Topic: CB500 carb conversion

[JScottB]

To make a long story short I have a 75 CB550k that amongst many other things was missing it's carbs when I first got it. I nabbed the set of 627B carbs  off the CB500 parts bike just to get it fired up but I now have acquired 2 sets of 022A CB550 carbs  that are in serious need of TLC in order to make 1 set out of them. I know the 627B and 022A carbs are essentially the same EXCEPT for the slow jet, and possibly the emulsion tube and needle jet. The 500 carbs are clean and ready to go so my question is can I swap the slow jet, emulsion tube and needle jet from the 022A carbs into the 627B carbs thus allowing them to perform as a stock 022A carb and not waste my time cleaning the really cruddy 022A carbs or are there other differences between the carbs?

Also on the needle jet, in what groove is the clip that adjusts the height of the needle supposed to be in in stock config? In both sets of 022A carbs the needle jet has a total of 5 grooves, in 1 set the clip is in the 2nd groove from the top and on the other set it's in the 4th groove down. The reason I want to know is because I'm running pod filters and a 4 into 1 exhaust and I'd like to know where it's supposed to be in stock config so I can tune the carbs from there.

[Accolay]

TT has a chart in the Carb FAQ with CB500/550 specifications. As far as the configuration, since you're running pods you'll probably just have to experiment with plug chops and whatnot. How's it running on the 627B carbs?

[JScottB]

Yeah but which one is correct? I've got conflicting info from this site, 1 says the 022A is supposed to have a #40 slow jet and another says it's supposed to have a #38 while both having a #100 main jet. Just so you know both sets of 022A's that I have came off completely separate bikes and both have #38 slow jets with a #100 main jets. The 627B CB500 carbs have #40 slow jets as well as a #100 main. Someone could have messed with the 022A's before I got them but being they come form different owners makes it kind of too coincidental. I'm just trying to make sure what I have.

[Accolay]

I would definitely go with the chart.

[TwoTired]

I put #40 in the chart long ago because of my 74 Cb550 with 022a carbs.  I got it in 1975 and it had 1500 miles on it (Wrecked). It has #40 in it for the slow jet.  Every other 550 carb (with that style of carbs) has had #38 in it.

It isn't likely very critical, and I suspect Keihin had a large stock of #40 left over from Cb500 production and just used them up until they either got the right parts or ran out of the #40s.

I would now assume that #38 is the correct pilot jet for the stock 022a carbs.

Also, since I made that chart in the FAQ.  Someone on this forum posted (below) from the pages of a little booklet for Honda Mechs.

With pods and an exhaust change, none of the stock carb internal settings will apply.  As the carbs cannot adapt automatically to the back pressure changing cylinder demands, and the pods direct change to the carb throat vacuum level pulling fuel from the jets.

Cheers,

[JScottB]

How's it running on the 627B carbs?

With the 627B's in CB500 config it ran lousy. Looking at similar intake/exhaust configs on this site I went ahead and ordered a set of #110 main jets which have still yet to arrive so I nabbed a spare set of #100's , chucked them in a lathe and drilled them out with a #57 drill but which from what I understand (and I could be wrong) makes it the equivalent of a #109 jet. At WOT it ran awesome so much so it was slipping the clutch, I know the clutch plates are good so it must have weak springs but it was lousy and erratic at part throttle. Keep in mind carbs still need synced.

[TwoTired]

A twist drill makes a larger hole than the size of the drill.  They also leave irregular edges which change flow rate due to turbulence effects.
Cheers,

[JScottB]

Great info guys. Thanks a bunch.

[JScottB]

I cleaned up and installed a set of 022A cb550 carbs on my 550 to replace the 627B cb500 carbs that were on it and the bike is finally starting to run like it should. Still needs more fine tuning but both WOT and part throttle is good. The 627B carbs may very well have responded the same if I had them set to 022A specs but having the correct carbs to start with helps with the process of elimination while fine tuning. Just so you know the 022A carbs are using #38 slow jet, #115 main jet and the jet needle set 1 notch/slot richer. I initially tried #110 mains but that seemed a bit lean however the 115's at least for now seem a tad too rich. Now that the engine is pulling strong the clutch slips like crazy at WOT and the gearbox seems to be making some bad ominous noises when the bike is idling, in neutral and the clutch released. I've got new clutch springs on order but I'll save the gearbox noise issue for another topic.