tuning a Lemans IV

[bentombed]

Hi,  I need some pointers to tune my LeMans IV, the bike is new to me and has done around 110,000ks

The PO had cable tied the throttle cables all over the place and the bike was really out of sync, i undid all that and rerouted the cables and tried to sync the carbs with Carbmate tool

The bike rides well but there is a lot of vibrations through the bars at low revs, more than before, what should i be looking for to smooth out the ride?

the bike has not been modified.

Thanks heaps

[Chuck in Indiana]

First, welcome to WildGuzzi.  Normally, vibration is caused by carbs/throttle bodies being out of sync. Did you sync the carbs at around 4K rpm *and* idle?

[pehayes]

Tell us where you are located.  Perhaps someone nearby to coach you.

Tell us about your procedure for synchronizing.  There are two phases to manage these carbs.  First, you need both sides to be in balance when they are resting at idle.  Second, both sides need to lift off of idle at exactly the same time.  You might wish to read the following:

http://www.thisoldtractor.com/moto_guzzi_loopframe_carburetor_balancing_synchronizing.html

Patrick Hayes
Fremont CA

[bentombed]

First, welcome to WildGuzzi.  Normally, vibration is caused by carbs/throttle bodies being out of sync. Did you sync the carbs at around 4K rpm *and* idle?

that might be it-  i worked my way through the Carbmate dials but did not rev the bike that high during the process.

[bentombed]

Tell us where you are located.  Perhaps someone nearby to coach you.

Tell us about your procedure for synchronizing.  There are two phases to manage these carbs.  First, you need both sides to be in balance when they are resting at idle.  Second, both sides need to lift off of idle at exactly the same time.  You might wish to read the following:

http://www.thisoldtractor.com/moto_guzzi_loopframe_carburetor_balancing_synchronizing.html

Patrick Hayes
Fremont CA

Sorry mate - Brisbane Australia! G'day!
from the link you posted and the other reply i am figuring that I did not get the carbs to sync at high enough revs.  the steps seem to be; double check the idle settings, get them right then try syncing the carbs again.

Thank you!   

[wirespokes]

I've found with mine, if the cables aren't bent at the carb end, I can get it pretty close by adjusting the free play at the throttle end. If they're bent at the carb end, carefully straighten them out. Seems like they get bent removing or installing the barrel end first, so be careful there. Pull the housing out of the stop first, then remove the barrel.

[fotoguzzi]

The PO had cable tied the throttle cables all over the place
[/quotes new set of cables might be in order or at least make sure they work in sync.

[double.d]

Hi Bentomed, I'm in Brisbane (Greenbank) and would be happy to help. I have a Carbmate as well but don't use it any more due to poor connections and air leaks.

Cables are very important and its imperative that both arms on the carbs move exactly the same on the slightest opening. With the tank off its hard to eyeball both arms at once so put a finger on one and watch the other one while you put slight pressure on the throttle, you will know straight away if one is moving more than the other. Adjust the cable to suit.
Adjust both idle screws so revs are at 1500, pull a plug lead (if the engine stalls go to higher revs) and go to the opposite side carb and turn the mixture screw until that pot reaches its highest rev, then do the same with the other side.

I have had mine since new and have been using this method for years. Have a go and let me know if you can't sort it and we'll get together and work it out.

You could also try Tom at Don Newell Motorcycles at Buranda, he is the local expert.

There is also the issue of points and timing, are they good?

[earemike]

Awesome, I’ve just been trying to get the slides to close at the same time...

[double.d]

In my experience if they open evenly they should close evenly, given the return springs are the same but slides and bores wear out so if you still have the original items it may be time to tear them down and inspect them.

[bentombed]

Hi Bentomed, I'm in Brisbane (Greenbank) and would be happy to help. I have a Carbmate as well but don't use it any more due to poor connections and air leaks.

Cables are very important and its imperative that both arms on the carbs move exactly the same on the slightest opening. With the tank off its hard to eyeball both arms at once so put a finger on one and watch the other one while you put slight pressure on the throttle, you will know straight away if one is moving more than the other. Adjust the cable to suit.
Adjust both idle screws so revs are at 1500, pull a plug lead (if the engine stalls go to higher revs) and go to the opposite side carb and turn the mixture screw until that pot reaches its highest rev, then do the same with the other side.

I have had mine since new and have been using this method for years. Have a go and let me know if you can't sort it and we'll get together and work it out.

You could also try Tom at Don Newell Motorcycles at Buranda, he is the local expert.

There is also the issue of points and timing, are they good?

Hello!!  I will try your method tomorrow - I have had the bike down to Tom, he checked over it pretty thoroughly, the points, timing, uni joint and brakes are all good. Tom changed the fluids for me but we didnt get to the tune. He has little time and i have little money :(  I'm up in Moorooka

Thanks heaps!

[bentombed]

The PO had cable tied the throttle cables all over the place

 new set of cables might be in order or at least make sure they work in sync.

on that - i have some coming

[Furbo]

Hi Bentomed, I'm in Brisbane (Greenbank) and would be happy to help. I have a Carbmate as well but don't use it any more due to poor connections and air leaks.

Cables are very important and its imperative that both arms on the carbs move exactly the same on the slightest opening. With the tank off its hard to eyeball both arms at once so put a finger on one and watch the other one while you put slight pressure on the throttle, you will know straight away if one is moving more than the other. Adjust the cable to suit.
Adjust both idle screws so revs are at 1500, pull a plug lead (if the engine stalls go to higher revs) and go to the opposite side carb and turn the mixture screw until that pot reaches its highest rev, then do the same with the other side.

I have had mine since new and have been using this method for years. Have a go and let me know if you can't sort it and we'll get together and work it out.

You could also try Tom at Don Newell Motorcycles at Buranda, he is the local expert.

There is also the issue of points and timing, are they good?

I'd usually balance the carbs at 4k rpm with carb stix. This takes care of a balance when you need it (while the motor is pulling) as well as being easy to see if the carbs are opening together.  Then I'd use the method above to set the idle on both sides. Also - installing a balance tube between the carb manifolds is an old trick for smoother idle - but it must be blocked while setting idle on a single cylinder. Good luck!

[pehayes]

I hope I don't start a war here.  Different folks have different techniques and opinions on carb balance/sync.  I differ from many others.  I'm happy with what I do.  YMMV.  Up to you to experiment with various techniques and settle on what you are confident and competent with.

Dual carbs have two issues.

The first is BALANCE.  At a resting idle, both cylinders should be working equally.  We measure and test by analyzing the vacuum created in the intake manifold.  The vacuum draw on each side must be equal.  Not quite so easy to inspect or adjust when the instrument is pulsing up and down with each engine cycle.  You have to get a mechanical 'fell' for what equal means.  When the carbs are in balance at idle, the cables should be slack and the carb slides are resting firm on the idle speed adjusting screws. Done.

The second issue is SYNCHRONY.  You will hear many describe adjusting the carbs at some higher rpm.  From a seat-of-the-pants effect, I doubt you or the motor would be able to detect a few percentage points of imbalance at those rotational speeds rolling down the highway.  If I were tuning a drag bike or land speed bike I might be more anal about the high rpm measurements.  To me, the most important practical, on the road feel is how the carbs react when you are feathering the clutch and pulling away in first gear from a traffic light.  Even the slightest variation here is going to display as a significant vibration or roughness.  To me (again, YMMV) it it imperative that both carbs begin to open and open at the same rate for the first 20 yards from a dead stop.  Unless you have some other significant mechanical cable issue, if the two carbs start to open together then they should remain together or fairly close throughout their full range of utilization.

So, I balance at idle.
Then I just slightly and gradually crack the throttle and watch for vacuum changes.  The cables are now taut and have lifted the carb slides off of the idle speed adjusting screws.  I adjust the cables so that they are slack at idle but they tighten and lift simultaneously.  Crack and adjust.  Crack and adjust.  Verified by watching the vacuum drop as the carb slides just begin lifting.  I'm done.  The system is now both balanced and synchronized.  If I were to raise the rpm and alter the cable adjustment at speed then when I return to idle I would find a balanced idle but a distorted and unequal draw coming just off idle.  IMHO, the the off-the-line draw is far more important to a smooth and relaxed Guzzi in traffic.

If you're happy then continue to do it your way.  I'm merely pointing out that there are variations in technique.  If you continue to struggle with an uncomfortable traffic bike then perhaps experiment with someone else's idea.

PS:  Call me archaic.  I've never been happy with using rotary analog vacuum gauges.  I much prefer my old fashioned, dual-column mercury Carb-Stix.  When traveling I can get by with a solid state floppy needle device.  I'm lucky to have the rare HARMONIZER which is out of production.  I also  have the TWINMAX but the HARMONIZER includes an rpm feature.

Patrick Hayes
Fremont CA

[wirespokes]

I'm with Patrick on this one. I don't synch at cruising RPM, just idle. But when I'm done I rev up the engine to see if the vacuum stays matched between the two. I use the tuin max and it's worked well enough for me.

[Furbo]

I'm with Patrick on this one. I don't synch at cruising RPM, just idle. But when I'm done I rev up the engine to see if the vacuum stays matched between the two. I use the tuin max and it's worked well enough for me.

Wire, Pat,

no man - y'all are the Artists. I am the archaic one.  Like the guy who refuses to bag his lawn, I really don't care much about the idle. I set my timing dynamically at Full Advance, and balance my carbs there as well. I used to refine my idle using the one plug method on my SPIII (last guzzi tourer), but on the current Sport 1100 - if it's still idling at about the right speed after I balance - I just leave it be. Dont be like me... ;)

[pressureangle]

Start by adjusting the carbs to close at the same time on the bottom of the body, not the idle screws. After you find your idle speed with the throttle, adjust the screws to catch  the slides evenly.

Have you checked valve lash? I found mine to be more sensitive to valve adjustment mismatch between cylinders than I'd have thought.

[Idontwantapickle]

Have you checked valve lash? I found mine to be more sensitive to valve adjustment mismatch between cylinders than I'd have thought.

This.
If the valves, points and timing aren't right then you will not be able to get the carbs right either.

[bentombed]

So i went and tried tuning the bike this afternoon - i dont think it got worse, i also don think it got any better.... I found that the cables are different lengths -  i dont know the technical terms here - but the exposed bit of cable that goes from the bracket to the carb, they are noticably different lengths.  So i messed around and got them to feel the same amount of slack, i tried to use the adjusters but ended up bending the brackets. Itried my carbmate tool but that was not really helping, plus i broke two of the intake tubes.  ON the plus side i did get the bike to Idle much better.  i'll take it for a spin and see if i done any damage....

[wirespokes]

There is no cable adjustment at the carb end - it's at the throttle. Did you have trouble at the throttle end? What happened there?

There's an adjustment at the throttle, two screws with springs. One adjusts tension on the throttle, the other adjusts where it stops. If there's not enough or too much slack in the cables it can be adjusted there.

The brackets at the carbs don't, or shouldn't, need to be bent.

Since the only change made is un-zip tying the cables, it's only logical adjusting the cable free play would get you back to square one.

It's a good idea when zip tying cables to not cinch them up real tight. Allow them to move back and forth.

[Chuck in Indiana]

There is no cable adjustment at the carb end - it's at the throttle.

Uhh.. Every one I've worked on has an adjustment at the carb. Maybe I'm misunderstanding?

[Antietam Classic Cycle]

Uhh.. Every one I've worked on has an adjustment at the carb. Maybe I'm misunderstanding?

Dellortos with the bellcrank tops don't have any adjuster at the carb, other than bending the metal cable bracket. Adjustment is done at the throttle end elbows. 

[Chuck in Indiana]

Ahhh, got it. Thanks, Charlie..