2-stroke 'over heating' myth...

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Venice Motor Bikes

Venice Motor Bikes

Custom Builder / Dealer/Los Angeles
Mar 20, 2008
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I'm posting this to finally put to rest the misinformation about 2-strokes over heating...

I don't know why everyone continues to believe this nonsense about 2-stroke bicycle engines only being able to run for 20 minutes at a time because they'll over heat... IT'S SIMPLY NOT TRUE!!!

If you mix your gas & oil correctly, you can run a 2-stroke 'HT' at wide open throttle all day long without any issues of it over heating!!

I'm sure this will spark up a some debate here... & I have nothing against riders who simply prefer a 4-stroker; but this misinformation about 2-stroke bicycle engines has got to be put to rest once & for all! :rolleyes:
 
bairdco

bairdco

a guy who makes cool bikes
Aug 18, 2009
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i agree. i've ridden bikes all day in 100 degree heat with no probs.

the only time i blew a headgasket wasn't from overheating, it was from not letting it warm up and going full throttle right away in 40 degree weather. and it was probably my fault for neglecting the bike. if i woulda checked the head nuts, it probably woulda been fine, but i was working a lot of nights and riding the bike everyday for 3 miles each way to work.

but i wouldn't let a bike idle all day in the heat, though...:)
 
biknut

biknut

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Sep 28, 2010
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That's pretty much been my experience riding in 100 + Texas summers. My bikes don't seem to have any problems with over heating

Maybe a high compression head would be a little different, I don't know.
 
Maxvision

Maxvision

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Jun 13, 2009
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I melted down a 2 stroke once going up the north side of Mt. Soledad on Hwy 101 in La Jolla, WOT trying to keep up with the 4 stokes. Got about 3/4 of the way to the top before I lost compression. Even had a shift kit.

Ask Scotto-, he was there! But that's an extreme situation.

If there's an exception to the rule...I'll find it...I live it...I'm IT!
 
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2door

2door

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Sep 15, 2008
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I concur 100%.
Now let's blow some of those other long standing myths out of the water while we're at it. Examples:
You must have a spocket adapter because the rag joint won't work.

A bigger petcock will make your stock engine run better.

Every flower nut needs to be adjusted out of the box.

etc, etc, etc. :)

Tom
 
maniac57

maniac57

Old, Fat, and still faster than you
Oct 8, 2011
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My Pig:
Stock rag joint (been on three rims so far...)
Stock petcock
Never touched the flower nut.
Still running strong as of yesterday (too cold to ride today)
 
bairdco

bairdco

a guy who makes cool bikes
Aug 18, 2009
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living the dream in southern california
i've stated my experiences with the stock petcock on a hopped-up motor, and proved to myself it wasn't providing enough fuel to my carb, but i'll just let that one go for now...

wait... i just re-read your post. you said stock motor.

nevermind...
 
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Moto

Moto

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Jan 7, 2012
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San Francisco, CA.
myths:
"my engine will be ruined if I dont run 16-1 and baby it..."
"2 strokes are un-reliable..." - yes they are if its your first build and you dont do your homework. After a few builds not so much. of course compared to 4 strokes on the other hand...
 
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biknut

biknut

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Sep 28, 2010
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Seriously though, two things.

My eye sight has been getting worse, and I don't believe a properly tuned china girl, with a correct oil raito will overheat just from continuous running. Mine have run hard for 40 miles or more in very hot weather and I've never experienced an overheating event. It does lose some power when it's very hot, but so does every other air cooled motor.

I think there's a limit though to how much power you can make with a china girl motor before overheating could become a factor. China girls have fairly low compression. I don't think higher than 8:1, and probably more like 7:1. That works real well with the size of the cooling fins. When you start increasing the compression like so many people like to do all bets are off. There's probably not enough surface area to shed much more heat than they already make.

Just for comparison sake, take a look at the difference in the size of cooling fins between a 66cc China Girl motor, and a 49cc Slovenia Girl motor with 10:1 compression.




 
16v4nrbrgr

16v4nrbrgr

Active Member
Mar 17, 2012
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The cooling fins are about the same size but the jug is cast iron on my KTM clone, and I have a meat thermometer stuck in the head, it runs at 110F with airflow, and idling stopped it goes up to 180F, this thing must have 13:1 compression or more, I lapped it to the perfect squish and it has a tiny hemi combustion chamber. The aluminum jug on the HT will cool better, especially if painted flat black, that goes for the whole engine really. Use high octane and run rich when you're high comp, or holes in pistons can occur! 8-O
 
2door

2door

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Staff member
Sep 15, 2008
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Littleton, Colorado
bairdco said:
i've stated my experiences with the stock petcock on a hopped-up motor, and proved to myself it wasn't providing enough fuel to my carb, but i'll just let that one go for now...

wait... i just re-read your post. you said stock motor.

nevermind...
Click to expand...
Baird and I disputed about this a couple of years ago so I'll elaborate a little and repost a simple test that anyone can do to prove what I'm saying.

Before you do this test you must have a clean fuel tank, in-tank filter, petcock and in-line filter, if used.

Fill your fuel tank. Disconnect the fuel line from the carburetor and stick it in a container big enought to hold the fuel in the tank. If you have a stopwatch, good, if not just use the second hand on your watch or clock. Open the petcock and start timing how long it takes to drain your tank. Of course tank size will have a bearing on how long this process takes but generally speaking you're going to see an empty tank in something like five to ten minutes. This is assuming you are able to get a steady flow, not dripping, from the disconnected fuel line.

Now, reconnect the fuel line, refill your tank and go for a ride starting timing when the engine starts. If you can, run the bike at WOT (wide open throttle) until the tank runs dry. How long was your ride? I have no doubt that you rode your bike, even at WOT a heck of a lot longer than it too to drain the tank into a container.

I'll go so far as to challenge anyone, in spite of modifications, to run their tank dry while riding in less time that it took to drain it into a can. It ain't gonna happen.

If your engine uses a gravity flow fuel delivery system and your filters and petcock can deliver a steady stream of fuel, doesn't need to be a fire hose, then there is no way that the engine can consume fuel faster than it will free drain from the tank. Therefore I submit that petcock size has absolutely no bearing on how the engine runs. I have seen a couple of defective petcocks where the rubber insert wasn't drilled/molded correctly and a steady stream of fuel wasn't possible. And, we've all heard a hundred times, or more, about clogged fuel filters because someone didn't clean their fuel tank before installation.
Those are exceptions to my test. Your fuel delivery system must be functioning properly.

I'll stand by that. Sorry Baird. You and I usually agree on most things. This is one where we differ.

Tom
 
biknut

biknut

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Sep 28, 2010
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Part of the petcock equation may be that quality control is so poor that one stock petcock may flow twice as much fuel as another stock petcock.
 
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