Throttle butterfly design

[tris]

We all (or at least we should by now) know the pain and suffering that can be had by messing with the "sacred screw" on the CARC bikes.

So, my simple question is:-

Given the sensitivity of positioning the throttle butterfly via the stop to achieve the design airflow at idle , why don't the designers just let the edges of the butterfly close off all air and simply drill a hole in the butterfly with the cross sectional area that gives the desired flow

[rodekyll]

Some throttle plates do have a hole.  But even they don't close completely.  One reason is that butterfly sticks in the bore just a little if it's allowed to go fully closed.  You'll see plates that are beveled to present a flat instead of sharp edge to the throttle body.  Over time plate stiction scores the bore, shaves the butterfly, and wears the shaft and shaft bore, linkage, and so on.

[Kiwi_Roy]

What are the sacred screws on a CARC bike, the throttle stops.
Is there a throttle balance procedure similar to the VIIs
Sorry, I wasn't watching in class, I never dreamed of owning a Griso.


Sent from my shoe phone!

[Idontwantapickle]

What are the sacred screws on a CARC bike, the throttle stops.
Is there a throttle balance procedure similar to the VIIs
Sorry, I wasn't watching in class, I never dreamed of owning a Griso.


Sent from my shoe phone!

There is a small screw near the shaft of the LH throttle body that can easily be mistaken for an idle adjustment by the uninitiated. Idle balance is by bleed screws, the ecu will control idle with a properly set TPS etc.

[pete roper]

Yes Roy, the throttle stop screws. Most importantly the one on the left hand throttle body. There is one on the right too but it's well hidden and so less likely to be messed with.

The balancing procedure for a W5AM bike is ludicrously simple. Once the valves have been set connect Guzzidiag or whatever other tool you're using and your manometers.

Close both air bleeds and start the motor allowing it to warm up to above 60*C, (Although with the 2V engine there is no real need to be obsessive about this as viewed on the scan tool as the engine temperature sensor signal is usually pretty crap. Get it up to operating temperature really is what is needed.)

Then using the bell crank adjuster screw on the LH throttle body balance the TB's at around 4,000 RPM.

Once that is done kill the engine with the kill switch, (Not the key simply because if you use the key it will disconnect the scan tool and you'll have to go through the rigmarole of reconnecting again.). Balancing the TB's at high speed will of changed the TPS value so wind the throttle open and let it snap closed and then re-calibrate the TPS.

Once that is done fire the motor up again and whichever side has the higher manifold depression open the air bleed on that side to bring the two manifold pressures into sync. Only one air bleed should ever be open. If the idle balance is perfect with both bleeds closed? That's fine. But they should never both be open.

Unlike the V11's and Calis you don't try and manipulate the idle speed by opening or closing the air bleeds. The target idle is hard coded into the ECU and is controlled by the stepper motor, an air over idle valve, between the two throttle bodies. The ECU monitors engine speed and if it drops below the target the stepper opens allowing more air through. Leaner mixture-higher idle. If the idle rises to high the stepper closes cutting off more air, enrichening the mixture so the idle drops.

It's an incredibly easy and simple system that in most circumstances works very well. The only things that will screw it up are over filling the sump with oil which then gets pumped out through the breather system and can clog and foul the butterflies and/or stepper preventing them from closing properly or on early models with the metal bodied stepper they can sometimes get sticky for no apparent reason leading to a high idle.

If someone screws with the throttle stops it sends the whole system to hell in a handbasket.

Pete

[Kiwi_Roy]

Pete
On behalf of all the CARC owners thank you for the detailed explanation, rest assured I'm not going to do a thing until I get used to the tools, and understand what I'm doing.

The bike seems to be running fine at the moment, I assume Gord in Chilliwack gave it a good going over for the previous owner.

 
 

[tris]

The reason I started this thread was because I had started a to get a consistently low idle - circa 1000 RPM

I therefore decided to pull the TBs to check them over.

I found that around the butterflies there was some crud that has now been ostracised and the ICV was not moving freely and now is

I had filled the bike to its marks at one point and now know that this is a bad thing, but once the bike had dumped what it didn't like in to the ICV/TBs the level has remained constant at 1/2 full!


I also am seeking to un-FUBAR the SS that the previous owner had messed with.

I've been working to get it back to where it should be for a while and find that, more by luck than judgement I'm sure, it wasn't far off the 0.05mm(2 thou) gap/28.6mm from leading edge to the front of the TB as variously recommended by this and other forums

I did find that whist I can get circa 2 thou on both LH & RH TBs, there was a 0.3 difference using distance from the leading edge. I feel that the 2 thou is more important and repeatable so that is what I went for


I guess we'll see if I have been successful in my mission once I get it all back together with no bits left over 


PS Pete- I went looking (EDUCATIONAL PURPOSES ONLY!!) for this second screw but found nothing - it must be well hidden or has fallen out!!!!

[tris]

........The target idle is hard coded into the ECU and is controlled by the stepper motor, an air over idle valve, between the two throttle bodies. The ECU monitors engine speed and if it drops below the target the stepper opens allowing more air through. Leaner mixture-higher idle. If the idle rises to high the stepper closes cutting off more air, enrichening the mixture so the idle drops.......

I wonder how many bikes have had the SS touched because the ICV wasn't working as designed and sticking (or working from the wrong reference because it bunged up) causing either a high or low idle speed because the bike had been filled to its marks!