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09-26-2018, 02:21 PM
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#1 |
 Join Date: Sep 2018
Posts: 5
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49cc 139qmb will not start... Help!
Hello,
So I have a 2008 Tank Urban Sporty with a 49cc GY6 139qmb motor that will not start, it cranks, but will not start. Let me get in to the details... I got it this spring and it didn't start. I wasn't sure how long it had sat around so I put in a new spark plug, new battery and cleaned the carb. Boom, it started. It had very little power, I had to somewhat push with my feet to get going from a stop sign and it took nearly half of a mile to get up to maybe 25 mph, but you could still comfortably ride it around. I decided to put on an aftermarket exhaust and an unrestricted CDI (not a "racing" CDI). The two upgrades made a marginal difference, but it was now able to go 30 mph. Over time it gradually started to run worse and start with a little more difficulty whether I used the kick start or the electric start (the kick start always seemed to work better). The engine was running lean so I cleaned the carb again and adjusted the idle mixture while the engine was warm to get the best idle. It would still bog down while accelerating and wouldn't go much past 6000 rpm. Soon it became very difficult to start, it would take 5-6 attempts to finally be able to idle, each attempt would get closer to starting. Once it was able to idle (which was very low) it would die as soon as you even thought about touching the throttle. It felt as if the motor wasn't getting fuel. I decided to do a slight overhaul and replace the carb with a new one with slightly larger jets and a new electric choke, replace the fuel pump and replace the fuel filter. While I was doing this I replaced the rollers with 6g rollers, replaced the contra spring with a 1500 and replaced the clutch springs with 1000 springs. After this it did not start at all. The engine would crank but would not start even when I used starting fluid. I have fuel to the carb. I have vacuum. I have spark... I adjusted the intake and exhaust valves; intake (.002 in), exhaust (.003 in) as these gaps are stated in the manual. I got yet another new spark plug. (new ignition coil is on the way)........... .....Same story...... It will not start I do not believe I would have messed up the timing as I did not remove the cam or the chain, I merely turned the motor via the flywheel to reach "Top-Dead-Center" when doing the valve adjustment. I have done nothing with the stator as I do not want to spend any more money until I have a better idea of which direction to go from here... I am at a complete loss as to why this motor will not start. I would greatly appreciate any help I can get. I find myself frequently visiting this forum as there are a lot of people here with far more expertise than myself. I apologize for such a long post but I wanted to be as detailed as possible so that someone somewhere might see a glaringly obvious flaw or missed opportunity in my process... Thank you in advance! |
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10-01-2018, 04:49 PM
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#2 |
 
Join Date: Oct 2008
Location: Hyde Park, NY
Posts: 1,131
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The flywheel has a T and an F mark on them. When you set the valves did you use the T or F? T is top dead center the F is where the spark plug fires which is always in advance of the piston reaching top of the crankshaft throw.
I made that mistake once and it upset my cam timing and valve adjustments. Resetting everything right had the motor humming.
__________________
2008 Eagle Milano 150- 9,679 miles 2009 Honda Rebel 250- 10,434 miles 2009 CF Moto Fashion- 16,023 miles 2009 MC-114 50cc Cub Clone- 4,317 miles twowheeler.yolasite.com/ That's 30,049 China Scootin miles and Counting. |
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10-22-2018, 05:04 PM
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#3 | |
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Join Date: Sep 2018
Posts: 5
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Quote:
Is it likely that my motor has lost compression??? .....I do not have a compression tester, although I could rent one, but I'd still have to buy an adapter to fit that size plug. Would a compression test be worth my $? |
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10-23-2018, 01:13 PM
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#4 |
Join Date: May 2015
Location: Lanoka Harbor, NJ
Posts: 63
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If you can get your finger in there, try holding it over the open plug hole while cranking the engine. It should puff your finger off the hole. While not a measurement, it would be a quick indicator if there's compression, or not.
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10-29-2018, 09:02 AM
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#5 |
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Join Date: Sep 2018
Posts: 5
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So I ran the compression test.... <25 PSI....
I have made sure that all hoses are properly connected and checked for any additional leaks. It seems that a rebuild is in the near future? Does anyone have a tried and true technique for testing for leaks? It is my understanding that I should have a minimum of 100 PSI for starting, and around 150 PSI for proper operation... Can anyone confirm this? How about any good recommendations for a rebuild? I'm not looking for crazy power, just a quality rebuild. |
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10-30-2018, 09:26 PM
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#6 | |
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Join Date: Sep 2015
Posts: 13
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Quote:
As far as kits go, I have this 72cc kit on my scooter and it runs great even though i have stock everything else [even the jetting] right now...its a very noticeable power increase over the stock 50cc and the kit was machined well. I do know that some people run the 80cc kits [advertised as 100cc] and thats fine, myself i am weary of that as i have heard they put wear on your crankshaft so i go with a 72cc kit due to that instead. Thats just my preference. Keep in mind that the kit below says it is a 80cc but that is just advertising, similar to how the "100cc" kits are really 80cc. The kit below has a 47mm piston/cylinder which = 72cc. https://www.amazon.com/gp/product/B0...f=scootdawg-20 And if you need a great video on clocking the rings, this video is for a 150cc gy6 but the same ring clocking works just fine on smaller CCs and it runs great. |
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| Tags |
| 139qmb, 49cc, 50cc, gy6, will not start |
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