Red line = very sharp throttle response, but why?

[Simon Davey]

This is not a post to tell everyone that I had a fast spurt today, we  all do that now and again, but I do have a genuine question.....

Having spent 75% of the time I've owned my bike, trying to get it running nicely, it now does so.

Luckily, it was sorted before my confidence building trip to Germany, where I learned to "ride" it.

I've had the odd occasion on a straight road where I've taken it to the 10.5k red line, and at almost 20 years old, it does this with an incredible amount force, I have no doubt that a modern bike would be faster and perform with even more G-force.

 

Today I noticed something different, I didn't just red line it, I had a long straight road with no traffic and I took it to the line in 2,3 and 4, it felt ballistic, but of course, needs must and I had to consider the speed.

 

To the point (at last)....

 

Why did it then become seriously snappy and very sharp off the throttle? What was it that mechanically/electronically changed that the next four roundabouts with nice straight bits in-between became so lively without having to barely twist the throttle? Considering it's not EFI but carburetted.

Although I was keeping the rev's higher, it wasn't that, I've done that before, but not gear after gear.

I'm not complaining  , it was nothing short of phenomenal (for me) but I'm curious.

 

Is it mapping?

Does it learn (my car does) to respond according to how it's ridden/driven?

I'm 100% certain it wasn't imagination on my part.

Once I'd then ridden through a village 30Mph, it was back to being "not so savage".

 

I wonder if anyone would actually know.

Edited November 10, 2024 by Simon Davey

[Tinkicker]

Perhaps you blew out some rust that was partially clogging the exhaust?  Or gobbled down that bit of rag you forgot to remove from the inlet port....

[Simon Davey]

I'm proper confused, at least I have an excuse to try it again. 

Might try to get the GoPro involved, it's quite possible that I'm just not used to giving it such a caning, despite riding 3k, including belting around the German hills. 

 

Naaaah, something changes, I'm sure of it. 

Maybe it's the heated carb's, as the engine gets that bit hotter, it also makes the carb's hotter. 

Edited November 10, 2024 by Simon Davey

[Davidtav]

I don’t think you have imagined it. But I wonder if this is related to our brains and perception of time?  I read a very interesting book by Jean Paul Zogby … The Power of Time Perception. A fascinating read.  The essence of it is that our perception of time is related to our brains and how quickly they are working. Our eyes record information in chunks. This is sent to our brains where it is stitched together and seems seamless. When we are young our brains are efficient and stitch together more chunks of information. So time appears slower when we are younger.  The same effect happens if we are involved in an accident.  And I have experienced this.  Our brains start to work very quickly. And the result is that time seems to slow down.  This is such an interesting phenomenon. For example top sportsman use this to their advantage. Without realising it probably.  Top tennis players can return shots that look impossible because they have trained their brains to work faster and in doing so make everything seem to happen in slow motion to them.

 

So my thoughts are that by riding your bike hard your brain was working more quickly than normal.  And somehow this state persisted for a few roundabouts and altered your perception of speed and time in some way?

[Mississippi Bullfrog]

I think you will find that is called "The Italian Tune Up".

 

Old school mechanics would often get a car in that wasn't running very well, they would take it out and thrash the living daylights out of it, and the customer was very happy to have their car back running so much better.

[bonio]

1 hour ago, Simon Davey said:

I'm proper confused, at least I have an excuse to try it again. 

Perfect outcome. 

I like the hot carb theory. But I kind of suspect you've blown some grot out of something or eased something up and the thing is now working more like it should.

[Simon Davey]

@Davidtav

That's very, very interesting. 

I'm so much more alert and switched on in general when riding my bike, throw in some 120 adrenaline and that theory becomes a very realistic theory. 

Doesn't explain the very sensitive throttle though. 

Edited November 10, 2024 by Simon Davey

[Simon Davey]

20 minutes ago, bonio said:

Perfect outcome. 

I like the hot carb theory. But I kind of suspect you've blown some grot out of something or eased something up and the thing is now working more like it should.

 

My mechanic was explaining that I had heated carb's, and that they connected to the cooling system. I can't help questioning this. However, he's done a superb job of rebuilding and balancing them. 

Edited November 10, 2024 by Simon Davey

[Tinkicker]

Bingo.  You have heated carbs.  That means your model of bike is prone to carburetor icing.  Carb icing generally occurs at low throttle openings in moisture laden air.  It can occur up to 25C.

 

You caned it and the ice broke free from the carb bodies.

 

Edited November 10, 2024 by Tinkicker

[Simon Davey]

5 minutes ago, Tinkicker said:

Bingo.  You have heated carbs.  That means your model of bike is prone to carburetor icing.  Carb icing generally occurs at low throttle openings in moisture laden air.  It can occur up to 25C.

 

You caned it and the ice broke free from the carb bodies.

Thanks matey. 

The problem is, I really enjoyed it

[Tinkicker]

You need to ensure that heat is actually reaching the carbs and that the pipes from the coolling system are not blocked ( or someone disconnected them in the misguided search for more power).

 

Carb icing is very well known to piston engine aircraft pilots and many smaller aircraft have a control fitted that floods the carb with hot air from around the exhaust when actuated.

 

Edited November 10, 2024 by Tinkicker

[Simon Davey]

Ironically, when it's too cold to ride, I'm stripping off the fairings to replace the main bracket, I'll remove the tank and airbox and have a look. 

My temp gauge barely rises, maybe there is a blockage. I've replaced the thermostat. 

[Mississippi Bullfrog]

It's not unusual for bike temp gauges to read low in normal riding. I've had carb icing issues but normally it's more a case of very poor running rather just a drop in performance.  

 

I suspect that you'll find the improved performance will be more consistent than just when the carbs get hot. Don't be afraid the wring the neck out of bike engines. They are designed for it. Just ride for a couple of miles before going full loco to ensure everything is warmed up a lubricated properly.  

[RideWithStyles]

Carb icing is really when it’s really cold and more so at start up, unless your high up in the mountains in winter. 

 

for the answer of why it was really snappy…it was hotten up really well an works best at the upper end.
Old bikes like carbs and the engines do a really good job but it’s a compromise! They are designed to work best at the upper end and bikes have a lot higher revs, but less crank/flywheel drag than a car. so more drag and just doing it once in one gear doesn’t do much or switch much on.
So yes depending on the bike and ecu it could be an algorithm /setting you tapped into with the bike, performance or track if you wish to think of it in that way… so it may have adjusted the timing, spark, fuel, exhaust, air , coolant as a list it could do if the program allowed it.

so if it was suddenly snapper off throttle then its not adding fuel or adjusting the timing to increase torque backup from the engine for drag. So it’s sort of applied rear brake in layman’s term. Less road friendly setting and More racer. But then after a very short time slowly goes back to what it was normally when you behave Normally then that is what is happening.

[Hairsy]

Carb icing is quite a complex thing. It's mainly a function of moisture content of the air / dew point and the velocity and path of air in intake system. Dew point is the temperature at which the air absorbs moisture and changes constantly with atmospheric conditions. Carb icing doesn't really happen above around 20 degrees C but does happen in temperatures well above freezing. Clearly it can also happen below freezing but it's more about the moisture.

 

I've experienced carb icing in aircraft a number of times and it's never been on a particularly cold day.

Edited November 12, 2024 by Hairsy