• Ciao Guest - You’ve landed at the ultimate Guzzi site. NEW FORUM REGISTRATIONS REQUIRE EMAIL ACTIVATION - CHECK YOUR SPAM FOLDER - Use the CONTACT above if you need help. New to the forum? For all new members, we require ONE post in the Introductions section at the bottom, in order to post in most of the other sections. ALWAYS TRY A SEARCH BEFORE STARTING A NEW TOPIC - Most questions you may have, have likely been already answered. DON'T BE A DRIVE-BY POSTER: As a common courtesy, check back in and reply within 24 hours, or your post will be deleted. Note there's decades of heavily experienced Guzzi professionals on this site, all whom happily give endless amounts of their VALUABLE time for free; BE COURTEOUS AND RESPECTFUL!
  • There is ZERO tolerance on personal attacks and ANY HYPERLINKS to PRODUCT(S) or other competing website(s), including personal pages, social media or other Forums. This ALSO INCLUDES ECU DIAGnostic software, questions and mapping. We work very hard to offer commercially supported products and to keep info relevant here. First offense is a note, second is a warning, third time will get you banned from the site. We don't have the time to chase repeat (and ignorant) offenders. This is NOT a social media platform; It's an ad-free, privately funded website, in small help with user donations. Be sure to see the GTM STORE link above; ALL product purchases help support the site, or you can upgrade your Forum profile or DONATE via the link above.
  • Be sure to see the GTM STORE link also above for our 700+ product inventory, including OEM parts and many of our 100% Made-in-SoCal-USA GTM products and engine kits. In SoCal? Click the SERVICE tab above for the best in service, tires, tuning and installation of our products or custom work, and don't miss our GT MotoCycles® (not) art on the BUILDS tab above. WE'RE HERE ONLINE ONLY - NO PHONE CALLS MADE OR RECEIVED - DO NOT EMAIL AND ASK QUESTIONS OR ASK TO CALL YOU.
  • Like the new V100, GuzziTech is full throttle into the future! We're now running on an all-new server and we've updated our Forum software. The visual differences are obvious, but hopefully you'll notice the super-fast speed. If you notice any glitches or have any issues, please post on the Site Support section at the bottom. If you haven't yet, please upgrade your account which is covered in the Site Support section or via the DONATE tab above, which gives you full site access including the DOWNLOADS section. We really appreciate every $ and your support to keep this site ad-free. Create an account, sign in, upgrade your account, and enjoy. See you on the road in 2024.

The Sacred Screw, the elusive 4.8, my story

Vince!
You are brilliant! Not only were you able to decipher all my mumbo-jumbo and make sense of it and make it work for you, you have also added the drawings that were so badly needed to make it easier to understand. When I posted the original, I had never added a picture to a post, and because I could understand my own explanation, I never thought of taking it that step further. Thank you!
You should have seen some of the things I rigged up in my shop at the time, to determine what that number 4.8 really meant!
With the stepper motor and the TPS all referring back to that throttle valve setting, it can be a mess when you do not know where the valve is at.
I did not have the luxury of re-setting my TPS at home. As the bike warmed up, and the stepper motor went to the minimum air position, it would no longer idle. At this point I had no doubt I was on the right track, so I nursed the Breva 35 km out of town to a shop that did the re-set for me, and BINGO!
My bike had a similar story of sitting for more than 2 years (startus interruptus issue)before my time. Removing and cleaning the injectors also made a very noticeable difference in running at the time. Give your stepper motor some love while you are at it, and you will (like me) love the Breva.
Your donation is incredibly generous. This site has been invaluable to me, and we are all better off for it's existence. So thank you....we are all in this together.
And thank you Scott for getting involved and encouraging Vince on his quest.
 
Morning Chaps!

Sorry to resurrect an old thread but I've only just found it!!

My 2005 B11 also came to me with a molested sacred screw but I didn't know such a thing was a problem until it was too late. Hey ho you live and learn.

ANYWAY.
Can you measure the dimension with the throttle bodies on the bike or do they need removing as Vince did?

Cheers

Tris
 
Hello Tris

I would strongly recommend to take out the throttlebody. Its also a good chance then to clean it.
I fixed it in a vice and the with a calliper you can make it very exactely. A digital calliper is in that case better, because you can set it in any position to zero and then turn up or down to 2.40mm.

You can also check aproximately the second throttle (synchronise) it with the connection link. In my case it was almost perfect, but you can change this then later when you synchronise and set the idle at warm engine.

I wish you good luck
regards from switzerland
Vince
 
Cheers Vince

The bike has got to work for the next 2 weekends so I wont touch it for a little while, but I have one more question

Is the position of the butterfly very sensitive to the adjusting sacred screw? ie does a small change to the screw result in a large change in the distance to the edge of the butterfly

Anyway the "job list" is building up:-
  • Dash to Carmo - LCD keeps going black
  • Clutch thrust rod
  • Reaction rod bush change
  • Sacred screw fondling back into position
I might call the riding season to an early conclusion this year so I can get this lot nailed down!

Thanks again

Tris
 
You will love the result of the reaction rod silent bush.
Measuring the throttle valve with the T/B in place can be a tad awkward, but if you move a couple of the relays (starter etc.) out of the way so they do not interfere with your calipers, you should be able to get a good measurement, at least to get you to the end of the season, if you need to clean your throttle bodies.
It has been some time since I did this. I went back and re-measured a year or so later, still with the t/b in place. Everything in order, and I have not had an issue since.
An Allen key has six sides, each representing 60 degrees, either one flat to the next, or corner to corner. Once you have the throttle set, take a picture of the position of the Allen key "hanging" in the throttle screw, or commit it to memory. Set your TPS here. If you find the idle a little high for your liking (in traffic on a hot day it can climb over 1200 rpm, which seems a little frantic), a roughly 30-40 degree turn will lower the idle speed about 100 rpm. The original Power Point presentation gives you a window of 4.5-4.9 inclusive. If you are in this range, they say a re-set is not required. So there is a bit of wiggle room at the end of the assembly line.
If you lower the idle speed a tad (as I have done, to good effect), I suggest going back to that original idle screw setting for your next tune up (t/b balance) and TPS re-set.
Not very scientific. I call it "Fumbling towards ecstasy".
 
Cheers!

Things have moved on since I last wrote

a) Reaction rod fitted and .... all is good!
b) After a ride in the rain last Saturday the bike decided to disconnect its ECU and had to come home in a breakdown van :(

I find its quite tricky to adjust the idle speed when the engine wont run :D

Hey-ho - these are the joys of Guzzi motorcycle riding!!
 
When I started this journey in 2013, I did not have much to go on. The actual idle speed did not seem important, and my 3 sources of information all said 1100 +/- 100 rpm. In an exchange with Todd E back then, he told me "The system is designed to idle at 1,250 rpm".
I filed this info in the back of my mind, thinking it seemed a tad high.

To make it short, this is the key to the whole issue (Thank you Todd). You can only buy the complete throttle body assembly (part # 05112530, same for G11 and B11), with the two TBs assembled on the mounting plate that will also hold the stepper motor in the end. Weber sets up the assembly at 4.8 mm fully syncronized on a flow bench (this is my own theory).
At the end of the assembly line, it is hooked up to diagnostics, TPS and learning parameters set, then started, the idle set to 1250. Shut down, re set TPS and parameters, good to go. The stepper motor set-up is proven and reliable, so no need to go to full operating temperature.

Your stepper motor MUST be in order.
Fully warmed up, set the idle at 1250 (the tack is accurate, but hard to read, diagnostics is best). Your stepper valve is in the min. air position. Your next cold start should see the following: Idle settling @ 1250 within just a few seconds, and staying there through the entire warm up. On a hot start (gas station), it will rise briefly to 18-2000 rpm, while the stepper valve goes from max air to min air , settling at 1250 in maybe 5 seconds.
If it struggles a bit on a cold start, the airbox orifice that feeds air from the airbox to the stepper motor may be too restrictive. I will open mine up with a 15/64th (6mm) drill to match the intake pipe on the stepper motor. More on this below.

In the zone:
Best power ever, with flawless low speed fueling (stock w/K@N and O2 optimizer).
Fuel consumption computer extremely close to fuel metered into the tank.
Less Carc rattle @ idle.

There is a G-11 in my life for the last year. It is set up the same way, and acts exactly the same.
It had other issues; a severe restriction in the airbox feed to the stepper, significant enough that I will make a separate post in the Griso/Bella section. Horrific when you look back at the history of the early models.(Griso only)

Why is the screw "sacred"? Why the dire warnings from MG?
If you alter the screw to somewhere outside the parameters, then re-set the TPS, your bike may no longer meet Euro-3/ CARB emission standards.
In the past I had to over-think all this to assure myself I was doing it right.
In the end it seems so simple.
I am now looking forward to a few years of uncomplicated riding!
 
An interesting insight Nordi

I purchased my B11 with a futzed sacred screw before I knew of such things and have been slowly trying various things to get it back where it belongs

Its not far off now, and I shall see if mine reacts as you describe above.

However, I found this from GrahamNZ which I found interesting as allows you to remove one of the variables when trying to get things correct https://www.guzzitech.com/forums/threads/stepper-motor-on-off-kit.3025/page-4#post-28926

I'd be very interested to know if you plug the stepper feed on your sorted bike whether it now idles at 1k RPM as Graham suggests

Cheers
 
Thanks for the link, I have red the whole thing.
On your Breva, you can reach the air pipe from the right side under the tank. It is the size of your pinky, and comes down vertically from the bottom of the air-box, then loops around to the stepper motor.
If you reach in with a pair of long nosed pliers and pinch the tube shut, the idle rpm should drop about 200 rpm, as the stepper is always passing air, even in the minimum air position when idling a full operating temp.

An interesting aside re. B-11: the owners hand book boasts about a cold starting function programmed into the system, that will be activated below freezing temperatures. During a late October overnight cruise with minus 3 deg.C (frost on everything), this was nowhere to be found, so throttle was needed to light the fire. It added to my suspicion that the air supply is somewhat restricted, and may not being able to keep up with what the ECU requires to make this function work.
 
Cheers Nordi - I really think you're onto something here.

Its interesting that you observe that blocking the feed drops the revs by 200 RPM and right into Grahams target range.

After setting mine up using Grahams methodology, I've found that mine struggles a touch from cold and I think that I'll disconnect the feed from the air box as an experiment

If there is a restriction is in the connection on the air box, I should ;) see an improvement in cold starting

When I get time to play with the bike I shall experiment some more!

Thanks again
 
Last edited:
Just checked the air supply orifice in my Breva airbox. It is the correct size (6mm or 15/64") to match the intake of the stepper motor, so there is no restriction there. Just to make sure, I reamed it slightly with a 1/4" drill bit, making sure to dis-connect the hose first to keep the stepper motor clean.
 
I know this is an old thread but I’ve been curious as to why you would need to replace the the body of screw has been turned. Maybe I over simplify things in my thinking but to me it looks like a mechanical adjustment,getting it set properly may require knowledge and equipment that I don’t have but I can see no reason why it would need to be replaced. Somebody somewhere made the initial adjustment and I can’t see why that couldn’t be replicated. The way the manual makes it sound doesn’t make sense. Really enjoyed this thread . Nice to know I’m not the only one that figures things out at 3am.
 
I know this is an old thread but I’ve been curious as to why you would need to replace the the body of screw has been turned. Maybe I over simplify things in my thinking but to me it looks like a mechanical adjustment,getting it set properly may require knowledge and equipment that I don’t have but I can see no reason why it would need to be replaced. Somebody somewhere made the initial adjustment and I can’t see why that couldn’t be replicated. The way the manual makes it sound doesn’t make sense. Really enjoyed this thread . Nice to know I’m not the only one that figures things out at 3am.


When the throttle bodies are assembled at the factory, they have a fixture that puts the butterfly at the required degrees of open. Some bikes it is 4.6, others 4.8. Without that fixture it is next to impossible to set at throttle body at that opening without some type of setting device that can accurately position the butterfly. So far, not one has developed a tool to set that opening that I'm aware of though some claim to be able to do it, but I question their accuracy. So, don't mess with that screw.
 
I know this is an old thread but I’ve been curious as to why you would need to replace the the body of screw has been turned. Maybe I over simplify things in my thinking but to me it looks like a mechanical adjustment,getting it set properly may require knowledge and equipment that I don’t have but I can see no reason why it would need to be replaced. Somebody somewhere made the initial adjustment and I can’t see why that couldn’t be replicated. The way the manual makes it sound doesn’t make sense. Really enjoyed this thread . Nice to know I’m not the only one that figures things out at 3am.

The throttle body is set up on a calibrated air plenum flow bench. Without one, you will never get it set back correctly. This will cause physical operating conditions to never match logical conditions inside the ECU map - Hence, poor running torever.

People make fun of the moniker “sacred screw” but those of us who have tried to undo the damage from somebody messing with the settings, know that the factory isn’t kidding.

Like John says, don’t touch it. Ever.
 
Why can you not measure the gap between valve and body on one that’s not been messed with. Something I worked on in the past,can’t remember what,you set the opening on #1with a wire gauge and then used vacuum gauges to match remaining cylinders to it.
 
Why can you not measure the gap between valve and body on one that’s not been messed with. Something I worked on in the past,can’t remember what,you set the opening on #1with a wire gauge and then used vacuum gauges to match remaining cylinders to it.
it would have to be the same body, before and after, but sure.

but why? there's no improvement to be had, only risk.
 
I’m saying someone get an accurate measurement for reference in the case of maybe buying a used bike that someone’s been screwing around with. Like the original poster
 
I’m saying someone get an accurate measurement for reference in the case of maybe buying a used bike that someone’s been screwing around with. Like the original poster
I don't think that's possible, the whole point is that the adjustment is body specific. if it was a static value, this issue wouldn't exist.
 
I'd like to suggest what I feel is the simplest way to reset the "sacred screw" and verify mechanical sync of the throttle bodies on a 5AM Guzzi. This is prior to doing anything with the air bleed screws, messing with steppers, or even having the engine running -- it's just to establish a proper reference base mechanically and ensure that the TBs are in fact physically in sync and the sacred stop is where it should be. The idea behind this method isn't new and was hinted at by Rafael way back when but I can add a few little specifics.

You will need a Diag or a VDSTS for this, in order to see the TPS reading in real time and reset the TPS. Connect the tool to the bike so it shows the TPS value and proceed as follows:

1. Disconnect the throttle body linkage from the right-side TB. We now know that the right throttle body, which houses the TPS, is fully closed.
2. Reset TPS. It becomes the reference value -- let's say for the sake of this example it is 4.8 (like on a Griso). So we now have a fully closed right-side butterfly and a TPS reading of 4.8
3. Back out the sacred screw fully so it does not prevent the left throttle body butterfly from fully closing. We now have the left side closed as well. The TPS reading should be unaffected and still at 4.8, as the linkage is not connected and there is no mechanical link between the TBs.
4. Connect the linkage rod back. Snap the throttle a couple of times. Watch the TPS reading. If it changed from our reference 4.8 (likely, unless the TBs were in perfect sync to begin with), use the TB balance screw (NOT the "sacred screw" -- that still remains fully out!) to bring the TPS reading back to 4.8. At this point we have both TBs in sync; fully closed. The TPS is still reading 4.8.
5. Now slowly screw in the "sacred screw" until your TPS reading shows DOUBLE of the reference value -- 9.6 in our case. We are essentially opening the butterflies from fully closed to 4.8 (as per the software; we don't even care what the units are). The reason this works is that these TPS sensors are linear, at least in the range we are talking here.
6. Reset the TPS again. It is now back to 4.8 At this point we are done: both throttle bodies are in sync and we know that the once sacred left side throttle stop is set correctly :)

Hope this is of help for someone.

This is how it was explained to me by my Guzzi Regional Tech and worked great on 3 bikes now.
 
This is how it was explained to me by my Guzzi Regional Tech and worked great on 3 bikes now.
That’s very interesting and easy to understand. So you use the tps as a measuring device and contrary to service manual throttle body is not a total loss from turning the screw. I’m not having a problem with mine I just try to make sense of things that make no sense. Putting an adjustment screw in place of a non adjustable or tamper proof screw and then saying if you adjust the screw the throttle body is trash doesn’t make good sense to me.thanks
 
Back
Top