Direct bike DB50QT-15B 2015 (50cc) 72cc big bore kit?

Hi All

First post, my daughter has just bought a 2015 50cc Direct bike DB50QT-15B. It runs 28mph on the flat/downhill, if I unplug the little wire it will do 37+mph…. But not uphill! Uphill it struggles to do 20mph! I've replaced the Variator and had a fruitless play around with roller weights!
(I've many years on motorbikes with what I now appreciate as "lovely gearboxes", variators are a dark art I've no desire to master!)

I've changed the airfilter, put a new plug in, (edit: fitted the "performance" coil pack), cleaned the carb and still it couldn't pull the skin off a rice pudding!

I'm starting to think it’s a 3yr old piece of Chinese junk and it's never going to do 28mph on an uphill slope!
Does anyone have any experience with a 50cc Direct Bike? Are they just junk at 3yrs and I'm wasting my time?

It's got to the stage where I'm eying up a 72cc top end!
https://www.ebay.co.uk/itm/Big-Bore...375645?hash=item2cce94225d:g:OdYAAOSwmRFacz-A

I know you can also get 80 and 90 cc ones but I just want to give the bike the torque I feel it probably had when new. So that going up hills doesn’t put her life at risk from holding all the impatient car drivers up.

Has anyone fitted one? Do you know what other work will be needed? Will the old head fit? Will it need rejetting? Is the original carb ok? Does the same pipe fit!

Any help would be greatly appreciated.

Cheers
Dad!
MT09

 

Same pipe will fit a 70cc Head
Carb will need a rejetting

You could get a complete performance varaitor kit that would save you the head ache of trying hundreds of rollers as they come set up out the box and have a dramatic effect on the way what little power is delivered....

 

Thanks for the reply. I've had a google for "performance varaitor kit" and it just shows me variator kits with the word performance in there somewhere! Usually with the "performance" (orange) coil pack (which I've got already) + a belt & clutch(?).

I'm assuming a performance variator kit is the multipacks of weights, so you can try different combinations. Or is there more to it than that?
Trouble is I've no idea if the thing has a sweat spot to tune the power output to! lol Or what rev range that would be if it had one.
I've bought 4 sets of weights and swapped out/mixed and matched sets of 3 etc.... and it revs more... or revs less! lol

 

If it's dropping down to that speed up hills, then that would indicate that either the variator or clutch isn't allowing it to drop into a lower "gear" so to speak.
What weight rollers have you tried so far?
You could also look at putting a stronger torsion spring (the big bugger) on the clutch or change the smaller clutch springs for stronger ones.

 

I just had a thought about your first post.....................
When you got it to do 37mph by unplugging the wire, did you up-jet the carb to suit?
By un-plugging it you are effectively de-restricting the bike, which means it creates more power, which in turn means it needs more fuel to maintain that power.
Have you also checked the exhaust for any restrictor cone in the mouth? Head end. That needs to be removed as well if it has one.

 

I've no scales which weigh such small amounts! It's a fair few years since I've needed to worry how many grams anything is! lol
The replacement Variator says the weights are "between" 5g and 6g! The weights the bike came with are lighter than this, but not as light as the ones I've bought. Which were 3.75g and 4g packs. I've mixed and matched in distributed sets of 3. But the ones it came with are probably the best. (They are worn, but I can't weigh them to know what to replace them with! I've been looking for my local dealer to see if I can borrow his scales! No joy yet. )
The newer 5g/6g ones, the engine probably doesn't rev enough.
The 3.75g definitely revs too much!

My assumption of the wire is it's a rev limiter, it goes to a pick-up which once a certain rpm is reached, stops the bike going any faster, maybe retards the ignition? So you're not adding any more power or needing a mixture change, just removing the rev limiter. Which potentially means you're reving into the red and the motor will go pop much faster!

If there is any difference in acceleration rate with the cable connected and without, it's imperceivable.

Does the clutch have any influence on your gear ratio? My assumption was that once you've pulled away it's work is done and the variator regulates the gear ratio? or am I way off?

 

How the clutch and Vario work together......now there's a can of worms. There is a thread on here somewhere that explains it all. Basically it's an auto box without gears.
Heavier rollers are easier to throw out so require less engine power, vice versa for lighter ones. They control how the clutch pulley opens and closes. But here's the rub. Heavy rollers stay at the top of the ramps longer, keeping the belt low down in the clutch pulley which effectively keeps it in a higher gear. The engine has to dramatically . reduce revs in order to "shift down" so to speak. Changing the big torsion spring for a stronger one let's it push the clutch pulley halves together sooner.
It's a game of balance between the variator and clutch.

 

See if you can get the mollosi mutivar google it and have a read they come with the perfect rollers for the bike plus correct contra spring ..it’s sole purpose is to keep maxpower and any rev/speed there worth there wait in gold in my opinion

Solved all my sketchy running issues

 

FFS, he's here again with the malossi multivar. You love that thing so much, you should marry one.

 

Ffs that’s becouse 9 times out of 10 every scooter based problem on here is roller/varaitor problems and by getting that “Thing” you say I love so much saves so much time

I’m trying to help so stop hating and trying to make me look like a mug it’s uncalled for and I don’t appreciate it tbh

 

No offense meant Sam, didn't mean to rub you up the wrong way in any sense, but you do mention it a lot.

 

I’ve mentioned it a lot lately as it warrants being mentioned

Instead of just undermining me maybe you could show me the same respect and courtesy I have shown you

 

I feel something special going on here guys!