Strange "chuffing" at idle on left cyl

[brider]

My Cal 2 has been doing this strange thing at idle, more so now since I've rebuilt the heads, installed new rings, and tried to fiddle with the timing to get the LH side retarded to match the right. I'm as close as the dizzy adjustment will allow at this point; bike starts and runs fine, plugs seem to be burning correctly.

But at idle, there is a periodic (every 15 sec or so) "chuff" phenomenon in the left cyl; not a backfire, not a misfire, it's kind of like a hiccup. Has anyone experienced something similar? I'm going to assume it's because of my timing, and for this (and other) reasons I think a winter Dyna kit is in order, but I wonder if I can interpret it as too far advanced or retarded on that cyl? Maybe it's carb-related? No symptoms above an idle.

[pehayes]

If it were timing or ignition parts I would presume it to happen on every stroke.  15 seconds sounds like something intermittent.  Have you replaced or swapped the plugs left/right?  How old are your spark secondary wires?  Are you leaking a spark occasionally?  Try swapping the wires.  Also try swapping the coils left/right to see if you can move the fault to the other cylinder.  That might narrow the diagnostics.

Sounds a bit like a momentary lean running sneeze.  Note exactly where the recessed screw is positioned in the left carb.  Back it out half a turn and see if it alters the condition.  You can always return to the original screw position.

Could be a differential in the float height on the left carb causing an occasional leaning of mixture.

All guesses.

Patrick Hayes
Fremont CA

[brider]

If it were timing or ignition parts I would presume it to happen on every stroke.

Of course!

Have you replaced or swapped the plugs left/right?  How old are your spark secondary wires?  Are you leaking a spark occasionally?  Try swapping the wires.  Also try swapping the coils left/right to see if you can move the fault to the other cylinder.  That might narrow the diagnostics.

Plugs and wires are spankin' new, coils are not! I will swap and see.

Sounds a bit like a momentary lean running sneeze.  Note exactly where the recessed screw is positioned in the left carb.  Back it out half a turn and see if it alters the condition.  You can always return to the original screw position.

Now there's something I haven't dabbled with, and I'll give this a try, too. Actually, I was going to do my first attempt at synching the carbs very soon, but if the coil-swap shows no effect, I'll try this on the left and see what happens.

Thanks!

[Chuck in Indiana]

Actually, I was going to do my first attempt at synching the carbs very soon,

You *really* need to sync the carbs..

[pehayes]

Actually, I was going to do my first attempt at synching the carbs very soon,

DOH!  I foolishly presumed you had already balanced and synchronized the carbs. (two different things).  Surely a MAJOR reason for any side-to-side inconsistency.  Do you have a vacuum synchronizing tool?  If you've never done this before, give a good read here:

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

You likely have round slide carbs, but the tuning logic will be the same.

Patrick Hayes
Fremont CA

[brider]

DOH!  I foolishly presumed you had already balanced and synchronized the carbs.

Between you and Chuck I am now ashamed that I brought this subject up before "doing" the carbs.

Case closed, I will refrain from further embarrassing myself now.

[Chuck in Indiana]

since I've rebuilt the heads,

Have you retorqued the heads/adjusted valves since then? If not, do that before trying to sync the carbs. No shame involved. We are all in this to learn and have fun, after all.

[TOMB]

If you go to Greg Bender site this old tractor do a little searching there's a piece in there about how to modify the points plate for the left cylinder I did on my convert and I was able to get enough movement to retarded to the correct position that I needed seems as though the points plate that screws in the screws hit the opening and limiting the travel that required to modify the plate according to the pictures you'll have enough movement that you can retard the timing to any position you want
TOMB

PS
For those that feel they need to criticize my no punctuation marks read the message disregard the grammar

[brider]

Yes, I modified my points plate per Bender's instructions, but apparently I didn't provide enough relief because the left STILL won't retard far enough to match the right. I have them adjusted now to an average that so far doesn't advance the left too far. Plugs look good, no detonation/pre-ignition noises (had those before I rebuilt the heads, when the left cyl was blowing smoke).

So I am going to go Dyna during the winter, I won't pull that points plate off again without replacing it with the Dyna. I'll pack it as a spare.

I also wrote a PM to a member on this thread asking about the home-made (SERIOUS Guzzi-content) manometer for carb-tuning. does anyone know the thread size offhand for the PHM30 manifold tuning port?

[Chuck in Indiana]

^^^^ That would be M6X1.

[John A]

For adapters use MiG tips. Miller mig tips for the smaller welders are 6x1mm

[s1120]

Between you and Chuck I am now ashamed that I brought this subject up before "doing" the carbs.

Case closed, I will refrain from further embarrassing myself now.

Dude... I had a bad skip/misfire on my bikes that kept getting worse and worse... Tracing connectors, and testing sensors, I started removing the tank, and found no gas in it... your good..  No need for shame. :)