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lanshark

Distributor question

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lanshark

I set my timing to 10 BTDC on my 99 sportster. It is carbed. How can I check to be sure the timing is advancing as the RPM's go up? And if it isn't. What can be done to fix this, besides a new distributor?

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justgary
3 hours ago, lanshark said:

I set my timing to 10 BTDC on my 99 sportster. It is carbed. How can I check to be sure the timing is advancing as the RPM's go up? And if it isn't. What can be done to fix this, besides a new distributor?

Your timing light will show advance as you rev the engine.  You should see the timing mark on the crank pulley (or balancer) move with RPM.

Spark advance is primarily a function of RPM because the fuel-air mixture has a specific rate of combustion, and you have to start the fire before TDC in order for it to be at its peak pressure just after TDC.

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Rednucleus

Just curious what was your procedure to set timing? 

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lanshark

I put the timing plug in the distributor and after starting I applied 12v to pin b. plugs c and d are jumped. I used a timing light to set the timing to 10 BTDC. My distributor is old and I am trying to verify it is working properly. I heard that once the timing is set. can increase the RPM's to 2500 or 300 and it should be around 25 degrees BTDC . I am not sure of that and could use a little help.

Thank you.

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justgary

It should change timing if you removed the jumpers and other things. 

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Woodski

The GM small block 350 wants full advance to be 33-34 deg BTDC @ 4,000+ RPM and idle is 8-10 deg BTDC.  There are variations depending on who the marinizer is as they calibrate the engines.

@lanshark - personally, I would be wary of that 2,500 RPM number as that can be a transition area in the spark curve.  You should be able to get a spark curve from the marinizer.

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