Help troubleshoot sputtering bike

Hi all, hope someone out there can help to troubleshoot this thing...
I just did an oil, oil filter and spark plug change on my CB400.

One day later it started sputtering a little when travelling at slow
speed; the problem then kept getting worse and worse until now, when
it sputters like badly at any rpm below 3k...

Does anyone know what the problem could be? A bad plug? Dirty air
filter? Dirty fuel? Exhaust pipe leak? Rectifier going?

Given that it's a sudden occurance that's getting worse quickly, I'm
guessing that it is something electrical; tell me if I am wrong!


Regards,
Gary

 

Maybe even loose spark plugs.

 

Or improperly gapped...

 

Depending on exactly what you have, there are a couple of possibilities.
Pulling on the plug cap to remove it can dislodge the wire from the
plug cap.
There's often a resistor in the cap that can get broke.
I've experienced NEW spark plugs that were bad.
mike

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It's hard to guess specifically what's wrong, but for a bike to splutter
it's either not getting fuel or a spark or either.

Fuel problems are either starvation or contamination. If it's starvation
maybe either you have compressed the fuel hose when putting the tank back on
or have obstructed the breather. Is the fuel tap fully on? Contamination
would be either moisture in the fuel due to condensation (especially if the
bike has been sitting or is only used occasionally) or you may have stirred
up some shit from the bottom of the tank which may have gotten through to
the carbs.

I'd take the tank off check all the hoses etc and pour about a litre of fuel
out from the petcock to drain any water or low sitting contaminants, drain
the carbs by undoing the drain screw underneath each float bowl and check
the discharge for any contaminants, if it looks clean and not too many brown
particles then leave it at that, refill the carbs and start er up and see
how it goes.

When the tanks off recheck all the connectors etc, check none of them have
moisture in them and if they do dry them out completely and clean with an
contact cleaner. I had a bike that kept missing intermittently, in the end I
pulled apart each connector, dried it, cleaned it and that solved the
problem, don't know which one it was though.

I'd assume at this stage something you have done is causing the problem only
because the bike started running badly after you had worked on it, any time
my bike has any problems after me working on it I always recheck where I
have been.

Paul

 

Ok guys, thanks so much for all the helpful suggestions. I was rather
intimidated by all the possibilities but fortunately, I noticed that
the scottoiler(an auto-chain oiler) pressure fitting had broken off.
Since this chain oiler taps pressure from one carb, that was the cause
of the problem. Replacing the fitting cost $5.