CV carb operation

[VT1000r]

I've asked this before and got good answers but I'm still confused even after hours of useless research. The question that's been keeping me awake is factory pro says that at full throttle 7500 to redline is main jet and full throttle I think like 4500 to 7500 is needle but wouldn't any rpm at wide open throttle lift the slide all the way up I know it's not as quick as a carb with cable connected to slide but wouldn't the slide still raise up all the way if you went WOT at say 1000rpms long before it reached 7500rpms. Please explain this to me I've been reading everything and still haven't found a good explanation of what happens to the slide when you go WOT at a low rpm.

[freeridenick]

The throttle doesn't act on the slide directly so it doesn't matter how open the butterflies are (throttle action). The slide is operated by the suction created by the engine - low revs equals low suction through the carb and the slide doesn't open much. When you're up around 10k rpm there's bucket loads and the slides are up. But they are not static, as I think another post has said, they are moving all the time just very fast: intake open = slides open; intake closed slides closed i.e. suction; no suction.

This shows it clearly but remember that the slide doesn't move straight to fully open when the butterfly wide open, it moves slowly as the amount of air sucked through the carb increases. That's why the holes in the slide are so important and various tuning brands advocate different things regarding the holes.

[8541Hawk]

Well if you would like I can PM you my cell number as it might be easier than writing a novel for you.....lol
Though quick question, have you ever driven any vehicle with a "vacuum" gauge?
If so, when you go wide open throttle, have you noticed the gauge drop to a very low reading and then climb again as the RPMs rise?

This is the signal the slides are "seeing". So at WOT at low RPMs there is not enough of a pressure differential (or vacuum signal) to raise the slides all the way.

In order for the slides to raise a large enough pressure differential must be created in order to overcome the spring pressure holding them closed.
So the slides will never go all the way open until the engine is spinning enough RPMs to create the pressure differential required to open them

Also the RPM numbers you are getting from FactoryPro are just ball park numbers. For example, on this bike, in my experience you come off the pilots closer to 3500 RPM and by 4500 you are well into the needles.

[VT1000r]

Well if you would like I can PM you my cell number as it might be easier than writing a novel for you.....lol
Though quick question, have you ever driven any vehicle with a "vacuum" gauge?
If so, when you go wide open throttle, have you noticed the gauge drop to a very low reading and then climb again as the RPMs rise?

This is the signal the slides are "seeing". So at WOT at low RPMs there is not enough of a pressure differential (or vacuum signal) to raise the slides all the way.

In order for the slides to raise a large enough pressure differential must be created in order to overcome the spring pressure holding them closed.
So the slides will never go all the way open until the engine is spinning enough RPMs to create the pressure differential required to open them

Also the RPM numbers you are getting from FactoryPro are just ball park numbers. For example, on this bike, in my experience you come off the pilots closer to 3500 RPM and by 4500 you are well into the needles.

I was under the impression that more Rpms equals more pressure?

[8541Hawk]

Not sure what you mean by that.....higher rpms = a larger vacuum signal.
This is what allows the slides to open.

I guess the simplest answer to all this is that the slides on these carbs are only fully open at 7-7.5K RPM or so and above by design.
The engine needs to run at those RPMs to generate a large enough vacuum signal to overcome the spring holding the slide close.

It doesn't matter what the throttle\butterfly setting is....WOT, 1\2 throttle, 1\4 throttle.....doesn't matter. Until you hit a high enough RPM to generate enough pressure differential to overcome the spring pressure, the slides stay closed.

Or in short, the needle all the way up at 1K RPM is impossible, by design, on these carbs.
Slide opening is RPM dependent.

[VT1000r]

Not sure what you mean by that.....higher rpms = a larger vacuum signal.
This is what allows the slides to open.

I guess the simplest answer to all this is that the slides on these carbs are only fully open at 7-7.5K RPM or so and above by design.
The engine needs to run at those RPMs to generate a large enough vacuum signal to overcome the spring holding the slide close.

It doesn't matter what the throttle\butterfly setting is....WOT, 1\2 throttle, 1\4 throttle.....doesn't matter. Until you hit a high enough RPM to generate enough pressure differential to overcome the spring pressure, the slides stay closed.

Or in short, the needle all the way up at 1K RPM is impossible, by design, on these carbs.
Slide opening is RPM dependent.

Oh, ok I think I understand now, me and fluid dynamics get along about like this lol. So does the slide get its vacuum signal from the holes in the slide? I hate these darn cv carbs just because of the complexity of tuning them I wish they would have put fuel injection on them idk why they wouldn't. The ducatis like 996 and 916 had fuel injection and even the Suzukis like tl1000 had fuel injection so why not the vtr1000 or at very least they could have put some fcrs on the vtr1000. Tuning these darn things perfectly is a pita especially when you don't understand them.

[MacV2]

Not sure what you mean by that.....higher rpms = a larger vacuum signal.
This is what allows the slides to open.

I guess the simplest answer to all this is that the slides on these carbs are only fully open at 7-7.5K RPM or so and above by design.
The engine needs to run at those RPMs to generate a large enough vacuum signal to overcome the spring holding the slide close.

It doesn't matter what the throttle\butterfly setting is....WOT, 1\2 throttle, 1\4 throttle.....doesn't matter. Until you hit a high enough RPM to generate enough pressure differential to overcome the spring pressure, the slides stay closed.

Or in short, the needle all the way up at 1K RPM is impossible, by design, on these carbs.
Slide opening is RPM dependent.

Oh, ok I think I understand now, me and fluid dynamics get along about like this lol. So does the slide get its vacuum signal from the holes in the slide? I hate these darn cv carbs just because of the complexity of tuning them I wish they would have put fuel injection on them idk why they wouldn't. The ducatis like 996 and 916 had fuel injection and even the Suzukis like tl1000 had fuel injection so why not the vtr1000 or at very least they could have put some fcrs on the vtr1000. Tuning these darn things perfectly is a pita especially when you don't understand them.

Simple answer...Cost... Storm was always a bit of a budget bike, just look at the suspension...You want more power & Injection ? Buy an SP...

[tony.mon]

But then the later Varadero had FI (too small to transfer to a Storm) so it's not as though Honda couldn't do it at the price...


Back then FI wasn't very smooth, so the transition from closed to open throttle would have been interesting, with the torque available low down.

Perhaps it's a simple case of "if it ain't broke...", particularly late in the model run.

[VT1000r]

But then the later Varadero had FI (too small to transfer to a Storm) so it's not as though Honda couldn't do it at the price...


Back then FI wasn't very smooth, so the transition from closed to open throttle would have been interesting, with the torque available low down.

Perhaps it's a simple case of "if it ain't broke...", particularly late in the model run.

From your experiences what rpms does the needle play apart in and does it have to be at WOT or does the carb slide open at the same rpm no matter the position of throttle?

[tony.mon]

A cv carb slide and throttle position are not directly linked at all.
There's an indirect link as the intake vacuum causes the slide to lift varied by the butterfly and slide holes, which "choke" the vacuum by permitting a limited amount of air to flow to the upper side of the slide.
Don't try to think of them the same way as a standard carb.

[freeridenick]

But then the later Varadero had FI (too small to transfer to a Storm) so it's not as though Honda couldn't do it at the price...


Back then FI wasn't very smooth, so the transition from closed to open throttle would have been interesting, with the torque available low down.

Perhaps it's a simple case of "if it ain't broke...", particularly late in the model run.

From your experiences what rpms does the needle play apart in and does it have to be at WOT or does the carb slide open at the same rpm no matter the position of throttle?

Have a look in the readme for new members section and read the carb setup post. I think you need to stop thinking of the separate circuits as individual parts and think of the carbs as a whole. Sort your top end out and work back from there as the carb setup post describes.

[tony.mon]

But if you're going in balls-deep, buy a copy of the Haynes Fuel Systems Techbook, it answers every question you could possibly ask, and a lot you won't have thought of.
I bought one a few months ago, I'm still on chapter three....

[fabiostar]

interesting reading folks after my last few months of trials and heartbreak i have to say

[felix barrao]

I actually prefer the carburated engines.. Yes, injected engines have better fuel consumption, they are more eco friendly, etc, but, imo they don´t have the feeling and character of a carburated engine.

[VT1000r]

But if you're going in balls-deep, buy a copy of the Haynes Fuel Systems Techbook, it answers every question you could possibly ask, and a lot you won't have thought of.
I bought one a few months ago, I'm still on chapter three....

I didn't know they still made books lol. I checked it out its only 30usd so I may end up buying it I can definitely use the knowledge.