One for the Bing carb cognoscenti

[Nin]

Hi folks

I’m setting up an R100GS for a mate. It’s serviced (valve clearances, air and oil), dynamic timing is spot on, it has new wedge tail electronic ignition, new coils, new plugs, new cables, new inlet rubbers. Carb is balanced with a harmoniser and the ‘spoke’ method.

But it’s giving a poor transition from the pilot jet to main jet - tickover is fine but it bogs a bit at transition, then picks up fine. Balance is ok throughout.

Thoughts?

Nin

 

[Gelandestrasse]

Sorry, not an expert but I've done a few in my time. There's a lot in this. You don't mention the choke springs - do they return the enricher all the time?

It's a mixture thing - perhaps too much air for the available fuel, or vice versa. If it goes ok at tickover and at speed, it may be the setting of the needle on the main jet or the idle mixture screw not right. Could also be the air is getting in due to the intake hose clamps not being very tight or holed. Diaphragms could be holed, floats not working properly, butterfly valves in back-to-front...

And there's this: https://bmwmotorcycletech.info/bingcv.htm and briefer this: https://www.leadingedgeairfoils.com/pdf/TuningBingCarbs.pdf

 

[DrFarkoff]

Are the initial airscrew settings correct ?? Carb type on front casting edge It would not be unheard of for the carbs to be changed and maybe even mismatched on some of the ones that I have had in here to work on One had even connected the cables the wrong way around

Earlier carbs had 1 and a 1/2 turns out where later monoshock were 3/4 out (From Vague recollection)

Are the main needle and jet in good condition Badly worn can be overly rich in that transition period

Choke gaskets in good condition and Choke returning to off stop?

And are they OE spec diapraghms or the thicker chinese poop?

The thicker ones can be a bit cumbersome

 

[SteveHop]

Have you adjusted the idle circuit mixture ?

 

[Nin]

Thanks gents.

Yes I started at 3/4 out for idle, then adjusted using the spoke method (isolating one cylinder, adjust until just running).

Inlet manifold sleeves are new.

I’ll check that needles are at same index position, that could be it.

 

[DrFarkoff]

Thanks gents.

Yes I started at 3/4 out for idle, then adjusted using the spoke method (isolating one cylinder, adjust until just running).

Inlet manifold sleeves are new.

I’ll check that needles are at same index position, that could be it.

Are they the original carbs is what I was asking earlier Nin ??

Oh and Plus matching Numbers Well One digit change but you know what I mean

 

[(RIP) Bin Ridin]

Diaphragms on my R65 were leaking, and it was only when replaced that I realised how much of a negative effect they were having. Was like a new bike. So, be sure to check carefully for any holes or tears. you will be in there anyhow checking the needle position.

 

[Nin]

Are they the original carbs is what I was asking earlier Nin ??

Oh and Plus matching Numbers Well One digit change but you know what I mean

Oh, got it. Yes. And cables correctly attached!


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[Nin]

Needle is 2 notches up from lowest, right?

 

[mikeyboy]

IIRC
Should be 3rd notch from top

 

[Nin]

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[Nin]

That’s much better, it was one notch out. Probably not helped with some rubbish old fuel.