Poor runnung at small throttle opening

[vuzzi]

In several topics poor running at low revs and small throttle opening have been adressed. I too have been working

on the tps setting for this reason.

I like the set up according to mr bean (http://www.v11lemans.com/forums/index.php?showtopic=13188&hl=Micha&st=0):

Step one - Set your valves to world settings

Step two - Set your bleed screws to open 1 full turn

Step three - Synch throttle bodies at just off idle (around 1800 rpm)

Step four - Set idle to 1100 using left idle screw adjuster only

Step five - Set TPS to 3.6 degrees (I forget what that translates to in mv..someone here will know)

Step six - Ensure idle trim is set to zero

 

I noticed he adviced to open the air bypass screws a whole turn instead of half like the manual. I have been wondering what the effect would be of opening the ait bleed scews to a greater or lesser extend to the mixture. So I tried to figure it out using my basic high school maths. This is what I did:

I calculated the opening of the of the throttle, starting at 3.6 degrees, using the cos of the angle. This is not a

liniear relation. See first figure. I then added 20% opening through the air bypass in another column in my spreadsheet.

 

Opening the air bleed screws results in a bigger opening and higher revs. This must be corrected by decreasing the angle of throttle, while setting the tps back to 525 mV, making the cpu think the nagle is still 3.6 degrees. The result is an offset of the opening which has a bigger effect on the total opening (throttle + air bypass) at bigger openings. See second figure.

 

However, in relative terms, the effect is different, namely a reletively large difference at small openings and a small difference at large openings. See thirth figure.

 

In the example I simulated a bypass opening of 20% of the throttle opening at idle. This results in a 5% smaller opening for the air flow at small trottle angles, and thus a richer mixture.

 

The exact numbers are not so important, but most important is that by opening up the bypass screws the mixture in general gets richer after correcting the tps, namely at small trotle openings. It may help against backfire and poor runing at small tp and low revs

Too bad it's winter now, but I'll experiment with it next spring.

 

I hope all is clearly written down and maybe some of you have better maths skills than I have and can check this.

 

Any thoughts are welcome. looking forward to reading them

[Desdinova]

I haven't been logged in for awhile, but I still subscribe to the forums and saw this topic come across my email...

 

Based on my experience, the most important FIRST step, is to ensure the mechanical aspects are working as they should.

 

I had a "rough" problem that plagued me for several years. I could move the rough idle all over the RPM spectrum, and even mask it with Power Commander tricks, but it wasn't until my fast-idle cable broke that I was able to clear it up.

 

It turned out there was a small burr on the linkage of one of the throttle bodies that was preventing the throttle from going to its fully closed position. Upon normal inspection it really looked like it was seated but it wasn't until I was up close and intimate that I found it. In fact, the "trigger" to get me looking at it was replacing the fast idle cable resulted in the bike acting like a screwed up the whole mapping scheme. That just didn't seem right. In fact, with the fast-idle cable off the bike, it would barely start. The burr was on the linkage and only scraping with the cable attached, and only keeping the throttle open an almost immeasurable amount.

 

Please excuse the over-emphasis... but once I cleared off the burr.. tuning the bike from scratch, and setting up the power commander and having to figure out new mappings... all without a Dyno... took but a few hours. It was so easy because everything reacted now as it should.

 

The bike has run like a champ ever since. Starts every time, idles fine, loads of torque, no backfire.. etc etc..

 

I'm not saying that a burr on the throttle linkage is a symptom/cure for every rough idle issue... I AM saying, we should always check EVERYTHING.

[Kiwi_Roy]

In several topics poor running at low revs and small throttle opening have been adressed. I too have been working

on the tps setting for this reason.

I like the set up according to mr bean (http://www.v11lemans.com/forums/index.php?showtopic=13188&hl=Micha&st=0):

Step one - Set your valves to world settings

Step two - Set your bleed screws to open 1 full turn

Step three - Synch throttle bodies at just off idle (around 1800 rpm)

Step four - Set idle to 1100 using left idle screw adjuster only

Step five - Set TPS to 3.6 degrees (I forget what that translates to in mv..someone here will know)

Step six - Ensure idle trim is set to zero

 

 

It seems to me that opening the bypass screws must result in a weaker mixture at idle because the ECU thinks the throttle is less open, The throttle angle has very little effect for the first few degrees however at low throttle settings the bypass screw sees the greatest pressure drop

It's interesting that the throttle is similar to a typical butterfly control valve. If you look at the chart for a butterfly valve you will see the flow characteristic is very non-linear, very little change in flow for the first few % of angle the flow change for opening angle is greatest around 30 - 70% Further adding to the confusion is the pressure drop, flow is related to the square root of differential pressure and as you open the throttle the pressure drops, the ECU must have a non linear calculation to take care of that.

I built myself a little box that allows offsetting the TPS mV while riding, unfortunately mine was so rich I didn't see any change and I ended up buying a MyECU so I could have some control over the mixture.

BFly cv.pdf

[vuzzi]

It seems to me that opening the bypass screws must result in a weaker mixture at idle because the ECU thinks the throttle is less open, The throttle angle has very little effect for the first few degrees however at low throttle settings the bypass screw sees the greatest pressure drop

It's interesting that the throttle is similar to a typical butterfly control valve. If you look at the chart for a butterfly valve you will see the flow characteristic is very non-linear, very little change in flow for the first few % of angle the flow change for opening angle is greatest around 30 - 70% Further adding to the confusion is the pressure drop, flow is related to the square root of differential pressure and as you open the throttle the pressure drops, the ECU must have a non linear calculation to take care of that.

I built myself a little box that allows offsetting the TPS mV while riding, unfortunately mine was so rich I didn't see any change and I ended up buying a MyECU so I could have some control over the mixture.

 

The mixture should stay the same at idle, since the tps is adjusted to 525 mV, indicating 3.6 degrees opening for the cpu.

 

The flow data is interesting. It shows an even steeper relation between throttle angle and air flow. This might be because the relation between angle and air resistance in not liniear either. Edge effects play a large role in the resistance and since the total edge increases to a lesser extend than the opening as the opening gets bigger, so the edge/opening ration gets smaller. I asume this supports the effect of a richer mixture at small throttle openings. But I guess it 'd take a specialist in airodynamics or a hydrologist to fully figure that out.

[v11cafe]

I think bypass screws control quantity of air

fully closed=less air to fuel

opening them up 1/2 turn, 3/4 etc =more air to same fuel quantity=leaner

 

As for correcting Tps, How?

by the butterfly screw or moving the whole tps?

[gstallons]

You would be correct if it was a carb. engine where you were adjusting an idle mixture. This is an idle bypass screw meant to trim the idle speed.

[Kiwi_Roy]

 

The flow data is interesting. It shows an even steeper relation between throttle angle and air flow. This might be because the relation between angle and air resistance in not liniear either. Edge effects play a large role in the resistance and since the total edge increases to a lesser extend than the opening as the opening gets bigger, so the edge/opening ration gets smaller. I asume this supports the effect of a richer mixture at small throttle openings. But I guess it 'd take a specialist in airodynamics or a hydrologist to fully figure that out.

It's part of my job to specify control valves, we have a computer program for calculating control valves which are rated in cV.

Iiquids are easy but gasses are quite another thing.

The data I posted is done with water at 1 psi difference but the throttle body has an ever changing pressure drop.

Roy

[vuzzi]

I think bypass screws control quantity of air

fully closed=less air to fuel

opening them up 1/2 turn, 3/4 etc =more air to same fuel quantity=leaner

 

As for correcting Tps, How?

by the butterfly screw or moving the whole tps?

 

You would be correct if it was a carb. engine where you were adjusting an idle mixture. This is an idle bypass screw meant to trim the idle speed.

 

 

Opening the bypass screws indeed adds more air and increases idle speed, but this is compensated by closing the throttles (compare left and right throttles in the picture). This is done by backing off thhe small hex screws at the bottom of the trottle bodies. In this way the total air flow at idle can be kept constant.

Turning back the small hex screws at the bottom decreases the angle of the throttles and results in a smaller voltage read by the tps. The tps can however be offset by the two small hex screws at the top of the throttle bodies, making the tps read 525 mV and making the cpu think the throttle angle is (still) 3.6 degrees.

 

The offset angle affects the whole range, but in the end turns out to have a bigger relative effect on small throttle openings -> less air flow at the same mV reading of the tps or at the same throttle angle for as far as the cpu knows.

[gstallons]

It is imperative to start out with both throttle plates to be at the same angle for base idle.This syncronization has nothing to do with idle speed. This is done with the idle speed control screw. You control the small difference in cylinder contribution with the air bypass screws.

[vuzzi]

I prefer to set the throttles at the same angle by closing the air bypass screws, and than using the synchronisation rod adjuster at 2500 rpm. in that way you know throttles are not influenced by the air bypasses.

 

Once the throttles are synchronised, the air bypass screws should be opened. Both equally. As I tried to explain in this topic, the air bypasses have different effects at different throttle angles. Air bypass and throttle angle can not be exchanged just like that.

Opening the air bypass at one side more than the other will lead to uneven mixture and thus uneven running of the cilinders, namely at small throttle angles.

 

Idle speed should be set with the idle screws at the bottom of the throttle bodies.

[Kiwi_Roy]

I prefer to set the throttles at the same angle by closing the air bypass screws, and than using the synchronisation rod adjuster at 2500 rpm. in that way you know throttles are not influenced by the air bypasses.

 

Once the throttles are synchronised, the air bypass screws should be opened. Both equally. As I tried to explain in this topic, the air bypasses have different effects at different throttle angles. Air bypass and throttle angle can not be exchanged just like that.

Opening the air bypass at one side more than the other will lead to uneven mixture and thus uneven running of the cilinders, namely at small throttle angles.

 

Idle speed should be set with the idle screws at the bottom of the throttle bodies.

Just to clarify:

How do you hold 2500 using the throttle, as if you were riding or against one of the mechanical stops. (I just noticed it was Mr Bean said 1800 in Step 3, probably not significant)

 

I found using just the LH idle screw resulted in a slightly different TPS mV reading each time the throttle was blipped with a corresponding loss of sync. My bike has over 70k on the clock, perhaps the linkage is a bit sloppy. I set both screws to make contact at idle.

To clear up any imbalance at idle, Idle screws or bypass screws?

 

I find riding my bike idling set at 1100 the engine braking effect is much less than I want so I ended up with a lower idle speed but then it tends to sneeze and stall at the lights, it's really hard to get a happy median

But what the heck, a V11 Sport was never meant to ride in the city anyway!!!!

 

Cheers

Roy

[vuzzi]

Just to clarify:

How do you hold 2500 using the throttle, as if you were riding or against one of the mechanical stops. (I just noticed it was Mr Bean said 1800 in Step 3, probably not significant)

 

I found using just the LH idle screw resulted in a slightly different TPS mV reading each time the throttle was blipped with a corresponding loss of sync. My bike has over 70k on the clock, perhaps the linkage is a bit sloppy. I set both screws to make contact at idle.

To clear up any imbalance at idle, Idle screws or bypass screws?

 

I find riding my bike idling set at 1100 the engine braking effect is much less than I want so I ended up with a lower idle speed but then it tends to sneeze and stall at the lights, it's really hard to get a happy median

But what the heck, a V11 Sport was never meant to ride in the city anyway!!!!

 

Cheers

Roy

 

The 1800 rpm was suggested by mr bean. The exact rpm is not that important. Most important is that you use a small throttle opening, cause only than you can measure small differences.

 

Indeed a bit strange if you read different voltages. Some difference (10 mV) is not that big a problem. I think you should be able to feel it at the lh side (at the adjustemt wheel) if the linkage is sloppy.

 

I'd say unbalance at idle should be corrected with the idle screws. The bypass screws should be set equal, that is, both half or both full turn out.

 

I noticed too that engine breaking is much less with idle at 1100 rpm. But maybe that is a good thing for the drivetrain.

 

Coughing and sneezing, and even blowing an intake rubber of is terrible. Good balance helps, and also equal valve settings. After my bike had the heads off and got new gaskets, my bike blew the intake rubbers of after a 30 km ride. Back at home I found that the intake valves were 0.1 mm of at one side. After adjustment the bike run as normal.

 

Looking forward to setting the bypass screws and all that in spring. Right now my bike is under a cover with 10 cm of snow on top....

[motoguzznix]

Coughing and sneezing, and even blowing an intake rubber of is terrible. Good balance helps, and also equal valve settings. After my bike had the heads off and got new gaskets, my bike blew the intake rubbers of after a 30 km ride. Back at home I found that the intake valves were 0.1 mm of at one side. After adjustment the bike run as normal.

Vuzzi

 

When the valve play decreased, your gaskets had settled and the head nuts need to be retightened. After retightening the valves have to be adjusted as the play decreases further when the gasket will be compressed.