Picked up a low mileage 125cc black/aluminium executive model a few weeks back. Well chuffed with it. Saves me so much time on my daily commute along the A13 in to and out of London. However, since I have owned it it has suffered from an erratic idle and occasionally cuts out when you come to a stop. I have carried out a major service using OEM parts i.e. NGK iridium plug, NGK plug cap, all mahle filters including the fuel filter and motor and transmission oils. I removed and cleaned the injector and idle valve. These looked and sealed OK to me. The injector wiring also looks OK. The idle has improved slightly since the service but is still erratic in my opinion. I am only using super unleaded >97 RON. Any pointers as to what could be the cause?
Also how is the top speed limited? At about 65MPH it feels as if the engine is hitting an rev ECU limiter i.e. a hard ignition cut. Is this normal?
Thanks for your anticipated help.
Better not use more than standard 95 petrol as it may burn your valves ( especially when committing on motorway where engine operate on high rew). Does bike has valve clearance checked/adjusted? Check your spark plug condition after few tanks as it may indicate potential problems with engine. Does variator was regressed/checked, belt replaced ( don't go for other than original Bando - saves a lot of hassle in future)? Battery terminals nice and clean? Have you checked main earth connection to frame if not corroded? Hope it helps.
Bike has done 10k so valve clearances havent been checked yet. Have you done this personally before?
Valves should be checked early in the engine's life at around 1000 miles. Stalling when warm is a classic symptom of tight valve clearances. This needs checking soon or the valves will get damaged.
It's not the easiest job to do, but is certainly possible at home. The swing arm needs to be released (disconnect the shock absorbers, wiring harness support clips and any other bits which stop the engine pivoting down) and lift the bike in the air on a suitable jack so that the engine pivots down. This makes the top of the engine accessible through the seat opening and you can remove the cover and get to the valves to check the clearances. If they need adjustment the cams have to come off and new shims put in.
A very brief description of what's involved. The workshop manual has all the detail if you fancy a go.
Although you have checked the injector, I suggest you check it again, this is a classic symptom of an air leak around the injector seal. With the bike idling try wiggling or pressing down on the injector and see if it makes any difference. If it does it is most likely an air leak around the injector seat. You should inspect the o-ring and replace if possible. I think I once saw VarioBob (number 1 C1 expert) add a couple of extra ones to cure the problem once, but I am not 100% sure about that.
The 65MPH limiter sounds odd, I have heard talk of a rev limiter but I have never personally hit it, but then I rarely max out top speed. If it is hitting a rev limiter it sounds like the engine is spinning too fast for road speed which would indicate a problem with your variator.
You're right about the extra o-ring - I recall Variobob fitting one to Simon's bike in Germany last year. It cured the stalling/idling problem and we rode to Germany and back this year with it still in place.
Thanks for your replies guys.
I will check the injector seal once again. I will also inspect the variator and change the belt this evening.
If you have some brake cleaner or something else flammable and you feel brave, give it a squirt round the injector while the engine is running and see if the idle increases briefly. Don't get it on the exhaust though!
Battery terminals maybe loose?
although the air leak problem is most likely at the injector o ring seal, it can also occur at the throttle valve shaft, the vdo idle control unit and the piece of rubber hose between the throttle and injector bodies.
while engine is idling, pour a thin stream of water over these parts and listen for change in engine speed. no, the water will not damage anything.
Having serviced the variator (greased version), replaced the drive belt and greased the crank and transmission shafts the C1 now pulls away quicker and smoother. The cutting up/hesitation at approx 65MPH has also disappeared. That must have been the belt slipping at high engine speeds. Now to resolve the idle issues.
Stripped down the throttle body assembly today. Gave it a good clean. Flipped over the throttle body to cylinder head seal. Are the injector O rings still available from BMW? RealOEM states that they were ended. Does anyone know the size of them? If you move the injector quite forcefully then you can hear a vacuum leak. I did adjust the idle speed ever so slightly by adjusting the bowden cable at the throttle end. Has anyone ever used that techique to improve the idle?
I suspect adjusting the idle speed is just covering up another fault. The ECU does everything it can to maintain the required idle speed but leaks and injector wiring faults are too much for it to cope with. Have you tried the water / brake cleaner test around the potential leak areas? That will help eliminate air leaks as being the problem.
Does it stall when the engine is cold or only when it's hot? As mentioned above, hot stalling only is usually valve clearances.
the throttle o ring is quite robust and will usually do with a smudgde of medium grease to ensure a good seal.
note that the o ring sits inside a plastic insert pressed or glued into the head port, which may have loosened. if so, remove, clean, liberally grease or apply silicon sealer and press back in.
idling is regulated by the ecu via the vdo idle control unit and not adjusted on the bowden cable.
have you tried the water dribble test?
O-Ring Size is 7,52x3,51
Part Number was 136441437474
It probably needs to be Viton, or something oil/fuel resistant.
Don't apply too much force to the injector, it definitely will leak if you do that. I think the problem is that the injector doesn't "float". The fixings at the upper end can force the injector against the lower o-ring, distorting it, which cause the leak.
Try loosening off the two fixing screws to allow the injector to centralise itself in the o-ring. With the engine running, gently tighten the screws and listen for any change in the idle. If the idle changes, you may have overtightened the injector, so then back the screws off again.
Only tighten the screws enough to stop them vibrating out, and check regularly until you are sure they won't fall out.
to add to bor's mail:
the injector is fixed down on two pastic posts in such a way that , when properly seated, the top of the post and the injector plastic eye part sits flush under the screw and flat washer. this gives a slight injector float and prevents squashing the two o rings.
Both top and bottom 'O' rings now replaced. All symptoms now gone. Got them from www.britcar.com, PN: LR000525. £0.35 each.
Thanks for everyone's input.
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