Inaccurate electronic tacho?

[XTlegend]

I bought a really nice GSX750ES a while ago and apart from an annoying oil leak its great! However I soon realised that it would red line (not that I did!) at a lower speed than it should. So I thought that a previous owner must have changed the gearing.

Sure enough, on counting the teeth on the sprockets, the rear is standard but the engine sprocket has 1 tooth MORE than standard! The oppostite of what I expected. So, I can only think that the tacho is reading high. Is this possible?? As indicated it would red line in top at about 90MPH so its quite a bit out.

[posplayr]

I bought a really nice GSX750ES a while ago and apart from an annoying oil leak its great! However I soon realised that it would red line (not that I did!) at a lower speed than it should. So I thought that a previous owner must have changed the gearing.

Sure enough, on counting the teeth on the sprockets, the rear is standard but the engine sprocket has 1 tooth MORE than standard! The oppostite of what I expected. So, I can only think that the tacho is reading high. Is this possible?? As indicated it would red line in top at about 90MPH so its quite a bit out.

electronic tacho comes off the coils and in unaffected by gearing.

Speedo comes off the front wheel and is also unaffected by gearing.

gearing does affect acceleration and top speed

[Dogma]

So, the problem is something like dead or dying components on the tach's circuit board?

[XTlegend]

electronic tacho comes off the coils and in unaffected by gearing.

Speedo comes off the front wheel and is also unaffected by gearing.

gearing does affect acceleration and top speed

?? I know all that. The relationship between tacho reading and speed is affected by gearing and its wrong. I repeat - with the current gearing it should redline in top at maybe 130mph. Its doing it at just over 90. I suppose I should use a strobe on the crank to check the tacho calibration.

[salty_monk]

Those early electronic Tach's are renowned for failing... I would suspect it's faulty.

You probably need to re-solder all the traces on the board & maybe replace some of the components which might or might not help....

Even with one tooth up (by the way this is the correct way for what you're seeing, smaller front sprocket, larger rear = more revs for the same speed) you would see something like 1-2% difference

[XTlegend]

Those early electronic Tach's are renowned for failing... I would suspect it's faulty.

You probably need to re-solder all the traces on the board & maybe replace some of the components which might or might not help....

Even with one tooth up (by the way this is the correct way for what you're seeing, smaller front sprocket, larger rear = more revs for the same speed) you would see something like 1-2% difference

1 tooth up on a 14 tooth sprocket is a 1/14 * 100 % difference= 7%?

1 tooth up on gearbox sprocket will lower RPM for any given speed right?

[hampshirehog]

1 tooth up on a 14 tooth sprocket is a 1/14 * 100 % difference= 7%?

1 tooth up on gearbox sprocket will lower RPM for any given speed right?

The percentage difference in speedo reading will depend on the different ratios between the front and back sprockets. Although your maths is wrong you're right that a bigger front sprocket will lower the rpm for a given speed. To work out the % speed difference divide the no. of teeth on the front sprocket into the no. on the rear - do the sum for both fronts and you'll see the % difference.

As Dan says, more than likely the gremlins have got in to the circuit board or connections. If you clean it all up etc and still can't get an improvement I think I've got a unit (untested) you can have.

[posplayr]

?? I know all that. The relationship between tacho reading and speed is affected by gearing and its wrong. I repeat - with the current gearing it should redline in top at maybe 130mph. Its doing it at just over 90. I suppose I should use a strobe on the crank to check the tacho calibration.

OK I get it, however there is no way the tach accuracy is affected by the gearing on your chain which is the answer to what I believe is the "colonial" interpretation of your question.

[salty_monk]

Yes... I read your post the wrong way. 1 tooth up on the front will lower RPM by about 7% for any given road speed.

As Pos says, none of this will affect the tach directly.

[posplayr]

Yes... I read your post the wrong way. 1 tooth up on the front will lower RPM by about 7% for any given road speed.

As Pos says, none of this will affect the tach directly.

Lets see, if my GS1100 stock tops out at 130 mph at 7.5K RPM, and then I drop a 1230 into it and now it will go 155 at 9000 RPM, does that mean my electronic tach is off?

[SqDancerLynn1]

If you want to try and fix it ? I would replace the capacitors on the circuit board

[XTlegend]

OK I get it, however there is no way the tach accuracy is affected by the gearing on your chain which is the answer to what I believe is the "colonial" interpretation of your question.

Oh, well I dont understand what I have written could have given that impression. If you hadnt messed around with all that tea in Boston then maybe there wouldnt be an interpretation issue ;-)

Anyway - my tacho is not right, that at least is clear. I'll live with it.

Cheers.

[posplayr]

Anyway - my tacho is not right, that at least is clear. I'll live with it.

Cheers.

Thats good because if you were to replace the tacho with a "good" one, you would be disappointed as you would probably get the same result.

[tkent02]

Rocket science again. Ride the bike, don't look at the tachometer. Accelerate in second or third gear until the torque peaks, the engine will be screaming, power increasing smoothly with RPM, then it will feel like the power and acceleration is decreasing. Speed will still be picking up, only slower than before. That is the torque peak, and it will be about 1000 or 2000 RPM below red line if the engine is stock. Now look at the tach, is it reading something like 14,000 or so? If it is that's an error. Is the needle just jumping all over the place? Also an error. Like the other guys said, resoldering the connections on the circuit board will probably fix it.

[posplayr]

Rocket science again. Ride the bike, don't look at the tachometer. Accelerate in second or third gear until the torque peaks, the engine will be screaming, power increasing smoothly with RPM, then it will feel like the power and acceleration is decreasing. Speed will still be picking up, only slower than before. That is the torque peak, and it will be about 1000 or 2000 RPM below red line if the engine is stock. Now look at the tach, is it reading something like 14,000 or so? If it is that's an error. Is the needle just jumping all over the place? Also an error. Like the other guys said, resoldering the connections on the circuit board will probably fix it.

I think if he does a 530 conversion it will help his tach.