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CBF 125 All Better, But WHY?
Blog Date - 15 March 2013
So this morning, at 0730 after a porridge breakfast I went into the shed. As I suggested last night I ventured to check the flow from the fuel pump with a mind to diagnose if there was any blockage. I replaced the pump, save for the high pressure outlet pipe, got my 1 litre jug and proceeded to switch the bike on and off every 2 seconds, running the pump through it's "prime" cycle.
It filled the 1 litre jug in no time at all. It pumped happily, firmly and without hesitation except for my having to turn the key off and on again. Good...and DAMN! Good because it suggests the fuel pump is not blocked and is working fine and it is an expensive part. DAMN because if it's not the pump then what is it? There is one other test for the fuel pump, a pressure test. This however requires a specialist Honda part which I'm sure would cost a fortune. I did consider rigging up an old tyre pressure gauge but I had visions of petrol soaked clothings, fire, explosions and general devastation.
If it's not the pump could it be air starvation? I got down to the air filter and it is dirty, I must replace it, but not such that I think it would cause my high-speed running problems. Anyhow I couldn't be arsed taking the whole bike apart again to get the air filter out when I haven't yet got a new one to put back in. Damn. I put the bike back together. After a cup of tea it was getting time to head off to a job. Stuff it I thought, there's a all-town route to Rochdale, I'll take the 125 and see if anything's different.
And it was! She's running just fine. Fine in the 30's as expected, fine in the 40's even up the steep hills and fine around town hard on the gas. What the deuce?! After an hour or so in Rochdale I came home via a rain soaked motorway at 55 to 65 mph and she never missed a beat. Who knows what's going. And that's the end of the relevant part or this tale. What follows is a dissection of my thoughts on this subject. To those not of a technical persuasion or those who don't like to listen to silly middle aged men ponder their navel, stop reading. If however you're really bored, boring or interested in these things...read on.
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Due to the nature of the problem being poor running at high speed, when their is a high fuel flow requirement, I thought there may be a blockage in the fuel system. I also suspected the fuel pump as there is a well documented issue with CBF 125 fuel pumps overheating. This particular issue however only affects new bikes at low mileages and on hot days.. My fault started on a very cold night on a motorcycle with almost 12,000 miles on the clock. But the kangarooing I suffered is a symptom of the fuel pump on new bikes so maybe it was an indication of a fuel pump issue on mine.
First I tried fresh fuel, no difference. Then I removed the pump and checked for a good flow as above, that was fine. I replaced the pump and at the time of writing the issue has disappeared. So what has happened? My primary suspicion is that there was indeed a blockage in the fuel pump, but my removal and complete draining of the pump has somehow dislodged the foreign object and returned normal service. There are however countless other possibilities.
- Maybe there was water in the fuel that got into the pump. This would cause poor running and with petrol being lighter than water it remained at the bottom of the pump causing lubrication and overheating problems. By emptying the pump I removed the water.
- Maybe I disturbed something while removing the pump. Moved a wire that cleaned a contact, nudged a pipe that was leaking air or fuel, shook some sediment away from the outflow on the tank or released a trapped breather pipe.
- Maybe disconnecting the fuel pump from the computer allowed the computer to reset some digital setting. Who knows the dark art of the program that lurks within the brains of this most simple machine.
- Maybe the wet weather today is stopping the pump from overheating. Although it was bitterly cold on the night it started air is a good insulator while water cools things very rapidly.
- Maybe the atmospheric conditions have altered and come back within the boundaries of the settings within the program.
- Maybe when I removed and checked the spark plug I dislodged some dirt from it, or disturbed a wire, or allowed the computer to reset.
I am of course guessing. The point is that there are many many possible explanations along with the ones I have listed. And that is what makes diagnosis so very very difficult. If you can look at an engine and see a con-rod poking out you can safely say in a mid-west American accent "Thaaars ya problem". If a bike refuses to start and you remove the tank to find the cables to the coil have fallen off, you're onto a solution pretty quickly.
If however all appears well, all is within tolerances and specifications, all is connected, oiled, intact and functional then you have a problem if it's not doing what it should. I hate those kind of problems. I'd hate to be a Doctor too.
Reader's Comments
john said :-
Lets just hope its not a temp fix and reverts back to fecked up mode Ren.
01/01/2000 00:00:00 UTC
Gonzalo said :-
Hello Mate, did it happen again? Im having exactly the same issue inmy cbf 125 2009, i drove from spain to Iran with it with no issued and today it started "kangarooing" in the Heat. No really genuine Honda mechanics here. So would appreciate any advice, thank you!
15/06/2018 15:36:27 UTC
Ren - The Ed said :-
Hi Gonzalo. When this happened to me it was a good while ago.
As stated in the post I removed the pump and replaced it and all was fine and has been since. The bike now has 74,000 miles on the clock with the same pump from new. I'd suggest removing and draining the pump as a starting place.
The pumps have a reputation on some of the models (2010 if I recall) of going awry. I'm sure your research has brought this up - if not look for it.
Check the obvious! I have had 2 spark plug caps fail although this was worse in the rain than the dry. That also caused poor tickover. Check the valve clearances. In fact ensure you give the bike a thorough service (plugs, filters etc)
Hope you find a solution.
15/06/2018 16:21:47 UTC
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