CB550 carbs

[K2-K6]

There is a lot of overlap of jets when going from idle jets to main jets, so at 3500 rpm it could be either jet. Nigel (K2-K6) posted a brilliant graph showing the overlap but i can't find it again now. Also, as long as the vacuum gauges are showing parity, it doesn't matter what the reading is within reason.

I can't find that either Julie even though I thought I had a copy tucked away somewhere here.

For your current jetting though,  as you plan,  put the needles down a notch to try it and see what you get.  Obviously you've got progress with the new idle jets and it's just moving something else now to bring in other sections of mixture to where you want it.

If you've got room to bring the idle screws out another 1/4 turn it's worth trying that.  It should delay the point at where the idle jet gets to full flow at it's 38 capacity and be matched with the throttle slide being a little higher when it occurs.  That and dropping the needle a notch combined will effectively lean out the middle range throttle opening and may get you into range.

[K2-K6]

An additional point to consider,  the airbox on these can have different configurations I believe from other's experience on here.  Deltarider?  They have a different air entrance to make some market models quiter I think, these are paired with smaller main jets, from memory, and run at slightly smaller mains it seems.

Someone with that knowledge may be able to help here in identifying the parts you have.

[paulbaker1954]

There is a lot of overlap of jets when going from idle jets to main jets, so at 3500 rpm it could be either jet. Nigel (K2-K6) posted a brilliant graph showing the overlap but i can't find it again now. Also, as long as the vacuum gauges are showing parity, it doesn't matter what the reading is within reason.

I fo [ Guests cannot view attachments ] und this chart some time ago that may help

[deltarider]

An additional point to consider,  the airbox on these can have different configurations I believe from other's experience on here.  Deltarider?  They have a different air entrance to make some market models quiter I think, these are paired with smaller main jets, from memory, and run at slightly smaller mains it seems.

Good you brought this up. BTW, on the international forum I also follow the thread about airflow with interest and I find some intuitions that I had, confirmed. http://forums.sohc4.net/index.php?topic=179850.0
Actually my first post in that international forum, I believe in 2006, was a question: why did the CB500 models for most countries on the European continent (France being the only exception) have the 649A carbs? These carbs have #78 main jets and for the rest everything the same as in the 627B carbs: #40 slow jets, needleclip in the 3^rd (middle) position and an advised airscrew setting of 1 turn ± ¹/₈. These models also have a socalled airduct over the airfiltercase. Realise that at the time there was no legislation on emission in these countries, Germany, Holland, Italy and Switzerland to mention a few. Realise also that none of these countries had a national speed limit and were very competive markets indeed. I have one source that states Germany had legislation on air intake noise however. Hence that cover over the airfilter case and I can assure it works as such. How could it be these models performed equally good as the ones with the 627B carbs? At first I have thought it had something to do with the quality of gasoline. Countries like Germany, Holland, Italy and Switzerland always have had the better gasoline, the US about the worst, a finding that's shared by more. But that still could be subjective. From all what I've read, I can only conclude it must have been related to this legislation on air intake noise. The cover does NOT restrict airflow such (if it restricts at all!) that power output is less. Tests including my dyno test have proved this. Ofcourse I have, like some Germans, experimented with #100 main jets and the airduct removed. It brought nothing but extra intake noise. What the airduct maybe does, is reducing turbulence at the intake, resulting in a more laminar flow, who knows?

[deltarider]

Can't read that as it's in german but I'm wondering why it's saying the bike has 2.15 rims front and rear when it came with 1.85 rims from the factory. Unless of course you've changed the rims at some time.

It's not about my bike. I live in The Netherlands. Listed are the max. rims widths that are allowed on this model in Germany. TÜV is the German test agency. In Holland we have no such thing, not for motorcycles. Hurray! 

[Moleskins]

Thank you Nurse Julie and K2-K6 there’s a few things for me to go at there.
Currently (pun intended) I’m sorting out a wiring ‘situation’ because the new battery went flat.
This made me wonder if combustion was going off because of a weak ignition circuit.
I’ll get back onto carbs tomorrow / the weekend.