ET: Engine (Twin) Occasionally missing a beat

Sakura

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Just fitted a new set of 276's to my Rapide. They're properly balanced but the pilot mixture may not be 100% correct yet. Only done a few miles but when pulling up a hill at 30mph in 3rd it occasionally missed a beat. Nothing dramatic, just slightly annoying. It ticks over slowly and reliably but I'm thinking the pilot mixture maybe a bit rich. I know I can play with it but has anyone got any thoughts?
 

Chris Launders

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If you've just fitted them new they are going to need setting up to suit your bike, every one is different and the settings provided are only a rough guide.
 

brian gains

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I understood that under certain riding conditions there can be a noticeable transition between pilot / needle / throttle body cutaway/ main jet. This can be reduced by altering needle position and/or amount of cutaway in throttle body but have been told that usually you just end up moving the 'blip' around.

Sure someone will chime in with more technical description of adjustment finesse.
 

brian gains

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second thoughts, ignore the cutaway as a solution if that is incorrect it just runs generally poorly at that throttle opening.
 

greg brillus

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Have you changed or adjusted the settings at all after installing the new carb's..........?..........It is not uncommon for the clip fitting carb's to not be a snug fit on the manifold stubs and may leak air. The mixture screws should be around one to one and a quarter turns out from fully seated. Replace the plugs with two new correctly gaped ones and see what plug readings you get............Generally I have found the new 276 carb's to work very well straight out of the box with minor adjustments.
 

Sakura

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Have you changed or adjusted the settings at all after installing the new carb's..........?..........It is not uncommon for the clip fitting carb's to not be a snug fit on the manifold stubs and may leak air. The mixture screws should be around one to one and a quarter turns out from fully seated. Replace the plugs with two new correctly gaped ones and see what plug readings you get............Generally I have found the new 276 carb's to work very well straight out of the box with minor adjustments.
I'm generally well pleased with the carbs. They carburate well throughout the range and tick over reliably. Plugs are new and the colour looks good. Carbs are a good fit in the stubs. I'm nitpicking, it only misses a beat every now and again and obviously I can keep experimenting with the pilot mixtures or even cutaway. I'm pretty sure it's in the range of pilot to cutaway and you can usually cover the transition with pilot mixture. I was just hoping to save time and effort using someone's experience, like Greg, who has trod this exact path before. My feeling is it's a bit rich and I'll just ease the screw out a little.
 

Sakura

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30 in 3rd uphill?
I would be in 2nd, much less stress on engine and transmission...
Peter B
Fairly gentle slopes and it seemed happy enough to me. On the level it will pull down to 30 in top but 3rd feels better. Surely the whole point of the Vincent engine is torque?
 

greg brillus

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The slight miss could be just the fact it is cold............An engine that performs perfectly when cold is generally too rich in the carburation. My Rapide is a bit like that, but I run the VOCS foam filters which I feel have very little drag/restriction to the air flow, the plugs show a rich though not absolutely sooty black colour.
 
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