I know its asked a lot but its jetting problems

Okay so a few months ago I fitted a Leo Vince zxr to my Yamaha jog r and I upjetted from a 70 to a 74 and it worked fine. Now I have a fitted a 70cc kit and its seems worse when I upjetted again I tried from 86 downwards and the best jet seems to be the 74 that was working with the standard cylinder and exhaust so should I go lower in jet size because 74 is the smallest I got at the moment

 

I got the standard carb its a gurtner py12 and standard main jet is 62

 

Be better off changing the carb.need a 17.5 starters to get that setup singing,depending on the 70 kit...21. Maybe.should get it to work on the 12 but it ain't gonna thrill.

 

How much are the bigger carbs usually? Thanks

 

Well.you can get a cheap chinky one for about £35 or go to a nice dellorto quality one for about £60 ish.some have different cables so need some modding.i think merlin or stevep have had some experience of swapping these about.

 

I'll have a look around, I still don't understand why my scooter seemed to get better as I went down in jet size though

 

Scooter Works in stourbridge do a range of Naraku carbs now. 17.5, 19 & 21mm
I've had a couple of 21mm off them and they work well.
They come with a 70 main jet fitted.
They have manual cable type chokes fitted, but can easily be changed to the manual pull up type choke fitting. It all depends on how easy it is to access the choke position of the carb from outside the bike when it's installed. In other words, is it easy to get to first thing in the morning when you don't want to mess about.
Jetting is easy, they take the Dellorto type jets, 5mm, not 6mm threads, and there is a big bolt head on the bottom of the float bowl that you take out and have direct access to the main jet without taking the bowl off all the time, thereby saving the bowl gasket.
I've got a 21mm fitted to the zip. That also has the PM Tuning 70cc ali kit, malossi variator, and other stuff on it.
Goes well with it.
The other one is fitted to the Katana, but i still have to play with that.
Cost is just under £49 +postage.

 

I have noticed that increacing or decreacing engine capacity does not require re-jetting the way changing exhaust or ignition does.
I swapped out a top perf 50 for a stage 6 70 cc sport pro on my Gal's scoot. No change in jets. I put a Doppler (MVT) ignition on there. Plus ten points for the jet.
I also removed a Stage6 sport pro from my scoot and put on a stock cylinder. Worked great without changing anything.

It's exhausts and ignitions and changes of airbox which require radical rejetting. Not Cylinders (all else being equal).

 

I'm thinking I need a 70/72 size jet but Im not sure why I'd be going down in size because 74 worked good with the standard cylinder... Well it did struggle going up hill but still worked fine on flat. Can someone explain the "go up by 10 points" does this mean go from like 70 to 80 or from 70 to 10 jet sizes bigger? I'm confused

 

Your first guess was the best. If you're at 70 and someone says 'go up 10' then that means an 80 Jet.
I would also go with your intuition. Stay with your 74 jet if you don't change anything on the intake side. But be prepared to lighten the rollers a smidjun.
Good luck !

 

Fair enough I was thinking about lightening the rollers after I fitted the exhaust but I never bothered its got 5g in at the moment so should I drop about a gram or buy 3g and mix them? Thanks for the help

 

Errm - Yes and Yes !
There is no way of getting the rollers right that I know of that does not involve using three of one weight and three of another.
And yes, I would suggest trying lighter rollers ! 6x5 is 30g total. I don't know many variators/kits/exhausts that work with that kind of weight. Not good ones anyway.....

Lighten those rollers but keep an eye on the colour of the plug.

 

Right just gotta wait till I get paid now, thanks for all the advice

 

No sweat bro - it's easy when you've got the same scooter and you've tried it all before ! At least - the same engine....

 

What scoot have you got?

 

Water cooled Ovetto 50 (or Neos). Same engine as the Jog R (or Mach G if it's an MBK). Same engine as the Nitro (or Aerox). Mine's just a little bit different, that's all.

 

Little bit different?????
Seriously??

 

Oh right, the 50 cylinder is back on now, with the 74 jet I'll buy a pack of jets and some rollers when I get payed and try and figure it all out with the 70 kit

 

Yeah. It's just a tiny bit quicker.

 

Right so I tried the 70 jet and it was better but it still wouldn't pull much so I went down a few more and it seemed best at 68 but the plug seemed to look like I was running lean, is the reason its not pulling because of the 5g rollers