Vento Arrow Big bore " 105cc (52mm) " Build "

[ermaganish1995]

Hello, I'm rather new to this forum and would like some help with my scoot, Which is currently stock mostly.

Current " setup " is following;
139QMB (12" model) (actual motor code says QMB, not QMA)
Stock 50cc
Stock 19mm carby
4Gram sliders
Yellow clutch springs (1500RPM)
Blue (1000RPM) contra spring
" Sport Exhaust " (Freeflowing exhaust)
Stock gearing



What plans I had for the bike was to upgrade it with a bigger bore cylinder, better cylinder head (maybe), Better cam (Maybe), Bigger carby (20mm)


The bigbore kit i had in mind is this one; www.ebay.com/itm/281781308521?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT 

What I mainly had in mind was mostly sheer acceleration, Tho I dont want alot of top speed, Cause I'd like to be able to do wheelies more easily and such, Pretty much make it as a sleeper, Tho is there some parts you guys and gals can recomend? As for contra spring, Weights, Clutch springs etc.. I am not the biggest bugdet so I'd like to get the items as cheaply as possible.

A Good question would be would the stock crank hold for the 52mm kit? Currently my bike has  7360 km or roughly 4600miles on it

A Friend of mine told me that a 47mm kit would be well enough for power and safe gains without destoying the crank and such, Would it be a better approach , 47mm kit instead of 52mm?



Here's some pictures of my bike.

[90GTVert]

The stock crank may not last long with a 52mm kit. 47mm is the popular big bore choice when engine life is a concern. More info on that topic here :
www.49ccscoot.com/faq/whichkit.html

You may be able to save some money on tuning the CVT if you modify your rollers. Another popular option is a tuning kit. That's a bunch of rollers in different weights that are pretty cheap. They will not last long before flat spotting, but you can get in tune and then order a good set of weights. Lots of info on CVT tuning here with links to info about modding weights :
www.49ccscoot.com/faq/faq.html

[ermaganish1995]

Alright, Got ya, I think i'll stick with the 47mm bigbore kit to be on the safer side; Tho one thing I am woundering would be; should i change my timing chain soon concidering the milage? And can that be done without splitting the cases and such??

[90GTVert]

It should be alright. If you do decide to change the chain you can't do it without splitting the cases because the chain is around the crank.

[ermaganish1995]

I suppose I'll change the chain if i ever change the crank or something.

By the way, the inner part of my variator have slipped out when i opened the variator, can this be a reason my engine was revving about 9500-10 000 rpm at start? (really brief free-revs before it goes down to about 7-8000)

Also I didn't notice any top speed difference with 4 and 5 gram weighs, the difference is probably better engine life along with better fuel economy cause cruising at 40km/h in the city the engine revs about 6000-7000rpm, instead of 7-8000rpm

I do have a blue 1000RPM contra spring with the 4/5Gram weights, tho i have a yellow one, should i try that with 5Grams? I don't have too much understanding when it comes to contra springs, Any good tip on that part?
One thing is for sure, when my friend had stock contra spring with 72cc, i could hear the belt slip very badly and with 2000RPM contra spring and alot heavier weights (9gram) the belt stopped slipping and the bike was really good compared from before ( it was alot slower then mine even tho its technically the same engine)

I would guess 8-9 Gram weights with 2000RPM contra spring would be a good base with 72cc? or do you have to use such a stiff spring?


Picture of the variator part that was loose:

[90GTVert]

The first thing I would do is replace the variator. Always have your CVT in good working order before trying to tune it.

I usually stick with a 1000RPM contra spring and adjust roller or slider weight as needed.

[ermaganish1995]

Yeah, have a few spare variators that are in good condition so i changed.

As for 1000RPM spring, Does that still apply to 72cc, or is this only applying to stock 49cc?


Edit; By the way, I figured when it comes to the time where I change my bearings in my gearbox, I have to buy a blindhole puller, Tho the problem is, the bigger kits are more expensive and such, there are smaller kits, where like the smallest puller is 12mm - 16(ish)mm will that size work for the bearings or do i need a smaller puller?

[derbiman]

I had a Malossi Multivar do the same thing. The bushing would move inward about 3mms. The scooter acted like it was taking off in high gear. It took me a while to figure it out. I staked it back into place and ran a bead of superglue around the edge of the bushing. No problems with it since. ( knock on wood) lol

[90GTVert]

As long as the belt doesn't have a bunch of slack in it from a weak spring and I'm not seeing black marks on the drive faces from belt slip, I start with a fairly soft spring on about any engine.

[ermaganish1995]

So here's 3 variators, The left one is the original one that came with the scoot, still usable i'd say,
The middle one is a variator i bought off ebay, Tho it got destoryed cause i think there came in water with grit in it that ruined the variator.
The one to the right is a " koso high speed cam "variator , Not too sure about it and all, tho its brand new and all. So i might use that when i get my BBK cause it seems rather beefy, or atleast beefier then original variator 
with the original variator, i used 1500rpm contra spring, 4Gram sliders, with the second one i used the same, Tho I did not see any black marks on the drive face (the one that doesnt move)


Also does any one know how to take apart the rear variator? the rear variator clutch assembly on mine takes appart quickly, Tho unfortunently one i bought off an aliexpress seller was leaking with more like oil then grease, So i wanted to take it apart to change the grease etc, tho i cannot take off the "collar " that holds in the grease and pins, any tips?
Thanks

[90GTVert]

I'd try the Koso.

Here's help with the rear pulley :
youtu.be/2EjW-iSP-Q8?t=12m2s

If it's real tough, I tap the screwdriver under there (using a thin flathead). Try to keep at the smallest angle you can so you aren't going to damage the surfaces.

[ermaganish1995]

Thanks man, I'll try for that when and if I get the chance to do it soon.

Abit of an Emergency note; I upgraded to 72cc today, Everything seemed to be fine and all that, but whe it came to install the new valve head it did not work, i could not tighten the fasteners etc, what I suspect is I had 64mm valved head before and 69mm valved head now, when i checked them side by side, the new one seemed slightly bigger with the valves, even tho they seemed like 64mm valved heads, So the problem is i cant tighten the camshaft holder, and neither adjust the valves cause they are like pressed against he valves so you cant even adjust them, So this seems like I need to get rocker arms for 69mm?

Edit; When looking at your video 90Gtvert, about the valve difference,  I do not see that " raised part " on neither on the heads which confuse the heck out of me.. I also tried with a ruler.. by the video, both are 64mm heads.. tho it doesnt work.. what the heck..

[iwiketuddlz]

You sir need different rockers!!!! Not sure which ones though .... They usually come with the kit!!!

[ermaganish1995]

Nov 2, 2015 20:33:30 GMT -5 iwiketuddlz said:

You sir need different rockers!!!! Not sure which ones though .... They usually come with the kit!!!

Obivously i need different rockers.. tho the vavles seems to be similar length and the valves dont snatch on a ruler or nothing as a normal 69mm valve head does.. I really wanna do the BBK with the BBK-compatible head, tho if im gonna have so many problems cause of it, i wounder if it would be best to just use the original head, even tho its alot smaller with inlet and exhaust ports..
I cannot either take the valves apart to check, dont have the tools so r.i.p me

[90GTVert]

Method # 3 here requires hardly any tools to remove valves :
49ccscoot.proboards.com/thread/11800/remove-install-valves-different-ways

AFAIK there are only 2 kinds of rockers so if you have one kind, the other kind should be what you need. You could miss out on a little power with the standard head. It depends. Sometimes the aftermarket combustion chambers are so large that compression drops enough to negate any gains from flow.