Peugeot xr6 50cc (70cc bore kit) what size jets ??

[cameron1590]

hi all,

well a few weeks ago I put a 70cc kit on my bike, it went to the garage to have the chain and sprockets changed and I asked them to up the jetting but think they forgot to do it as it still seems to want to give more but cant ? I was just wondering what size jets I should want to be sticking in the carb ? im running standard air filter ect just the 70 kit on the bike.

thanks

cameron

[st3v3]

Did you ask, and pay for a jet change while it was in there?
____________________
Roger wrote: Women don't get damp for clingy puppies. Get some better happy pills, hit the gym & buy a medallion the size of a dinner plate. Job done

[cameron1590]

[cameron1590]

*bump*

[at106]

Check the spark plug colour it should be brown ish. If it's grey/white its running too lean, if it's black it's running too rich.

If the plug indicated that a rejet was needed i would upjet by 3 or 4 sizes and then recheck the plug colour. You may be better off buying a jet kit which has a range of sizes for about £10.

[kingsmith]

MODIFICATIONS

Different modifcations need different upjets, so here is a general rule.

Note - where applicable i have stated a 50cc and a 125cc option, bore kit and carb for example.

70cc/172cc Kit - 8-12% upjet (depending on kit, some need over 12%)
Exhaust - 5-8% upjet (depends on exhaust, some have been known to need 15%!)
Open Filter - 5-10% upjet (depends on setup)
21mm/25mm carb -4-6% upjet (depends on setup)

HOW TO

How to upjet is a commonly asked question, not just how to physically change the jet, but how to go about making sure the jetting is correct.

To change the jet you need to drain the float bowl of the carb, undo the float bowl and simply swap the jet for a larger one, then refit, suck the vaccuum pipe to refil the float bowl, and kick till it starts.

To make sure the jetting is correct you need to listen to the bike (this takes some practice), if it is running lean it will make a flatter noise (barrel noise, not exhaust) if it is running rich it will make a duller noise.

Another way to check is the do a plug check or plug chop, which is where you run the bike at full throttle and quickly shut the bike off and check the colour of the spark plug, white is lean, black is rich, and brown is goooood.
note - some bikes have automatic chokes, which will need to have opened before a plug chop can be done.

WHERE TO START

A general rule of where to start on jetting is to overjet, so to make the bike run rich, and work down until its just right, running rich is much better then running lean, as a lean mixture causes more heat and so more risk of seizure.

DIAGNOSIS

As i have said before you will tell the jetting by either the sound, or the colour of the plug, but you can also tell by how the bike reacts to different levels of throttle. if you are just changing the main jet then the only level of throttle that should change is past half throttle. if it is running lean it will still rev but it wont have any power behind it, whereas if it is rich it will not rev at all and will bog down and in extreme cases will cut out.

FINAL NOTES

Some people have trouble understanding the use of percentages when explaining jetting so here is a quick example using the higher of the suggested upjet.

Standard Jet - 60
70cc Kit Added - 12%
New Jet - 67

and so on and so forth...

taken from
https://www.scootershack.co.uk/
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[st3v3]

[jimmyRS]

just the cylinder mod? no airbox or change of carbs or bottom end etc?

If you've literally jus bolted on a 70cc top end, dont expect it to last, or your bottom end. A disaster waiting to happen imo, you shoulda atleast gone with an endurance crank or something a bit more supportive to give the engine a chance to survive. If youve been running the kit as you say 'feeling like it has more to give' chances are its lean, and if its lean and you've been running around on it, dont expect it to be pretty

Upjet as above by around 10% and go from there, i would think in the 80's mark provided you kept the same carb n airbox, if you put an airbox on add another 10 and go from there

[cameron1590]

hi guys thanks for the good reply's ! well i pulled the plug and it was brown-ish so does that mean its been jetted correctly ? just seems like it has more to give

thanks

cameron

[at106]

[cameron1590]

Hi, thanks for the reply, I saw a gearing kit on adrenaline pedstop costly at £255 but it's a replacement gearbox for after 70cc kits to give a higher output, or would a sprocket do the same ?

Thanks

[at106]

[jimmyRS]