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Discussion Starter · #1 ·
Anyone ever mounted a TPS to a Mikuni BDST38 (SS900)?

I'm planning to install a Ignitech and since this unit is compatible with a TPS sensor I was wondering if such a sensor can be mounted.

I searched the internet but I can't find anyone who did this. I found some brackets to fit on a Keihin but none for Mikuni.
I did find a guy who did this on a MZ with a different type Mikuni but that's it...

Making any kind of bracket isn't the problem. I know some technical guys at work who can make me any bracket I should need. :grin2:
But that's it... :frown2:

The carbs have some moving parts (the 'ring' where the throttle cables are attached to is the obvious first choice) and there is the part circled in red in the attached picture. Anyone know what's behind this cap? I assume it's the end of the butterfly-valve rod. But I can't get the cap off and I'm afraid to ruin something if I use brute force. Anyone ever removed this cap?

So, any kind of information is welcome.
Did you ever mounted one?
Know any websites with useful info? Best sensors? 12v to 5v converters? Wiring? A thread on Ducati.ms concerning this issue?

Thanks all!!
 

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the old Yamaha TRX850 Euro-only Twin uses the same Mikuni BDST38 with a TPS....here is the part # of the TPS used...

4HM858851000 THROTTLE POSITION SENSOR ASSY

I found in a partsbook from a 1996 TRX850.
4HM-85885-10-00 Look at item #64 in this link to partsbook page from a Euro website

https://www.megazip.net/zapchasti-d...8/trx850-9688/4un1-774491/carburetor-13450981

A trip to a Yamaha dealer parts department would be your next move, I think. Wish I could be of further help, but TRX was never even sold in the US!
 

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On your very last point about 12 to 5 V

USB ports are 5 V so an auto (12V) to USB should work.
I don’t know if voltage stability would be an issue at minuscule dc current.
 

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Discussion Starter · #4 · (Edited)
the old Yamaha TRX850 Euro-only Twin uses the same Mikuni BDST38 with a TPS....here is the part # of the TPS used...

4HM858851000 THROTTLE POSITION SENSOR ASSY

I found in a partsbook from a 1996 TRX850.
4HM-85885-10-00 Look at item #64 in this link to partsbook page from a Euro website

https://www.megazip.net/zapchasti-d...8/trx850-9688/4un1-774491/carburetor-13450981

A trip to a Yamaha dealer parts department would be your next move, I think. Wish I could be of further help, but TRX was never even sold in the US!
Great tip!! Thanks!

I knew the TRX uses the same carb but I didn't knew it came with a TPS.
As far as the first photo's I've found it seems that the cap in the photo I attached needs to be removed. That's were the TPS is mounted on a TRX.
The TRX-version of the carb has some TPS-attachment points around that point which the Ducati-version has not. But I can make a bracket for that.

I just hope that the end of the butterfly rod is the same in a Yam and a Ducati. It would make the install of the TPS on the rod much easier.
I should probably check with a local Yamaha dealer, hoping he has more info/parts.

But first, I'll do some more research and your info is a great start!
Thanks again!!
 

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Discussion Starter · #5 ·
On your very last point about 12 to 5 V

USB ports are 5 V so an auto (12V) to USB should work.
I don’t know if voltage stability would be an issue at minuscule dc current.
Thanks for your reply Punch!

I saw an article about using a cigarette-lighter-plug to USB for that but it seemed to be a bit more difficult than just connecting some wires.
I don't know enough about electronics to understand all of the article but the phrase "Please note however, that this is not a cheap project to build for two reasons." in the article got me worried... :|

Electricity is not really my thing but I've found some "12V to 5V converter regulator" like this one on Amazon. €10 euro for a unit like that. Makes me wonder why anyone would try and make one following the description in the article on easyeda.com... I'm probably missing something...
For the 12V to 5V I'll check with some guys at work, there are a few geniuses there on electro-mechanics. :nerd:

About the voltage stability: I suppose a TPS needs a stable 5V input. If think the output from a TPS at let's say half open throttle will be different with an input of 5V then it will be with an input of 5,5V.
So maybe the stability is an important issue when it comes to changing the bike's 12V to 5V.

More research ahead, but hey, doing the research for a project is half of the fun, isn't it? :laugh:
 

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I have designed up a retro fit bracket that is away been machined at the moment to adapt the TPS to this carb as per the TRX. Is a couple of weeks away and I am going to fit it to a bike I will be picking up in a couple of weeks.
 

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Thinking again.

Wouldn't the Ignitech unit have a 5 V supply for the TPS?
I.e. 5, 0 and TP voltage.
 

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ignitech does have 5v output. i used one years ago when i ran a map sensor. the v88 ignitech has a dedicated map input, which can be used to mimic a tps. only problem with map is that it's not an obvious scale like tps is. 0 throttle on a tps is 0, with the map 0 throttle is the most vacuum generated at the given rpm, so it varies somewhat non linear.

you really need to map vacuum and relate it to riding - cruise, accel, etc, to get an idea of what it all means.

previous ignitech you could use the map to mimic tps, but the resolution was at the wrong end of the table so to speak. you'd be cruising at what it thought was 80% throttle or so.

also, you need a flywheel with an extended lump, or use the efi timing gear (which requires a "different" unit). otherwise the most advance you can have is the end of the lump. you can push the pick up holder all the way clockwise, but that only earns you about 4 degrees ime. i have an old flywheel with a lump welded on that gives up to 60 degrees from memory. i put some oem kokusan units on it once and it wouldn't rev at all.
 

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Thinking again.

Wouldn't the Ignitech unit have a 5 V supply for the TPS?
I.e. 5, 0 and TP voltage.
Indeed, I have Ignitech with Keihin carbs and have fitted a (Keihin) TPS that simply plugs into the Ignitech, no other power source required.

It certainly made the bike run smoother, before the TPS the throttle response was very on/off - now it still pulls like a train but a controllable one...
 

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Discussion Starter · #10 ·
I have designed up a retro fit bracket that is away been machined at the moment to adapt the TPS to this carb as per the TRX. Is a couple of weeks away and I am going to fit it to a bike I will be picking up in a couple of weeks.
Great!! I'm glad I'm not the only one playing with the idea of fitting a TPS to the Mikuni's.

I assume you removed the cap that hides the end of the butterfly rod. Can you fit a TRX-TPS to that rod or do you have to machine/buy some kind of connector/rod/axle?

Hopefully you get the TPS fitted with the bracket you are waiting for.
Looking forward to your findings!

Thanks for the reply!!
 

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Discussion Starter · #11 ·
DukeDesmo, Punch and belter: you're right!
The ingnitech has all the connections (5V, ground and TPS-input)! This is great news. It means I don't have to worry about looking for and fitting a 12V to 5V converter.

I never looked at the wiring diagram of an Ignitech unit before because wiring diagrams are mostly Chinese to me, but I checked and all these connectors are there.

So, the wiring-problem is already solved.
Moving on now to fitting a TPS to the carb.
Most likely the TRX-sensor will be the easiest one since it's made for this specific carb? Or does anyone know a cheaper or easier-to-fit alternative?

Btw: thanks all for the replies! This forum has been more helpful to me than all the rest of the internet was!
So glad I registered here!
 

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Discussion Starter · #12 ·
Indeed, I have Ignitech with Keihin carbs and have fitted a (Keihin) TPS that simply plugs into the Ignitech, no other power source required.

It certainly made the bike run smoother, before the TPS the throttle response was very on/off - now it still pulls like a train but a controllable one...
That's exactly what I'm looking for. And the fun of completing a project like this!

And yes; I know some guys will think like: "Go buy some Keihins. Better performance and TPS-ready! Stop messing with the Mikuni's!!"

But I got my own reasons not to go for Keihins.
First of all: the price. A set of new Keihins costs me half of what I payed for the bike.
Second: the Belgian climate makes me doubt about non-choke carbs.
Third: I'm happy with the power produced by the bike with the Mikunis. I'm more looking for a smoother ride, not extra horsepower.
 
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