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Old 16-10-11, 12:20 AM   #1
saintnick
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Default Throttle Position Sensor

On the carbed mk1s, does removal of TPS help smooth out low down fuelling? Someone mentioned this to me, I have no idea whether or not its complete bollox. I associate the TPS with FI - I know that the throttle sensor has played a part in aggrevating fuelling on some KTMs, for example, and the SV is a bit snatchy at low revs for a carbed bike. The jetting itself is pretty good, we had her on a mate's dyno and apart from running a tad lean coming off idle, fuelling was pretty much spot on (68 bhp at wheel). Which made me wonder about the TPS.
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Old 16-10-11, 02:54 PM   #2
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Default Re: Throttle Position Sensor

Throttle position is a good indicator of engine load, as such the TPS is effectively a load sensor, it's connected to the ignition system and the ECU will alter timing slightly to account for load.

Checking its setting is worthwhile if you think throttle transitions are not as smooth as they should be, but in my experience such problems are most commonly carburation.
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Old 16-10-11, 06:48 PM   #3
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Default Re: Throttle Position Sensor

this was interesting....

Because of the AF mix on the dyno print out, I'm fairly sure that it is a TPS issue rather than the carbs, we shall see.
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Old 16-10-11, 08:23 PM   #4
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Default Re: Throttle Position Sensor

Do you have setup figures for the sensor?
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Old 17-10-11, 01:14 AM   #5
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Default Re: Throttle Position Sensor

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Originally Posted by Sid Squid View Post
Do you have setup figures for the sensor?
Nope, only figures I have are from the dyno, runs were done with TPS in situ which as far as I know is in standard trim.

Looking at that thread, I reckon that disconnecting a TPS on a carbed bike would simply leave the ignition at max advance and thus have no negative implications. FI bikes may respond differently to bypassing the sensor since FI and a TPS work hand in hand (in theory). That's why I was surprised to find that carbed SVs employed a TPS in the first place: not many carbed bikes did.

It's an interesting one because some carbed SVs are a little unusual in that they can be jumpy when bringing power in, say exiting a bend, and that is something I associate more with FI. Since the fuelling seems to be OK, its probably worth while disconnecting and seeing what happens. Unfortunately the pix in the thread relate to the FI model which presumably is different in the connector department, if anyone has bypassed on a carbed bike, I'd be interested in where you unplugged the thing.
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Old 17-10-11, 07:14 AM   #6
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Default Re: Throttle Position Sensor

Quote:
Originally Posted by saintnick View Post
Looking at that thread, I reckon that disconnecting a TPS on a carbed bike would simply leave the ignition at max advance and thus have no negative implications.
Could be - I've never measured that, but as for no negative implications, I disagree, as said it's essentially a load sensor - there's no question it will run without the sensor/sensor set wrong, but it's definately better with it set correctly, it's not the difference of pulling a plug lead off, but there is a difference.
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FI bikes may respond differently to bypassing the sensor since FI and a TPS work hand in hand (in theory).
FI system work very differently - but the TPS is still a load sensor in the same way - of course it also does other things too.
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That's why I was surprised to find that carbed SVs employed a TPS in the first place: not many carbed bikes did.
Many late carb bikes of my knowledge do, mostly from the mid 90s forward.
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Originally Posted by saintnick View Post
It's an interesting one because some carbed SVs are a little unusual in that they can be jumpy when bringing power in, say exiting a bend
This is why - not withstanding your obvious careful attention to the carburation - I'm thinking that something else is possibly the problem, SVs are neither notably smooth or notably rough, by what measure do you feel that the bike is not right? I appreciate this is difficult to express in a forum post.
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If anyone has bypassed on a carbed bike, I'd be interested in where you unplugged the thing.
If you wished it disconnected then at the sensor is as good as anywhere else.

TPS setup, (from Suzuki's own workshop manual):

Looking at the end of the connector you will see it is roughly heart shaped, there are three pins, two next to each other at the wide end, and one at the narrow end, call the the single pin at the narrow end 'A' and the upper left hand one 'B' and the right hand one 'C'

Throttle shut - 3.5 - 6.5 K-ohms between 'A' and 'B'
Throttle open - Resistance between pins 'A' and 'C' should be 78% of the resistance of the resistance between 'A' and 'B'.
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Old 17-10-11, 02:42 PM   #7
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Default Re: Throttle Position Sensor

Cheers for that, especially the last bit, I reckon the only solution is to sse what happens. The old SV - which was an ex minitwins JHS bike - had no throttle position sensor and from memory is what a lot smoother getting on the throttle low down. That's how best to desscribe what I'm feeling, getting on the gas from a closed throttle the bike reminds of a 990 Superduke.... or in fact lots of FI KTMS... all or nothing stylee.

It does seem that the thread on this subject had people reporting similar findings, and remedied by ditching (or by passing) the tps.
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Old 17-10-11, 03:07 PM   #8
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Default Re: Throttle Position Sensor

As said, the TPS on the carbed engine is a part load ignition advance device, just like the vacuum advance capsule on old distributors. My SK1 has it.

The engine needs more ign adv at part load to achieve the best combustion (economy). It's well worth setting it up correctly. There is no advantage in deleting it, it's lose/lose, it won't run as well at light load and will give worse economy.

As said, the most likely candidate for poor off idle running is carb adjustment. Balancing the carbs for vacuum is easy, adjusting the idle mixture on a running SV engine is more tricky due to where the adjuster screws are situated. They really need to be set while the engine is running to allow for variations in manufacture (jet sizes etc)

There are special angled-drive tools like this example , but they tend to be expensive.

I have managed it with a thin thermal glove and a short screwdriver, I can just get my hand through the frame gap but it's tricky and you need to know where the adjusters are by feel because you're working blind. People often find the screws are corroded and won't move, so the carbs need to come off for cleaning anyway.

US bikes had anti-tamper plugs fitted to the screws.


Also double check the choke cables and plungers are free, stuck plungers will ruin light load running when warm.
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Old 17-10-11, 03:27 PM   #9
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Default Re: Throttle Position Sensor

Interesting.

Are you sure the TPS wasn't emissions related rather than economy related?

It could be that coming of idle it needs a tweak, one reason why I thought the problem was TPS related was because members reported this problem and suggested TPS removal as remedy in that thread.

Unfortunately dyno runs are buch better at showing you what's happening when you're on the throttle where everything looked good, so the dyno charts don't really help. Ta to both of you for the info.
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Old 17-10-11, 08:05 PM   #10
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Default Re: Throttle Position Sensor

Done some research. Yup, late 90s carbed bikes did use them like you suspected, and yup - they are strictly emissions related. What they do is retard the ignition at part throttle low down the range , because that is where the emissions legislation was severe.

My other bike (carbed) had a TPS, which was disconnected by the tuner. (The cdi reverts to default, ie an open throttle map = optimum advance throughout.) Since I ended up with 130 brake at the wheel as opposed to 90 I don't think the bike misses it, although obviously there are other mods

With FI, the TPS can do more sophisticated stuff, but the TPS on the SV just retards the ignition until revs are out of the emission zone - if its anything like the Kwak K-Trick system. This may be wrong, but looking at bikes of a similar vintage, that does seem to be the story. Proof of pudding will be in eating, but I am bearing in mind that there may be other issues.
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