton needles with no shims and have stock pilots.
Would shims or pilots fix this condition?

Also if I remove the air box baffel how will that change the jetting requirements.
 

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My best estimate is that if the lean hesitation is that obvious then you are probably going to need at least a shim or two to mitigate it. That said, I agree with Pokeyjoe - we have to know specifically where your settings are now (inluding pilot screws) to figure out where you need to go. A good dyno operator can help you fine tune the pilot jets, if necessary. Good luck.
 

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Discussion Starter #4
I not sure of the mixture screw setting, I think it is 2 turns out, I will check. Is 2 1/2 to 3 out ok.
 

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I not sure of the mixture screw setting, I think it is 2 turns out, I will check. Is 2 1/2 to 3 out ok.
2.5 turns out from lightly seated is the base-line setting and then up to about 0.5 of a turn either way to fine tune. I wouldn't go out much more than 3.5 out or the screws may drop out - if you need to go further out than this then you should be considering larger pilot jets.
 

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If you haven't done so already, I highly recommend surfing around for the Jenks Bolts guide on carb tuning for the bonnevilles. You should be able to find a free copy but if you can't, the price in only $5 or something like that.

I had a flat spot at about 2500 and Jenks recommended thrux needles instead of shims or jets. I went with their reco and was very pleased with the results.

The beauty of the Jenks guide is that they explain what part of the carb set-up is operational at each rev range so you can pretty quickly and accurately diagnose your problem by yourself. Should avoid too much trial & error.

Good luck!

P
 

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Wait a minute. Before you start throwing shims around - tell us, how long has it been doing his and did you make any change in the bike that caused it.

It could be dirt and gum in the carbs... it could loose or cracked intake boots, old spark plugs, a number of things. I would fix this first before modding it.
 

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Discussion Starter #9
sal, I take your point and will do some checking before doing the shims.
I first noticed the problem after I fitted the K&N air filter and removed the snorkel. Its not bad but its time to fix it.
The pluges look ok, half the centre of the plug is brown and half is white. how long should get from the spark plugs.
 
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