Forum

[Thack]

Gwilly writes: "Sooo, does the efi enrich mixture dependant on the signals received from the sensors? ie temperature and throttle position."



Yes. It's a very straightforward system, clearly designed to be low cost. Even so, it works pretty well, in my view.

[Thack]

Michael writes: "Presumably, if the enricher device thingy (air bypass thingy - whatever) is stuck in the 'on' position then it is chucking a whole load of extra air past the throttle air meter sensors (are there any?!), which is compensated by a whole extra bunch of fuel by the o2 sensor in the exhaust, thus resulting in a rich mixture... much in the same way that an air leak in the intake of a car EFI engine can result in a rich (not lean) mixture... "



The O2 sensor isn't used during a cold start.



During normal, warm, running the O2 sensor signal is used by the ECU to make sure the mixture is stoichiometric - neither rich nor weak - and I think therefore the ECU will compensate for an air leak by injecting only enough extra fuel to turn the mixture from weak to stoichiometric, not rich.



I'm not familiar with the phenomenon you describe where an air leak causes a rich mixture, so I'm afraid I can't comment on that.

[Michael]

Yup, forgot about that! Open loop until warm... so is it perhaps that my problem might be linked to the point when open loop becomes closed loop (i.e. when the o2 sensor kicks in when the engine is warm) as that would be about 5-10 minutes into a ride?




If so... I think I may have it! When the engine is warm, the o2 sensor kicks in. IF the exhaust is leaking (ahem, mine might be - I fitted it!) then it will draw air into the exhaust directly from the environment, thus fooling the o2 sensor into thinking there is a weak mixture... it compensates by chucking in extra fuel.. thus actually rich. Now, if that is even remotely correct (it does seem feasible), why does the problem get a bit better after a further 5-10 minutes, often after a stall and restart, I might add?

[Michael]

BTW how would I test this?

[Thack]

Michael writes: "IF the exhaust is leaking [...] then it will draw air into the exhaust directly from the environment, thus fooling the o2 sensor into thinking there is a weak mixture... it compensates by chucking in extra fuel.. thus actually rich."



OK, let me be up front and say that although that scenario sounds feasible, I don't know if it will ever actually happen. Can the exhaust draw air in if there's a pipe/head leak with anything other than a tiny throttle opening? I simply don't know. We need someone with more experience to join in.



"...why does the problem get a bit better after a further 5-10 minutes, often after a stall and restart, I might add?"
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This has been bothering me, too. Right now I'm still puzzling over it, and that's why I'm not in a position to predict what the problem might be.



If it were my bike I'd start by unplugging the temperature sender, which I think will force the bike onto its internal default map. It would be interesting to see what happens. If the fault goes away (although I guess it might make cold starting harder) then I'd test the sender in hot water.



Meanwhile, I hope someone else will dive in with suggestions.

[Michael]

New plug is just like the old one after 30 miles riding. No obvious intake air leaks, and the bike ran very poorly/not at all with the temp sensor disconnected. Workshop manual suggests clean throtttle body and check all sensors... it also was v hard to kick over at times. Not starting, but just kicking/turning over the engine with kick start... high resistance from time to time ie I could put all my weight on the ks to not effect, but return the ks to its starting point sometimes fixed this. Not having a good time today!!!!!

[PeteF]

Don't the EFI engines have a auto decompressor? If kickstarting if difficult that might be the culprit.

[Michael]

They do have an autodecompressor in the exhaust cam. Would that cause my rough running issues too? I did notice the bike sounded a little clickety-clackity when I was test running it last night. Apparently that is a possible noise from a dodgy autodecompressor... however, the resistance to turning the engine over on a kick felt 'odd'. So at some points in the cycle I met very high resistance (i.e. I assume at compression?) and I could essentially stand on the KS... otherwise the cycling the engine with the KS seemed slightly mor resistant than normal, almost like the clutch was dragging or something (it was in neutral though - it just felt a bit draggy)?

[Nettshubby]

Michael, assuming a decomp fault, is it possible that if the exhaust valve didn't return fully, that the piston could touch it? I don't know the full ins and outs of this decomp system, but if piston could touch valve, it may be bent?

[Michael]

Ok, so back from hols and I thought I would tackle this beast... throttle body and inlet manifold all removed tonight, and all were pretty black inside. Cleaned them up, and will do it again with carb cleaner tomorrow and will order all new rubber orings etc to freshen up the system. Removed the air flow thingamies from the throttle (idle screw and bistarter piston) and both could do with a clean inside too. Again, will complete the tidy up tomorrow. Now, if air-fuel mix was correct, am I right in thinking I shouldnt expect a lot of blackening of throttle parts, including the butterfly? Will check map, tps and temp sensors once things are cleaned up and back on the bike, will also check injector if possible. Will keep all posted