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Old 03-16-2019, 09:26 PM   #1 (permalink)
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Efficient motor

I was thinking of buying a particular 125cc motorcycle although this motorcycle turned out to have bad fuel economy and I figure it is due to the push rod motor that was used.

I want to learn more about what features enable a motor to be more efficient so I can make an informed decision.

Is there information available can make this possible?

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Old 03-17-2019, 11:02 AM   #2 (permalink)
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Quote:
Originally Posted by Spaghetti Man View Post
I was thinking of buying a particular 125cc motorcycle although this motorcycle turned out to have bad fuel economy and I figure it is due to the push rod motor that was used.

I want to learn more about what features enable a motor to be more efficient so I can make an informed decision.

Is there information available can make this possible?
Well, some basic things you can look for are an undersquare engine, fuel injection, and a higher compression ratio. Sounds like whatever bike you were looking at has a really old engine design. Even the 1960s Honda 50 had an overhead cam. If you end up getting a bike with a carb, make sure the carb is tuned right and not just dumping fuel. You should be able to achieve great fuel economy even with a carb.
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Old 03-17-2019, 11:10 AM   #3 (permalink)
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What DasChicken said, and also... it sounds like you didn't buy that 125cc bike. If you are still hunting, there are used bikes with great fuel economy. I have not owned a motorcycle in many years (except a scooter I don't ride), but here is a list I found through a google search: https://www.totalmotorcycle.com/Moto...MPG-under500cc
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Old 03-17-2019, 12:26 PM   #4 (permalink)
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I'm surprised a 60's Yamaha trail 80 tops that list. My first bike was something like a 1968 Yamaha trail 80, it certainly seemed to outpower my buddy's Honda Trail 90, maybe because it was a 2 stroke? Maybe his wasn't running right because he had to jump off on a few steep hills. Maybe his was one of the really early ones without the low range, or even a 55. I also currently have a tired 1963 Honda Trail 55 that won't climb my yard, but I only have the high speed sprocket, and my butt is 3 times heavier than it was in 1978. None of these bikes seem like they would get anything near 100 mpg, but maybe.
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Old 03-17-2019, 01:14 PM   #5 (permalink)
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Pushrod? What the heck was it?

I've owned a few bikes over the years, and even the one that was older than I am didn't have a pushrod engine.

Cam timing/overlap, gearing, fuel delivery system, # of engine strokes, and engine size each have a notable effect on efficiency.

If you want MPGs, you need something that suits the use you'll be putting it to best, and for us to make suggestions we need to know what/how you'll be using it...otherwise if it's purely about MPGs, a decent bicycle with a 4-stroke weed-eater engine will get you 200mpgs; But I don't think that's what you're looking for.
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Old 03-17-2019, 06:55 PM   #6 (permalink)
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The Vetter Challenge motorcycles were in the 175-250 cc range with body shells and gearing changes, and cruised at 50 -60 mph. A motorized bicycle would cruise at 25-30 mph with a stock small engine.
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Old 03-17-2019, 11:24 PM   #7 (permalink)
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Quote:
Originally Posted by Spaghetti Man View Post
I was thinking of buying a particular 125cc motorcycle although this motorcycle turned out to have bad fuel economy and I figure it is due to the push rod motor that was used.
Some random Chinese copy of the Honda CG 125 engine? BTW in the end an engine being OHV or OHC won't really affect fuel-efficiency so much as it was supposed to. Cam timing/phasing and port sizes might be more relevant.
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Old 03-19-2019, 12:28 AM   #8 (permalink)
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Quote:
Originally Posted by California98Civic View Post
What DasChicken said, and also... it sounds like you didn't buy that 125cc bike. If you are still hunting, there are used bikes with great fuel economy. I have not owned a motorcycle in many years (except a scooter I don't ride), but here is a list I found through a google search: https://www.totalmotorcycle.com/Moto...MPG-under500cc
I have seen this once before.

I want to isolate what makes the engine efficient.

A 25cc motor will be super efficient compared to a 250cc motor however the 25cc motor cannot travel at 110km per hour.

Even engine capacity is not a definitive indicator as an engine may be poorly designed or not designed for efficiency.


I am specifically looking for 110km per hour top speed and lowest possible fuel consumption. If I can get a scooter that would allow for recumbent seating but scooter CVT motors are heavy.

We don't have Honda Wave here in Australia.
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Old 03-19-2019, 03:35 AM   #9 (permalink)
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Quote:
Originally Posted by Spaghetti Man View Post
I want to isolate what makes the engine efficient.
Efficiency might be achieved through different pathways...


Quote:
A 25cc motor will be super efficient compared to a 250cc motor however the 25cc motor cannot travel at 110km per hour.
You might be looking at efficiency from a perspective of fuel consumption per a given amount of time, while considering the specific fuel consumption for power provided is more relevant (often mentioned as BSFC - brake-specific fuel consumption).


Quote:
Even engine capacity is not a definitive indicator as an engine may be poorly designed or not designed for efficiency.
That's one of the reasons I'm unfavorable to the "people's car" policy in my country considering simply the displacement up to 1.0L in order to grant lower taxation. Similar models available in neighboring countries with slightly larger displacement such as 1.2L or 1.4L achieve better fuel-efficiency due to the higher torque at lower RPM bands and higher gearing.
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Old 03-19-2019, 12:58 PM   #10 (permalink)
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Interesting that the Yamaha XV-250 made this list. For all the bogus stuff on this bike (the phony rear exhaust pipe, for one) it's still pretty light for a twin at around 325 lbs. It's also under square in it's bore and stroke. Best of all it's been imported in the U. S. since 1988 meaning parts will always be available.

I'd venture to bet I could get it down to under 300 lbs. easily.

On the modern end of things folks I know with Yamaha WR-250R's are easily getting 80 MPG. Imagine what you could do if you streamlined one of these puppies.

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