Throttle Body Balancing

[Seweryn]

I have tried another trick as I couldn't get rid of the abruptness - the engine hesitates between 4.6 (fully closed) and 5+ deg. of the throttle opening angle.  The engine jumps the revs to about 2k rpm from 1.2k on idle when very gently increasing the throttle opening angle.

I thought the issue must be caused by too lean mixture on idle / just off idle, so I tried what was mentioned elsewhere on the forum - I sprayed some silicone lubricant into the stepper inlet today and I noticed the improvement - much smoother throttle response from off position without the jerkiness.

What do you think - is it temporary improvement or will the stepper function OK from now?  Did anyone get the problem resolved this way?

[Huzo]

You can look at a graph in real time as you open the throttle therefore deflecting the plates.
That will show you if the TPS is tracking correctly.
Guzzidiag has this feature.

[Seweryn]

Thanks Huzo,

I had a look at this and found no malfunction in the TPS.

[Huzo]

What does your manometer say at the point where the anomaly is ?

[Seweryn]

What does your manometer say at the point where the anomaly is ?

It is more / less in balance.  And by observing the linkage it seems that both throttles open together.  I believe the issue is in the stepper which delivers too much extra air - it is noticable only at very low throttle opening angle.  At that point the extra air leans the mixture to the point that it can't ignite.  The lubricant cured the symptoms yesterday, but I am not sure will that last long.

[Huzo]

Mmmm…

[Seweryn]

Well, I am sure time will tell, but I hope the symptoms never return.  I was happy enough yesterday to at least know what is causing the jerkiness after working on the issue for the last few months.  Not a cheap part if needs to be replaced, but will see.

[Seweryn]

Do you know if the stepper motor (the plastic one) is the very same model used for all 4V / cyl. engines (or all 1200 engines)?  I have installed a second hand set of throttle bodies complete with the stepper and it seems the thing is probably faulty as the idle doesn't go lower than 1,400 - 2,000 rpm.  The important screws are untouched and I have done the balancing and TPS reset, etc.

[guzzisteve]

Stepper is same on all Guzzi's 2V & 4V, 1200 & 1100. If you pinch off air does it return to normal idle? It may be dirty.

[Seweryn]

Thanks Steve,

I will test the airline this evening by blocking the supply (I have a temporary cut off valve I used before, so may install it this time).  I just have a bad feeling the stepper is not functiong, but maybe cleaning will help.  I will update.

[Seweryn]

So after installing the manual air inlet restriction valve and blocking the air supply to the stepper, the engine idle speed is about 1300 rpm.  I don't understand why.  The TPS was re-set and sits at 4.6 degree as of yesterday.  The bypass air screws are closed with one half turn open.  If the bypass air lines are blocked it means the ECU injects too much fuel probably.  Any ideas?

[Huzo]

My cell is +61437070946
Text me yours and I’ll explain. Idle speed is increased by leaning idle mixture (addition of air)
You possibly have an air leak.

[Seweryn]

Thanks Huzo, I have messaged you on that number.  Appreciate your reply.

[Speedfrog]

Someone recently posted on the **Griso ghetto having successfully found a generic replacement for the stepper motor. I’ll try to find the link and post it here.
Here it is: https://www.grisoghetto.com/t7715-lilian-tech-stepper-repair-easy-to-find-and-money-saving-automotive-part

[Seweryn]

Here is my other theory of the problem - the new stepper is faulty and stays in open position, which means the air can flow between the two inlet manifolds.

When doing the balancing I remember I had to open the right throttle a good bit (balancing screw about a half - one full turn clockwise direction), which means the engine gets more air delivered and that is impossible to compensate down...

[Bulldog9]

Just re-read the thread.

I've had two 8V Norge (2014 & 2012) a 1200 Sport, and 1100 Griso. I no longer have the 2014 Norge, but the other three suffer under my ownership 

I've TB balanced all, cleaned the Stepper on all, and done all the variations. The biggest change or help with the abrupt throttle response (low speed snatchy throttle response) was to eliminate slack from the throttle cables on the push and pull. On the Griso specifically, the Beetle Map slowed down initial throttle response. This made a huge difference.

When it comes to the evap systems and TB air ports (where you connect the manometer), I have 3 different setups.

1. Griso - System left in place with ball bearings stuffed in each of the lines going to the TBs with the check valve disabled. This basically allows the tank to vent/breathe to atmosphere through the charcoal canister.

2. 1200 Sport - System completely removed and the TB air ports are connected with a vacuum line. This acts almost the same as an exhaust crossover balancing the intake charge. The tank vents/breathes to atmosphere to lines at the bottom of the motor near the airbox oil bleed tube and gas overflow hose.

3. 2012 Norge - Completely Stock.

On the 2014 Norge, I removed the system to try and fix a running issue (wouldnt rev past 6K. This ended up being a cam being out of sync). When trying to sort this, I removed the evap system and plugged the TB air ports with rubber caps. They started leaking and really messed with the running with symptoms similar to yours. I ended up connecting the ports with a vacuum hose and clamped tight with ottiger clamps and the stumble, low speed issues and lumpy idle disappeared.

So at a minimum, check to make sure your TB air ports are sealed. Hope this helps!

FWIW, I use the Seafoam upper cylinder spray cleaner to clean the stepper. I spray a bunch while running, then spray and shut off to let sit for a while, overnight preferred. Then I restart, respray, hook up GD and cycle the Stepper Actor to get it to cycle. The result has been flawless  stepper function.

[pressureangle]

I have just inspected the valvetrain and found that the left cylinder inlet valves were both loose - I guess they were at 0.3 - 0.4 mm.  The rest of them were more / less OK.  I then ran the vacuum test and found that I needed to correct the high rpm ballance by almost third of the turn of the screw (clockwise) for the vacuum balance.  Does that seem right?  It means that I now need to increase the opening angle of the right cylinder throttle by about 0.5 degree (roughly measured with Guzzi Diag).  Then to compensate for the idle I will need to open the left cylinder bypass screw (currently both are closed).  It all means there will be more air getting into the engine at idle.  I started the balancing work yesterday but didn't finish yet as the correction values were surprisingly high to make it in balance, so I had to sleep with all this in my head.
 
Your valuable comments would be appreciated.

This point is obvious but too often missed in the discussions of balancing TBs- it's not hard to visualize how vacuum is affected by the intake valve opening time. A couple thousandths makes a big difference. A proper valve adjustment should always precede a balance.

[Seweryn]

I have checked the balance again and ended up in more less the same place.  The engine runs rather well when cruising and is even a little smoother at low throttle opening angles, there are no obvious vacuum leaks, but it idles at near 1400 rpm (or just over 1300 with the inlet to the stepper completely blocked using a shut off valve - which means the stepper works OK).

The important screw looks factory intact, but what do you think - should i try to alter the position of the special screw?  I believe that should help setting the idle speed to 1200 rpm, but I wanted to eliminate any other potential installation error with this new set of throttle bodies, but all seems to be OK apart from the elevated idle speed, which I believe is caused by the higher air flow through the throttle bodies.  Just my theory, but I would welcome your comments.

[Huzo]

I have checked the balance again and ended up in more less the same place.  The engine runs rather well when cruising and is even a little smoother at low throttle opening angles, there are no obvious vacuum leaks, but it idles at near 1400 rpm (or just over 1300 with the inlet to the stepper completely blocked using a shut off valve - which means the stepper works OK).

The important screw looks factory intact, but what do you think - should i try to alter the position of the special screw?  I believe that should help setting the idle speed to 1200 rpm, but I wanted to eliminate any other potential installation error with this new set of throttle bodies, but all seems to be OK apart from the elevated idle speed, which I believe is caused by the higher air flow through the throttle bodies.  Just my theory, but I would welcome your comments.

Sorry mate but my ‘phone dropped out of range..(Central Australia).
Even if you do adjust the sacred screw, a properly functioning stepper will just re set to achieve the target value and you are on the road to ruin…
Have you properly re seated the screws in the intake manifolds after disconnecting your balance tool ?

What was the damage to your original throttle bodies ?

[Seweryn]

No worries P., thanks for calling, it's great to have a chat anyway.

There was no damage to the original throttle bodies (there is now).  I replaced them, because of the faulty stepper that I managed to damage.

[Huzo]

No worries P., thanks for calling, it's great to have a chat anyway.

There was no damage to the original throttle bodies (there is now).  I replaced them, because of the faulty stepper that I managed to damage.

Are the originals irredemably buggered ?
What happened to them ?

[Seweryn]

Unfortunately, yes.  There was no TPS in the new set so I had to cut the outer casing to salvage the old TPS to fit it into the new set.

[Huzo]

Unfortunately, yes.  There was no TPS in the new set so I had to cut the outer casing to salvage the old TPS to fit it into the new set.

Hmmm….
Are you certain that the “new set” are not for a 1200 Sport (larger bore) or an earlier 2VPC Norge or similar ?

If they are not a proper match, then the mixture and all the commands to the ECU will be monumentally unreliable. They need to be removed and the bore accurately measured at the cylinder end.
The 1200 4 VPC Sports and the like, are a quite different size to the earlier Norges and such.

[Seweryn]

That's interesting.  I thought the throttle bodies for 2V motors are slightly different with the bypass air screws in a different location.
My model is the 1200 Sport 4V and should have the latest throttle bodies.  I have measured the old set removed from the engine and the throttles are 50 mm.  The new replacement I bought on eBay was described as for a Norge 1200 GT 2011+.  I haven't checked the diameters yet as this would require some dismantling, but I don't believe they would be any different or smaller?

[Seweryn]

So just a quick update.  The bike now runs well with the air damper (cut off valve, but left in the open position) in the air inlet pipe to the stepper.  But without the damper it it's very jerky off/on throttle at lower rpm, which suggests too much air getting into the engine.  Stepper works OK.  After checking all I could think of and re-balancing the throttle bodies again the only conclusion I have is that the throttle stop screw (never to be touched) is slightly off the correct position, although it hasn't been altered from the factory.  The idle speed is around 1300 - 1400 rpm on hot engine, running good.
Another observation - there is no bad (unburned petrol) fume smell on idle as it was when running with the old original throttle bodies.  That means the mixture is leaner which supports my theory above.

[Huzo]

You might try taking the stepper off with the two black TB supply hoses attached and after blocking them off, submerge the stepper in water, supply low pressure air from a source (compressor) via the central supply hose and see if bubbles come from the stepper body.
This would test for any potential leakage points in the stepper body or plumbing.
Remove the TPS first…