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Discussion Starter · #1 ·
A couple days ago I was riding in 95 degree weather. The bike seemed to run funny, not exactly missing but noticeably different. When I shut it off it run backwards for a short time, seconds maybe. Anyone experience this? I am thinking possibly to hot a plug. Your thoughts?
 

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What ran backwards? Your motor? Like your bike lurched backwards in reverse for a few seconds? I'm confused, but if it actually did that, it's NOT your spark plugs.......

On a side note, as far as the bike running funny at 95* temp, warmer air is thinner than cooler air. That's why they turn better times at the drag strip when the sun goes down. Cooler/thicker air= better compression. Only a minute (tiny) difference, but it's there.
 

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Also the heat range on a spark plug has absolutely NOTHING to due with air temperature.

In electronics heat = Resistance. The use of a "hotter or colder" spark plug is to prevent fouling the plug. Not a thing to do with air temp.... It's already living in and creating an explosion.
 

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Discussion Starter · #4 ·
Ok so you are saying when it is 50 degrees out your air cooled engine runs the same temp as when it is 95 degrees. And the the plug is cooled at the same rate. I guessing you folks have never experienced pre ignition or dieseling, whatever you want to call it?
 

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Also the heat range on a spark plug has absolutely NOTHING to due with air temperature.

In electronics heat = Resistance. The use of a "hotter or colder" spark plug is to prevent fouling the plug. Not a thing to do with air temp.... It's already living in and creating an explosion.
I was just about to come say this. I see this a lot on the Harley sub reddit. Not sure why so many people ask about it.

Basically, don't change spark plug heat rating ever. There's almost never a need, unless you're seriously modified for actual racing.

Ok so you are saying when it is 50 degrees out your air cooled engine runs the same temp as when it is 95 degrees. And the the plug is cooled at the same rate. I guessing you folks have never experienced pre ignition or dieseling, whatever you want to call it?
No, the engine won't exactly run at the same temperature between 50° and 95° ambient (outside) temperature (though it will be pretty close when running and will eventually run at close to the same temperature). Nobody said that, dunno how you got that out of what was said.

Dieseling is usually caused by an idle mix that is too lean. The mix being too lean can be from a lean tune, or it could be from an air intake leak.

It could also be the ignition timing is too advanced.

Plenty of us have experienced it.

Again, plug heat range has nothing to do with the running temperature of the engine or the outside temperature, forget about spark plug heat range.
 

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Ok so you are saying when it is 50 degrees out your air cooled engine runs the same temp as when it is 95 degrees. And the the plug is cooled at the same rate. I guessing you folks have never experienced pre ignition or dieseling, whatever you want to call it?
Dieseling is caused by the spark timing being incorrect... Pre ignition is valve timing. You honestly think 20 or 30 degrees of air temp will change the internal temp of a running engine? Not a chance!

Air temp most definitely does change air pressure as does altitude. This changes how much oxygen there is in the fuel / air ratio on the intake stroke. In other words it changes the amount of oxygen in the burn per stroke. This is controlled the intake system on the engine (Carb or EFI). Again, nothing to due with the spark plug.
 

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Ok so you are saying when it is 50 degrees out your air cooled engine runs the same temp as when it is 95 degrees. And the the plug is cooled at the same rate. I guessing you folks have never experienced pre ignition or dieseling, whatever you want to call it?
Do you really think a 40° difference in air temp is going to have much effect on a 4500° combustion?

Temperatures in the combustion chamber of the engine can reach 4,500 F (2,500 C), so cooling the area around the cylinders is critical. Areas around the exhaust valves are especially crucial
.

Heat range of a spark plug only has to do with how fast the spark plug tip temperature is transferred to the head, affecting the self cleaning action of the spark plug.
 

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Heat range is about "self cleaning" (yes)
However, (to add) heat range is also used on a built motor to control pinging.
Higher compression (for the most part) will require a colder plug.
A big increase in compression will also call for a smaller gap to avoid "blowing the flame out"

In the OP's case, if he goes to a hotter plug on a air cooled engine, what he will do is increase risk of pinging.

If his 1st thought was plugs, when were they last changed?
Going to expand on this, might be misunderstood.
No i do not believe the plugs caused the issue. When he thought plugs,
Makes me think they are do for a change/been in awhile.
 

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When I shut it off it run backwards for a short time, seconds maybe. Anyone experience this? I am thinking possibly to hot a plug. Your thoughts?
If you have the correct spec spark plugs in your engine and they are in good condition, forget about them.
A 4 cycle engine cannot run backwards.

Dieseling is caused by the spark timing being incorrect...
Dieseling is when the engine runs on after the ignition is turned off, it has nothing to do with the spark timing.

Dieseling occurs when the engine is overheated, usually there will be very hot part inside the engine, such as a glowing piece of carbon, or a damaged tip on a spark plug.

Pre ignition is valve timing.
Pre ignition is not caused by valve timing.

Pre ignition occurs when a hot part in the combustion chamber causes the fuel air mixture to ignite before the spark occurs.

Pre ignition will destroy an engine quickly.

Detonation and Pre Ignition
 

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If you have the correct spec spark plugs in your engine and they are in good condition, forget about them.
A 4 cycle engine cannot run backwards.



Dieseling is when the engine runs on after the ignition is turned off, it has nothing to do with the spark timing.

Dieseling occurs when the engine is overheated, usually there will be very hot part inside the engine, such as a glowing piece of carbon, or a damaged tip on a spark plug.



Pre ignition is not caused by valve timing.

Pre ignition occurs when a hot part in the combustion chamber causes the fuel air mixture to ignite before the spark occurs.

Pre ignition will destroy an engine quickly.

Detonation and Pre Ignition
Good article! Thanks for posting this!
 
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Discussion Starter · #12 ·
Dieseling occurs when the engine is overheated, usually there will be very hot part inside the engine, such as a glowing piece of carbon, or a damaged tip on a spark plug.

Pre ignition is not caused by valve timing.

Pre ignition occurs when a hot part in the combustion chamber causes the fuel air mixture to ignite before the spark occurs.

Pre ignition will destroy an engine quickly.

Thank you someone gets it.
 

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and preignition/ping/knock can be caused by improper plug heat range.

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Pre ignition and Knock (detonation) are not the same thing.

A spark plug of incorrect heat range can cause Pre Ignition, but not detonation, remember; Detonation does not occur at the spark plug, it occurs away from the spark plug.
 

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Sorry Dan, but yes an incorrect heat range plug can cause ping. No one seems to take me serious, so i posted a link detailing the info.
 

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"COMPRESSION RATIO
  • Significantly increasing the static/dynamic compression ratio will increase cylinder pressures and the octane requirement of the engine. Knock may occur more easily. If the engine is operated near the knock level, a colder heat range spark plug may be necessary due to the resulting increased cylinder temperatures."
I mentioned in a previous post also that improper heat range not matched to cr will cause ping.

If the OP goes to a hotter plug, he will increase chances of pinging
 

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46* and help build engines with my cousin who took Pro stock trophies.
you want to doubt me, ok you dont know me.
However, I just posted info right from a leading spark plug manufacturer.

Check Champion, their rule is 1 colder for each point raised in compression until approx 12. to 1
Higher ratio will require 2 ranges*
 
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