Calling all 625SMC owners

[Wobbly]

So can someone with a 625SMC do a quick test ... warm the bike up and go for a quick squirt around the block with some stop/start stuff and a couple of wheelie opportunities. Then come back and unplug your TPS and repeat and see if there is any difference...

[Muzzard]

Whats going on over there Mr Milne.
You fiddling again?

[Wobbly]

No, just wanting to either give people a pleasant surprise or dispell a growing interweb myth ;)

[ZuluFoot]

So can someone with a 625SMC do a quick test ... warm the bike up and go for a quick squirt around the block with some stop/start stuff and a couple of wheelie opportunities. Then come back and unplug your TPS and repeat and see if there is any difference...

TPS?

[Muzzard]

Throttle Positioning Sensor Murray.
Fitted to the side of the FCR's mostly...
Detects the throttle opening usually coupled to a gearbox indicator and supposed to match ignition curve from CDI map to correct gear and throttle opening for optimum performance.
In laymans terms anyway...

[kroosn]

from what ive heard its does the same as removing the power control solenoid, so instead of the solinoid not opening because its not there it just doesnt get the signal from the tps that the bike is full throttle. i can give it a go on the 640 tomorrow but it has a different carby to the 625.

Kroosn

[Wobbly]

The reason for asking is that there is a bit of talk on SMJ at the moment that the TPS only seeks to retard ignition < 6000rpm, presumably in the interests of emissions and dealing with very poor grade fuel. Disconnecting it on the husky seems to fix some intermittent surging/missing problems and 625 guys are claiming that it also fixes similar issues with the ktm, but was interested to hear from people here whether they concurred or not...!

[Muzzard]

I will try it tomorrow on the WRF and see as it also has those dreaded surging problems and requiring adjustment on the air screw regularly to get the best 'in traffic' ride.
Advancing the CDI (YZ Curve) makes it better and I wondered if the TPS was the culprit here too.

[Wobbly]

Quite possibly - there was one guy saying his yz450f ran much better without it connected as well. Its funny with the husky as it cleared up the surging problems but seemed to add a much greater variation in idle speed.

About time the world went efi and be damned :lol2:

[Muzzard]

If it makes the difference then I will advance the exhaust cam again and set the CDI curve at YZ spec to improve the bottom end.
When I did this last time it still ran quite hard in the upper RPM range but the bottom and mid range were a heap stronger.
If I could get rid of the surging it would be less stressful on the gearbox in the traffic and it might be a bit slow riding friendlier than it is now...

[Wobbly]

Just modulate the clutch in the same rhythm as the surging :lol2:

[Muzzard]

I'd end up with arm pump from inner Melbourne then .. :lol:

[Muzzard]

My Yamaha seems to have a slight difference when disconnecting the TPS.
The surging is less noticeable and the throttle more precise.
Engine wise though was doughy down low and didnt want to pull.
Reconnect the TPS surging reappears and doughiness was gone.
Maybe just jetting without the TPS connected and the YZ map would be the trick.

[tambi]

I have no idea what guys are on about but maybe keep an eye on this thread Muzz.....
YZ turbo switch?? - Supermoto Junkie

[Shamus70]

I'll have alook on mine this arvo Neil and will get back to you ASAP with results.

I'll look at it in a sec in the manual,

where is it and how do I disconnect it? (Just asking cause I'm lazy :D )

[Shamus70]

http://ktmtalk.com/index.php?showtopic=204880

[Wobbly]

I'll have alook on mine this arvo Neil and will get back to you ASAP with results.

I'll look at it in a sec in the manual,

where is it and how do I disconnect it? (Just asking cause I'm lazy :D )

Just an electrical plug attached to the left/top side of the carb...

[Shamus70]

Done, I like it, nothing astounding, but definitely more responsive down low, and doesn't mind decelerating on the throttle as much either.

Definitlely doesn't hurt the performance at all. I'll leave it for a few days and then swap back again, and report back with a comparison.

Has anyone asked 625SMC if he's tried this yet also?

I'd recommend at least trying it anyway.

[kroosn]

theres alot of talk about the 625 but has anyone heard of it being done on the 640 different carb and all and its also a different looking TPS.

Kroosn

[dicky]

If the TPS is only controlling the ignition curve then simply disconnecting the sensor could do two things.
1. Permanently map the ignition to the Low Throttle curve (Bad, to be avoided)
2. Permanently map the ignition to the High Throttle curve (Better, depending on where you ride)

To check this out a bit more scientificamaly, get a multimeter.
Disconnect the TPS and measure the resistance across the terminals on the carby connector. Do this with the throttle fully closed and again with it fully open. There should be a difference, if not, turn on the ignition and try again.

Let me know the results, alternatively, bring your bike to my joint and I'll figure it out once and for all.

The 625SMC has a flat slide carby, so the bypass solenoid as used on the CV carby on the 640LC4 can't be used.

dicky.

[Shamus70]

From the SMJ forum:

"I very recently upgraded the carb on my '01 520 from the 39mm bore WITH TPS to a 41mm bore WITHOUT TPS. So, I researched the TPS.

The early EXC, MXC, and even SX bikes used the Mikuni FCR carb with TPS. The purpose of the TPS is to increase tractabilty of the bike at low RPM to keep the wheel from breaking loose. To do this the TPS sends an electrical signal to the CDI (the black box). When the throttle is low, the CDI simply retards the ignition, effectly lowering power, thus making the bike grip the ground better.

I have a 2000 400 SX and it has the TPS system (CDI and carb). So early on KTM even used the TPS on the motocross bikes.

In '03 KTM realized (I reckon) that this was not necessarily an advantage for all motorcycles. Mikuni removed the TPS from the new generation FCR carb that KTM used on the SX. This carb is refered to by Mikuni as the MX FCR carb. Figuring that in motocross you want all the power you can get, all the time, and low RPM traction wasn't much of an issue. KTM just didn't change the CDI on those bikes.

Newer SX (motocross) bikes have the TPS removed from both the carb and the CDI.

Remember, KTM doesn't design the carb, Mikuni does. KTM chooses which carb to use on which bike. Maybe KTM thought retarding the ignition and creating better low RPM traction would have some advantage on the LC4? Maybe they wanted better traction in the rain so fewer people would crash and sue them. Dunno!

Since I convereted my MXC to supermoto, I'm not worried about the rear wheel braking traction on pavement. I want all the nut I can get at all RPMs, so I didn't really want the TPS when I went to the larger carb (FYI, I am also using the 525 head which has an increased inlet port from 39mm to 41mm to make use of that larger carb; that is the only real "difference" from the old '520' to the '525', thus I often refer to my supermoto as a 525 now).

I love the MX FCR 41mm carb with NO TPS on my supermoto. I don't miss the TPS at all. Honestly, I noticed almost the same improvements on my MXC when I changed carbs and dropped the TPS. Runs smoother at all RPM's, even sounds better. Is it the carb, or the lack of TPS? I'll never know since they both came together, I just know the front wheel loves to be off the ground..."

[dicky]

Who in this forum has a Mikuni flat slide carby on their KTM?

While I know that the manufacturer makes little difference in theory of operation, the TPS circuit may still be different.

Also, like the SMJ author states, he went up 2mm in carby throat diameter so he doesn't know what made the difference, just that it's different.

dicky
<Possibly more confusing than enlightening>

[kroosn]

makes sense to me, ill give it ago when i get a chance on the 640 to see if it makes a difference with the CV carb. any more power is always a benefit.

Kroosn

[Wobbly]

The theory goes that the TPS is retarding the ignition advance below 6000rpm, presumably for emissions reasons, and that disconnecting it will move it to the full advance map.

The scientific test is obviously to run it with and without it connected and see which wheelies more easily :lol2:

[Shamus70]

Okay had it disconnected for a couple of days, definitely different.

I think it pulls a bit harder down low, but not as much in the midrange??

Was causing some popping on deceleration as well!!

I've reconnected it now and will get back to you after a couple more days hard riding, with my conclusions, and if I get the chance i might do the quick comparison Neil suggested round the same route with and without it connected.

Had a chat to the mechanic i see and he seems to think it'll change the ignition timing through the whole rev range, he suggested it probably wasn't a good idea, regarding performance anyway and to leave it connected.

CYA

[SMC690]

I have only just found this thread due to my recent forum inactivity but unfortunately my bike is off the road now due to base gasket issues.
I am hopefully getting my bike to a dealer soon to fix the warranty problem and the dealer I have in mind also has a dyno.
I will try a dyno run with the TPS connected v's the TPS disconnected and post the graphs if he can fit me in sooner that my delivering dealer.

Stay tuned.... Watch this space.

The real dyno v's the seat of the pants dyno should either confirm or dispell this rumour once and for all.

For the record, the whole time I have had my bike I have had the TPS connected, I never thought of disconnecting it as I was under the impression the 640SM with the CV had the retardation due to the SAS and the Mikuni CV carb. :)

Cheers,
Juz.

[SMC690]

I just attended the thread mentioned on SMJ and I would be surprised if over the 22 pages those mofo's had the collective IQ of that claimed of Martin Bryant.

FFS.

And Howard follows Bush like a blind sheep, got help the lot of us.

No wonder I stopped reading their shit and no, I have not had my tablets today. ;)

[Shamus70]

Base gasket... I know what that's like. :x
All fixed and metal now. :)

[Prowl]

Just going through some old threads and came across this, gave it a crack as it it took a whole minute to find the TPS cable and disconnect it.

Thoughts so far? I can definately feel a difference :D not saying some monumental HP gain but more of a seat of the pants feel. Definately more snappy low in the revs and actually feels like it pulls harder. Feels smoother too no more surge and I've noticed that going around corners especially round abouts is easier in 2nd where previously the low revs would cause a liltle stutter, there's less of that now. Wonder why :-k

Have only just done this last night so gonna see how it goes for a week or so, but so far so good.

If you have an LC4 I reckon give it a crack, it only takes a minute, you either like it or you don't.