anyone familiar with ASTRA scooters?

[chicago]

a few years back, I was gifted an ASTRA 125 (I believe) scooter... though if I were to go out and buy a scooter on my own, it would not be this one (especially after finding it so difficult to find parts, etc for this brand). anyhow, I managed to track down the importer and was ultimately able to order a few much needed switches and brake pads. in the process, I've been inspired to consider beefing up the motor so to speak. which puts me at square 1 what type of motor does this thing have? you see, somehow whomever sold the scooter initially asked that the paper work indicate that it was a 49cc motor... after speaking with the importer, it turns out that the only models that astra offers are a 125cc and 150cc... intuitively I would imagine that this is would have to be bigger than a 49cc, as it tops out at roughly 45-50mph (75 km/h), not to mention that when I brought it to a repair shop when I first acquired it, the technition was certain it had to be closer to a 150cc.

so, I looked over the motor and found a serial number etched into the motor on the gear side... it read: 139QMB followed by *05046017*

I googled both and only came up with info on the first part (139QMB) and it appears this may be a honda style motor of the GY6 nature??

also, when opening the stock air box to check air filter, there was the following serial number: 17211-GY6-9400 (further confirming my best guess as to it being a GY6 style motor)

anyhow, growing up around cars and v-8 motors and the likes, I was thinking about potentially changing out the air-filter and exaust in hopes to give the bike a little more pep... upon finally discovering this forum and reading through some of the many very helpful threads, I'm beginning to really wonder if I should even bother (as I'm finding that re-jetting may be necissary to offset air fuel balance, etc... not to mention all the sensitivities of changing roller weights, springs, etc when it comes to the transmission)

ultimately, if anyone could help me confirm the size of this engine, that would prove extremely important before anything else... from there, if anyone has opinions with regards to intake and exhaust options that may be appropriate... that would probably be a logical next step

and of course, if the suggestion to leave the thing alone and just enjoy it, would also work

so many thanks in advance!

[tiba_karotsu]

sounds like a brand of thread for sewing. LOL j/k

[chicago]

yeah, I hear ya... imagine being in my shoes, trying to work on the darn thing. it has not been the easiest road to travel, to say the least.

[tiba_karotsu]

the difference between the GY6 125cc & 150cc engine is the bore & valve sizes, it's got the same crankshaft stroke, i'd prefer the 150cc as it's got bigger valves but have very restrictive ports, you can gain some power by porting (streamlining) the intake & exhaust ports, fabricate an exhaust pipe with an inside diameter of 25mm for the header with the rest of the rest of the pipes increasing in size like a stepped header, the outlet shouldn't be any bigger than 1.5 inches & that includes the muffller too.

as for rejetting just increase the main & pilot jets but don't remove the airbox or it'll be impossible to tune the carb.

[chicago]

I really appreciate the information you've shared thus far... just to clarify, It's looking more and more as though this is a 125 I have on my hands. not sure this makes a huge difference but probably worth mentioning.

the suggestions are well received, but I have some questions regarding the instructions you provided... with regards to forging an exhaust pipe with said internal diameter, etc... I'm not sure I would be of much use in making this myself unfortunately (not a very experienced welder, etc). are there any "performance exhausts" that I can perhaps order online that would fit reccomended specs, etc?

also, regarding polishing the "restrictive" ports... (again relatively new to small engines) where do I begin while dis-assembling and what sort of tools are ideal for this task?

I've heard time and time again people referring to this process in the automotive realm... would de-restricting the exhaust alone noticeably increase performance? or more in the combination of changing out the jets, etc?

speaking of jets, again pardon my lack of experience, what is a good source for purchasing such items? sizes? how big should I go?

finally, you suggest keeping the standard airbox due to nearly impossible carb tuning... what about all the various alternatives (like the cone shaped high flow deals that attach directly to the carb, etc)

in all honesty, I just find the big airbox to be a little tacky in terms of appearance. but if vanity will create more problems than it's worth (that would almost make sense), I guess leaving it on is ok too.

so yeah, to recap...

does unrestricted exhaust alone produce noticeable / significant difference in performance?

changing jets necissary? how significant of a difference may be found there?

is standard air filter sufficient after above mods have been applied (or would the engine potentially be gasping for more air)?

cheers!

[tiba_karotsu]

if you have the 125cc engine then the exhaust port is more restrictive, i have modified some GY6 engines in the past & trust me when i say the ports on the 125cc heads are the most restrictive, the boss around the valve guides almost block the ports completely so just trimming them down can significantly boost airflow without enlarging the ports themselves.

adding an aftermarket pipe will increase power along with rejetting but with the stock ports it will not be significant as the system can only flow as much as the smallest orifice.

the reason for keeping the airbox is the fact that the needle is nearly straight, if you remove the airbox completely, even running the biggest mainjet won't do a thing as the needle itself is limiting the fuel flow from the jet at the discharge nozzle.

as for jets you can buy them at Sudco as the stock carbs are Keihin copies from the genuine GY6 engine.

if you haven't got porting tools from dremel or foredom you'll have a hard time getting to the guide boss.

[chicago]

I have a dremmel, so suppose trimming the boss around valve guide would be a possiblity... of course, I would have to identify said area.

is there anywhere I can find a scematic or drawing of what exactly you propose I trim? also, is this something I can get to from the exhaust port (like if I remove the pipe and muffler for example), or would this mod require further / deeper disassembly?

if so, where to begin?

again, small engines are new to me (but suppose taking appart and putting back together is not exactly rocket science)

if it's the case that this sort of thing would require deeper disassembly... might as well do as much internal mods in the process (as I would rather not open the motor up more than once if not necissary)

all the best! (many thanks again)

[tiba_karotsu]

a 4stroke engine is a 4stroke engine whether it be a small GY6 125cc single or a small block chevy 350 pushrod V8 engine, same basic principles apply, it's just the design & size that is different.

you should shape the boss around the guide into a teardrop shape, much like a cross section of an airplane wing, the valve size for the 125cc engine is 24mm intake & 21mm exhaust so you can imagine how small the ports are. it is best if you have a slim handpiece attachment to your dremel, preferably the old model with a 1/2 inch handpiece so you can stick it inside the port.