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Post by motorhead on Feb 3, 2011 20:05:42 GMT -5
Why is it a stock honda metropolitan performs like a 50cc 2 stroke and does 40-45mph out the box with no modification and still gets 100+mpg. But a 139qmb scoot doesn't go beyond 30 unless its downhill or with a BBK. And even then it takes 80cc for a qmb to do 45mph.
I would think that at this stage of the game. Someone has opened up a metropolitan engine to see how its built and take that knowledge and make a speedy 50cc 139qmb that wont back up traffic. Of course, mets cost so much no one would buy one just to do this. But isn't there someone here who has worked on one that knows what makes a chf50 is different form a 139qmb.
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Post by 90GTVert on Feb 3, 2011 20:26:40 GMT -5
Never crossed my mind because the only Metro I've been around was a dog. Something was wrong with it I suppose and it couldn't top 25MPH with a 160lb rider. Maybe it was a Met II?
Liquid cooling, better timing curves and fuel control, cam setup, valve sizes, cvt setup / gearing, the aluminum frame, better engineering in general?
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Post by motorhead on Feb 3, 2011 20:42:56 GMT -5
Oh no, Metropolitans are not dogs. When working they go as fast as an 80cc 139qmbs. I thought the metro's advantage was that it was fuel injected but really It's carbureted. Liquid cooling would be a benefit but at 50cc I doubt it's much. The engine bore, stroke and compression ratio are very similar.
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Post by 90GTVert on Feb 3, 2011 20:55:29 GMT -5
Even if quoted compression is similar, I'd bet the Honda is on spec. The QMB may be way off of what gets quoted.
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Post by shakerdriver on Feb 3, 2011 21:03:47 GMT -5
The misses has a metro that I've had the pleasure of riding a couple times and me on it at 360lbs. that little metro would fly. I've had it open a couple times and its a whole lot different than any qmb I've ever seen. the fuel tanks mounted below the engine so its got a fuel pump, but it only carries 3lbs of pressure. The carb looks nothing like the qmb carbs, the entire frame is aluminum, and the cvt is just a little different also. next time I'm in there I'll take some pics for ya. If it wasn't for the fact they are so small and I'm so big I'd have one for myself. it is truly an amazing machine for a 4t.
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Post by 90GTVert on Feb 3, 2011 21:24:50 GMT -5
Aren't Rucks, or at least some of them, the same motors as the Metro? If so, there's an option for bigger folks. It does weigh 20lbs more than a Metro though.
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Post by stepthrutuner on Feb 3, 2011 22:21:11 GMT -5
We are speaking of planet Earth aren't we? A stock chf50 will do 45? scootdawg.proboards.com/index.cgi?action=gotopost&board=discussion&thread=28197&post=297179While I would accept that the average speed of a typical lot of say 10 chf50s would better the average speed of a similar lot of 139QMBs just due to quality control issues. I would also say that there are stock 139QMBs that are just as fast as any stock chf50. When production tolerances, by pure chance, pretty much all err in the direction of superior ignition and valve timing as well as toward superior charge and exhaust flow and superior fuel atomization that little QMB will scream with the best Honda Metro lumpett. Longevity is another matter altogether. |
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Post by rocketdog on Feb 4, 2011 7:16:54 GMT -5
I think ya'll hit the nail on the head with "tolerances". I checked one of my QMB139s for timing and the flywheel key was cut 3 degrees retarded at TDC. Not a lot, but enough to make a difference. An offset key got it close to perfect.
RD
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Post by 90GTVert on Feb 4, 2011 8:12:04 GMT -5
I had that trouble with the SunL, but my flywheel was about 10 degrees off. lol It was like a new scooter with a flywheel positioned properly.
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Post by motorhead on Feb 4, 2011 9:14:40 GMT -5
This is exactly why I asked the question. I've read all manner of de-restricting guides and not one brought up the issue of flywheel spark retardation. When you get a new scooter you think that everything was machined on point. After all, Honda worked with the chinese for years and they developed the GY6 together. Yeah the chinese probably cut corners on their bikes but at the same time did they forget how to time a :censored: bike.
So, how does one check their flywheel timing??? Would I have to buy one of those timing guns at the auto parts store?
As for as longevity goes I will vouch for chinese scooters. A 2004 CPI 125 came through my shop with 31,000km. And my wife's Meitian espresso is going 11,000km strong.
Don't forget that the original Metropolitan had crank case venting issues and only lasted 10k miles. Just like the honda car guys are apologists for their cars, so are the honda scooter people, when a problem happens on a honda their attitude is "its just a fluke or I did something wrong." The Honda machine gets no blame.
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Post by 90GTVert on Feb 4, 2011 9:24:58 GMT -5
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Post by motorhead on Feb 4, 2011 9:38:57 GMT -5
21 degrees off :jaw: No Way. Its a miracle the bike started up and ran at all. That leads me to assume that if you have a 139qmb you gotta take the engine apart and recheck and re-time every moving part. I'm thinking of getting hold of a metropolitan spec sheet or factory manual and completely retiming the whole ignition system. Like you said earlier vert, I bet the compression is way below where it needs to be.
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Post by 90GTVert on Feb 4, 2011 9:49:23 GMT -5
It actually started really easy thanks to the timing being retarded. lol It just wouldn't make much power, even with all the goodies. I wouldn't say that you need to pull your engine apart and go over everything if you own a 139QMB. I would say that if you are experiencing a lack of power and can't find other restrictions, it's a very good idea to check the timing as shown.
Another big problem is not just that tolerances can be so far off, but parts may be different from one scoot to the next. Some 139QMBs have been found with 44mm bores that make them faster, some are shipped with heavy rollers that can really hurt performance. It's often said that Chinese factories use whatever is available or cheapest that day.
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Post by motorhead on Feb 4, 2011 10:04:18 GMT -5
My wife has a 139qmb with a 50mm cylinder from the factory titled as 50cc:o does 45mph with my 310lbs on it. The Meitian retro Turbo. I guess turbo means BBK. I've also ridden some some of those hockey mask bashan scooters that felt way to peppy too be 50cc. They are totally illegal, and if you have insurance and you wreck one and they inspect it you could be in big trouble. If you are on a chinese 4T 50cc and can do over 30mph, its probably not 39mm.
Anyhow, my next goal to pickup a cheap true 50cc qmb on craigs list and metropolitize it.
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Post by stepthrutuner on Feb 4, 2011 10:25:43 GMT -5
This is exactly why I asked the question. I've read all manner of de-restricting guides and not one brought up the issue of flywheel spark retardation. When you get a new scooter you think that everything was machined on point. After all, Honda worked with the chinese for years and they developed the GY6 together. Yeah the chinese probably cut corners on their bikes but at the same time did they forget how to time a  bike. So, how does one check their flywheel timing??? Would I have to buy one of those timing guns at the auto parts store? As for as longevity goes I will vouch for chinese scooters. A 2004 CPI 125 came through my shop with 31,000km. And my wife's Meitian espresso is going 11,000km strong. Don't forget that the original Metropolitan had crank case venting issues and only lasted 10k miles. Just like the honda car guys are apologists for their cars, so are the honda scooter people, when a problem happens on a honda their attitude is "its just a fluke or I did something wrong." The Honda machine gets no blame. Service life of any product always boils down to basically three variables - build quality, maintenance and pattern of use. Any product that has not escaped rigorous and competent quality control measures in the manufacture and assembly of components, has had maintenance schedules performed faithfully at or before due times and has been operated consistently below maximum design parameters will outlast any product that has found neglect at all of these factors. Mainland Chinese scooters are notorious for excessive porosity in castings and poor assembly. Day-to-day, month-to-month, year-to-year quality can vary considerably for any one brand. I've read advise to not use synthetic motor oils in Chinese 4ts because of the porosity problem. Girls, women and old retired guys will always get more use from any given scooter than will teen age boys. I will continue to advise people to buy European, Taiwanese or South Korean built scooters if they knowingly can especially if they are not mechanically inclined or lack the time to hassle with their scooters. On the other hand, if one likes to twiddle and fiddle and play parts hunt then buy the cheapest that can be found.... always have a backup though.  |
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