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CBF 125 Poor Running Problem

Blog Date - 13 March 2013

OH NO!  The CBF 125 is not a happy bunny.  Late on Monday night whilst blatting down a stretch of dual carriageway she started coughing, spluttering, kangarooing and not being nice at all.  She'd felt a bit "wolly" beforehand but nothing was definitely wrong, now I was sure there was.

I put the bike away, hoping it was just "one of those things".  It wasn't.  The next day while out with the gf, 2 up on the 125, she started again.  For the rest of the ride it got worse until 30mph was the maximum speed she'd reliably run at and that's if there was no hill.  Oh dear.  Oh dear oh dear.  Deary deary me.  This is one of them there modern bikes too.  If I can't find an obvious issue then it's going to be computers, swapping expensive bits and spending lots of money, something I particularly hate.

I'm thinking fuel starvation.  At a steady 30 with no real load on the motor she feels fine, so fine I keep on hoping the problem has magically solved itself and get all giddy on the next 40, 50 or 60 zone.  She feels great and I smile inside until a few moments have passed and then we start to pogo on and off the power like someone's remotely flicking the kill switch on and off.  I roll back to 30 and she'll struggle for a few more moments then carry on as if nothing has happened.  It's as though there's not enough juice getting through to sustain the higher speed.

The CBF 125 has a well documented issue with the fuel pump.  Google "CBF 125 Fuel Pump" and you'll find plenty of websites telling tales of woe.  Usually new or newish bikes get the kangarooing at low mileages and on hot days.  My bike has got almost 12,000 miles on it and when the problem came to the fore it was minus 4 degrees centigrade, not exactly a hot day on a low mileage bike.  But, but but, the kangarooing is a sign of fuel pump problems so maybe my pump is on it's way out too.

The first and most obvious thing to do is run the bike with the fuel cap loose.  Maybe the tank breather is blocked, so that will confirm or eliminate that issue.  Next is to check fuel flow.  Make sure it's dribbling out the tank, make sure the pump squirts fuel when disconnected from the throttle body (NB...BIG fire risk doing that) and check any fuel filters.  If all that checks out OK then Mr Haynes has a method of checking the amount of fuel pumped in 10 seconds meets a certain value.

After all that is checked and if I've found no issues, what do I do?  Diagnosis is a blooming nightmare.  It could still be the fuel pump.  It could be one of the many sensors feeding the wrong information to the computer.  It could even be the computer.  It's possible it's even the motor.  Hell for all I know it could be the wind blowing from the North that's causing the problem.  In the meantime I'm either going to have to use the 600, which I'm trying to "save" for my forthcoming trips, or the tin box.  I do hope it's just some dirt in a filter...

cbf 125 with top box and in silver
Please...please...please be something simple that a normal human being can fix...

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Reader's Comments

John. said :-
Check the suppressor cap, and HT lead Ren. even the spark plug, it might be a bit loose.

http://cbf125rider.wordpress.com/2011/06/27/the-dreaded-kangaroo-hopping-problem/

Might throw some light ont problem Ren.

does sound like a fuel pump problem though. :( .
UTC
Ren - The Ed said :-
Yeah John, that's the website that I first came across re the fuel pump. The only thing that's odd is mine ain't new and it sure as hell was not a warm day!

I can't find a price for a brand new fuel pump but I'm reckoning around the £170 mark. I'd like to check everything else before I take that option. I've checked the plug so far and that's OK but I'll fit a new one to be certain.

Start with the simple things first.
UTC
john said :-
Also they dont have an inline fuel filter on that bike, you could always put one in. :)
UTC
Ren - The Ed said :-
If you google 16700-KWF-952 you can find the part for sale...OVER £250!!!

YIKES!!! If that's the case I can see me giving a second hand one a whirl. I'm gonna be REAL sure it's the pump first I reckon.

Now...who do I know with a CBF 125 who's fuel pump I can borrow...
UTC
Tom McQ said :-
I don't even understand why they feel the need to fit fuel pumps. What's wrong with gravity??
UTC
Ren - The Ed said :-
Tom! Fuel injection. As fuel is squirted in it needs presure, in the case of the CBF 3 bar. Modern 2009 model with low emissions.
UTC
john said :-
Ren, might be a long shot mate, but contact the guy from india and see if he can suggest anything, he might know someone who has over come this problem, you know they are very savy over there and can keep bikes running in all sorts of strange ways.
UTC
Ren - The Ed said :-
John...you're right...far more in tune with FIXING things rather than replacing things over there. We've become soft in the head here. If I get nowhere on my own I'll drop Arjun a line.

I bet he can get me a nice new fuel pump a lot cheaper over there too!
UTC
John said :-
That was my thinking Ren. :)
UTC
Karna Deshar said :-
I was having exact same problem with my CBF 125 (Stunner- carburetor version) for almost 9 months since last November. Went through all the mechanics recommendation from piston repair, air filter change, carb cleaning, fuel tank cleaning, battery replacement ....., but none helped. Finally, an idea struck, maybe the problem is with the spark plug and went for a spark plug change last week. To my amazement, the problem was solved immediately and haven't seen that problem since. The problem troubling me almost a year and costing me more than $200 over the year, solved by just a $2 spark plug. Give it a try guys....
UTC
Ren - The Ed said :-
Hi Karna Deshar. Sometimes it's the simplest of things! I've seen motorcycles stripped right down...only to find the kill switch is in the off position.

Nobody said it was easy. Thanks for the tip!
UTC
lumoruk said :-
Same problem, been happening around freezing temperatures. The spark plug cap is perished so will get that replaced and give the spark plug a clean/ check gap.

Had fuel pump replaced last march. Bike is now out of warranty though.
UTC
Ren - The Ed said :-
Hi lumoruk. This is an old post now but you're quite correct about the plug cap!! I've recently had another tickover issue and after much wailing and gnashing of teeth it turned out to be dirt and road salt in the plug cap. I only spotted it when messing with the bike I saw it arcing out like a lightening storm.

You're not the first person to mention this. I wonder if there's something curious about the way the plug, cap and cylinder head are shaped that causes the cap to collect crud. The solution is simple, just clean the cap out once in a while!
UTC
 

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