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sb6r missfire?

 
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mk2sean



Joined: 04 Apr 2016
Posts: 38
Location: Scotland

PostPosted: Wed Jul 20, 2016 10:19 pm    Post subject: sb6r missfire? Reply with quote

Hello lads and lasses.

so posted a while back about a bike I inherited from my old man. Its an sb6r.

I now have the bike at home. The bike had previously been drained of fuel due to the ethanol issue. I charged the battery and put some super unleaded in. I think my mistake was putting the choke wide open. I wound it over on the starter but wouldnt start. The battery was then flat. So I charged it up again. Repeated the same process. It fired up and runs. But wont idle with the choke shut and sounds off a cylinder. I kept it running till the water temp was up to 78deg. I then shut it off.

I have bought cr98 plugs. I am about to change them tomorrow. The tank has about a galkon in it. This will be my first time taking off the tank. Is this a different task? How do I stop the fuel pouring out the tank over the bike on disconnection? Any checks to carry outwhile its off? Anything else to remove to change the plugs?

I understand these are ridiculously stupid questions. Please bear with me. I am more used to cathedral diesel 2 stroke engines on super tankers.

many thanks for any advice you can give.
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Evilchicken0



Joined: 12 May 2010
Posts: 2996
Location: London

PostPosted: Wed Jul 20, 2016 10:47 pm    Post subject: Reply with quote

If it runs rough then check if it's on 3 cylinders ... Check all 4 exhaust pipes are hot. Changing the plugs should help but really you need to clean the carb jets ... it sounds like the slow running jets could be part blocked.
Don't fit iridium plugs in this bike
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mk2sean



Joined: 04 Apr 2016
Posts: 38
Location: Scotland

PostPosted: Wed Jul 20, 2016 11:10 pm    Post subject: Reply with quote

NGK Cr9e arent irridium though right?

Is cleaning the carb jets simple enough? Safer to remove them to do that job? would that need a gasket kit? Where do you guys get spares from?
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brian



Joined: 22 Aug 2011
Posts: 3769
Location: Australia

PostPosted: Thu Jul 21, 2016 12:36 am    Post subject: Reply with quote

If it won't run without the choke then there is most likely a blockage in the pilot circuit. You'll need to remove the carbs and strip them to clean all of the jets and passages. Put everything back exactly how it came apart. You need to note all the settings as you're stripping them, in particular float height and numbers of turns out on the pilot screws.

Pay particular attention to the pilot screws and passage ways. Very tiny holes in the pilot circuit and easy to miss a blockage.

CR9E are the correct plugs (not iridium)
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vort28



Joined: 22 Mar 2010
Posts: 2194
Location: Northwest , UK

PostPosted: Thu Jul 21, 2016 7:24 am    Post subject: Reply with quote

mk2sean wrote:


Is cleaning the carb jets simple enough? Safer to remove them to do that job? would that need a gasket kit? Where do you guys get spares from?


Don't need a gasket kit to clean carbs, (well should'nt do unless you find something). Probably could do in situ but quicker/easier to remove.
Best guess is a blocked idle jet/float valve or a sticking float . Might be crap in the transfer fuel line .
As Brian says , reasonably simple job just a bit fiddly. Take your time , clean and replace jets as you find them. Me methodical and all should be OK.

Whilst in bits general stuff really if bike sat for a while. Linkages , grease bearing , hose's( fuel/water/hydraulic) , brakes , tyres , wheels,electric connectors etc .
Generally sb6 quite a reliable bike.
No better way to get to know your new ride than to take it apart !! Very Happy

Spare's ? now that is a good question. Depends what you after. Running gear/service parts are generic off the shelf stuff generally , bodywork/bimota unique is a bit more difficult but can be found through a number of European specialists .
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Jonny B Bad



Joined: 05 Dec 2009
Posts: 555
Location: NE London

PostPosted: Thu Jul 21, 2016 9:56 am    Post subject: SB6R Reply with quote

The SB6R has one or two issues which throw out the usual diagnosis process. If the vacuum fuel pump is still fitted (in the air box) it tends to over-fuel at part throttle and could have fouled the plugs - hence a difficult start. CR9 are the correct plugs and there's nothing wrong with iridium, but I wouldn't waste a premium-priced plug until you've got it running right. You need to take the carbs off and look into them from the engine side. If you see a cream-coloured paste, there's a problem with the tank that needs addressing. What mileage has the bike done - or have the clocks given up the ghost? It probably needs the valve clearances checking. This bike is 20 years old now and needs a proper re-furb if it's to be reliable transport. Also, there are a number of fasteners that need to be taken out and lubed before they seize solid and need drilling out. Fasteners are best tackled with a rattle gun, to avoid rounding out the hex. If it's still wearing the original chain, it should go in the bin - even a cheap new one will be far better (i.e. less likely to break) than the rubbish that was put on originally. I've cheerfully put an original with a couple of hundred miles on it in the bin.

After this time it probably is worth doing a full re-build on the carbs, particularly float valves, needle jets and needles. Gasket kits, including float valves and seats are around £20 per carb. Needle and needle jet is about £25 per carb. If it's very low mileage - sub 5,000, you can probably do without the needles and needle jets, but it's good to be able to tick one bit of the bike off completely, for when you start setting up. You should have 150 genuine mikuni main jets in there, if it's still running the original exhaust. If they're still there, you can heave a sigh of relief that the thing hasn't been interfered with by somebody that thought that an aftermarket jet kit might improve things.


Good luck.
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