Rev limit @ 10 000 - Surely this isn't right?

[Nick V]

Hi, all!

A friend of mine has just bought a GK75A Bandit 400V, with the tacho redlined at 13 000 RPM.

The bike seems to be a later-generation 53 BHP Japanese model; it has the headlight which comes on automatically when the ignition is switched on. The engine has the VC variable valve timing, and still has it's standard exhaust.

I took it for a test ride, and the bike refuses to rev higher than 10 000 RPM in any gear, which translates to an indicated maximum speed of slightly over 160 Km/h (100 MPH) in 6th gear. (It definitely feels like a rev limiter kicking in - the engine revs quite smoothly up to 10K, then 'hits a ceiling'.)

Can anyone shed some light on what might be wrong? Could it be a malfunctioning VC system?

[Maniac]

Could be VC I suppose, not familiar with how it's setup.

Could also be fuel starvation. Maybe the floats need adjusting, or the fuel tap screen is partially clogged, or maybe the jetting is wrong. Hard to say, really.

[Nick V]

I can't delve any deeper until it's the weekend, and I have the workshop manual. So my deduction, at the moment, is just an educated guess.

My old 59 BHP VC Bandit redlined at 14 500, with the VC audibly switching in at 12 000. The motor on my friend's bike redlines at 13 000, so it seems a reasonable guess that the VC might switch in at 10 or 11 K.

This doesn't feel like fuel starvation: there is no spluttering or misfire or gradual tail-off in power. Just smooth, strong revs until 10 K - then BAM! Feels (and sounds) like the bike has run into an electronic rev limit.
Almost like the engine is *expecting* the VC to take over - but it doesn't.

[canyonbreeze]

If it is a model intended to be sold in Japan then it is most likely a rev limiter built into the ignition module.  There are some posts around here somewhere about how to de-restrict it.

[Unique]

this may help you!!

http://forums.banditalley.net/index.php?topic=11897.30

[Nick V]

If it is a model intended to be sold in Japan then it is most likely a rev limiter built into the ignition module.  There are some posts around here somewhere about how to de-restrict it.

Canyonbreeze, any ideas on which posts? Can you post a link? 

Unique, thanks for the link! :) It seems tha's purely for speed de-restriction, though, which is going to be done to the bike anyway.

[canyonbreeze]

See his link above.  The ignition has no clue of speed only of RPM.  Therefore it can't limit speed, it limits power by limiting the engine RPM.  The speedometer is purely mechanical and has no connection to the ignition.

[Nick V]

See his link above.  The ignition has no clue of speed only of RPM.  Therefore it can't limit speed, it limits power by limiting the engine RPM.  The speedometer is purely mechanical and has no connection to the ignition.

Canyonbreeze, true, but that's the posting for speed de-restriction of the Jap Bandit by splicing a 1.5 Kiloohm resistor into the green/yellow wire on the CDI.

My trouble is that although the bike's tacho is redlined at 13 000, there is SOME kind of problem - nature of problem as yet unknown - which is preventing the engine getting past 10 000 RPM in ANY gear - even neutral.
I can't as yet download the service manual for this bike, so I was hoping that someone who had experienced this problem before might be able to help by highlighting a possible root cause.

[Vested]

I think that's his point. The motorcycle doesn't ever see the speedometer speed, so it can't limit the bike using an input from the speedometer. It also doesn't see the gear besides neutral, so it can't limit only in top gear. Therefore, to limit the motorcycle's top speed they limited the engine RPM completely, with no allowances made for a higher RPM in different gears.

[canyonbreeze]

^^^  What he said, yes ^^^

[Unique]

^^^  What he said, yes ^^^

i second that

[Nick V]

I think that's his point. The motorcycle doesn't ever see the speedometer speed, so it can't limit the bike using an input from the speedometer. It also doesn't see the gear besides neutral, so it can't limit only in top gear. Therefore, to limit the motorcycle's top speed they limited the engine RPM completely, with no allowances made for a higher RPM in different gears.

I'm not sure if I can explain this situation more clearly than I already have.
I never mentioned the speedometer. I'm familiar with the principle used to speed-restrict the bike: using the gear-position sensor as an input, the rev limit is lowered in 5th and 6th gears to cap the bike's top speed at a theoretical 180 Km/h. The way to get around this is to splice a 1.5 Kiloohm resistor into a particular wire on the CDI unit.

This doesn't explain why, when you ride the bike, the revs abruptly cut off at 10 000. I hear the sound of the VVC system switching in, but in the split second after that. the bike simply refuses to rev any higher.
Just smooth, strong revs up to 10K, then nothing.

1. It FEELS like the VVC system - or some crucial part of it - is malfunctioning.
2. 10 000 RPM in 6th gear on this bike works out to 160 Km/h - so it never even gets a chance to hit the Japanese-legislated top speed cap.

This has nothing to do with the bike's speed restriction. It feels like a VVC fault. So, can anyone help?

[tomacGTi]

Pull off the tops of the diaphrams on the carbs and see if there is a 33hp restrictor ring placed into it. I know you Brits have those for learner bikes.

Barring that, it can be jetting, something with the VVC, limiter.

My .02$$

[Nick V]

Pull off the tops of the diaphrams on the carbs and see if there is a 33hp restrictor ring placed into it. I know you Brits have those for learner bikes.

Must be my Queen's English.  I'm actually in South Africa.
Ah, it's all good. We're all colonials in one way or another...

It's almost certainly a Jap-model bike, but I'll check the carb tops anyway. Thanks for the suggestion!

[Chris H]

If it stops dead at 10000rpm in any gear theres a real chance its the vvc. On the top of the motor theres a valve thats feed with oil from the bottom of the motor, this has two wires going to it and at 10000rpm the cdi sends a signal that switches the valve so as the oil runs a different way through it, this causes the cam followers to switch hi or lo. The oil is always flowing, it just switches from one hole to another. You can check the oil valve by disconnecting it and puting 12v across it and listening if it switches, if this works it is most likley a fault on one of the safty switches that fit on the ends of the cams to sense which position they are in.