Honda-SOHC
SOHC.co.uk Forums => CB500/550 => Topic started by: Honda Al on September 02, 2016, 07:42:27 PM
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Hi all,
My CB500 K1 is running rich and I need some advice with where I can go next. All four plugs are sooty, all four have the same appearance. The exhausts are sooty at the ends. The bike will start without the need for choke, and although it runs it always sounds and feels lumpy, especially the lower rev range. Fuel consumption has increased. The bike is standard.
This is what I have done so far -
Clear tube test to determine fuel/float levels. They settle ~2mm below the top of the float bowl. Also used a gauge to set the floats 22mm.
The carbs have 40pilots and 100 mains. All clean and in place.
Air mixture screws are 1 +1/8 turned out.
If you apply the choke whilst running it gets worse, and I removed the air filter and it rode marginally better.
What next steps can I take or do to determine why she is running rich?
Thanks, Alan.
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check your ignition timing,it may be retarded,
are you using points? or electronic" pointless" ignition>
also,try turning the air screws out 1/4 turn at a time,see what happens,
my CB500 has the same jets etc,with electronic system,but runs with a 33thou plug gap,and airscrew over 2 turns out,since
balancing the carbs with gauges ,I have gone from 10miles per litre,to 12miles per litre,
an extra 20 miles further before going on reserve ,
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Using electronic ignition. I'll take a look at the plug gap and try turning the screws out some more.
Cheers, alan.
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I'd say the airfilter, but if you say it runs just marginally better without...
and 100 mains. All clean and in place.
The little O-rings around the main jets, are they still good and do they seal well?
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I'd say the airfilter, but if you say it runs just marginally better without...
and 100 mains. All clean and in place.
The little O-rings around the main jets, are they still good and do they seal well?
It's sharper on the throttle response, but still don't need the choke to start it.
I've replaced the little o rings and they sit well in the hole.
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Is yours a UK CB500K1 or USA? What is the stamped carb number, 627B, 649A? Do you know if someone has changed the needle position?
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USA K1. The carbs have 627B on them. Not sure about the needle setting.
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USA K1. The carbs have 627B on them. Not sure about the needle setting.
I'd check the needle clip position, it should be in the middle IIRC
For some reason the yanks had the aircrews 2 turns out and the needle in 4th groove. This according to an American Honda Motor spec booklet published in 1977. If your needles happen to be in 4th groove (in Europe they were in 3rd, middle position), it's well possible you run too rich. I'd start with the easiest: opening the airscrews more. Please report back.
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I've adjusted the air screws and they are now 1 +3/4 out. Bike picks up better from a standing start (before it was always a little boggy) but I still don't really need the choke to start it.
I'll see how I get on with this tank of fuel.
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500's only ever need a bit of choke just to start, maybe all of it for 10 seconds in the dark of winter
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500's only ever need a bit of choke just to start, maybe all of it for 10 seconds in the dark of winter
That's good to know. Thanks.
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500's only ever need a bit of choke just to start, maybe all of it for 10 seconds in the dark of winter
Yes, I myself only apply the choke when I start and in the seconds immediately after that I slowly open the chokes again. Within 10 seconds at the most chokes are completely open again. That's the way it was ment. Honda didn't want us to fiddle with that chokelever whilst riding. Maybe you should try airscrews two turns out and see what that does.
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Maybe you should try airscrews two turns out and see what that does.
I started at two but the engine sounded a bit rough when accelerating. 1 + 3/4 seems to be better.
I'll keep you updated. :-)
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That makes sense, all 500s and 550s with the oldstyle carbs need a relative fat idle for good pickup and driveability whilst accelerating.
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Hi Al
I think you may have replied to my post on a similar issue. My 500 four was running very rich at low throttle and was a pig to get off the line
Eventually I bit the bullet and bought a set of carb service kits (jets, floats, needles etc) from Rusty riders in the US. But the main thing i did was borrow the ultrasonic cleaner from work and fully stripped and cleaned all the carbs. I found in the process that 3 Of the pilot air circuit circuits had been blocked and the cleaning cleared them fantastically
I have just got it all back together and it I'd running like a different bike.
I recommend you strip the carbs get them ultrasonically cleaned (you can buy a cleaner on fleabay for around £40. - you need a 3L tank) and change all the jets etc. It's quite a lot of work but well worth it in the end in my experience
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I don't need an ultrasonic device to clean the jets. They're easily removed, inspected and cleaned.
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Aren't the jets the smallest bores in the fuel system? After removing the jets a squirt of carbcleaner (brakecleaner) is usually all what it takes. But I'm open to new insights. BTW, I wonder if anybody ever cut a disposed carb open to see how and what runs inside. I myself don't have the tools but it'd be interesting.
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When making sure your carbs are not blocked.............
This may be a bit hard to describe but i will try (I'd post a pic but my carbs are now back on the bike)
The jets of course should be clear as should the emulsion tubes but as Oddjob says it is imperative that the holes in the carb body are also clear and some of these are VERY small bore. The pilot circuit especially has a massive impact on both smooth idle, pickup off the line up tp 1/4 or so throttle.
For the pilot/idle circuit there are 4 holes in total involved:-
1) There is a small hole on the side wall inside the bore of the carb at 90 degrees from the top if you are looking down the carb towards the engine side. It's just after the choke, this joins up with....
2) The pilot jet hole that you screw the pilot jet in to and then this in turn is connected to.....
3) The idle airscrew hole (the one where the air adjustment screw goes on the carb body)
All these 3 holes above lead in to a chamber in the base of the carb which is where the air/fuel combines and the mixture then squirts out from
4) A really, really fine hole you will find on the bottom of the bore on the engine side. It's just in front of the throttle slide.
The best way to check if the pilot circuit is OK I found was to pucker up your lips over the air screw hole and cover the other 3 holes with various fingers and thumbs. If you then lift each finger/thumb one at a time you should feel air blowing (It's a bit like playing a wind instrument and a bit fiddly but easy to do).
I found on my bike that there were blockages in these circuits that ultrasonic cleaning cleared really well.
If doing a rebuild its probably also worth doing a complete jet renewal, float, needle etc as you never know the history of the bike. I got a set of 4 complete rebuild kits from Rusty Riders in the USA via eBay for about £50 inc shipping. My only complaint was that one of the float valves would just not seat properly so I ended up using one of my original ones. On teh plus side these kits are significantly cheaper than NOS or DS etc...
Now it's all back together it peforms like a completely different bike, more power overall, fantastic pick up from standing.....I am amazed at the difference and at how bad it has been since my rebuild was finished.
I have spent months trying to get my bike right and my, now well learned, advice with 500 four carbs is if you are doing a rebuild it will save time, much effort and stress to fully ultrasonically clean the carbs and replace all jets etc. I learnt the hard way-there is no shortcut here when it comes to carbs !!
I hope this helps