T4 distributor

[RobertK]

My T4 is normally solid but lately it has been running erratically.  It is often reluctant to accept throttle when moving off and sometimes dies when the throttle is closed.  It also feels like it might be down on power.  I've checked and cleaned the carbs and set the tappets, but since it's an intermittent problem it seems more likely to be electrical and probably ignition related.  There are no obvious loose wires or bad connections at the coils etc.
The bike has Newtronic (Piranha) electronic ignition which I believe retains the use of the mechanical advance on the original distributor.  With the points plate removed the bob weights etc. move freely, but the larger of the two springs does not seem to be seated properly.  I tried to take a picture but it's not very clear. Unlike the smaller spring, the ends of the spring which loop round the pins are not a snug fit in the locating grooves, with one or both loose.  This is probably because of a weakened spring and must affect the spark advance?   Or is it meant to be like that? Before I fit a new spring, I would welcome anybody's thoughts on this.  It seems to be crucial not to stretch the spring, and the Guzziology recommendation is to open up the ends of the spring first before then fit it and close up the ends.  I really don't want to mess this up and have to go through the whole thing again.

[guzzisteve]

Put on the new springs, or you could even put on ones from a LeMans motor which will change timing from 2* to 8*. Could also be the electronic part in the set-up getting old. Only way to be sure is to catch it when it is happening with a timing light. Make sure the advance is lubed under the screw on top & tightened just snug not real tight.

Where you at? We never got T4's in the USA.

Edit: Scotland !!!

[jhem68]

  If the timing chain is worn/stretched that could create these sorts of issues, how many miles are on the motor in total?




John H

[RobertK]

Thanks for the replies.  A previous owner removed the fairing (same as SP1000 top fairing) so it's basically like a late T3 (even the side-panel badges).  I've had the bike about 6 years and it only has 64 000 miles on the clock but I doubt if that is anywhere near accurate.  I put a new timing chain and spring-loaded tensioner on about two years ago, so hopefully that's not the problem. 
I'll use the method described in Guzziology to put on new springs and take it from there.  I haven't been able to find a picture of correctly installed springs on a T3 etc. distributor (with one large and one small spring), but common sense says both ends of the large spring should be fully located in the pin grooves (like the small spring).  But common sense and old Guzzis don't always go together.    I have a spare le Mans distributor and may think about installing that, but from graphs in Guzziology the advance curves look quite different and I'm not sure how that will affect the running of the bike.  I also remember replacing the springs on my le Mans.  It was a fiddly job and tricky to not stretch the springs during installation.
Thanks for your help.

[moto]

I recall that the longer of the two springs is a loose fit on the pins and not under tension at rest. Things change as the motor revs up, and the bob weights pull things apart. At some point the long spring is completely engaged and thereby changes the advance curve of the distributor.

Though springs can be stretched permanently I don't think this usually happens in a distributor, and in any event would not happen quickly enough to give the sudden onset of the symptom you describe. I'd look elsewhere. Good luck!

[RobertK]

Thank you, that makes total sense.  Thinking about it, it doesn't seem likely that a spring would ever stretch enough to become loose on the pins, and as you say, certainly not fairly suddenly.  Not really what I wanted to hear though!

[Frenchfrog]

the loose spring is correct....but a good thing I did with mine when running a Piranha was to use LE Mans springs  which give a less stepped advance curve .Wasn't much of an improvement but also meant that the ignition timing was correct at static and full advance using the LM figures .The roadster set up was possibly a bit of a bodge from the factory for emissions purposes and you cant get both correct.

[moto]

...Thanks for your help.

By the way, Robert, I really like your paint job. It looks a little like mine!





As for your motor's problem, I would be thinking about the coils and maybe the plugs and ignition wires, given your symptoms. It would probably be good to try replacing some of those components instead of going after a new electronic module.

[RobertK]

Thanks to everybody for their thoughtful replies.  It's great to have a group of very knowledgeable people willing to share their experience.  Mr Moto, that's a beautiful and very purposeful T3. They don't get like that without a lot of hard work. 
My plan at the moment is to replace the larger distributor spring with a le Mans spring and reset the timing statically.  Then work backwards from the plugs to the coils to try to isolate the issue(s).  Once it's all decent I'll check and adjust the advance.  Fortunately I also have a 1977 le Mans with exactly the same ignition set up, plus a spare working distributor with points so I won't have to buy any parts until I know exactly what's causing the problem.  It might take a few weeks but I'll post again with any updates.
If anyone's interested here's a recent Guzzi related post I made on Adventure rider: https://www.advrider.com/f/threads/scotland-bikes-and-hills-2.1824273/

[moto]

Robert, your art is astonishing. Is there a way for ones such as we to see more?

All, don't miss the charming videos at the end of the Advrider post.

Bravo!

[Moparnut72]

I am trying to resurrect a T3, even though I am a long ways away from the end I am thinking about colors. It was originally black but not down the road. Your bike has added another cog to the wheel. Burgundy, a Guzzi green now a bronze? 
kk

[RobertK]

Hi Mr Moto,

I'm glad you like my adv rider post.  I had an previous one but need to update the pics, which will hopefully happen in the next couple of weeks:  https://www.advrider.com/f/threads/scotland-bikes-and-hills.1614451/  The text is tongue in cheek, but the Danny Macaskill videos are wonderful.  Other people added their own pics which was great. 

Moparnut: good luck with the T3 rebuild and colour choice.  It will be nice to see the end result.

[Moparnut72]

Don't hold your breath as I work my way through former neglect and more recent neglect and abuse. It is going to take me some time.
kk

[turboguzzi]

use a timing gun and check/set the no advance and full advance points for both cylinders. only then you can proceed to search for other issues systematically.

it will also tell you if you have an issue with springs or not.

tip - it helps a lot to identify the timing lines on the flywheel beforehand and enhance them with white ink marker. makes using the strobe light easier.

@mr.moto - nice paint scheme! specially the "logo band". was this original? never seen one like that!

[moto]

I am trying to resurrect a T3, even though I am a long ways away from the end I am thinking about colors. It was originally black but not down the road. Your bike has added another cog to the wheel. Burgundy, a Guzzi green now a bronze? 
kk

The original V7 came in two or three shades of green, including this one that I tried to approximate:




(page 105 of The Moto Guzzi Story by Ian Falloon, 1st edition, Haynes, 1999.)
I think this was informally called Legnano green, after the color of Legnano racing bicycles, then famous. The bicycle paint was multilayered, applied over copper(?) plating, and iridescent. The paint I chose as a close substitute for that particular original color was a Subaru one applied to recent Crosstreks, Plasma Yellow Pearl.

[moto]

...
@mr.moto - nice paint scheme! specially the "logo band". was this original? never seen one like that!

It's not original, but inspired by certain original V7 Sports. Professionally painted, the stripes are paint instead of decals. Glad you like it.

Edit: the "logo band" has golden guzzi eagle decals on the black stripes ahead of the MG emblems. Hard to see in that photo unless you zoom in. Some Sports had different eagles there.

[Moparnut72]

I have a long time to decide on colors, the bare frame is still sitting on the floor. The wiring is a mess and I am going from an 850 to a 1,000 motor so a couple of changes there as well.
kk