Hyosung SF 50 Rally - wont do more than 60km/h

[digitalinsite]

Hi,

I bought a Hyosung SF50 Rally a few months ago bog stock.





Since then I've done the usual mods to try to make it run a bit faster...

*Rev limit CDI wire cut behind headlight
*Exhaust taken off and flange removed
*Rollers reduced to 42grams total - was total 80grams when I got it
*removed a stack of stuff like the center stand to reduce weight
*installed 72cc BBK from Scrappydog
*installed 85 main jet and set needle clip to one up from richest setting
*installed pod filter on carb (also tried with standard airbox and seems the same)
*Intake restrictor plate removed
*Bit of paint here and there to make it look a bit better

The scoot goes real well and torque and acceleration is great but I just cant seem to get it to go any more than about 60 km/h on the flat. Downhill I can get it to about 67km/h but not sure why I wont do more. It does burnouts on the dirt no worries but top speed seems to evade me. It's like it hits a wall at about 60km and wont go much more than that - feels like it should be going faster I reckon.

I expected the BBK would give it a bit more go but seems about the same top speed as when it was a stock 50cc???

I'm running the stock exhaust - is that my problem for not getting better top speed? I've heard that the intake is very small on these too.

Or is it something else like belt slippage or needing to put a stiffer torque spring in or something? Do I need a different variator on the SF50 Rally to get to to rev out and get the belt to climb more? Do I need a different CDI?

I've has a PGO Gypsy scoot before with a 70 kit/variator/pod/gianelli exhaust that did 85km/h easy. Keen to get this one somewhere close.

Any ideas appreciated - thanks

[buiditright]

Digit,
I can tell you first hand you will not do much better untill you get rid of that stock exhaust. I have a technigas II on my UM XSpeed 50R which is the same as your prima. Also I got rid of the rollers and run 3-6gr and 3-4.5gr Dr Pulley sliders and I run a constant 48MPH up hill flat it does not matter it runs like hell. I did get rid of the stock air box and run a K&N type free flow air filter. I also run an 80 main jet. You did take out the little washer between the front and back varator plates didn't you?? That seems to be the only restriction you did not mention.

Bill

[digitalinsite]

cool stuff - yeah, i thought the exhaust might have been what is holding me back the most. so about 60 to 65km/h sounds about right for the stock exhaust?

I've swapped the rollers a few times now and didnt see any washers etc inside the variator or on the boss tube. I assume the previous owner had these removed.

time to start saving for an exhaust...

thanks for the tips

[thiess87]

hell yea that is what im talking about!!!!! very nice. love the tint on the rear tail light let me c what u got here

[thiess87]

i was running my stock exhaust on my 72cc for bout 1000km n did a good 83km all day long. urs doesnt seem to add up

[thiess87]

ive been searching everywhere for that handle bar set up i love it

[thiess87]

r u sure u did the right wire on the cdi?

[buiditright]

NOw Sean don't be telling this gentlemen a bunch of stuff. He has it running good he just needs an exhaust and some good Dr. Pulley sliders and get rid of those rollers.,

[thiess87]

i understand that bill but u pretty much have the same thing he has on urs done but ive read threads that people cut the wrong wire? jus a thought

[buiditright]

Just kidding with you Sean and it is a good idea. But if he cut the wrong wire he would of had other trouble and it would of not ran. nut that is a good point.I had mine out yesterday and man it runs sweat and it felt so good to put her in the wind.... LOL

Bill

[thiess87]

yea i accedently did it with mine when i got that cdi that is apprently for a jog in one of the updates i ordered it took mine off n got to it it doesnt even have the same connectors, so when i put my cdi back to gether i didnt mark any of the cords so i was guessing which hole to do with which one it took bout a hour i got it running. usually when i get home i use the engine killswitch it didnt work took the front piece off the one plug that popped out or i didnt put in as soon as i did it worked so idk with this rally scooter tho if he cut one on the 4 prong side we kno its wrong on the 2 prong side he had to do the right one

[thiess87]

i mean a torque spring says it in its name it gives u more torque its not called a hell of a power spring lol or somin its not clutch springs. he has a 72cc big bore kit from scrappy now those r the 2 that broke on me with the c clip cuz they r made very badly maybe the rally has a restrictor in the exhaust idk?

[Panaramaguy]

The stock exhaust will peak out the engine at about 7800 rom. Going to say a Technigas RSII will......or maybe Next will let it climb to 9500 rom. This should get you to about 42 mph. Typically the RS is for 70cc and the Next is for 50cc. There are many other expansion pipes out there too. Do your home work as you don't want to buy a pipe twice.

Putting on oversized tires will let you go 10% faster and correct the optimistic spedometer so that what is says is the acutal speed you are going.

Then there are variator mods........to get the belt to rise higher. And you would likely want a new carb/modified intake to match the exhaust pipe.......gotta have a matched system to get the most out of what you got.

No final gears are available for this scoot.

Do everything you can and it could go 52mph.

[thiess87]

couldnt have said it any better myself but guy what do u think is holding him back with this power? i mean i had pretty much the same n i was goin way faster??? any thoughts?

[buiditright]

Now this person (Guy) knows how to tune a morini motor. His scoot is done the correct way and the only person who has ever been able to really tell me how to do things with the proper parts to do it with.

Guy thanks I still am hoping to find the money to finish my scoot. As for now I have to how it at 48 MPH and that is a strong 48 up hills on the flats just solid..

Bill

[thiess87]

yea ive known guy for a while jus got out of the hospital heys on the korider hyosung website

[digitalinsite]

thanks for the replies guys

yeah, i didnt think it added up right either. To be honest with the 72bbk it actually struggles to get to the same top speed as when it was a stock 50cc. Very strange. I'm sure it's got more power than the 50 tho. I'd say it gets about 62km/h on the flat and sorta hovers there like its being held back. It doesnt really 'ring out' like the two stroke scooters i've had in the past.

I havent done a compression test yet but I'm pretty sure it's ok. It starts first or second kick every time and doesnt feel like the motors struggling at all. I figure if it was bad compression it wouldnt start and would run rough etc.

I think my jetting might be a little off tho. I'm running a 85 main jet with the needle set one off the richest setting. Tried a 90 main and it was much worse. 77 main jet was maybe better power wise but the engine was getting quite hot and would bog down after 10 mins of hard full throttle riding and then shut off. I figured it was overheating and this went away with a bigger jet.

What are you guys running for main jet? Im using the stock carb, intake plate gone, stock intake, stock exhaust and 72cc BBK.

Maybe my 72BBK isnt quite right. I installed it all by the book. Made sure the rings all lined up, gaskets all good. Even used liquid gasket as well to make sure it sealed. Probably only 5km riding on the BBK so far tho.

I didnt cut the CDI wire (previous owner must have) but I had a look yesterday and it was a black wire thats been cut and taped off. Like you said, if it was the wrong one I'd expect other issues.

[digitalinsite]

i'll upload some new pics soon - done a bit more painting and decals.

[digitalinsite]

also, anyone tried cutting open the stock exhaust to allow more flow? Reckon it's a worth a try or is it just too crap to start with? I doesnt look like it has much of an expansion chamber

[digitalinsite]

oh yeh, i thought it might be the rings so I pulled the block off and all looks good in there. Piston looked quite good - no big scrapes and rings all intact.

I ditched the crappy C clips for the wrist pin and bought $5 malossi ones. Spent 3 days trying to get the damn cheapo ones in - took 10 seconds with the malossi ones and needle nose pliers.

[buiditright]

Digit,
I have the UM XSpeed 50R and I cut the Brown and White I think Or the Brown. But I am pretty sure it was the B/W. I checked out the conversion and did not realize that you were only running 37mph. Before I cut my wire it would only do about 33 or 34 and that was it. It would not go any faster even down hill. You MAY NOT have the correct wire. But I still do not think it would not run if it was not the right wire... I know that my scoot 50CC with the stock exhaust would only do about 38mph..

But now I have the Technigas exhaust and I love it. I run an 80 main jet with the needle 2up from center. I run a K&N clone free flow air breather... As I said in my other post I run 48mph strong up hill on the flats in the wind.. Down hill it is another story it flies down hill..

My pipe gives me what I want and for A 50CC it runs pretty good. I am happy with it. I also run 3-6gr and 3-4.5gr. I run a stock varator cause I am not sure where or what kind to run performance wise.

If you know where to get one Guy please send me a PM and let me know. I am not sure if I already asked you that..

Bill

[fast150]

Im not knowledgable enough with scooters to say what may be wrong.. I just want to say that scooter looks freaking mint. Does that small windshield actually help with the wind?? I wonder if I could find one for my 150 Z-Bike...

[thiess87]

im telling u bill its got to b his cdi

[digitalinsite]

yeah, i think maybe CDI and exhaust. I'll take the front off and check the wire and let you guys know...

[thiess87]

yea cuz mine when i first got it stock was doin 42mph with all restrictors off so urs doesnt add up besides ur cdi cuz i had my 72cc with stock pipe doin 55mph plus

[jimh]

Yeah, it's the brown/white wire...stock exhaust is holding you back. If you get a technigas pipe make sure it's made for your 72cc. I, like Bill, have kept mine a 50cc and run the technigas next r which is specific for 50cc. I also run an 85 main jet.

[thiess87]

can u tell me the price of which kit u bout from scrappy dog? or which one??

[digitalinsite]

yep - i got the suzuki AD50 kit from scrappy dog. we basically worked out the hyosung motor is the same as the 1990's Suzuki AD50 design.

www.scrappydogscooters.com/TGB_Sachs_scooter_parts.html

Full 72cc 47mm Big bore kit - its the 47mm one $175 USD + shipping

fitted it myself last week in the garage at home. it wont fit the crankcase properly at first - fins wont slide in so you need to grind out the side walls of the crank case a little bit with a drill and some $5 grinding bits from the hardware store - make sure you rag up the crankcase and stuff. dont want metal filings in there. I vacuumed and oil cleaned mine after i did it and all good.

stacks more torque and power than the 50cc - piston and bore is HEAPS bigger

thinking mine just needs to be run in. i'd say i havent even got 5km on it total after doing the BBK. see how it runs with fresh good oil, new trans oil and maybe 100kms on it or so...

[digitalinsite]

just took it for a good 1/2 hr trash. Pretty much full throttle the whole time. Tuning seems good - i reckon the stock pipe and the 7 grams rollers are the main thing holding it back now

Got it to just touch almost 70km/h downhill and getting a little faster on the flats now. Probably about 60 to 63km/h

maybe the BBK needed to be run in. My father in law who's a guru with engines said the rings will bed in the more you ride it. seems to be the case for me I hope.

scrappy dog has an exhaust for $150 that looks like a technigas copy - seeing how much shipping is

[thiess87]

Ok now I'm pretty smart on these scooters but does ur cylinder head match the one in the picture on the site the one with the spark plug outlet on a angle???