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Old 09-25-2013, 08:40 PM   #1
some kid OP
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Metropolitan no power - carburettor issue

Just picked up an '05 Met for next to nothing as a flipper bike (I've always thought they were cool) and cleaned the carb, put a new battery and fresh gas in it and got it running. The bike is not making any power - won't go over about 15 mph and I have discovered that the CV diaphragm is not rising as it should. I have taken the top cap off the carb with the engine running and for some reason the diaphragm is being sucked down instead of up when it is revved.
As an experiment, I took the spring out and placed it underneath around the needle to hold the slide in the up position, re-installed the cap and the scooter was much more powerful and could almost reach top speed. Just can't figure out why there is vaccum under the diaphragm. Any clues as to the causation of this carburettor canundrum? What am I missing here?
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Old 09-25-2013, 08:57 PM   #2
tortoise2
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Quote:
Originally Posted by some kid View Post
I have taken the top cap off the carb with the engine running and for some reason the diaphragm is being sucked down instead of up when it is revved. . . . What am I missing here?
Basic CV carb theory!





tortoise2 screwed with this post 09-25-2013 at 09:15 PM
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Old 09-26-2013, 07:09 AM   #3
Dabears
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So from the very cool diagrams I presume the most logical answer to the OPs question is that the vacuum port to the diaphram is blocked and instead the diaphram is being sucked down as the butterfly valve opens. True?

Alternatively, as I've never seen the above happen, check or replace the diaphram too- I have seen those fail a number of times.

Hope you're able to fix it easily.
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Old 09-26-2013, 07:53 PM   #4
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Wow thanks for that - It looks like I was over-thinking it. Turns out the Met. uses the type of CV actuation shown in the pictures where the intake vacuum goes through the slide then pulls from above, so with the cap removed like I had it, the slide wouldn't be able to go up anyway (d'oh!). With that being the case, I think I will re-investigate all of the jets and passages whenever I have the time, as I'm now thinking that something underneath might still be clogged.
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Old 09-27-2013, 09:10 AM   #5
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Should be able to observe if carb slide is rising properly and fuel spray.

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Old 10-03-2013, 09:17 PM   #6
JerryH
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I would definitely "flip" that Met as soon as possible. the '05 and older models had a defective crankcase venting system, which causes rapid sludge buildup, and results in a very short lived engine even when properly maintained. That was fixed for the '06-'09 models.
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Old 10-03-2013, 09:30 PM   #7
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'05 and older models had a defective crankcase venting system
Related discussion.
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Old 10-07-2013, 06:30 PM   #8
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Finally got a chance to mess with the Met again. I took apart, checked all of the passages then reassembled the carb for the 3rd time then started the engine with the air box boot disconected so I could look down it's throat. Sure enough, when opening the throttle even fully, the slide is only going up about halfway then just stopping. The diaphragm appears to be in perfect nick, and I have even applied a small amount of Honda-Bond around the cap to make sure it is not leaking vacuum.
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