70cc upgrade - jetting issue ?
 

I upgraded my scooter to 69cm^3 last night. I had to milled down the crank a bit to fit it: got an eton beamer and i bought a typical JOG cylinder upgrade.
But anywho, I kept everything else stock and this morning I cranked it up rode it around to break it in.

Power and throttle improved but only does 30mph. Is it just the breaking in process thats limiting the speed ? or do I need jetting (increase fuel ?)

My old 49cc cylinder can do 35mph.

What do you guys think ?
:thanks:

Nevermind guys,
I put a 3/64 drill bit through the main jet and now its reaching 40mph.

Weird though, I was driving and all of a sudden it shut off. Scared me for a second, thought I blew a cylinder/piston. But I gave it a kick and it started right up again.

Another Nevermind guys,
I searched around and found that I was running hot. The fan shroud had these seals tubings that went missing so air leaked around it. Beside that I was running a Champion plug which wasn't rated for the upgraded cylinder. I went and got the NGK BR9HS which runs cooler - or can take alot higher temp.

That is called soft seize but not only the shrouds but being lean not enough fuel will cause your motor to run hot.I about sure that running lean is the issue more then the shrouds

The hotter or colder plugs dont effect the temperature of your motor, you need to up jet or drill it out bigger

Surprised it runs with a 3/64 drilled jet.. that equals 1.190 mm or a #120 jet!! Should be slobbering rich with that large a Jet...most 70 BBK's like a #85-#95 jet.:hmm:

lol, idk, i think its the exhaust thats restricting and holding back the hot gas. Im thinking of getting a Leo Vince pipe. The jet runs great, plenty of gas...too plenty, the exhaust can't handle it.
Also, im getting a new fan to get more air to the head.

Ordered some chinese made pipe...looks like it will increase power too from its design. Like that of a ram jet.
Got some cheap suspension for the rear as well.
Shiet, yall im spending too much on this little scooter...lol

Ported the hell outta the cylinder and piston! Can't wait to put it back in.

nice :scoot: picture always make a thread better if you can post some. keep us posted on results

A "restricted" exhaust will not cause a lean condition. You really need to get your fuel mixture richer. "Soft seize" is overheating which these engines really hate. Even a slight overheat can nuke the lower end (bearings). If this bike has overheated to the point of stalling, you should IMMEDIATELY change the oil!

I highly doubt your jet is equivalent to a 1.190mm (#120) jet, as it would be super rich, and it would bog terribly and reek of gas.

spend the $3 on a #75 to #85 jet and get your shroud right, cooling is super-crucial to the JOG

Most stock pipes only work to 8,500 RPMs where performance around 10,500 and racing 14,000 . Here is a great article on 2T exhausts http://49ccscoot.proboards.com/thread/1391 Leo Vince is a great brand and worth the extra money . My scooter dealer has a Yamaha with a 70cc and LV HM70 pipe and its a wheelie machine and not too loud . I have a PM Racing pipe and its louder than a Yamaha YZ 80 as at top speed it makes my ears ring and echoes off large trucks and buildings . Takeoff was less since its not restricted and does not build up backpressure but midrange and top end it zooms .

What mm is yourcarb ? Most have a 17.5mm but mine has a 19mm TK and works great for the BBK and when it was a 50 . Do you have the airbox and stock pipe ? I have a Uni airfilter and use a 120 MJ since I live just below The Blue Ridge Mountains and its so darn humid at times . I like to run just a hair rich to be safe rather than dead on it . Stock it had a 68MJ and I put in a 75 . I installed a small Uni vent cover around half the size of the big red Uni and it ran like a boss with a 90 MJ . I bought the proper Uni and my dealer and all the other scooter and motorcycle shops in town ( over a dozen ) none had Mikuni VM11/22 MJs . Well being impatient I put it on anyways . It had just a slight bog but not like anywhere close to stalling and dang it the engine seized in less than a 1/4 of a mile going around the block . I would get a jet kit like this http://www.partsforscooters.com/114-...ategory=133078

I use NGKBRP8HIX the iridium .

Do you use the oil injector or premix ?

Update:

I have an Eton Beamer (2002) first version. It actually comes with 85mm jet, but even that didnt give it enough fuel on the 70cc cylinder. What I drilled was actually the main jet (one that the long needle goes in for idling/throttle) Went and bought a 90mm jet and it was bogging with too much fuel. So I swapped the old one back in.

Tried to get a pic. of the ported cylinder but I guess i didnt save the pics, but did get the piston pics:
Superman logo on cylinder head lol
http://imageshack.us/a/img11/9913/zjfu.jpg

Intake ram (45*)
http://imageshack.us/a/img51/9341/x60o.jpg

Soft seize:
http://imageshack.us/a/img543/4056/u8cq.jpg

This scooter comes with an oil injected and oil/pump throttle on the engine case, so i've been running it as is. But it seemed like it does get alot of fuel since the carbon built up in just under 20miles.

I went and got this big fan:

http://i.ebayimg.com/t/Yamaha-Aerox-...lSQ~~60_58.JPG

and this little scoop:

http://i.ebayimg.com/t/FAN-COVER-SCO...(m!~~60_57.JPG

Then sealed the plastic cover with high temp silicon so that the air wont leak around but go straight onto the cylinder/head.
So far, i've been running it just under 40mph and no soft seize but it does put out alot of smokes from the pipe- OEM pipe so alot of restricting. Full throttle is at around 50mph but I get too nervous going at that speed with this scoot...afraid of a solid seize and off I go flying... lol

New pipe coming in Monday. Got this one here:

http://i.ebayimg.com/t/50cc-PERFORMA...2Pw~~60_57.JPG

Chinese copy for $99. Was going to get a LV but the seller was being an ass, didnt take my offer and then after I bought that one, he listed it for alot less than what i offered... so F- him, ill just stick with the chinese pipe since the bike is chinese made..lol

Also got this chinese suspension: works great so far too

http://i.ebayimg.com/t/11-Air-Shock-...3uQ~~60_58.JPG

An aftermarket pipe as well as a Uni or K&N style airfilter it will be lean you so will need a larger jet again . My scooter dealer told me about a 2T that ran hot and would soft seize . It could idle for every but would seize under 1,000 feet . Now it did have the 7 plug and was lean . Replaced the plug with the 8 version and larger main jet and it was good .

Are you going to reuse the cilynder ? If so use a honer wet with oil to smooth it out . I had a wristpin come out and it ate up the piston , head and cilinder . I first tried just replacing the piston with a new one but the head was ate up . I did smooth it so it would seat but no start . Put on a new head and cylinder it fired up the first time . If the oil pump pumps too much oil it can also be lean since not enough fuel . I learned this since I put in a sip of oil in the gas tank thinking it would be a fail safe option in case the pump did not deliver enough oil but plug chops told me it got lean with the extra oil . Make sure you wet the piston real good with 2T oil or even better engine assembly grease to prevent a dry start . Be carfull about switching out the fan even though it may be lighter so less drag it may not cool as good according to what I read from those who did that mod .

I tried a hot plug on my CR 125 it never seized since I ran jets so large it was set up for WTFO or racing not trail riding but I could feel the heat diff and it did not run as good . I tried this in the summer . Put the old plug back in and ran like a champ

You can adjust the cable to the oil pump to allow less or more oil in to your mix but a true jet size is important imo, are you using the stock air box with snorkel or something else you should be able to get more then 40 mph just need to do a little more tuning fuel wise hows the is the cvt stuff looking and the pistion you might have weakened it with the engraving like that i brunt wholes in two different ones with out them be weakened
http://i1111.photobucket.com/albums/...924_184543.jpg
http://i1111.photobucket.com/albums/...817_113717.jpg