F3 Fuel Pump – WHY???!!

RideCBR.com Forums Specific CBR Model Discussions 600F3 Forum F3 Fuel Pump – WHY???!!

This topic contains 5 replies, has 3 voices, and was last updated by Profile photo of saturnv saturnv 2 years, 1 month ago.

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  • #70813
    Profile photo of saturnv
    saturnv
    Registered Member
    RideCBR Guru
    Points: 23,190

    Hi Guys,

    Following on from several previous posts, I’m still on a never-ending quest to achieve perfectly smooth idle on my CBR 600 F3-V (1997).

    Not quite there yet despite having bought the bike back in March and spent most of the ‘Summer’ (as we quaintly call the rainy season in Britain!) doing various remedial work to attain this goal – please see below…

    The tickover seemed a bit lumpy and erratic but I thought that was due to the aftermarket exhaust can (Scorpion) so I replaced that with a genuine Honda one (OEM) from Ebay and although it was now much smoother and quieter through the revs, the idle still didn’t seem right. Next I checked spark plugs and HT leads – all OK – and replaced the fuel filter and airfilter then took the carbs out and cleaned properly and replaced the idle jets. Back together again and balanced the carbs using the Morgan Carbtune Pro vacuum gauge. Still not ideal and was checking the fuel pump and found it wasn’t even running.

    Referred to the maintenance manual and checked that with the ignition on and motor running there was 12V getting to the connector ok. So now I have taken the cap off that and found the contact breaker contacts are end-of life – tried cleaning and adjusting to no avail but the pump does run if I push down on the shaft so I’m fairly sure it’s just worn contacts to blame, which I have ordered from WEMoto.

    So really my burning question is how on Earth was the bike running all this time (and extremely well at various speeds including very fast on motorways – and accelerating like a fighter jet) if the fuel pump wasn’t running at all??? It strikes me that maybe the bike doesn’t even NEED the fuel pump (some of the earlier models didn’t have them – although I realise that the V (’97) has a slightly beefier set of carbs with bigger bore jets, etc. Maybe it could still get along fine without the pump though. As a final test I disconnected the connector to the fuel pump and started her up then revved to 4,000 revs no problem at all. By the way, all the other forums on this subject mention stalling, non-starting, cutting out on journeys which I’ve NEVER experienced…

    Any ideas or comments please? – apart from the boring fact that I am a frustrated author and take forever to get to the point but thanks for reading this far anyway – you deserve a medal :wink:

    #70815
    Profile photo of 74demon
    74demon
    Registered Member
    RideCBR Guru
    Points: 47,052

    It doesn’t need the pump to run. If I recall, it was put there to solve a fuel flow problem at high rpms when the bike was leaning way over. Bikes were getting over further than their predecessors in those days and lack of fuel was causing lean/cutting out conditions. Most don’t ride to that point on the street, so gravity feed is more than enough to keep up with fuel demand.

    Now, those pumps don’t run like a normal pump. They pulse slowly with very little pressure, just enough to help fill the bowls without overpowering the float needles.

    Those contacts were a common failure point.

    Have you checked your valve clearances? Maybe your non-smooth idle is not carb or ignition related.

    #70816
    Profile photo of saturnv
    saturnv
    Registered Member
    RideCBR Guru
    Points: 23,190

    Thanks for your reply – nobody seems to be around on the forum these days but maybe they’ve just got tired of my dumb posts lol.

    Yes I have a little electromechanical knowledge and I guessed that it’s a piston type pump definitely not a rotary one – the shaft pulses up and down caused by a make/break connection between the electromagnet and contact breakers if I’m not mistaken and the circuit operates similar to an electromechanical buzzer /bell.

    I did wonder whether it was an engine related problem – valve clearances or maybe loose cam chain? I keep reading that the cam chain tensioner is a common point of failure and people saying that they often need replacing at low mileages… But if the tensioner is faulty then there should be a rattle at certain revs and I’ve not heard any.

    I’m no good with engines which is why I’ve concentrated on the things I could do but maybe wasted a lot of time by doing so.

    Will get garage to check the valve clearances, thanks for your advice :)

    #70942
    Profile photo of saturnv
    saturnv
    Registered Member
    RideCBR Guru
    Points: 23,190

    @74demon
    Hey,
    Think I know what you mean now after checking the pump again, it’s just getting a pulse every few seconds right? If I increase the revs the frequency of the pulse increases say from 1 every 4 seconds to 1 every 2 seconds. The manual is extremely confusing because it says check for a 12V DC supply at the connector but it can’t be a steady 12V else the pump would run continuously like when I connect it to my spare 12V battery.
    So that pulse must be coming from the ignition control unit through the fuel pump relay and its frequency is proportional to the engine speed?
    Thanks

    #70956
    Profile photo of itinerant
    itinerant
    Registered Member
    RideCBR Newbie
    Points: 660

    @saturnv
    Ah, another one of the joys of F3 ownership… fuel pump points :bigsmile:
    Along with:
    Camchain tensioner – check
    Clogged jets – check
    Regulator rectifier – check
    Ridiculous access to spark plugs – check

    All of which are actually not too bad to put right.

    If you’ve replaced the idle jets and done a thorough clean of the passages, I agree that the lumpy idle could be valve clearances.

    You’ll know if the camchain tensioner is knackered. It’ll sound like a sewing machine at idle, coming from the right hand side. When you pull in the clutch the noise won’t stop.

    #70973
    Profile photo of saturnv
    saturnv
    Registered Member
    RideCBR Guru
    Points: 23,190

    Thanks @itinerant :)

    Guess I’ve exhausted (excuse pun!) all the other options now apart from putting the original carbs back in (should have mentioned in a previous post somewhere that these are my ‘spare’ carbs from Ebay in at the moment – but they were thoroughly cleaned and idle jets replaced and I still have the same symptom so I know it’ll make no difference…)

    No unusual sound from cam chain tensioner (yet!) by the way.

    Agreed that there do seem to be a few common failures with these bikes but I still don’t regret buying one – far from it – I think they’re amazing machines! I was on the point of buying a cbr650 but then I didn’t really wanna spend 7 grand on a new one when I found such a nice cbr600 for £2000. Even though I’ve spent a couple of hundred on stuff, not to mention a lot of time tinkering with it but that’s part of the fun ain’t it? I’ve enjoyed every minute of it and learnt SO MUCH! I never even remotely understood how a carburettor functioned before this learning curve now I not only know how it works but how to take it apart too. Thanks to you guys and this forum mainly :)
    No doubt I will buy a new(er) bike one day but right now I’m happy with what I’ve got!

    So valve clearances – check! Might even try that myself…

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