Bike reneges when the riders LHS ankle is shifted forward

[ed]

Hi all,

Here is another strange problem to add to the list!
First of all my carbs were overhauled end of last year, new emulsification tubes etc, etc. The bike in general runs well and it's great to ride, BUT at speeds over 60 MPH if I shift my left foot forward by 3-4 inches the bike starts to renege, its feels like the fuel mixture has dramatically changed or the chokes been put on.
I have checked all around the carb for poor sealing inlet/outlet rubbers, air box etc. I have even tried spraying a little ether around hoping to find any leaks - none. I've also checked for an intermittent side-stand switch as well.
The problem also appears as I pass lorries, the bike momentarily pulls back - it disappears as quickly as it appears.

A little more on the foot bit. As time has progressed I've tried pinpointing the exact area where the problem might be coming from, it always seems to be down the bottom of the engine somewhere. My guess is somehow at speed I am redirecting the passing air flow into an exposed or sensitive area, but where? The shift (and engine change) is only to do with the foot going forward, the actual position of my LHS knee makes no difference. I also tried redirecting the air as I ride with my left hand, around the area of my carbs and inlet as well - this doesn't do a thing.

My throttle position sensor (and its wiring) look fine.

Any ideas?

Thanks
Ed

[HansJ]

Airbox has been modded, i.e. someone has drilled a hole or two somewhere?

[ed]

Thanks for the reply, the air-box is standard and with no holes drilled. But saying that I'll check the seal when I strip it down this weekend.

Ed

[slow codger]

The dreaded side stand switch? its in the right area. Are you moving your foot from toes on peg to heel on peg, does the peg move, slight downward flex?

Dave E

[Mincehead]

TRX poltergeist?
Bl**dy weird one that, I would also plump for that sidestand switch.Mine doesn`t have one, took the useless gadget off, less weight is always favourable for me.

[ed]

The switch it self works fine, kills the motor instantly on moving off with it down, but I'll try it out of circuit anyway. The odd thing is, If I keep my foot in one spot, the bike will carry on for miles like it - lacking power and feeling like the chokes on, if it were the side-stand switch I'd expect a more stop/start action.

I work with a chap who makes top-fuel drag bikes, he suggested the next thing may be to try some makeshift wind-shields to
isolate where it is. Worth trying I suppose...

Ed

[Mincehead]

It`s VERY odd Ed, especially as the airbox intake faces forward.
There should be nothing down by your foot that affects the running of the bike.I wonder, is the riders seat pressing down on anything and as you shift weight it affects some electrical connections, or maybe connectors inside the seat unit that run along the frame maybe?

[slow codger]

Is it an import or UK spec, and if an import has anyone played about with the internals of the speedo and rev counter?

Dave E

[M.V.]

That's a very bloody odd fault... Sounds electrical... Battery connections?

I'd try getting someone else to ride the bike before you do anything too drastic, it might be something really simple that you're missing...

[Mincehead]

I was thinking more likely the plugs at the CDI or the multi pin relay nestling on the underseat plastics to the right of the fuel tap myself.
Shifting of weight pushing the seat and bodywork against wiring etc.