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Cb500 idle help [message #300216] Sun, 03 February 2019 12:28 Go to next message
jimcrux   United Kingdom
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Hi I'm looking for any friendly help with an issue with my cb500 (twin, 1998). It was running a bit rough when the weather got cooler so I've been working on it cleaning the carb, adjusting valves and new downpipes as it had a small blow.
The problem is that I now can't get it to run on idle. It starts and runs better than ever on the choke but as soon as it starts to warm up it cuts out and won't restart. Pilot jet is all over forums as a culprit but I've cleaned that and main jet and channels a few times with no joy. I've also checked coils and HT leads have continuity and still give a good spark when warm. Battery stays above 12.7 volts. No air leaks as I changed the rubber connectors and even added sealant so air input is only better. Fuel is running fine from tank and through the tap. Any suggestions on anything else I can look at? I expect the fuel/air mix is a bit off with the changes I've made but I cant tweak that until it idles and I wouldn't expect that alone to cause it to not run at all? I've tried the screw at different settings either side of default anyway. I do have to clean the spark plugs in between each attempt as they get build up on them and I thought that might mean over rich but I now think it is just due to starting and running too long on choke flooding it rather than a root cause.
It's not a valuable bike but I have some love for it and don't want to give up.
Re: Cb500 idle help [message #300217 is a reply to message #300216] Sun, 03 February 2019 13:15 Go to previous messageGo to next message
spagiratwink is currently online  spagiratwink   United Kingdom
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Hi , would say its still the carbs, I would take them off again ,return the pilot screws to 2 1/2 and take it from there , did you alter the float heights and needles?, what jets are you running smile
Re: Cb500 idle help [message #300218 is a reply to message #300216] Sun, 03 February 2019 14:46 Go to previous messageGo to next message
Kakugo is currently offline  Kakugo   Italy
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(18) Geoff Duke
It's still the carburetors: I've seen it happen too many times before.

I don't know what you used to clean the carburetors, but most commercial cleaners are just not up to the task.
You would need to put the whole carburetors in an pure acetone bath overnight (at least 8 hours) after stripping off anything you can. Pure acetone is easily available in hardware stores in 1 and 5 liter tins. Lacquer thinner is another valid alternative but needs a longer soak time (at least 12 hours) and is usually far more expensive.
If you want to be 100% sure to get rid of gunk you can replace acetone with a homemade formula: 90% diesel fuel or kerosene (whatever's available) and 10% industrial metal cleaner. Metal cleaners are usually methyl-chloride-based and that's what you really want to clean carburetors. Just be sure to wear gloves and to work in a well ventilated space: it's better to leave the bath outside overnight. Methyl-chloride must be handled wih care.

After taking the carburetors from the bath you need to use either a fine pipe cleaner (they are easily available on Amazon, eBay etc) or old steel guitar chords, if you have any, to clean jets and passages.
Jet do not always clean well, but they are cheap and easily available. Needles can wear out but, again, parts won't exactly send you to the almshouse. There do exist the possibility of a worn needle seat causing the needle to stick (don't ask me how I know it), but on those Keihin the seats are easily removed and replaced so it's not a big deal.
Re: Cb500 idle help [message #300222 is a reply to message #300218] Sun, 03 February 2019 19:35 Go to previous messageGo to next message
jimcrux   United Kingdom
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Hi thanks for responses - I didn't change the floats or needles but I checked they looked ok and that the heights were right. I used commercial carb cleaner for a couple of hours and blew air through (I've had them off 3 times now too). I've resisted poking things in as I thought that was bad but thinking about it that probably applies nainky to the jets (as the main bottleneck) and I'm running out of ideas so will have a go at that I think.
Guidance on the screws is 1 to 2 turns out and they were at 2 before I started fiddling (I've tried everything between 1 and 2.5 with my start attempts).
The jets look brand new still and I could see through that they were clear but I can't guarantee if someone before me kept them standard. I might see if I can find some online now. There are lots of carb kits out there with the gaskets and washers but I'm struggling to find the jets included. They are size 38 & 122 .. are jets quite standard fit if I just get any I can find in this size even if it doesn't say they are for my specific bike? They look about right in the pictures.
Re: Cb500 idle help [message #300223 is a reply to message #300222] Sun, 03 February 2019 20:13 Go to previous messageGo to next message
spagiratwink is currently online  spagiratwink   United Kingdom
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Yea matey 38 & 122 , has the needle jet got any shim washers on it smile
Re: Cb500 idle help [message #300233 is a reply to message #300223] Mon, 04 February 2019 20:38 Go to previous messageGo to next message
jimcrux   United Kingdom
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Hi, no shim washers on this one
Re: Cb500 idle help [message #300234 is a reply to message #300233] Mon, 04 February 2019 21:02 Go to previous messageGo to next message
spagiratwink is currently online  spagiratwink   United Kingdom
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Have a look at these
https://www.ebay.co.uk/itm/Keihin-Main-Jet-Short-8mm-99101-3 93-CVK-PE-PZ-Carburetor-70-190/142460015912?var=441460365522
https://www.ebay.co.uk/itm/Keihin-Pilot-Jet-N424-21-PWK-CVK- PE-FCR-Carburetor-30-80/142464833444?var=441463781514
Re: Cb500 idle help [message #300240 is a reply to message #300234] Tue, 05 February 2019 07:18 Go to previous messageGo to next message
jimcrux   United Kingdom
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Thanks again I've ordered rebuild kits plus these jets yesterday (but I was unsure if I'd ordered the right ones so your links are reassuring that I have). I also ordered some guitar strings and will soak it more this time. I only plan to poke at the carb parts so if there is any accidental widening hopefully the new jets still provide the right flow size. I'll have to be careful how I soak as I don't want to start separating them and I want to keep the cleaner off any rubber parts.
Re: Cb500 idle help [message #300242 is a reply to message #300240] Tue, 05 February 2019 08:12 Go to previous messageGo to next message
spagiratwink is currently online  spagiratwink   United Kingdom
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This might help
https://www.ebay.co.uk/itm/Motorcycle-ATV-Carburetor-Carb-Je t-Cleaner-Cleaning-Tool-Kits-case-Set-UK/173459361429?hash=i tem2862fbce95:rk:1:pf:0
and when you use the air line try not to blow into the jets, if there's any dirt in there you could block it up again Yes
Re: Cb500 idle help [message #300248 is a reply to message #300242] Tue, 05 February 2019 13:15 Go to previous messageGo to next message
jimcrux   United Kingdom
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I've ordered this too now - wasn't even worth thinking about for the cost of it
Re: Cb500 idle help [message #300252 is a reply to message #300248] Tue, 05 February 2019 22:01 Go to previous messageGo to next message
Kermit is currently offline  Kermit   United Kingdom
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(22) Giacomo Agostini
Might be a daft input but

a) are you sure you didn't alter whatever mechanisim acts as a throttle stop wether on both carbs together or each having their own
b) connected to the above but are the carbs still in sync eg static check when butterfly opens on one, the other cards butterfly opens exact same amount then if thats set about right by eye/feeler gauge and you can start and fast idle it, proper carb sync with vaccumn gauges


might also be worth cleaning the plugs with brass wire brush (not recommended if iridium tips) in case fuel rich running has sooted them up a bit much for smooth idle

[Updated on: Tue, 05 February 2019 22:03]

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Re: Cb500 idle help [message #300253 is a reply to message #300252] Tue, 05 February 2019 22:12 Go to previous messageGo to next message
jimcrux   United Kingdom
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Thanks it is shared throttle stop and I did increase the tickover for a few start attempts but put it back so think that one is ok.
I've been really careful not to mess with the carb sync so haven't touched that. It is in sync by eye but I don't have vacuum gauges for fine tuning.

Carbs are off the bike again and I've been liberal with the cleaner this time, just waiting on the ordered parts now.
Re: Cb500 idle help [message #300255 is a reply to message #300253] Wed, 06 February 2019 12:20 Go to previous messageGo to next message
Kermit is currently offline  Kermit   United Kingdom
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(22) Giacomo Agostini
My suggestions were a long shot just in case you'd missed the obvious but seem were well aware of both Thumbs Up

When cleaning the carbs, did you unscrew the jets as if not perhaps it might be worth doing as it'll be easier to tell if any are blocked if they're off and held up to the light.
Re: Cb500 idle help [message #300257 is a reply to message #300255] Wed, 06 February 2019 23:08 Go to previous messageGo to next message
jimcrux   United Kingdom
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Hi yes I took them out and soaked them and could see light through. However the new jets arrived today and the hole in the pilot looks a fraction bigger which is encouraging. Just waiting on the other bits I ordered so will hopefully be back on in a couple of days.
I hope it was just me being too gentle with my previous carb cleaning.
Re: Cb500 idle help [message #300258 is a reply to message #300257] Thu, 07 February 2019 06:23 Go to previous messageGo to next message
spagiratwink is currently online  spagiratwink   United Kingdom
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Keep us appraised Jim Yes
Re: Cb500 idle help [message #300276 is a reply to message #300258] Sat, 09 February 2019 19:46 Go to previous messageGo to next message
jimcrux   United Kingdom
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Hi - soaked in carb cleaner, new jets, float valves and gaskets and ... fired in to life and now running better than ever. Thanks guys, more than anything I think I needed some encouragement to take off the carbs yet again and be less fearful of going at them more aggressively with the cleaning. It's the first time I've been able to ride it in a couple months and reminded me why I still love it smile
Re: Cb500 idle help [message #300277 is a reply to message #300276] Sat, 09 February 2019 19:59 Go to previous messageGo to next message
spagiratwink is currently online  spagiratwink   United Kingdom
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Well done Jim, good feeling Eh, hope the weathers fine tomorrow so you can give it a good runout Clap Yes
Re: Cb500 idle help [message #300289 is a reply to message #300277] Mon, 11 February 2019 19:16 Go to previous message
Kermit is currently offline  Kermit   United Kingdom
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(22) Giacomo Agostini
A little worried (as I expect you may have been) that buying all the gaskets, jets etc might have resulted in same as before but RESULT Thumbs Up

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