How to balance throttle bodies

[Guest IanJ]

I have written up the procedure of balancing throttle bodies on a V11, and I thought some of you might like to see it. It's not actually complete as of this moment, I still need to document checking the TPS setting. Check it out, let me know if there's anything I got wrong, or how it might be improved.

 

How to balance a V11's throttle bodies

[Guest dkgross]

cool!!

 

one suggestion...change the colors on the page. That whole black w/white text is just too hard on these old eyes...

[al_roethlisberger]

Ian,

 

Great work

 

But a couple questions:

 

1) Why do you include fiddling with the air-bypass screws, since these are typically set with a gas-analyzer and not typically used to set idle/balance(as you note).

 

DO NOT use the air bypass screws to adjust balance and idle speed, no matter how much easier it looks. Air bypass screws should only be adjusted to change idle mixture, using a CO meter.

 

With the instructions about adjusting the air bypass screws soon followed by the warning above, I don't understand how they relate to the process.

 

I may have just gotten confused, but thought I'd ask in case I am missing a step when I balance my TBs... which BTW takes about 10 minutes with the TwinMax

 

When I balance my TBs, I only use the white plastic balance adjustment knob.

 

2) I'm not sure if you meant to suggest using the right idle set-screw when you mention it, but it's been recommended that both the right and left set-screws not be used in conjunction, as they inevitably will be uneven. It has been recommended to back out the right set-screw such that it is irrelevant, and only set idle with the left screw.

 

 

As an aside, my bike just idles high after my head porting, no matter what. It shows about 1300 rpm on the tach, but on the DynoJet sensor shows closer to 1900. It idled at about 1000-1100 according to the tach as stock, so I guess it's really only a couple 100 rpm "high" Carl Allison reported the same after his heads came back.

 

al

[roberto]

Thats right... back out the RH idle adjuster screw...

 

 

then, back it out a bit more...

 

 

then, back it out a bit further....

 

 

and a bit more....

 

 

then, allow it to fall to the floor and down the nearest drain.

 

 

IT'S USELESS.... THROW - IT - AWAY!

 

 

ok, you could keep it as a "spare"...

 

 

oh, and replace the LH screw with something that doesn't have a "tamperproof" socket. I just know I'm gonna have to hammer a hex key into that sucker one day.

[Guest IanJ]

RH idle screw: The reason to have the RH set screw around is so you can set an idle speed, then adjust balance so as to maintain that speed. Also, what if the left throttle plate is further open than the right with both screws backed all the way out? You'd need that RH screw to fix that condition. If the idle stop screws are uneven, the manometer will show that condition -- that's why you're adjusting the idle balance in the first place.

 

I'm not saying any of these things are necessarily true or going to happen, but I'm not going to toss a potentially useful adjustment.

 

Roberto, I don't know what kind of idle stop screws you have on your throttle bodies, but on mine, they use a 2.5 mm hex key. Nothing fancy (unless 2.5 mm is a fancy size somehow). Did MG change what they were using somewhere in the run?

 

Air bypass screws: Micha at MI suggested that they be adjusted to 1 turn out. He didn't say why he suggested that, but I believe it's to make sure that they're adjusted to the same value, so they don't throw off your balancing efforts with the idle stop screws. Perhaps it would be better to say that the air bypass screws shouldn't be touched unless you know what you're doing. I'll change the wording around the bypass screws: you're right, it's confusing right now.

[al_roethlisberger]

RH idle screw: The reason to have the RH set screw around is so you can set an idle speed, then adjust balance so as to maintain that speed. Also, what if the left throttle plate is further open than the right with both screws backed all the way out? You'd need that RH screw to fix that condition. If the idle stop screws are uneven, the manometer will show that condition -- that's why you're adjusting the idle balance in the first place.

 

I'm not saying any of these things are necessarily true or going to happen, but I'm not going to toss a potentially useful adjustment.

 

Roberto, I don't know what kind of idle stop screws you have on your throttle bodies, but on mine, they use a 2.5 mm hex key. Nothing fancy (unless 2.5 mm is a fancy size somehow). Did MG change what they were using somewhere in the run?

 

Air bypass screws: Micha at MI suggested that they be adjusted to 1 turn out. He didn't say why he suggested that, but I believe it's to make sure that they're adjusted to the same value, so they don't throw off your balancing efforts with the idle stop screws. Perhaps it would be better to say that the air bypass screws shouldn't be touched unless you know what you're doing. I'll change the wording around the bypass screws: you're right, it's confusing right now.

 

Thanks for thoughts Ian

 

To my point, from what I read in Guzziology(I believe, or similar) regarding the TB balance procedure, was that the RH idle screw was redundant since the both TB's are linked. If they TBs were not, then having both screws would be necessary.

 

Basically the point was, use one or the other, but not both.... as adjusting one will just pull the other off of it's stop, and negate it's effectiveness.

 

I think the left hand screw is suggested to be kept out of the two because it's easiest to get to

 

 

For example:

 

Let's say you adjust idle from the left, and get it "just right", but then adjust the right set-screw because your vacuum was off(instead of just going directly to the balance knob). If you are able to move the TB at all with the right screw, you've now also lifted the left screw off if's stop because the TBs are linked... throwing everything off again.

 

Using just one screw provides a more consistent result, and trying to use both is not just ineffective, but throws more variables into the mix.

 

No one seems to know why MG included two set screws on this setup, since adjusting either just negates the other, since the TBs are linked

 

BTW, both/either of mine are useless, as they are both all the way out and my idle just is "what it is" reading about 1300rpm <_>

 

 

YMMV of course , but this is just the process that I've read I could be wrong.

 

 

Thanks for the feedback regarding the air-bypass screws as well.... but here's a thought...

 

If Mica's advice is simply meant to make sure the AB screws are "balanced" as part of this process, but we also agree that the AB screws should not be grossly adjusted without a gas analyzer, perhaps a better approach and description would be to suggest screwing the AB screws all the way back "in" and carefully note their postion(how many turns).

 

Then(hoping both were close to even) one can back them back out to their previous settings evenly on both sides... if making them "even" is a goal.

 

However, I'm not certain this is a good goal?? I may be going out of my depth here, but I would have to guess that if the bike were in a good state of tune, and a good shop adjusted the AB screws while using the correct gas analyzer sometime prior, and ended up with slightly uneven settings.... that maybe adjusting them just so they are "even" may be counterproductive?

 

Maybe someone who has a better understanding of the function and impact of adjusting the AB screws can chime in here.

 

I've never touched mine.

 

al

[exwtk]

Ian,

Nice work!

 

Alloow me to make some remarks.

Like Al, I do believe it is not neccesary to use the RH idle screw.

But for a different reason: is it not that by adjusting at the right hand side

you put STRAIN on the connection rod between the throttle plates?

 

Greetings from

Co.

[Guest IanJ]

I just talked to Micha again, to pass on these questions, and this is what he said (paraphrasing, obviously):

 

RH idle screw: it doesn't matter to 90% of the owners, but to that last anal 10%, you have to use both screws to get the idle just right. I count myself among that last 10% in some things, including throttle body balance. There will always be play in the linkage between the two throttle bodies, which is why we have adjustments available. Very tiny changes in the idle plate angle won't translate between the two cylinders.

 

Exwtk: there's no way to put strain on the system by using the idle stop screws, since the higher one will pull the throttle stop off the idle screw on the other side.

 

Al: Micha prefaced his comments on throttle balacing to me by saying, "yeah, I need to rewrite that chapter in Guzziology, I just haven't gotten to it yet." Take that for what you will.

 

Bypass screws: Micha said that he recommended 1 turn out because that's what "always ends up being right" around Seattle (altitude-wise, at least). He said that he adjusts the bike to 1 turn on the AB screws, balances the idle and on-throttle settings, and the CO ends up being exactly where he wants it to be in later testing. I can't really comment on that, as I don't fully understand the impact the AB screws have on CO at idle or higher. I will say that my AB screws went from about 3/4 or 7/8 of a turn to a full turn when I did the adjustment, with no difference that I can discern in how the bike runs.

 

As far as re-setting the AB screws, or setting them to be exactly even, Micha couldn't really give me a good reason why he does it, but he does. Again, I can't really comment, since what I wrote up on my website is literally the first time I ever did the balance on a FI Moto Guzzi (or FI anything, now that I think about it). I think leaving them alone probably makes exactly as much sense as resetting them yourself, due to evolutionary changes in the engine over the miles.

 

Since it's so easy to check the rich/lean state at idle, my inclination is to say that you can do whatever you want with your AB screws, just check your plugs to see that the settings aren't overboard in either direction.

[docc]

While the factory manual calls for 1/2 turn on the air screws, one full turn will give you more relaible idling.

 

Also, be sure your valves are set before you begin to balnce the TBs.

[al_roethlisberger]

Just for everyones' clarification, 1 "full turn" from....

 

- 1 full turn back "out" counter-clockwise from closed(clockwise)??

 

or...

 

Just curious.

 

al

[Admin Jaap]

...but to that last anal 10%,...

He's obviously talking about you, Al

[roberto]

I guess there are many ways to look at this, but my reasoning for removing the RH idle screw is so that if I disconnect the throttle linkage at the ball joint, the RH throttle valve will close completely. I can then take a TPS voltage reading, reconnect the linkage, and everything is back to normal - idle setting 'n' all. If the RH screw is still there I would have to back it out fully, check TPS and then try to find the idle setting I had before.

[docc]

Just for everyones' clarification, 1 "full turn" from....

 

One turn out from fully closed.

[dlaing]

FWIW I am one of the few who need to use the right set screw to balance the idle.

There is definitely slack in the throttle linkage, so screwing in the right will reduce vacuum on the right, and screwing in the left will reduce vaccuum on the left.

For some reason the right side creates more vacuum at idle on my bike.

I have thought about running the valves a little looser on the right and watch the effect.

Maybe I have an airleak on the left intake???? But I can't detect it.

Or maybe it is the crack in the crossover??? But that should not have much effect.

[Gio]

Good job Ian,

 

I just used my Twinmax for the first time tonight and found your report very usefull. The Twinmax is certainly a lot easier to use than the old carb stix but I do miss the quantitative measurement (eg cm of mercury) which was usefull for comparison with previous readings.

 

I wonder if anyone would care to comment on the significance of say 1 division on the Twinmax scale (at max sensitivity). Here are my results for example :

 

A= LHS, B= RHS cylinder. Twin max zeroed and set at maximum sensitivity

Both by-pass screws set at 1 turn out. Valves just set (at 6 and 8 thou)

 

1) Before balancing

 

At TO = ~400 Veglia rpm* = 1250 power commander rpm gave 1.5 divs toward B

At ~2000 Veglia rpm = 3000 power commander rpm gave 1 div towards B

 

2) Turned bal knob ~1/5 turn clockwise

 

At TO = ~400 Veglia rpm = 1250 power commander rpm gave 1 div toward B

At ~2000 Veglia rpm = 3000 power commander rpm gave 0 div (ie balanced)

 

Almost no deflection on application of throttle...and bike rides just great.

 

What kind of results do you get?

 

Gio

 

* PS - I don't expect super accuracy in a tach but this is a bit much...