Verifying Ignition Timing Marks

What marks are you strobing to ?

Time Warp said:

The only way a Sprint (and I use that term loosely) 250 would do 90 mph is if it was pushed out the back of a C130.

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Did you get this tip from this VW Ad? :

Fast Eddie said:

What marks are you strobing to ?

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The marks on the rotor and the scale in the outer primary cover.

When I used the strobe on the original setting, the mark did not even appear in the opening.

Time Warp said:

The only way a Sprint (and I use that term loosely) 250 would do 90 mph is if it was pushed out the back of a C130.

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They claim a 250 Sprint won't wheel stand either but I wiped out the taillight the 1st day.

Dan1950 said:

The marks on the rotor and the scale in the outer primary cover.

When I used the strobe on the original setting, the mark did not even appear in the opening.

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But I thought your earlier point questioned the accuracy of your scale ?

Dan1950 said:

The initial reading with the strobe light showed ignition retarded off the scale. A static check with the Tri-Spark indicated 20* BTDC.

Setting the static timing at 29* BTDC yielded adout 22* with the strobe light.. That would suggest that the initial timing was running at around 13* BTDC.

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Very confusing. If the timing is accurately set at 29 degrees statically, it will strobe at 29 degrees at 3500 rpm. I've installed many of them and never been off more than 2 degrees in either direction.

marshg246 said:

What front sprocket?

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21t

Fast Eddie said:

But I thought your earlier point questioned the accuracy of your scale ?

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Yes I did but not having any other alternative readily available at this time I used the marks for reference. The bike runs fine snd starts easily st 29* BTDC as indicated with the strobe. I can now play with it to fine tune given that I have a starting point reference.

Dan1950 said:

21t

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Then the engine is pretty sick or jetted badly since 90 mph with a 21T is about 5200 rpm and it should make it to at least 6000 rpm in 4th gear. RPM/MPH with 21T front sprocket in 4th gear:

4000 68
4500 77
5000 85
5500 94
6000 102
6500 111

marshg246 said:

Then the engine is pretty sick or jetted badly since 90 mph with a 21T is about 5200 rpm and it should make it to at least 6000 rpm in 4th gear. RPM/MPH with 21T front sprocket in 4th gear:

4000 68
4500 77
5000 85
5500 94
6000 102
6500 111

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With the timing being retarded 17* from ideal I think that would rob a lot of power. I haven't had a chance to do a 4th gear pull since advancing the spark timing.

I'll play with the jetting if plug readings dictate.

marshg246 said:

Very confusing. If the timing is accurately set at 29 degrees statically, it will strobe at 29 degrees at 3500 rpm. I've installed many of them and never been off more than 2 degrees in either direction.

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Perhaps my static timing technique isn't accurate.

Dan1950 said:

Perhaps my static timing technique isn't accurate.

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What ign system are you running?

Dan1950 said:

The initial reading with the strobe light showed ignition retarded off the scale. A static check with the Tri-Spark indicated 20* BTDC.

Setting the static timing at 29* BTDC yielded adout 22* with the strobe light.. That would suggest that the initial timing was running at around 13* BTDC.

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Let me try to clarify ignition advance using Tri-Spark (nearly the same as points and auto advance unit)

The Tri-Spark advance range is 0-3500RPM; 0-25 degrees of crankshaft advance. This means:

At 1200 rpm, Tri-spark is adding 0 degrees of crankshaft advance. At 3500 rpm, Tri-Spark is adding 25 degrees of crankshaft advance. So, if statically set to 29 degrees or strobed at 3500 rpm at 29 degrees, at idle the crankshaft advance is 4 degrees. Between 500 and 1200 RPM, Tri-Spark is varying the timing trying to keep the engine running (idle stabilization).

So, if you mean you had 22 degrees at 3500 rpm, you were idling at 3 degrees AFTER TDC, not 13 degrees BTDC.

With points, read 24 degrees where I said 25 degrees since the AAU provides 12 degrees of camshaft advance (24 degrees at the crank).