Kings of 50cc help with my Scootermotard

[rabidnz]

I have a mikuni tm-28 in my box of bits, but im guessing that this is going to be a bit over the top for what im needing, and will end up very difficult to tune. If anyone wants to swap a 17-21mm suitable slide card id be happy to.

Also I can turn the engine over from the magneto with just a pinch, it gets tighter at a point, but is at no point hard to turn. What compression would i expect to see on the guage, if my rings and piston werent worn out (new ones in the mail regardless, its a 50, its gonna need them eventually and only 80 bucks)

[SS90]

Well, 28mm is a shade on the big side (under statement) you really want something in the area of 18 to 20mm in my opinion.
I recon the guys getting high 20's ps will be using carbs around the 28 mm mark...maybe bigger.

I will go vistit a local mofa dealer and in dorm him of your problem tomorrow, hopefully he can help.....I am pretty sure your situation is caused by a level of restriction.

When it comes to 50s, compression is something that many people fool themselves into thinking is too low (also, if it is a Dyke ring piston, don't for bet the compression when Turing over with your hand is always much lower than when it is kicked!

My experience with tuned 50's is pretty minimal (well, compared to the guys in this part of the world anyway) and I can honestly say I have never tested the compression with a compression gauge.

I am actually building an am6 this winter in the deluded hope of competing in next years European 50 cc Endurance race (already lost 10kgs now just need to lose 10 more)

I base my calculations on cylinder head volumes and trapped compression, and what I get in the sense of bar or psi to me seems irrelevent......

Personally, like I say, if it starts ok and idles, I would not suspect the top end too much....bit, as you say, not much work to check!

[bucketracer]

I have a mikuni tm-28 in my box of bits, but im guessing that this is going to be a bit over the top for what im needing, and will end up very difficult to tune. If anyone wants to swap a 17-21mm suitable slide card id be happy to.

I have some spare 22mm round slide Mikunis from GP100's. You can have one for free if you want, to play with. PM me.

[rabidnz]

thanks ss90 , please keep us informed on youre build, and progress towards the enduro champs, huge luck to you!

As the only 50s ive dealt with before are lawnmowers and stock nifty 50s, im not really sure how much compression there would be, it just felt as if there was significant blow by past the rings, as just as it should be gettin on the pipe it hunkers down, definitely not leaning out as the pipe are plug are rather sooty. I am heading down to get some muffler packing and a new plug, also going to try her with a race filter instead of the airbox, before i start playing with jets.

I would be stoked to try one of those carbs bucketracer, ive sent you a pm with offererings of beer.

Another thing, on the intake manifold one of the screws looks like a blank head, ie its just flat, i am proably just going to try and vice grip it off, and replace with a hex cap, never seen this type of security bolt with just nothing whatsoever to grab hold of.

[SS90]

Another thing, on the intake manifold one of the screws looks like a blank head, ie its just flat, i am proably just going to try and vice grip it off, and replace with a hex cap, never seen this type of security bolt with just nothing whatsoever to grab hold of.

I have a funny feeling that since there is a "break head bolt" on your manifold,( a factory bolt with a specific wasted section so that whether bolt is torqued up to spec, the head breaks off, leaving a somewhat "permanent headless fastener" holding the object in place. It could be fair to say that there is every chance there may well be a restictor in the reed block..... As in Europe all restrictors have to be "perminant" (like welded nuts holding pipes together and so on), I feel pretty confident to say that you are on to something there.

[F5 Dave]

Ahh, cunning. UK MB50s used to have extra fins cast into the barrels to limit the travel of the reeds.

I use a 28mm on a full house 50 after playing around with 24 & 26mm flatslides. Getting the 26 was interesting. It will be waaay too big for a std motor.

Forget the compression gauge, just pull the top off & measure the ring end gap. the guage will only work as a comparison tool once you have the initial numbers & it virtually worthless on a small engine.

People wibbile on about them on ATV forums & I'd never considered using one but I decided to try on my dirtbike 200 (also a GasGas) tried & measured the proper way & then with a com gauge. Raised the com, measured again & then with the comm gauge. oh yes, I see. So then I lowered the com a bit as it was too high & measured with the gauge. No change. yeah ok, stays in the box.

[rabidnz]

dont like the sound of that breakhead bolt, which is exactly what it looks like to me now i know they exist, do you think it would be possible to ezout, or probably a drill job? First ill try cutting a slot into it and hitting it with the impact driver or rattlegun.
Though i have read that the restrictor on the reeds is 12mm, which is the bore of the intake, and that it shouldnt restrict me unless I am trying to make more power than stock.
I repacked the can today and it made a decent difference to the top end, feels like i might be pulling 60ks now, which is probably "mofa spec". If i put a bigger front sprocket i should get around 65 hopefully, and also the gears will be longer as they are all done in about 50 metres at this stage.

Thanks for that tip dave, how do i measure the ring end gap, is that the distance between the two ends of the ring or the ring and the cylinder?

[SS90]

Don't panic about the break head bolt, they come out easier than you think - just use a small cold chisel on the edge, and knock it round a few times until, it unscrews - they (in my experience) never have loctite or anything on them and I have never had a problem.

Bike manufacturers use them for holding on ignition switches mostly.

I can't see you having to use an ezy out personally, vise grips can be a last resort, because as I say, they aren't really that tight.

To measure the ring gap, just remove the rings from the piston and put them one at a time half way down the bore ( with the gap facing the cylinder wall, not a port) and measure the gap between the ring ends with a feeler gauge.

Rule of thumb is 3 thou per inch of bore for an air cooled bike, and a smidge less for a water cooled.

In such a situation an "eye crometer" will give you a ball park figure!

[SS90]

I spoke to o a local mofa dealer, and he was pretty helpful.

Apparently all mfoa are restricted differently, but now most are done via the reed block as you suspect (the break head bolt is the giveaway)

The pipe will be costing a bit of power, but he said that it's not as much as you would expect.

The trick for pimple brigade seems to be to use a 21mm PHPH delorto, but I am guessing that will means you will need to change the inlet manifold (if you have a lathe and access to a welder you could make one in a dew hours I would say), as well as, like you suggested change the gearing.

Every single one I see around these parts has a performance pipe (way too loud, and this town has a bi law restricting motorcycles use to after 6am and until 10pm) and as best I can ascertain, with a pipe, carb and gearing change, over 100 km/h is possible, and I am flawed as to just how fast they get there (lord only knows what they rev to...... It's really high), but I am told as there are so many variances in market models, some may have a CDI that is restricted as well, and if you have still have a problem, let me know the number on the CDI, and apparently the most common ones only require a resistor to over ride rev limits (but others not)

I hope this helps.

[F5 Dave]

yeah as said take the rings off carefully, (evenly) & poke say 10mm down barrel, with a ruler or old piston so they lie flat.

feeler gauge rubbed between until dragging resistance. new should be say 0.3-05mm & after .6, .7 they are replacement time. At least that is from the top of my head for my 50, check a manual for an AM6, should be heaps of torents around.


You can asertain barrel wear to an extent by moving the rings to an area that the rings don't rub by checking the difference, but doesn't check ovality. The very top 2mm of the bore can be misleading to use as gets carbon on it.

As a comparison a std RG50 will indicate 118kph in perfect conditions which is a genuine 105kph

[rabidnz]

i will see if there is a reed restriction today, thanks for the tip ss90, was worried with images of drilling into nice soft ally.
I am gonna give her a couple of early xmas presents , carb and intake for now, cylinder and pipe later, as Id like to be eligible for f5 if i choose to be, so Im guessing ill need to have a factory cylinder on there, what about the pipe?

carbs im tossing up between

replica 19mm for $65
http://newmanz.co.nz/shop/index.php?...roducts_id=116

replica keihen 21mm ? for $140
http://shop.scootling.co.nz/index.ph...&productId=165

real deal dellorto pbhg 19mm $170
http://shop.scootling.co.nz/index.ph...&productId=752

so far the first cheap one is winning , unless im missing something :P

and for the inlet manifold

http://shop.scootling.co.nz/index.ph...&productId=766
not cheap but it allows some rotation for different positions of the carb since space is tight.

or just something plain that fits?


or

[rabidnz]

ps: i sure wish i knew it was now only 10 bucks less that registering my real bike for a year i sure woulda flagged a scooter, assumption surely mothered this fuckup :P

[Spearfish]

ps: i sure wish i knew it was now only 10 bucks less that registering my real bike for a year i sure woulda flagged a scooter, assumption surely mothered this fuckup :P

Yeah other than needing a bike licence there is no financial reason left to own a small engine scoot/bike. Might as well own a bike up to either a licence limit or rego class limit. Bring on the power weight restrictions rather than CC and save us some bucks!.

Sorry, a bit off your topic.

I guess you could give up the road use and fit into track only spec? $400 saved on the rego goes a long way to preparing a dedicated track bike. If your GF takes to riding she will outgrow the 50 quickly so at least she has this rego to find out.

[rabidnz]

turns out the nzta site is a bit gammy, it says it is 394.38 for petrol bike 0-60cc and and 405.63 for 61-600cc, which is what sent me into a tizz, as it mentions nothing about "mopeds" so I assumed they got rid of that classification.
Just got off the phone with nzta and it will be $166 per year. So big smiles and sigh of relief. So there is still a logical reason to have a scooter, apart from low purchase pprice brand new and low fuel consumption/maintenance or just being too scared of a real bike :P
Otherwise i woulda track biked it, but i coulda got an fxr on the track for the same price, and have parts support and a good knowledge base.

Glad thats sorted, now i can get my wallet back out

[Spearfish]

turns out the nzta site is a bit gammy, it says it is 394.38 for petrol bike 0-60cc and and 405.63 for 61-600cc, which is what sent me into a tizz, as it mentions nothing about "mopeds" so I assumed they got rid of that classification.
Just got off the phone with nzta and it will be $166 per year. So big smiles and sigh of relief. So there is still a logical reason to have a scooter, apart from low purchase pprice brand new and low fuel consumption/maintenance or just being too scared of a real bike :P
Otherwise i woulda track biked it, but i coulda got an fxr on the track for the same price, and have parts support and a good knowledge base.

Glad thats sorted, now i can get my wallet back out

Thanks for clearing that up I looked at the site myself, Its confusing because I just paid 188 for a years rego on a fifty.

Your project is going to be an interesting one however it turns out.