How to balance a V11's throttle bodies UPDATE

[Desdinova]

After much delay, mostly due to the fear of the unkown, I decided to celebrate the new year by getting my 2002 Le Mans up to speed (excuse the pun).

 

I had some issues with it recently, but as to not confuse this article, I'll cut to the chase.

 

I needed to balance the carbs and in the process found some extra tips not covered in the guide I was useing.

 

This How To article http://www.obairlann.net/~reaper/bmw-bike/guzzi/balance.html by Ian Johnston is excellent. It's straight forward, simple and works.

 

Here are some additional notes that I found useful.

 

Before you get started:

 

- If you don't have any other external tach, or have a PowerCommander on your bike (like I do) go ahead and hook it up to your laptop or whatever and use it as your Tach. I do not find the bike's tach as accurate, and I like to deal in digits.

 

- Again, if you have a Power Pommander, go ahead and Zero-Out the 0% TP if it isn't already. Do not Zero the whole map, as you balance the carbs at 0% throttle at idle (less than 1500 rpm).

 

- Spend the $35.00 (or less) and get a cheap set of Mercury tubes for JC Whitney or wherever. If this is the only time you use them, it's worth it.

 

Tips for during the balance process:

 

- The "choke" or fast-idle lever and mechanism can really screw things up especially if you have made any modifications like a lighter spring. Use a twist tie or similar to lock it against its stop. ANY freeplay can make this whole job and nightmare, and if you use it to hold the fast idle speed during the second part of the process, you can't insure it returns to where it was. DO NOT JUST DISCONNECT IT!!!! If you do, when the throttle is open, the fast idle mechanism is flopping free and will just stay open when you come off the throttle. Trust me on this one. DO NOT DISCONNECT THE CHOKE MECHANSIM !!!

 

- Although getting the right-side carb idle adjust is a little but of a pain, do this one first. Get the mercury as close as possible using this one, then go to the left side, which is easy to access and dial it in.

 

- For the part of the second half of the process, let me qoute the article so we are on the same page as this was critical to this tip.

 

" Now that the idle settings are balanced, use the throttle to rev the motor up to around 3000 RPM -- the actual speed doesn't matter, you just need to be using the right grip to set engine speed. Note the balance you see on the manometer.

 

If it's not close to balanced, you need to adjust the balance knob on the left side of the bike. Release the throttle grip, make the adjustment, and rev the motor up to the same speed. Note the difference in balance -- if it went the wrong way, adjust the knob in the opposite direction. "

 

I would say the "the actual speed DOES matter," at least on my bike, because when I rev'd the bike up to about 3000 rpm the left cylinder was off a bit, consistantly all the way up to 3000rpm and I could never get it to match, using the knob, would just come close. However, if I went up to about 3400 rpm, there was a drastic change in the balance (in my case left Mercury level went way up). After some experimentation I realized I needed to adjust the high rpm balance at or higher than the rpm point where this change occurs. When I adjusted the white knob below this level, although the merc tubes got close, the left was always higher, except at idle. When I took the reading at about 3400 rpm and made my adjustment to the knob... repeated a couple of times, I was able to dial it in dead even. When done... the Mercury level is side-by-side from idle all the way up!!!!! Remember, as the article states. Bring the revs up, look at the tubes, drop back to idle, move knob, repeat. It takes very little movement of the knob to make a change. Try 1/4 turn intervals, the first time to see which way you need to go, 1/8 turn adjustments or less to dial in. Only took me about four or five tries to get the mercury dead even.

 

As was later explained to me by a Guzzi tech, the ECU has a low rpm and high rpm range, hence the reason the balance needs to be done at idle and at a higher rpm. The ECU transitions to the high range at about 3000 RPM. For my bike it seems like 3400rpm it's fully in the high range. With no load on the bike, it's pretty obvious to know when it's in the high range as it is near impossible to get it to idle at one speed without it wanting to speed up. I really think finding the point where the ECU is fully transitioned into the high rpm range is critical to getting a proper balance across the whole range. I no longer have the little hickups that I and many other experienced at around 3500rpm. It's just smooth sailing.

 

As soon as you get it even, shut the bike down and let it cool off a bit. Remember to not overheat the bike.

 

- After it cools off a little, re-start and check to make sure they are still balanced, then shut down, disconnect everything and go for a test drive.

 

- I would only return any of the PowerCommander settings AFTER the test drive. In my case, the Dyno tune I had done was compensating for the carbs being out of balance at idle. Now that they were balanced, the fuel numbers at idle needed to be a little different.

 

I hope you find this useful, and my thanks to Ian for a great article.

 

My final comment is that my Carbs were not all that far off. However, after following this procedure, where they are now balanced up'n down the rpm range, there is a HUGE difference in the performance. The improvement was noticible immediately on the test drive.

[dlaing]

Nice Post!

Does anyone know what size threads the idle set screws are?

Mine are wearing out from adjusting too many times, or using too small of a hex key...but I swear I have every size

 

EDIT apparently they are five mm by about 14mm long.

I bought a pair of five mm by 16mm with standard hex cap, so I can use a bigger hex key

It went in very loosely, so Loctite is a must.

[orangeokie]

Evoluzione Throttle Body Synchronizer(clicky)

[dlaing]

snipped image

Evoluzione Throttle Body Synchronizer(clicky)

86745[/snapback]

Those look really primitive.

Do you have to remove the air filter to use it?

Maybe I am wrong but basic Mercury sticks work great until you suck mercury.

The Morgan Carbtune looks better, but maybe less accurate

http://www.carbtune.com/

The TwinMax is pretty portable and convenient and seems to be more than accurate enough

http://www.epfguzzi.com/twinmax.html

I still would love to develop an onboard constant monitoring meter to let you know when it goes out.

I have some ideas

But probably not worth patenting...

[Guest Nogbad]

The Morgan Carbtune is a great bit of kit and I have used mine to great effect.

 

I deal with pressure measurements a lot for my job. Dwyer make some good and reasonably priced kit you could use.

 

Expensive but useful

 

Or you could try coupling a low range differential pressure gauge across both carbs and adjusting to centre zero. I might try this method as I have a few of these gauges.

 

Diff pressure gauges

[jrt]

The twinmax works great. I used to have carb stix and this is a huge improvement- in large part because it stores so much easier.