Evo timing.
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Seasoned HDF Member
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From: West Central FL
Evo timing.
1993 FLSTC Heritage Classic. With the summer in full swing in Florida I'm noticing the bike running hotter and I'm getting pinging/piston rattle when accelerating hard. I'm assuming it's a timing issue so do I advance or retard the plate and which way is which?
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From: NC USA
If it's stock pistons (any thing else doesn't matter) and if the timing was previously set to 35 BTC, you have an intake leak causing the ping.
You would have to time it to about 25 BTC to cover it up, it would run real good because of the lean condition but eventually burn a piston. .
You would have to time it to about 25 BTC to cover it up, it would run real good because of the lean condition but eventually burn a piston. .
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From: Cental, MI
I guess I didn't see any RPM Mentioned.. and... anytime you can make the vacuum Drop in the manifold, Whacking WFO comes to Mind.. The VOES certainly responds!! RPM can be Quite High,,,and still, Sudden WFO, will Make the VOES Respond.. Put a Vacuum gauge on and Watch!!
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From: NC USA
I totally agree but on a stock module without VOES the timing is dictated by rpms. At low speeds it's the same only the VOES tells it "high vacuum - add timing". That's where the supposed extra fuel mileage comes from.
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From:
Is this a new situation?
Unusual for timing to randomly change.
A lower octane than usual combined with high heat or a compromised seal at throttle body along with high heat could be a cause.
Unusual for timing to randomly change.
A lower octane than usual combined with high heat or a compromised seal at throttle body along with high heat could be a cause.
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Seasoned HDF Member
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From: Cental, MI
Bad Stuff
One Common cause...due to Longevity, is Carbon build up. Which Increases working Compression...that and the Crap we are foisted upon us as Gasoline..Can be a Big Problem..
Last edited by Racepres; Jul 20, 2025 at 08:18 AM.
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From: Florida
I would retard (counter clockwise) a couple degrees for now.. make sure you’re not lean (carb settings) might be able to pop the carb off and shine a light at the back of your valves, or use a Amazon cheapy camera to look in through the spark plug hole to see if there is a lot of carbon build up.
Todays fuel just keeps getting worse in the Florida environment.. it’s like the sun thinks Florida is a toilet and it’s sitting right here dumping it’s rays. Some brands have better detergents than others. Switch to known name brand 93 octang gas. You can also throw a few cap fulls of Marvil Mystery oil in each tankful of gas.
“If” it’s really pinging due to hot spots and carbon the higher Octang might help with pulling a couple degrees of timing. Moving forward it might help prevent more and faster build up.
Not sure what ignition you have? If it’s after market you probably have a blink light for static timing.. If your not sure how to retard the timing, open the timing inspection hole, Timing points cover on the nose cone, with rear wheel jacked up, plugs out, turn wheel until you see the TDC in the timing hole. Right in the middle is 35, favor the front of the hole..
if that’s too much, just turn your ignition plate a couple eye lashes counter clockwise.
All that said, my money is on a mild vacuum leak. If you wanna check for leaks.. adjust your carb to idle around 900-1000. Spray small little bursts of something flammable like carb cleaner, starting fluid, deodorant… at the intake one side at a time. Small sections all around each head and where the carb attaches (CV). If the rpm races for a second… you got yourself a leak. Be patient and be thorough to rule out a leak.
If no leak… humor us.. raise your carb idle to 1500 and do it again just to be sure. Sometimes with more rpm and more vibration a very small intermediate leak can show it’s ugly self.
Todays fuel just keeps getting worse in the Florida environment.. it’s like the sun thinks Florida is a toilet and it’s sitting right here dumping it’s rays. Some brands have better detergents than others. Switch to known name brand 93 octang gas. You can also throw a few cap fulls of Marvil Mystery oil in each tankful of gas.
“If” it’s really pinging due to hot spots and carbon the higher Octang might help with pulling a couple degrees of timing. Moving forward it might help prevent more and faster build up.
Not sure what ignition you have? If it’s after market you probably have a blink light for static timing.. If your not sure how to retard the timing, open the timing inspection hole, Timing points cover on the nose cone, with rear wheel jacked up, plugs out, turn wheel until you see the TDC in the timing hole. Right in the middle is 35, favor the front of the hole..
if that’s too much, just turn your ignition plate a couple eye lashes counter clockwise.
All that said, my money is on a mild vacuum leak. If you wanna check for leaks.. adjust your carb to idle around 900-1000. Spray small little bursts of something flammable like carb cleaner, starting fluid, deodorant… at the intake one side at a time. Small sections all around each head and where the carb attaches (CV). If the rpm races for a second… you got yourself a leak. Be patient and be thorough to rule out a leak.
If no leak… humor us.. raise your carb idle to 1500 and do it again just to be sure. Sometimes with more rpm and more vibration a very small intermediate leak can show it’s ugly self.
Last edited by Rains2much; Jul 22, 2025 at 01:05 PM.
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