Howdy everyone. I just recently bought a new 150cc Sanyang “ye lang” (wild wolf) motorcycle. It was a replacement for my old Kymco 125cc motorcycle (not a scooter).
The new bike is nice, but one thing annoys me - the gas mileage is disappointing. I know that those of you who drive big gas guzzlers will wonder what I’m complaining about, but the old bike got 135mpg (56km/liter). The new bike gets 92mpg (40km/liter). By comparison, I had a Honda 250cc motorcycle in the USA which got 98mpg (41.2km/liter). Seems to me ridiculous that the extra 25cc of engine displacement in my new bike could be sucking so much additional gasoline. The new 150cc gets even worse mileage than my 250cc bike. All 3 bikes have carburetors, not fuel injection.
I am contemplating an experiment - putting smaller carburetor jets into the new bike. I would probably just take the jets from the old 125cc bike (that bike is pretty much junk now). But I’m a little concerned - the smaller jets might result in a leaner air/fuel mixture, and I wonder if this could result in engine damage (specifically, burning the valves). I’m not enough of an engineer to know if this is really an issue. I wonder if any of you have any experience or thoughts along these lines.
Your vehicle is extremely likely to have been built to its maximum potential regarding its engine’s design. I very much doubt that you will somehow pull off any miracle in gas mileage by reducing the size of its fuel valve.
The two biggest improvement alterations [regarding fuel economy] you can make to that bike are firstly the front~rear chain sprocket ratio and then the exhaust silencer. [You could always go on a crash diet too!]
I’m not sure what your sprocket ratio is at present, but I took my 125 commercial “ye lang” which has a very low ratio for hogging sacks of veg and dead cow to market, and I raised it. I lose torque, but what I gain is an enormously improved fuel economy.
The Exhaust silencers on the newer bikes are also fitted with a crude catalyst which helps to burn off excess CO, converting it to CO2. The catalyst is a restriction in the pipe however and causes greater back pressure, reducing power and increasing fuel consumption. You can either remove the restriction by faffing around, chopping and re welding your exhaust or you can simply replace it with a more basic, original pipe, designed for earlier models of “ye lang” which didn’t contain the restrictive catalyst.
I have already without exhaust mod increased the fuel efficiency of my bike so far that I don’t really care what it gets any more. Its WAAAAAY better than my old but new Kymco 125 scoot.
“ye lang” brags being the most fuel efficient bike on the local market, so if yours isn’t then either there is something wrong with the bike or perhaps the way you’re riding it. One tip though, keep the revs low and the choke in early (if you have one. They are better manual), they don’t like revvvvvvs!
Greetings Sulavaca, and thank you for those tips. Yeah, I thought that the carburetor tweaking might not really work, but I was out of ideas. The suggestions that you came up with are intriguing.
I don’t need a crash diet - I’m only 60 kilograms. But thanks for mentioning it anyway.
Replacing the catalyst is intriguing. However, I’m a little reluctant to hack the pollution control system, since I might fail the CO test which is occasionally required.
The sprocket idea has merit. How much did it improve your gas mileage? Do you still have enough torque to get moving up a steep hill (from a complete stop) with a passenger on the back? I’d hate to stall out in such a situation.
You didn’t mention what size “ye lang” you have. Is it 125cc or 150cc? What is your gas mileage now?
ALL the Sanyang “Wild Wolves” I’ve seen here, with the exception of some in Railway Police hands, have been 125cc. (The “Railway Police Special” was 150cc). There has, however, been some discussion elsewhere of a 150cc version being exported to the US, so perhaps they are standardising on that. Maybe the extra cc’s are to compensate for power-sapping/fuel guzzling anti-pollution devices.
Do they REALLY have a catalyst? Those things are bad news with fuel injection, but with a carb (and no lamda sensor?) it would presumably be running open loop, burning an uncontrolled but probably unecessarily large amount of extra fuel to keep the catalyst cooking. Am I understanding this correctly?
If I am, that’s awful. I’d take it off. You can always put it back on if you need it to pass inspection.
What model is / was the superior old Kymco? Most of their machines seem to be available here in both 125 and 150cc versions, though the 150cc’s are a lot commoner.
[quote=“Dog’s_Breakfast”]Greetings Sulavaca, and thank you for those tips. Yeah, I thought that the carburetor tweaking might not really work, but I was out of ideas. The suggestions that you came up with are intriguing.
I don’t need a crash diet - I’m only 60 kilograms. But thanks for mentioning it anyway.
Replacing the catalyst is intriguing. However, I’m a little reluctant to hack the pollution control system, since I might fail the CO test which is occasionally required.
The sprocket idea has merit. How much did it improve your gas mileage? Do you still have enough torque to get moving up a steep hill (from a complete stop) with a passenger on the back? I’d hate to stall out in such a situation.
You didn’t mention what size “ye lang” you have. Is it 125cc or 150cc? What is your gas mileage now?
best regards,
DB[/quote]
Well you can replace the exhaust with an original SYM exhaust for that model but one of the early ones that comes without the wire typical wire gauze inside. The older exhaust improves power and fuel economy. You only need switch exhausts at worst before inspection, but most likely it will either just pass anyway or at worst you first mark your mixture screw, turn it towards ‘lean’, pass the test then turn it back. The tester cares less how it passes the test, and neither cares that you intend to readjust after the test. The test is simply stupid in the first place. I haven’t changed my exhaust yet, but will someday once the one I have is rusted through and holed (another advantage of the older pipe with greater longevity and a nicer fully chromed look).
As I said I haven’t checked my mileage, I just know its way better, I estimate that perhaps as much as 15~20 percent since I changed the sprockets. (larger front, smaller rear) The sprocket alteration cost about 1,500 if I recall correctly and I had it done at Alan’s “Maxis” garage on Roosevelt Road, close to Keelung roundabout. I’m sure its easy to get it done at a lot of places however. I couldn’t be bothered to do it myself considering you only really pay for parts.
As I said, my bike is the commercial version and so only comes with a four speed box and very low ratio gears. Without changing the entire box for the non commercial type, then the sprockets were the easiest choice and least expensive. If you have a 150cc as opposed to my 125 then I assume you have the newer 5 speed box. I haven’t tried one though to understand the approximate torque and engine speed. My old low ration setup maxed my comfortable top speed to about 50kph which without the balance shaft found on KTRs meant that I was rattling my fillings out and wouldn’t want to go faster. Now I have an increased comfortable speed (I don’t know what top speed is, I’ve honestly never tried it) at about 60~70 and greater MPG. Up hill its fine too. I’ve had my 98kg dad on the back for a total 175kg load and the going was slow but steady and I never once conked out. It does require more revs in a lower gear of course on a gradient, but extreme gradients I feel are virtually hard to come upon during most of my travels.
Catalyst is a loose term really regarding the basic design of a now typical motorcycle exhaust. They usually have some sort of wire mesh or wool within the unit that easily glows hot, burning off additional fuel and partially burned fuel and oil, reducing harmful emissions, but increasing CO2 output and fuel consumption whilst reducing power. Its the reason the Japanese for the longest time were against placing cat’s on cars and why the oil companies love them.
Open loop would most commonly refer to a fuel injection system which provides a fixed fuel/air ration regardless of running conditions, to be basic. These bikes are carburetor controlled with no injector though and so would certainly have a fixed fuel/air setup set by the mixture valve. The fuel is not specifically adjusted to keep the exhaust “cooking”, but rather the exhaust designed to maintain an adequate temperature to burn off excess fuel/oil. These exhausts were incorporated to improve low level (city) ozone only and weren’t a big hit among many motor vehicle manufacturers who claimed they were an unnecessary restriction to performance and fuel mileage.
To make things worse many of these exhaust systems can gum up more easily over time and can eventually provide even more resistance to exhaust gasses, further reducing performance.
I would just add that we haven’t any idea about the maintenance that’s been done or not. Carb and air filter could be filthy and the bike is just running pig rich for this reason.
ALL the Sanyang “Wild Wolves” I’ve seen here, with the exception of some in Railway Police hands, have been 125cc. (The “Railway Police Special” was 150cc). There has, however, been some discussion elsewhere of a 150cc version being exported to the US, so perhaps they are standardising on that. Maybe the extra cc’s are to compensate for power-sapping/fuel guzzling anti-pollution devices.
[/quote]
They’ve had the 150cc for several years now. My only reason for buying it instead of the 125cc was because this is the only model they sell that uses the “international” gear-shift pattern: 1-N-2-3-4-5
All the 125cc models using the “rotating” shift pattern: -->0-1-2-3-4-5–>
I hate that one, because it’s so easy to be crusing along in 5th gear but you think it’s 4th, so you shift one more time and find yourself doing 70kph in 1st gear.
On this web page you can see the three “R Series” ye lang bikes. Two models are 125cc and the third is 150cc (just like mine).
Hmmm…Now I’m wondering if I should mess with the sprockets. Mine is a 5-speed setup, and at 60kph (the maximum speed limit here in Taitung County) I’m doing about 4500rpm, which seems to be near ideal. Perhaps 4000rpm at that speed would be best, but if a change in sprockets results in me only doing 3500rpm at that speed, I’d probably be lugging the engine. I seldom exceed the speed limit, perhaps 70kph at times (5000rpm), but that’s max.
I’m going to look into this exhaust-pipe thing. I wouldn’t mind forking out the money for a different pipe if it would give me at least a 10% boost in gas mileage. My biggest worry is that these old-style non-catalyst type of mufflers might no longer be available in Taiwan. Possibly they have been banned. If anyone has info on that, I’d appreciate knowing - thanks in advance.
It’s a brand-new bike, not even 1000km yet on the odometer. The only maintenance so far has been an oil change at 300km. I’m hoping that after the break-in period the mileage will improve, but I don’t expect it to change much.
Thanks for the comments and suggestions so far. Any and all suggestions welcome, so keep them coming. If I change the exhaust, I’ll report back to let you know if this worked any magic on the fuel economy.
[quote=“Dog’s_Breakfast”]
It’s a brand-new bike, not even 1000km yet on the odometer. The only maintenance so far has been an oil change at 300km. I’m hoping that after the break-in period the mileage will improve, but I don’t expect it to change much.[/quote]
Ah, I see. It would have been helpful if you’d included that info in the original question.
Get the older pipe as suggested. The spare parts store will have them for sure. You may have to re-jet after changing the muffler. Lowering the final drive ratio as suggested will also help.
[quote=“redwagon”][quote=“Dog’s_Breakfast”]
Get the older pipe as suggested. The spare parts store will have them for sure. You may have to re-jet after changing the muffler. Lowering the final drive ratio as suggested will also help.[/quote][/quote]
Hi Redwagon,
You mentioned rejetting. I’m assuming that you mean smaller jets. Larger jets would eat more gas.
How do I know if rejetting is called for? Mixture running too rich maybe (as evidenced by blackened spark plugs?). What other signs should I be looking for? How do I know if I’m running it too lean?
[quote=“Dog’s_Breakfast”]You mentioned rejetting. I’m assuming that you mean smaller jets. Larger jets would eat more gas.
How do I know if rejetting is called for? Mixture running too rich maybe (as evidenced by blackened spark plugs?). What other signs should I be looking for? How do I know if I’m running it too lean?[/quote]
Bigger jets do not automatically mean you will use more gas. You have a restriction now in the muffler which ruins efficiency and that means less power at any given throttle position. Removing that restriction would improve efficiency and therefore airflow. More air flowing means you will pull more gas from a given jet size. That in itself might be enough to compensate. If not you may have to fit a larger main jet. At this point you should have greatly improved the efficiency of the whole air throughput by reduction in pumping losses and other factors. It should be possible for example to cruise at 50kph on a smaller throttle opening than before simply because at the same opening more air would be consumed. Your overall mixture should end up a little richer but you be burning less air for the same net result, thus consuming less fuel in total.
It helps if you remember that internal combustion engines do not burn fuel to make power… they burn air. Fuel is needed to burn the air.
You are likely only to have to change the main jet. Quick set up for main jet size:
On a dry, warm day go warm the bike up to normal temperature. You want to find a long hill with just a few degrees incline. Accelerate up to say 4,000rpm in 4th gear and roll the throttle smoothly from 1/2 to wide open. If the engine bogs at any point try backing off the throttle slightly and see what happens. If the bogging stops and you resume accelerating then your main jet is probably too big. If the engine runs smooth but seems to lack power, then try opening the choke slightly. If you gain power from this then your main jet is probably too small. Once you have the main jet sorted you can take a look at the needle position. One step at a time.
[quote=“redwagon”][quote=“Dog’s_Breakfast”]
It’s a brand-new bike, not even 1000km yet on the odometer. The only maintenance so far has been an oil change at 300km. I’m hoping that after the break-in period the mileage will improve, but I don’t expect it to change much.[/quote]
Ah, I see. It would have been helpful if you’d included that info in the original question.
[/quote]
To be fair, he did say it was a new purchase, though things do seem to clog up pretty quickly here.
OP, thanks for the info on the 150cc model. I’m clearly not as observant as I thought.
