Topic: Cb500 Carb opinions needed

[CB500FourTurbo]

Hello Everyone,

I have a 71 CB500 four that i rebuilt and it's ready to be ridden but i just can seem to get my carburetor in order! Before i get into the problem i am having i just want to let you guys know i looked at almost every thread on topic on this matter and i am torn apart on the jetting size to use.
Originally the bike cam with 4 into 2 with idle jet at 40 and main at 105, i test drove it it ran OK, but i really didn't have other cb500 to compare too. in the rebuilding process i clean out the carbs which was very dirty i was surprised that the bike even ran. Recently got a 4 into 1 exhaust i believe its a Carpy's  and ordered some main jet 105,110, 115 and 120 with new 40 idle jets. When butting the carbs together i installed 40 idle jet and 115 main jet, the problem with this set up was at 1500rpm to 2500rpm it would sputter and would want to go in first gear off the line  but as soon as it hit 2500rmp it took of like a bat out of hell and had no issues through out the gears. So with that i figured i need to go up one more on main jet and it will fix problem so i did, i replaced the 115 main jet to 120 main jet and with that it fixed the problem that i was having with the initial off the line start between 1500rpm and 2500rpms. Now the problem i am having with this set up is when i open her up and back off then open her up again it takes a few second take off and from the sound of it the carburetor  sounds like it gets too much gas and hesitates to go. Also when i give it throttle and back of the rpm drops and the bike dies out and have to restart that happened to me in first gear i am not sure if this happens in all the gears. Now i know i have to now play with the needle either lean it out or rich-in the mixture, but my main question which main jet to go with and what position should i put the needle so i don't have this problem. Video of idling,

[Deltarider]

I have to say I'm always surprised how much rejetting, raising and lowering of needles goes on in this forum. What I remember from the 80s is that, with very few exceptions, manufacturers of aftermarket 4-1s always advertised with 'no rejetting required' and I can't remember I've met someone that undertook this. As far as the brass in CB500 carbs I strongly believe in inspecting the slow jets for cleanliness and that the small O-rings around the main jets still seal well. I'd leave the position of the needles as it is (I believe in US it's already one notch richer than here) and I cannot for the world see one would need larger main jets than 100, 105 maximum unless the head has been seriously tuned. For a good pick-up from idle to say 3000 rpm, airscrews play a role. For instance I can let my engine purr like a kitten at idle by turning (and leaning) out the airscrews only to experience acceleration is poor. I have my airscrews one turn out which is according to Honda specifications. I have seen an American Honda booklet that prescribes two turns out however (and needles in 4th notch where we have 3rd). I don't know why this is. I presume to reduce emision at idle like at traffic lights but who am I? Anyway, you needed an opinion so here is mine.

[Bankerdanny]

Where did you get your replacement jets from? If they aren't genuine Keihin you can't really trust that they are the size they are labeled.

[calj737]

Put back your stock 40 jets. Drop your mains to 105s. Make sure the emulsion tubes in your carbs are surgically clean. The needle should be in the second notch from the top. Fresh plugs, perform an idle chop. Post pictures. Then, do a WOT chop in 3rd gear somewhere safe, pull the plugs and post pictures. Final tuning based on those pictures.

[Deltarider]

The needle should be in the second notch from the top.

American Honda Company specifications booklet (ed 1977!) suggests 4th from top, in Europe it's 3rd (middle) for the CB500. Second notch would be a bit leaner, in fact it would be two notches leaner than US specs and one notch leaner than in Europe but you could try. I myself am not convinced of varying needles height so much (see above) and as for the main jets I wouldn't even go wider than #100 which is standard. But that's me. The only models that IMO can benefit of enriching somewhat are the K3 models that were already on the lean side when they left the assembly line (new laws). If you must go at the needles (if you must) than it's wise to use the right JIS screwdriver to unscrew the two tiny crossheads in there or you'll have a good chance ruining their heads.
In my archives I have an article (1979) about a then well known mechanic/long distance racer who bored CB500s to 651 cc, mounted them in Dresda frames, had the airfilter removed, changed the 4-4 for a 4-1 and nevertheless kept the standard 22 ⌀ Keihins with standard jets and the same sparkplugs everybody else used at the time (NGK D8ES-L).