Mount a 2 stroke upside down?

Because of the size and the way my bicycle frame is shaped it may be more convenient, strictly from a mechanical point of view, to mount a
2 stroke bicycle engine upside down. Maybe upside down and backward. If I did this the carb would need to be inverted because it is a float bowl type carb. I suppose I could use a pumper type carb instead but I don't know if I have one that is suitable as far as fuel and air flow are concerned. Besides, small engine pumper carbs tend to be kind of on/off devices in that they idle OK and and run wide open well but don't do so well in the mid range throttle settings. I suppose I could buy one but I'm cheap. So, if there is room to invert the carb what else do I need to worry about? Will the crankcase tend to get too hot since it will now be above the cylinder? And lets say that the engine is not only inverted but also turned around. Now the engine will be rotating the wrong way to drive the bike forward. Since the engine is a two stroke it seems to me that I will only need to change the ignition timing. I think this can be done simply by broaching a new keyway in the spinning magnet flywheel. The ignition is a fully electronic CDI type with no points. I assume the ignition works by sensing the voltage rise in the magneto primary winding as there is no other provision for detecting the position of the flywheel magnet. Have I missed anything? Thanks, Eric
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On Wed, 21 Oct 2015 14:01:25 -0700, snipped-for-privacy@whidbey.com wrote:

It sounds goods. Most 2-strokes don't care if they run forward or backward, as long as the ignition timing is adjusted.
If you showed us your engine, I didn't see it. One exception about running backwards is if the engine has a rotary intake valve mounted on the crankshaft. That's been used on some old off-road motorcycle engines and some other high-performance types, but it's very unlikely on most other applications. I'm guessing your engine doesn't have pump/squirt lubrication, which is another limitation on running backwards.
Lots of 2-strokes run upside-down. As you say, it's a matter of whether the carb has a float bowl and which way it thinks is "up."
--
Ed Huntress

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On Wed, 21 Oct 2015 14:01:25 -0700, etpm wrote:

Worry about plug fouling. I don't know if it'll happen or not, but oil drains down, and oil fouls plugs.
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Tim Wescott
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On Wed, 21 Oct 2015 14:01:25 -0700, snipped-for-privacy@whidbey.com wrote:

2 strokes have been mounted "upside-rown" in ultralight aircraft for many years. Mounted that way they do tend to foul plugs and flood easily when starting, but they generally run fine after starting.
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On Wed, 21 Oct 2015 14:01:25 -0700, snipped-for-privacy@whidbey.com wrote:

Model airplane 2 stroke motors are frequently mounted upside down and run all right although if you flood one it might be a bit more difficult to start and chainsaw run all right upside down.
As for running backward, I'm not sure of the efficiency as some modern 2 strokes use some pretty exotic porting that may be rotation directional in nature. I'm leaning on model engine experience but some glow plug designs of model engines seemed to run in either direction with no problems and other, different in design, wouldn't seem to run backwards at all.
But I don't think that you will do any mechanical damage by trying it.
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John B.
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On Thu, 22 Oct 2015 08:53:44 +0700, John B. wrote:

The rotation direction thing is what Ed was referring to -- most model airplane 2-strokes have intake ports that are timed by the crank, and that lead the piston by a considerable amount. This makes the engine prefer to run in just one direction. Cox reed-valve engines are direction agnostic, as are the really old piston-timed engines.
Weed-whacker and chainsaw motors are, to my knowledge, piston timed, with the intake port to the crankshaft opened and closed by the skirt of the piston rather than by the crank or a rotor attached to the crank. So, they'll run pretty much the same in either direction, once you get the spark timing sorted out.
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Tim Wescott
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On Thu, 22 Oct 2015 00:00:13 -0500, Tim Wescott

I'd really like to see the engine the OP is talking about. Chances are that it's a piston-port engine, as most bike motors have been since the beginning. My old O&R bike motor is a cross-scavenge, piston-port engine -- the basic 2-stroke design that powered everything including lawnmowers and ancient washing machines, and was used in all sorts of applications where you're after low cost and smooth running, rather than performance.

I think that both piston-port and reed-valve intake have both been used in chainsaws. Either one will allow an engine to run in either direction, given the ignition timing issue discussed before.
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On Thu, 22 Oct 2015 09:03:57 -0400, Ed Huntress wrote:

Me, too -- Eric, can you post a picture someplace, or a link to the seller's website?

I could see that -- chainsaws have a bit more need to be high performance in a small package than a lot of other 2-stroke applications. I suppose I wouldn't even be surprised at a crank-timed one (I'm kind of surprised that crank-timed 2-strokes only seem to be ubiquitous in model airplane use, and even there the really big ones are piston-timed, either because they've been repurposed from weed-whacker engines, or because they've been re-designed from such engines).

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On Fri, 23 Oct 2015 12:27:13 -0500, Tim Wescott

I've actually had my hands on only two rotary-valve 2-strokes: my old McCoy Red Head .35, which had a hollow crank with a window in one side for a port (very strange), and a Yamaha 175 dirt bike. I put a "Git Kit" in that bike, which included a new rotary-port disk, with different timing.
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On Thu, 22 Oct 2015 09:03:57 -0400, Ed Huntress

ED-the engine is piston ported. These engines are ubiquitous online. I know they are not all made in the same factories but they are all similar. See the link: www.californiamotorbikes.com I had, years and years ago, a Yamaha 80 that used the rotarty valve setup. It was interesting because the carb was inside the engine case on the right side. I think Kawasaki made a similar engine. Also interesting was the fact that there was a Honda motorcycle that not only looked a whole lot like the Yamaha but had some parts that were interchangeable. Like the front forks. These weren't the telescoping type forks so to swap forks the whole front end needed to be changed. Eric
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On Fri, 23 Oct 2015 12:54:23 -0700, snipped-for-privacy@whidbey.com wrote:

Aha. Yes, your basic piston-port 2-stroke.

There sure were a lot of oddities in those early Japanese bikes. They were pretty clever.
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The classic 3 cylinder 2-cycle Saab 95 would run either way. Car Talk once had a Puzzler on how one could beat a muscle car in a drag race. The answer was "backwards..." as the Saab could be started the other way and have 4-speeds of reverse...
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On Thu, 10 Dec 2015 19:40:30 +0000 (UTC), David Lesher

In my novice race at Lime Rock Park, in the late '60s, I got stuck behind a Saab 93 that had been race-tuned (squared ports, etc.). His secret weapon was that he smoked out anyone who tried to pass him.
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I have a weedeat, thats the brand name on it. I put it on my back of my bik e. I just happen to ha e a bike that had a braket that worked to put it on ther. Welk after i had it all set up realized that its upsidedown.. And it was firing and a few times acted lke it was going to start... But never di d... Now it is on the left side mounted on the bike..i spun the carburetor on it thinking it would work that way... But still failed to start... Thus is the firstbone i have made.. So any ideas on what i need to do... I trie d everything.. Cleaned everything... Still has spark..tried spraying gas in the carburetor.... Anyone have ideas... Please let me lnow thanks
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On 01/09/2019 10:24 AM, snipped-for-privacy@gmail.com wrote:

That's a crummy brand.

Get an Echo.
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There is no such thing as "upside down" for a 2 stroker. Just the carb (if it is a float type)
If you have compression, fuel and air in the right ratio, and spark it will run.
The only issue with "plug down" installation is it is easy to wet-foul the plug
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On Wed, 21 Oct 2015 14:01:25 -0700, etpm wrote:

Just a thought -- if you end up reversing rotation, make sure that there's not some feature already on the flywheel to accommodate that. I could see an engine company making it so you could just flip the flywheel over, or move the magnet to a different spot to reverse rotation, just to keep BOM costs down. You probably won't be so lucky, but keep your brain engaged when you open it up.
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Tim Wescott
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snipped-for-privacy@whidbey.com wrote:

Is rebuilding an engine really the easier option here? I just can't imagine that it is.
I have a bike with an engine strapped on. It's a decade old Golden Eagle kit with the drive ring and belt and a 25cc Redmax weed wacker engine. The only engine problems have been gas tank leaks from that ethanol shit in the gas. It starts in negative temps, or with old gas. Very solid little engine.
It sounds like you're going for the engine mounted inside the triangle of the frame and not something strapped over the rear wheel though. The fake motorcycle style is all I see these days. Never come across another belt drive bike like I have yet.
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On Thu, 22 Oct 2015 15:58:43 +0000 (UTC), Cydrome Leader

The "Whizzer" motor bicycle, and motor kits for bicycles, was made from around 1939 until about 2009 and there are some NOS still available.
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John B.
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That's the style of kit I see in Chicago. I still prefer the leafblower type as you just put a plastic bag over it and nobody knows it's a bike with an engine.
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