Static Timing

[moto]

On my T3 when I set the timing with a light I set it at idle to the idle marks on the flywheel. When I run the engine up to 5K RPM the full advance marks show up in the inspection window. Marks are good as I checked them with a degree wheel. Is my distributor different than stock?

good question. I measured 7° of advance from the static value at 1000 RPM back in 2004. I hadn't considered using the static marks for dynamic timing at idle speed, which I understand you to be doing.
 

[moto]

Dave Richardson included a typically thoughtful discussion of all this in Guzziology (Version 5.1, March, 2001) under the heading "Modifying big twin ignition advance curves." he actually measured the advance of both the high-performance and low-performance distributors, and found they both produced 26° at the crankshaft. he has a lot more to say than that. I concluded that the most important thing is to make sure the advance at 5000 RPM is exactly on the mark, not just in the window. my T3 seems to perform better at high RPM than others report. Maybe timing is a reason.

[n3303j]

good question. I measured 7° of advance from the static value at 1000 RPM back in 2004. I hadn't considered using the static marks for dynamic timing at idle speed, which I understand you to be doing.

Guzzi did make two versions of the distributor (S311A & S311B). I was lead to believe the difference was in the advance springs (and the resulting timing curve). Maybe the distributor you have is the version with the steeper advance curve?

Old school, we always put the strobe on the timing marks when doing a tune up. Car, bike, whatever. If you are real careful and your system is mechanically correct the static timing should exactly match that of an idling engine.

[moto]

Old school, we always put the strobe on the timing marks when doing a tune up. Car, bike, whatever. If you are real careful and your system is mechanically correct the static timing should exactly match that of an idling engine.

Not always true. Here is a quote from Dave R in Guzziology:

"A caution on timing big twins at idle with a timing light:

"I would like to reiterate an important point: on all Motoplat and point-ignition big twins except the V7 sport, 750S, 850 T, 1000S, big-valve California III, and Lemans I-V, the advance mechanism has already started to advance the timing at an engine speed below idle. For these bikes, and really all big twins, full advance is the most accurate timing reference.

"The factory service manuals and owners manuals all refer to only the full-advance mark for dynamic timing. All too often the static mark has been erroneously assumed to be equivalent to an idle speed mark."

I will also add that it is probably not a good idea to assume that a 50-year-old distributor is in perfect mechanical condition!

[n3303j]

Don't know if I can agree with that from an engineering point of view as I can see no purpose for an ignition to be retarded at a point beyond that required to start and idle unless it is a high performance unit requiring some unusually high idle to maintain operation.

But I do agree that it is very important that full advance is correct and not beyond what the engine is designed for. Any advance costs power and over advance destroys hardware.

[moto]

Don't know if I can agree with that from an engineering point of view as I can see no purpose for an ignition to be retarded at a point beyond that required to start and idle unless it is a high performance unit requiring some unusually high idle to maintain operation.

You can see plots of the advance curve in Guzziology showing the actual situation. I suppose that starting the advance below idle led to a simpler construction.

But I do agree that it is very important that full advance is correct and not beyond what the engine is designed for. Any advance costs power and over advance destroys hardware.

yes.

[Bob_Fla]

Now I have Carb questions. Should I start a new subject?

[n3303j]

Now I have Carb questions. Should I start a new subject?

Yup!