Throttle position thingy??

[Radio-active]

OK, Here's one for you electrical ECU Gurus!

I was wondering what the throttle position sensor? (electrical sensor on the side of the carbs) does?
I removed it when I changed the jets - to get the carbs out of the frame!, it fits back on a cam arrangment and duuurrr , I didn't mark its position when I removed it!
I put it back in the mid position, bike runs great, so, whats it do? how do you set it up? Does it matter?

[chronyx]

I thought only a fuel injected vehicle would have/need a throttle position sensor, but nope, there it is in the Haynes - 'Throttle position sensor'.

As for why, I haven't the foggiest! Must be for the CDI system, so it knows what you're doing with the throttle and can time itself accordingly, at a guess.

[djadams]

Yep, the TPS helps the ignition system get the optimum ignition timing.

Without it, timing can only be engine speed and conceivably engine/air temperature related, but with a TPS, it can be load related too.

Enables it to be nice and retarded at low loads to avoid pinking, but nice and advanced at high loads to generate best torque (power).

Old cars used to have a vacuum operated advance unit (which actually retarded with increasing vacuum) to do the same thing.

[Carport]

Of course, to get any benefit from it your carbs need to be balanced perfectly

[robelst]

Originally Posted by djadams

Old cars used to have a vacuum operated advance unit (which actually retarded with increasing vacuum) to do the same thing.

Yep, me Buell's got a thingy like that, called a VOES. Well, a Buell is sort of "old" isn't it?
From what year do AT's have this feature? I don't think my '94 AT has this (unless it fell off).

This brings me to David Silver, selling out AT carburettor banks for the R/S model ('94/'95) and a seperate one for the T model ('96). Looking at the exotic price tags of loose carb-parts I wonder if the £149 wouldn't be a sensible investment on my 50k / 11 years old bike that will need to last another couple of years. And then of course whether the T-bank may have this feature and might actually be the better choice, even on R and S models? I wonder if it helps mpg as well, later ATs always seem to be more economic than early ones

[djadams]

Originally Posted by robelst

...of course whether the T-bank may have this feature and might actually be the better choice, even on R and S models? I wonder if it helps mpg as well, later ATs always seem to be more economic than early ones

It would help economy as it would enable the ignition to run more advanced at higher load (more torque for same throttle position is same thing as less throttle position for same torque, so less fuel needed to push you down the road).

As for retro-fitting it, you'd need to retro-fit the whole ignition system too, as the earlier CDIs won't have an input for the TPS.

[xrv_jim]

Originally Posted by robelst

From what year do AT's have this feature? I don't think my '94 AT has this (unless it fell off).

Rob,

RD07's don't have 'em only RD07a's from 96/97 onwards.

Originally Posted by robelst

This brings me to David Silver, selling out AT carburettor banks for the R/S model ('94/'95) and a seperate one for the T model ('96). Looking at the exotic price tags of loose carb-parts I wonder if the £149 wouldn't be a sensible investment on my 50k / 11 years old bike that will need to last another couple of years.

I've been thinking the same thing myself. I checked the price of of carb diaphrams - £87 each from Dave Silver. £149 for the carbs is a bargain but you've got to add the VAT and post - still comes out at under £190.

Originally Posted by robelst

And then of course whether the T-bank may have this feature and might actually be the better choice, even on R and S models? I wonder if it helps mpg as well, later ATs always seem to be more economic than early ones

The T carbs will fit no problem (half a mm less venturi size and both main jets the same size is the only difference I can find) but the throttle sensor will do you no good - you need the loom wiring to plug into and the right CDI, ignition pick-ups and ignitors to make sense of the signal. There seems to be a lot of difference between the RD07 and RD07a on the ignition side.


Jim

[Radio-active]

Chronyx wrote

I thought only a fuel injected vehicle would have/need a throttle position sensor, but nope, there it is in the Haynes - 'Throttle position sensor'.

So does the Haynes manual say 'under no curcumstances mess with this' or 'mark position before removal'

[robelst]

Originally Posted by xrv_jim

The T carbs will fit no problem (half a mm less venturi size and both main jets the same size is the only difference I can find) but the throttle sensor will do you no good - you need the loom wiring to plug into and the right CDI, ignition pick-ups and ignitors to make sense of the signal. There seems to be a lot of difference between the RD07 and RD07a on the ignition side.

Thanks for that.
I think that when I replace the carbs I'd go for the good-ol' "Neanderthal" version, hardly seems worthwhile to change the CDI as well (unless I am "lucky" enough to break that as well ).

[chronyx]

Originally Posted by Radio-active

Chronyx wrote

So does the Haynes manual say 'under no curcumstances mess with this' or 'mark position before removal'

When I changed the the TPS on my Fiesta it was just a bolt on/off part. As long as the throttle is fully closed you should be OK - I imagine it will only go on with the throttle like this anyway.