fng
Scoot Member
Posts: 28
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Post by fng on Dec 4, 2011 15:50:21 GMT -5
Forgive me for ignorance, I asked this question over on scooterforum and FOX suggested I come here and ask...(cordially of course)
So here is what's up.
What I have:
2007 Roketa BOCA-50 (139QMB) -my daily rider
Also, I have an extra crank case, CVT, stator....basically the while lower part of the engine for a spare 139QMB - right up to the piston arm...wich it bent clear to crap (probably the reason the guy gave it to me with a rim and tire attached to it...)
What I want:
I want a big bore kit without spending $300 on a stage IV kit...scrappy dogs sells a big bore kit for $60...I'm asuming that's not all I need to get the most out of the scoot...FOX said he tried it and ended up shelfing it due to agrivation...not looking for a project as I ride this scoot every day...but I'm a big fat dude and would like a little more speed/power so u don't fall on my face going uphill...or even just into the wind...
Maybe someone here can't point me in the right way to getting more awesomenrss from my scoot kinda on the cheap...(gotta make a Christmas list...)
Or maybe a bbk isn't the right answer...I'm willing to try just about anything and I have a pretty good grasp on mechanic work...so...yeah...what do yall think?
Thanks in advance,
The F%&kin New Guy.
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Deleted
Deleted Member
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Post by Deleted on Dec 4, 2011 17:53:18 GMT -5
the bike i just bought with the blown motor has all the mods i would suggest, except for leaving the fan shrouds off. (this motor blew from overheating due to fan shrouds being left off)
47mm bbk
Pref. cam
free flow exhaust like P&P
88 main jet with free flow filter
irridium plug and orange coil
TZR 50 Racing CDI
oil catch can (dont do the decompression tubes you see on dealers sites it makes the oil harder to check and you still need a catch can. they leak and blow oil, they are only for short runs down the track.)
lighter than stock rollers like 5g-6g. a little lighter if you are over 180lbs like 4.5g
I installed a 50mm 82cc kit on my TMEC BD50QT-3 I am 180lbs. I did a soft breakin for 2000 miles and now run it WOT pretty much all the time. it runs better and better every time i ride. I have 4000 miles total on that bore now. some say go for 50mm some say stay away. I say do it if you are mechanically confident.
Another mistake on the bike i just bought was they used synthetic oil. always use conventional oil to break in the rings to the cylinder walls. I do it for 2000 miles then switch to synthetic.
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Post by stepthrutuner on Dec 4, 2011 18:48:42 GMT -5
I suggest getting a long 25"x1/4"drill bit from Harbor Freight and drilling through the three baffles in the muffler, raising the needle in the carb to it's highest setting (or possibly drilling the main jet a bit), matching the intake to the head (careful with the filings if you work on the head) and using a 1500 contra spring in the torque driver (to help takeoff and on hills). You might think about slotting the reluctor pickup by the ignition rotor to advance the timing a bit too. GT90vert has a nice write up on 139 mods in the Tech Section and I have a "Speed On The Cheap" write up there as well.
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fng
Scoot Member
Posts: 28
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Post by fng on Dec 5, 2011 8:14:47 GMT -5
so....something like enviromoto.ecrater.com/p/3956702/stage-4-72cc-power-pack-139qmb-a#would be a good start? would have to get a bigger carb right? and wouldnt it need a new CDI or do i just advance the timing to make the engine fire correctly? (or would i advance it at all?) on a side note, installing a bbk - what all work (if any) is needed on the valve head? and wouldnt a bigger bore benifit from oversizing the valves? 1fastqmb, you mention a free flow exhaust...dont these smaller engines really get touchy with engine back-preasure? or have i been told horse puckky... lovin this scoot, going to start chopping it up soon...might have to send a pic to barley ridable... |
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Post by Enviromoto on Dec 5, 2011 9:28:04 GMT -5
You use your stock carb with the Stage 4 powerpack and your stock CDI.
You could benefit from a larger intake valve, but I recommend using your stock head for starters.
The LeoVince exhausts are the best ones made for the QMB so if your thinking exhaust I recommend those.
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Post by 90GTVert on Dec 5, 2011 9:38:21 GMT -5
The stock carb will be fine with a BBK, but it would have to be tuned. That kit includes what you should need to tune it. I'd pick up a selection of main jets around what it comes with, but I'm picky with the tune and plenty of folks buy it and install what is supplied and it works well for them.
The only reason you'd need a different CDI is if yours is rev limited. You don't need to advance the timing. That might give a little perfromance boost, but it also makes detonation more likely. I definitely wouldn't advance the timing with a big bore kit that doesn't have a head to match the bore until I had rode it and made sure I didn't have any issues from the higher compression first.
Hopefully no work will need to be done to the cylinder head, but if anything needs to be done it would be modifying the combustion chamber to match up with the size of the bore. You'd do that if compression is too high (again, spark knock and overheating would be the symptoms you'd likely notice then). They could benefit from larger valves, but it's not necessary unless you need to squeeze every last bit from it.
The big bore kit will involve a good bit of time if you aren't used to this stuff. If you are lucky it will all bolt up with the jets supplied and it'll run great from the first start. I don't suggest expecting that. It's likely, but if you aren't willing to deal with a scenario where say compression is high and you have to mod or replace the head or the carb or CVT isn't quite right, then you should look into other options. The bad news is, the BBK is the best mod you can do to these IMO. I suppose if it worries you, you could price out some local shops and see if any of them can do a kit at a reasonable price.
If you do go with the BBK and have a few bucks to spare, a cam is a good upgrade for some extra top end power and you have to have it out while installing the BBK anyway.
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fng
Scoot Member
Posts: 28
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Post by fng on Dec 8, 2011 10:55:35 GMT -5
The head scratching and elbow grease needed for this project is not what's bothering me, what I'm iffy about is if it needs modified, I don't have access to a milling machine or anything...I have a dremmel and some grinding stones...would that be enough equipment to make any mods?
Hate to ask so many questions that seem like I'm splitting hairs...but I'm cheap (thus the reason I ride a scoot)that and you guys are a wealth of great info.
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Post by Pony66 on Dec 8, 2011 11:07:19 GMT -5
The head scratching and elbow grease needed for this project is not what's bothering me, what I'm iffy about is if it needs modified, I don't have access to a milling machine or anything...I have a dremmel and some grinding stones...would that be enough equipment to make any mods? Hate to ask so many questions that seem like I'm splitting hairs...but I'm cheap (thus the reason I ride a scoot)that and you guys are a wealth of great info. You dont need to dremmel or mill anything. I am partial to the 72cc kit most call 80cc.(The 100cc kits are 83cc) Either kit is a bolt on application. You dont have to clearance anything unless you start stroking the crank. You only need a couple wrenches and a feeler guage. Here is a guide with nice pics of whats involved. Except use lots of assembly lube and paper towels instead of rags. ebay.globaldc.com/scooterparts/borekits/100ccGY6/install/bbk.html |
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Post by 90GTVert on Dec 8, 2011 12:23:28 GMT -5
The only reason I say you may need to mod anything with a 70cc kit is that all 50cc engines are not created equal. Some seem to have a lot of compression with a big bore and stock head. Some come with a larger than 39mm (stock bore) head from the factory, some don't. Deck height is different on some. I just say be prepared. If the idea of needing to adjust something bugs you, maybe leave it alone. In reality an extra base gasket would probably solve any compression or valve clearance issues with a 70cc kit should they arise. Most seem to be successful just installing the kit, adjusting the carb and CVT, and hitting the road. The guide posted above is also available in our tech section since it's mine, copied by an eBay seller to their own page. 49ccscoot.proboards.com/index.cgi?board=4ttech&action=display&thread=350 |
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Deleted
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Post by Deleted on Dec 8, 2011 13:29:57 GMT -5
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