Mixture Control

[leswaller]

 have finally got my R60/5 on the road and am pretty pleased with the result. Just one query, the right hand cylinder is running richer than the left hand one. The needles in both carbs (Bing sliders) are set in second slot down, can I adjust this richness with the mixture screw or is it a needle problem. (can't tell what the needles are). I suspect the carbs are original from 1972 and may be worn, but if so I would have expected both to be worn rather than just one side running rich.
Or does anyone have any other suggestions. If I replace the needles and jets which ones do I need.
Les

[Barry]

Les

I won't repeat my carb info from the other forum as I guess you want to see if the guys her come up with anything different.

On another tack is it possible one side is burning more oil than the other and you are seeing the difference on the plugs. Worth shining a narrow light source through the plug holes to see if one piston is wetter than the other.

[leswaller]

Good point Barry, I will have a look at the pistons
Les

[tvrla]

What are the symptoms that lead you to the conclusion the right side is running richer?

[Ed Miller]

If you conclude that it is a mixture problem you need to isolate it to which stage of carburator opening.  Off the top of my head they can be float level/idle mixture adjustment, slide cut-away, needle jet size and needle setting, and main jet.  

That assumes that Bing slides have something in common with Amal Concentrics, as those are all I have ever dealt with.

[leswaller]

Wirespokes - darker plug colour on right hand side

Ed - Yes my experience is also with Amals as I was/am a Velocette man, hence my original question re adjustment of the idle mixture screw which on Amals, as you know, affects things most of the way through the throttle opening.
If I assume that the carbs are original and untouched then they should in theory have worn equally, and as the bike only has an indicated 43K miles, if this is true then wear should be well within limits. Assuming jets, sliders, etc are untouched then my brain tells me that the only way that one cylinder can be running richer than the other is that someone has fiddled with the adjustments. I havent got a colourtune or similar but I have balanced the carbs using a vacuum gauge.

Brian - have checked for oil in the bores and from looking at the piston tops there doesn't appear to be a problem.

Perhaps I am being too fussy as the bike is starting and running well, it is just that it bugs me that one plug is the wrong colour. I haven't tried new plugs yet as they are not worn and I have only just got the bike on the road, so maybe that is the next step.
Les

[Barry]

Les

Have you checked the idle air screw setting by carefully counting the number of turns in until they gently seat. That would tell you if there is a gross difference side to side.  The Bing data suggest they should be between 1\4 and 1 1\4 turns out which is quite a big range.

I first learnt that the so called idle mixture setting has an effect way beyond idle on a pair of Amals fitted to a Triumph Bonnie.  I used to have a graph that showed the idle jets were still contributing to the overall mixture at 70 MPH although that would still be probably only 1/4 throttle on what were over sized carbs. That's one of the problems with carb tuning. In the pursuit of the last HP at maximum revs which few will ever use most bikes have over sized carbs at the expense of more efficient running lower down.  

[Semper Gumby]

Hi Les.

For starters I use a colourtune plug to set the idle mixture.  The colourtune plug will also let you see how the needles are set.

Be forwarned...

The BING idle mixture screw changes the amount of gas mixed with the air.  This is backwards from your AMALS where you had a fixed idle gas jet and an idle air screw.  Open th eair screw on the AMALs made the idle mixture leaner.

So on the BMW when you open the idle mixture screw you are richening the idle mixture.

But there is so much more...

[Barry]

Bill they are not CV Bings like we are familiar with on our bikes.

Les has an R60/5 which had slide type Bing carbs so like Amals they have an air screw which means turn out to weaken and turn in to richen.