What happens to the timing if you advance the TPS?

So does anybody know? I want to advance the timing a couple of degrees but not necessarliy throughout the entire range. I run 100 octane unleaded so detonation isnt a worry.


Here’s what I know.

TPS positions are used to make computations based on a pre set map within the control unit.

On this bike, the CDI is the control unit, and within it is most likely some type of number crunching chip fed by formulas burned into an EPROM with which Yamaha has an algorhythm for what the ignition curve is given throttle application.

The TPS is essentially a potentiometer in which a current is controlled and delivered to the CDI of which dictates position.

Of course when you rotate the TPS clockwise, you're tricking the computer (or shifting your position on the map) causing the map to calculate a more open throttle position, (ie, you're at 1/2 and it thinks your at 3/4).

Now with all that aside, unless someone has managed to download the information in the EPROM, we really don't know what you'll be getting from various changes.


However, during my road race days, (on a different bike) I noted TPS voltage at closed and open positions, then correlated these to performance.

This however, shifted both fuel (EFI) and timing, causing the bike to burn cooler, and produce more power and emissions.

I sure hope someone has a more applicable answer.

If not, try it out and tell us what you find.


Say What? Profesional skateboarder?

If you had the race tuners kit from Vortex, you could program your own map with regards to the TPS settings... and see if they did make a difference...



Good description. Minor point, instead of programming a processor with the algorithms, they just burn a ROM chip with the map. There isn't any fancy electronics, just a ROM lookup table. Think of it as a spreadsheet, rows are RPM, columns are TPS, value in cells are the degrees to advance spark. On the 250F forum, look under 'CDI 101' post.

Good luck,


Ya What Dave Said I agree

Uh What exactly did the Professor say


Ya Skipper

All I know in stock from is this

1st gear, 2nd gear 3rd gear Break hard turn left, Hold on real tight, 3rd gear wfo 4th down shift break turn right, keep turning keeeeeepppppp turning oh gad a ktm what to do AHHH BERM SHOT 3rd gear WFO over the ktm

[ July 16, 2002: Message edited by: E.G.O.**** ]


We agree.

I'm just calling the ROM an EPROM, and I'm getting a little too carried away with the issue that there has to be something pulling numbers.

Aka, some form of higher processing power that’s reading the info off the ROM. But please correct me if it's simpler than that.

And I don't know of anyway of getting the info from the ROM without some serious hacking, something I'm clearly not capable of.

I'm sure someone out there has means for a programmable module.


If there is a plug in, one can connect a logic analyzer and pull the data. Once that is done you get very close to the edge of reverse engineering and domain.

I am sure Yamaha would be very perturbed if that is done and published with out written consent.

There is a guy on the cannoondale site that has been hacking his computer. Dont know how far he has gotten, but it is a concept that may work.

If there is a hook up one can hack anything

plus, I would assume Yamaha had the smarts to place a Non Writable rom / eprom in the gizzards of the beast, so one would also have to redesign for a read write rom/eprom


[ July 16, 2002: Message edited by: E.G.O.**** ]

Screw it, Im gonna do it. I can alway put it back. The only purpose of the the TPS is to prevent detonation at lower RPM an larger throttle settings, running pump gas.

Here is a better question that I just thought of. If the TPS is just a pot, Im wondering what the computer does when its open, or completely closed?


I guess I should have mentioned a few more things.

Unless a bike comes from the factory tuned for something other than ultimate performance (say emissions or ridibility for the masses), there's not much, if any, benefit in making this modification.

Ignition timing map changes are usually required when something with the machine is modified. The most influential are cam profiles and timing, but higher compression pistons and certain race fuels may warrant some changes as well.

Be cautious because shifts in timing can heat an engine up and may cause damage.

Lastly, what works best with the bike running, may result in a bike that won't start. Since, I'll have to assume there is a "consideration" in the map for a dead engine.

I guess I should have added this disclaimer before I said go out and give it a try.

Sorry about that.


Its OK DaveJ, Im a big boy, and I understand what Im doing. I just read on another post, on Dirtrider.net, a guy in the UK was doing some trouble shooting and disconnected the TPS during dyno testing. The only thing he found was the touque numbers were off just slightly at the bottom of the range. Im betting the differece came because of detonation on pump gas. It made no difference at all on top end performance. Which makes me suspect Im right in my theroy. Its easy enough to mark, change and replace the TPS, so Im going to try it and see what happens. If it runs hotter, Ill know its retarded, but IM going to do this with the engine runnging so I'll know what it does in the RPM scale I want to adjust anyway. This should be fun.


I assume you'll just disconnect it at the first connector. If you actually take it off the carb, let me know where you find the torx with the dimple in the middle.




Lisle Tools makes those.

Most automotive parts stores either carry them, or can get them.


I used to own a Suzuki TL1000R. This is a V-Twin sport bike. It had a tps. You could bridge the deal switch, which would put the digital clocks into dealer mod. This would give you a kind of graphical representation that could be followed to adjust the TPS. Most TL owner who checked their TPS found that it wasn't set correctly from the factory. This adjustment helped throttle resonse greatly on the Fuel Injected beast. I'm not sure how this would affect carburated motors.

Thing is, if the norm seemed that these weren't set correctly from the factory, then there is a good chance that our TPS were set correctly either.


i read earlier that the only reason for adjusting the TPS was for race fuel or a high comp piston...

well next year im going to be running a 13.5:1 piston, VP fuel, thunder alley pipe and silencer, a milled head with ported and polished intake and maybe ported exhaust.

will i REALLY need to adjust the TPS???

[ July 17, 2002: Message edited by: thumper4life ]


First of all, I don't think moving the TPS on this bike is going to do much at all. We'll let Shawn have the final word on that.

Also keep in mind that there's a difference in "changing the map" and "changing the timing", (crank position).

The only thing you may need to do, if anything, is a change in timing - unless you find the bike is impossible to start, or unless you change out your cams.


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