Think I Got the Hang of TBS - One More Question Please

[moshe_levy]

All-

 

Thanks to the board for leading this n00b through the process. Now, one more question: I've got idle synched perfectly. RPMs from 5,000 to idle in increments of 500, also synched well.

 

The question is - when suddenly "gunning" the throttle from idle to anything above 3,500, the Twinmax needle will pull hard towards the right (rider's perspective). The needle will to the right right only stay while under the extreme ramp up the rpm range - a fraction of a second - and once a steady rpm is reached, the needle immediately zeros again.

 

So, question is, is the goal of this to make sure both sides are synched at a given engine speed (which I've accomplished,) or also to make sure that the needle stays in zero (balanced) range as the engine's rpms are rising rapidly? In other words, is the needle supposed to stay zeroed no matter what you do with the throttle?

 

-MKL

[T__]

All-

 

Thanks to the board for leading this n00b through the process. Now, one more question: I've got idle synched perfectly. RPMs from 5,000 to idle in increments of 500, also synched well.

 

The question is - when suddenly "gunning" the throttle from idle to anything above 3,500, the Twinmax needle will pull hard towards the right (rider's perspective). The needle will to the right right only stay while under the extreme ramp up the rpm range - a fraction of a second - and once a steady rpm is reached, the needle immediately zeros again.

 

So, question is, is the goal of this to make sure both sides are synched at a given engine speed (which I've accomplished,) or also to make sure that the needle stays in zero (balanced) range as the engine's rpms are rising rapidly? In other words, is the needle supposed to stay zeroed no matter what you do with the throttle?

 

-MKL

 

 

Mkl, ideally you would like to have the exact same air flow & sync at ALL RPM’s, at idle, under pulling load, on throttle up, at dropped throttle, hot cold & in between.. In the actual real world things like dynamic fluid (air) flow, intake tract angles, air flow through the filter housing, throttle plate centering & plane, cylinder dynamic fill, etc, can cause some pretty drastic short term disruptions to that perfect world air flow..

 

About all you can do is make sure the sync is as close as possible at fixed steady state RPM’s & stable throttle positions & don’t worry about the fulgurations at moving throttle & changing RPM’s..

 

Twisty

[smiller]

Setting TB sync is always somewhat of a compromise and I've found that matching sync in dynamic situations to be just as important as static. Snapping the throttle open is a little severe (and perhaps not all that meaningful for the reasons Twisty mentions above) but matching sync as the throttle is slowly opened off idle is important. This is why many prefer a mercury (or water, or whatever) manometer as it shows these trends much more clearly than a Twinmax, although the latter is usable is you move the throttle slowly.

[ShovelStrokeEd]

About all you can do is make sure the sync is as close as possible at fixed steady state RPM’s & stable throttle positions & don’t worry about the fulgurations at moving throttle & changing RPM’s..

 

I tend to disagree with this. I don't use a Twinmax so I don't know how it reacts to changes in throttle but, when using either a mercury or water manometer, I do watch the columns closely for changes due to change in throttle position/load. I have to dampen my system down a bit to work with large throttle transitions but, they are reflected in the sync. When you get things so that the columns drop evenly on something like a Carb Stix, or don't move on a differential manometer, steady state sync will naturally follow.

 

Remember, the vacuum signal is indicative of the load on the engine. If one side is showing a much larger vacuum transition than the other, it means that that cylinder is doing more of the work.

 

I'd say, try it again and maybe go back over the related work to find the cause. Tight valves, air leak, bad plug or plug wire. Something ain't right.

[T__]

Remember, the vacuum signal is indicative of the load on the engine. If one side is showing a much larger vacuum transition than the other, it means that that cylinder is doing more of the work.

 

 

 

 

I have to disagree with that statement.. The vacuum signal is more an indication of intake restriction (pressure delta across any intake restriction) & not a true indication of cylinder loading or work performed.. Case in point: a diesel engine has little measurable change in manifold vacuum regardless of how much work it is doing.. A plugged exhaust or exhaust pipe can also have an effect as that effects the amount of air allowed to enter so that could directly effect the delta across the throttle plate (or venture if that was the smallest restriction)..

 

Twisty

[Don_Eilenberger]

All-

 

Thanks to the board for leading this n00b through the process. Now, one more question: I've got idle synched perfectly. RPMs from 5,000 to idle in increments of 500, also synched well.

 

The question is - when suddenly "gunning" the throttle from idle to anything above 3,500, the Twinmax needle will pull hard towards the right (rider's perspective). The needle will to the right right only stay while under the extreme ramp up the rpm range - a fraction of a second - and once a steady rpm is reached, the needle immediately zeros again.

Question.. did you do a VERY precise valve adjustment before doing the TBS? A valve adjustment that included minimizing the rocker arm end-float?

 

So, question is, is the goal of this to make sure both sides are synched at a given engine speed (which I've accomplished,) or also to make sure that the needle stays in zero (balanced) range as the engine's rpms are rising rapidly? In other words, is the needle supposed to stay zeroed no matter what you do with the throttle?

Mine pretty much does, but I'm anal about getting the valves right before even thinking about TBS. If the valves aren't right - the TBS is just correcting for errors upstream (the valves).. and you'll see things like what you're seeing.

 

I've also found that if I get the valves and TBS right (to my standards which are higher than BMWs) once - just setting the valves is enough to bring TBS right back where it was the next time I do a tuneup. It's been good enough I haven't had to touch the TBs. I expect it to stay that way until the cables start to wear.

-MKL

Too bad this wasn't a week or so ago - I did a tech session for our local NJ (not the armpit IMHO - unless you only count within 30 mile of NYC) club which covered doing the valves better than any dealer bothers to - and then doing a precision TBS. You would have been welcome to attend.

 

Went well - saw the "victim" this week, said his bike has never ran as well as it is now.

[ShovelStrokeEd]

Twisty,

First off, we are not talking about a diesel engine here. It is a gasoline engine.

 

Second, you might wish to place a vacuum gauge on top of your tank bag and go for a ride. As the engine encounters an increasing load, say a mild grade, you will notice, for a steady throttle, the manifold vacuum will drop. I would have to say that that is indicative of load on the motor.

 

A change in the relative vacuum level between the two cylinders, under a rapid throttle opening, as described, tells me that the throttle bodies are not in sync, period. The one with the larger drop is certainly doing more work. I will grant that it is probably due to the fact that its throttle plate is being opened more.

 

I always do my TBS using the throttle tweak method, watching the column heights and looking for differences in the delta as I transition the throttle. This sometimes results in an offset (slight) under steady state throttle with very light load but, IMHO results in a smoother running bike as progress down the road is really a collection of subtle throttle transitions, not a steady throttle, no-load situation.

[T__]

 

ShovelStrokeEd

 

”First off, we are not talking about a diesel engine here. It is a gasoline engine.”

 

I thought we were talking about internal combustion engines here (basically air pumps).. I didn’t realize the type of fuel burned changed the laws of physics. Obviously a diesel engine (as we are used to seeing them) doesn’t contain a throttle plate but remember a gasoline engine at WOT using a large throttle body effectively doesn’t either..

 

 

“Second, you might wish to place a vacuum gauge on top of your tank bag and go for a ride. As the engine encounters an increasing load, say a mild grade, you will notice, for a steady throttle, the manifold vacuum will drop. I would have to say that that is indicative of load on the motor.”

 

As a matter of fact I have (many times) not so much on my BMW but for sure on my Harley’s & GoldWings.. In the old days, before computerized equipment, using a vacuum gauge was a big part of performance tuning.. I pose a question to you; run your engine steady state with a vacuum gauge on both sides, then disconnect a fuel injector on one side, then with the throttle still held steady tell us what the vacuum reading is on both sides? You now have one cylinder doing all the work..

 

”A change in the relative vacuum level between the two cylinders, under a rapid throttle opening, as described, tells me that the throttle bodies are not in sync, period. The one with the larger drop is certainly doing more work. I will grant that it is probably due to the fact that its throttle plate is being opened more.”

 

Here is where you & I differ on what that vacuum reading is telling us.. You seem to only see what you are expecting to see.. On the other hand I look at the total picture & take into account other things can effect that vacuum reading.. Seeing as an engine is basically a simple air pump many things can (& do) effect the manifold pressure: such as exhaust restriction (or non equal exhaust back pressure side to side),, exhaust system negative wave timing/tuning,, intake length, diameter, & tuning (usually only at higher throttle plate openings),, engine dynamic compression,, valve timing & sealing,, any & all intake restrictions on the atmospheric side of the throttle plate,, any air leaks on the cylinder side of the throttle plate,, any undulations in the intake tracks that can disrupt the smooth flow of air at or through the intake tracks,, more but these are the basics.. A large part of vehicle high performance tuning is tuning the intake tract length to allow the standing wave to improve cylinder filling (i.e.-why does the GS intermediate intake tubes change the (perceived) torque on the R, RT? What if only one side GS intermediate intake tube was used then the throttle blipped (you get the picture here)..

 

If what you say is true (“A change in the relative vacuum level between the two cylinders, under a rapid throttle opening, as described, tells me that the throttle bodies are not in sync, period”) then I should be able to plug off one intake tract to allow just the amount of air required to operate at the specific pre blip RPM ,, then blip the throttle & see equal vacuum delta to the other (non restricted cylinder).. I trust we both know this isn’t possible..

ALL OTHER things being equal you could probably use the throttle blipping method with some confidence but in the real world I seriously doubt most systems are that equal side to side.. Don’t some of the oilheads uses an exhaust restriction on one side?

 

”I always do my TBS using the throttle tweak method, watching the column heights and looking for differences in the delta as I transition the throttle. This sometimes results in an offset (slight) under steady state throttle with very light load but, IMHO results in a smoother running bike as progress down the road is really a collection of subtle throttle transitions, not a steady throttle, no-load situation.”

 

 

We seem to differ here as I have more confidence in the steady state throttle balance as that more emulates the engine operation riding steady state in a gear/load range & the place where engine undulations are the most noticeable.. I do use a s-l-o-w throttle roll on roll off as a secondary check but have 0 confidence in using that as a main balance parameter.. On moderate to severe throttle change it is difficult to tell engine smoothness from spark table change, or fueling enrichment, or even drivetrain loading..

 

Twisty

[moshe_levy]

Hi Don-

 

I did perform a valve adjustment prior to the TBS - my first ever, so I'm sure it wasn't as precise as someone with more experience would be capable of. I replaced all 4 plugs as well. The bike has only 11,000 miles on it - truth be told, the valves weren't really off as far as I could tell. I did not measure rocker arm end float.

 

It would be great if somehow I could find out next time there's a tech day anywhere near NJ. Do you have a website or listing for your local club that would list upcoming events like this? Thanks.

 

-MKL

[ShovelStrokeEd]

Agreed, it is an air pump. The key feature you mentioned is that a diesel doesn't use a throttle plate and as such, is a purer pump than the gasoline engine. There is, of course a big effect on manifold vacuum when using the throttle plate.

 

A little difficult to reach down and do that but, I would expect that the engine speed change would mask the vacuum change. Open the throttle to maintain the speed and you will see the working cylinder vacuum drop a great deal more than does the non-working cylinder.

 

I know all the stuff you are spouting here, and more, and it is more or less meaningless to this discussion. And no, there is no restriction in one of the oil head exhaust pipes. We are talking about a healthy engine in proper tune. GS intake tubes get their increased motor torque from an increase in part throttle gas velocity and slightly longer tuned length. In general, the flow is more efficient and leads to better atomization of the fuel charge and higher swirl values in the combustion chamber. It also restricts top end HP but that is the subject of another discussion.

 

In the real world, at least mine, most of the systems are pretty equal from side to side and the flywheel helps to even out what little equality difference there is. Again, we come back to a proper state of tune and a healthy motor. A motor with say 40 lbs of compression difference from side to side is not going to be smooth despite the vacuum reading being even.

 

Steady state throttle balance, with the motor running on the stand, does not, in any way reflect the real world, except at idle. Running the engine under load is really the right way to achieve balance but, since most of us don't have a rolling road dyno handy, we have to make do. I submit that the light load applied to the motor by a moderate blip of the throttle more closely approaches that running condition.

 

Take a ride for yourself and see how little time you actually spend at "steady state" throttle. It comes down to where you want the motor to be smoothest. Under locked throttle 70 mph cruise, where the bike will vary in speed quite a bit as you progress down the road, or during the myriad small throttle transitions you make as part of a daily drive.

[T__]

ShovelStrokeEd, You seem to think whether or not a cylinder is firing has a large effect on intake vacuum & I don’t (we could debate this for ever so lets just agree to disagree on this one)

 

Take a ride for yourself and see how little time you actually spend at "steady state" throttle. It comes down to where you want the motor to be smoothest. Under locked throttle 70 mph cruise, where the bike will vary in speed quite a bit as you progress down the road, or during the myriad small throttle transitions you make as part of a daily drive.

 

You are correct in that most riding is under varying throttle positions but for MOST people that throttle change is slight & only a few degrees.. I guess the big difference between us here is I pride myself on smooth throttle roll on/off & seamless up-shifts/down shifts & you seem to be a throttle blipper..

 

Twisty

[smiller]

BTW this is what you get for asking 'one more question' on this forum Moshe...

[glwestcott]

Screw all this perfection stuff. Let's go riding!

[ShovelStrokeEd]

I would take offense to that last statement but, it is not worth it. Ask anyone who has ever ridden in my proximity about smoothness. A little research on the advise I have given folks about shifting might be in order as well.

 

Of course the throttle transitions are slight and only a few degrees. In fact, at least for me, they seldom involve any wrist movement, more of a subtle change in the grip on the throttle.

 

Back to the original poster's question. It is NOT normal, on a good running engine, for the vacuum to show a large differential under acceleration. At least not one that remains for more than a second or so. It has to mean that one throttle plate is opening/changing position sooner than the other. Again, I'm talking a healthy motor which is why I suggested he go back and look over all the other factors that could contribute to this.

 

When I use my Carb Stix, on my twins, both columns drop the same amount in response to an opening of the throttle and both return to the same height once equilibrium is established at the new RPM. Actually, it is the same on my 4 cylinder bikes. Again, and this is strictly a matter of personal preference, I like to use this as a final confirmation of good adjustment and will accept a slight, repeat, slight differential in steady state, no load condition if that is the result.

[daveinatlanta]

I have to dampen my system down a bit to work with large throttle transitions but, they are reflected in the sync.

I noted this response and while my question is a bit off-topic, what did you use to dampen your manometer? Or, better said, do you have plans for building one? I've read the references here on building one but I don't recall the specifics on how to build in damping..?

[ShovelStrokeEd]

On twins, I use a Dwyer slack tube manometer and the damper valves are built into it. Others have used cigarette filters, old carb jets, a bolt with the head cut off, two pair of hemostats and many other devices, nefarious or not. More or less whatever works to keep the silly columns from bouncing around. The shear mass of a column of mercury works pretty well also but, unless you are familiar with the stuff and take precautions in re vapors and the breathing thereof, I cannot recommend it.

[UberXY]

All-

 

Thanks to the board for leading this n00b through the process. Now, one more question: I've got idle synched perfectly. RPMs from 5,000 to idle in increments of 500, also synched well.

 

The question is - when suddenly "gunning" the throttle from idle to anything above 3,500, the Twinmax needle will pull hard towards the right (rider's perspective). The needle will to the right right only stay while under the extreme ramp up the rpm range - a fraction of a second - and once a steady rpm is reached, the needle immediately zeros again.

 

So, question is, is the goal of this to make sure both sides are synched at a given engine speed (which I've accomplished,) or also to make sure that the needle stays in zero (balanced) range as the engine's rpms are rising rapidly? In other words, is the needle supposed to stay zeroed no matter what you do with the throttle?

 

-MKL

 

One day, when BMW goes to throttle by wire, much of this stuff will go away. I have this system on my BMW car, which has 8 butterfly throttle valves opened and closed by a very fast electric motor run by the cars computer, and they haven't been synched in the 7 years I have had the car. I have also been told that first gear has a different fuel map than the other gears.

[moshe_levy]

My dad's previous car (745Li) was drive-by-wire as well. I had the same exact thoughts as I was performing the synch on the bike!

 

-MKL