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SOHC.co.uk Forums => CB500/550 => Topic started by: toucheturtle on February 01, 2016, 08:59:29 PM

Title: CB500 carb jets, European import
Post by: toucheturtle on February 01, 2016, 08:59:29 PM
I have a 500K2 originally imported from Italy, the engine was rebuilt some years ago by Bryanj and the carbs were rebuilt by a local bike specialist around the same time. I have recently heard the Euro bikes had different smaller jets to the UK bikes. My bike has never made it past 100mph despite running well and sounding healthy. Does anyone know if the jets were indeed different and if this would make a difference.
Title: Re: CB500 carb jets, European import
Post by: JamesH on February 01, 2016, 09:13:21 PM
I believe some euro spec 500's had 78 main jets..worth pulling a float bowl and checking yours.
Title: Re: CB500 carb jets, European import
Post by: Bryanj on February 02, 2016, 07:29:07 AM
The 500,s only went a little over 100 and not with a heavy me on them anyway, the later 500K3 (never in UK) had smaller jets and according to my old UK parts book only us mad buggers and the french had large main jets(apart from the Yanks and the Aussies) so could well be worth checking.
Sirius in Canada do sets at a reasonable price
Title: Re: CB500 carb jets, European import
Post by: deltarider on February 02, 2016, 08:07:36 AM
The CB500 for the European continental market had main jets #78, except France that had #100 like UK and US. The carbs with #78 main jets have the stamped in number 649A (see pic below) and the other markets with #100 had the 627B carbs. Slowjets, needle jets and airscrews are the same although their position may differ (!). I doubt that there are any differences in the venturi's.
The models that had #78 main jets, also had an air duct (partnumber 17340-323-610) over the airfilterbox. Why? We don't know. Maybe it had to do with regulations on intake noise in Germany, maybe it was to provide a better protection against ingress of water, maybe it had to do with the better quality of gasoline in countries like Germany, Holland, Switzerland and Italy. Fact is that the bike with #78 main jets in various tests proofed to run 179 km/h top and so performed equally good as the CB500 elsewhere and even better than the later CB550F2. Mine does 170 km/h on the open road with me on it (1,96 tall and 90 kg, nose between the gauges) and 185 km/h on the dyno. Like some Germans I've experimented with #100 main jets and the snorkle removed. It brought nothing but annoying intake noise and most of us returned to #78. Some argue the cover over the airbox is a restrictor. Seen the testresults I doubt this and - again - the experience is that removing it brings nothing extra. Others have argued that the gaze net (part number 83502-323-000) that covers the airfilterbox in other markets is in fact disturbing the airflow more with all its wires (turbulence). Anyway I've rode my bike with #100 and #78, with and without the 'duct assy. air cleaner' and I prefer the #78 main jets and the forsaid snorkle. But you can experiment yourself. Personally I wouldn't focus on top speed. A lot of factors play a role: bigger (softer) tires and even the slightiest dragging brakes can have influence. Much more important is to have a nice driveability meaning a good pickup in every throttle position.
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I have a 500K2 originally imported from Italy
The bike in your avatar as far as tankpaint and striping is not a CB500K2 (ED, F, G). The latter came in three colours: Excel black, Candy sapphire blue or Candy garnet brown. You can verify your engine- and framenumber on page 4 of: http://www.honda4fun.com/pdf_parts_list/pdf_spac500/CB500-76/CB500-76_1.pdf  It is always good to check frame-, engine and carbnumbers to determine model and area code.
Tests I referred to (including mine) were on bikes with standard 4-4 exhaust and stock airfilter setup.
The European CB500K2 (assembled around 1976) differs from the USA K2 (on the market in 1973) and shares many things with the CB550K2 '76 that was never imported in Europe. Quick check is to see if it has the grease nipple at the bottom of the swing arm instead of two (one on each side).
The CB500K3 is no comparison here. Of that particular model (see pic below) only around 4200 were assembled and exported to some Scandinavian countries. It's quite another bike that had lots in common with the CB550K3 and so had completely different carbs than ours.
Title: Re: CB500 carb jets, European import
Post by: toucheturtle on February 02, 2016, 01:15:50 PM
The tank and side panels are not the originals, I still have the originals which are black and with the later styling stripes. The air filter cover does have the snorkel. I will check the carb number tomorrow. If I won't notice a significant gain I'll leave it as it is as it does run well but is a bit asthmatic at the top end.
Title: Re: CB500 carb jets, European import
Post by: deltarider on February 02, 2016, 03:03:06 PM
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The tank and side panels are not the originals, I still have the originals which are black and with the later styling stripes.

Like mine probably (see pic below). What are your airscrews set at?
Title: Re: CB500 carb jets, European import
Post by: toucheturtle on February 02, 2016, 07:17:41 PM
That is what my bike did look like, to be honest I don't know what the air screws are set at, I just accepted it was set up correctly when I got it back after the carbs were rebuilt.
Title: Re: CB500 carb jets, European import
Post by: deltarider on February 03, 2016, 07:35:43 AM
You could check by turning them in (clockwise) slowly. Do not exercise force and note where they were before you started so you can return them in that position. Manual states airscrews should be one turn out +/- 1/8.
Title: Re: CB500 carb jets, European import
Post by: ST1100 on February 03, 2016, 05:57:04 PM
What I found out/MHO about the CB500K2:

The versions with #78 jets have the metal lid/flow restriction on the air-box, whilst those with the #100 mains utilize the plastic lid with the larger intake to match the avail air-flow to the increased fuel-amount...
Since I've no reliable info about which notch to set the cir-clip on the needles, I'll have to confirm/establish proper setting/ratio by use of a ColourTune kit later on...
Title: Re: CB500 carb jets, European import
Post by: deltarider on February 03, 2016, 09:22:54 PM
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Since I've no reliable info about which notch to set the cir-clip on the needles,
Standard is 3rd (middle) clip.
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I'll have to confirm/establish proper setting/ratio by use of a ColourTune kit later on...
Forget about that colortune. It won't work, not for the CB500/550.
I've commented before on this Gunson Colortune here: http://forums.sohc4.net/index.php?topic=45780.msg479406#msg479406
The idea was good, but for 500/550's the Colortune is useless and I don't think results will be any better with the other Fours.
Title: Re: CB500 carb jets, European import
Post by: Trigger on February 03, 2016, 09:32:01 PM
It is like tuning a old piano  ;) ;) do you agree Bryan and oddjob ;) ;)
Title: Re: CB500 carb jets, European import
Post by: toucheturtle on February 04, 2016, 12:25:07 PM
My carbs are stamped 649A, if I were to change the main jets would I need to change anything else, ie carb needles etc?
Title: Re: CB500 carb jets, European import
Post by: deltarider on February 04, 2016, 12:45:26 PM
No. If you change them for #100 main jets, just remove the air duct cover from the airfilterbox (and be prepared for a lot more intake noise). With #78 main jets you want that air duct on. Make sure the little O-rings around the mainjets are still OK and will seal well. Whenever you have the floatbowls removed, it won't harm to unscrew the slow jets and inspect them. It's also easy (from below and without taking the top of) to remove the needle jets if you want to check them.
BTW have you checked the position of the airscrews?
Title: Re: CB500 carb jets, European import
Post by: GiannisFour on February 05, 2016, 01:27:09 PM
Hi,
mine is a europen version,i clean rebuid the carbs with new keyster set and main jet std 78.
The air duct cover was missing... Test and run the bike...after 4000rps was not performing...engine was running lean...
Found the duct cover from ebay and fit it on bike,then test it on the road...all perfect!!! now runs smooth in all rpms!
Title: Re: CB500 carb jets, European import
Post by: mr wilkes on October 14, 2017, 06:11:13 PM
This post just saved my sanity, My bike is also a European model and thanks to you guys I have just got it running spot on.
Title: Re: CB500 carb jets, European import
Post by: deltarider on October 14, 2017, 07:27:21 PM
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This post just saved my sanity, My bike is also a European model and thanks to you guys I have just got it running spot on.
We're curious. Tell us more!
Title: Re: CB500 carb jets, European import
Post by: mr wilkes on October 14, 2017, 07:45:42 PM
Your post with the 649A reference for the 78 Main jets, helped me figure out why I couldn't get the bike to run good over 4000 rpm, was running rich and fouling the plugs, took a float bowl off and I was running 100 main jets so removed the lid off the air box and its running perfect now! new jets are on order. Thanks Delta.
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