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Upjetting a moped.

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Pompey_Jake
L Plate Warrior



Joined: 06 Mar 2015
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PostPosted: 18:18 - 13 Jul 2015    Post subject: Upjetting a moped. Reply with quote

Hi,

I need to upjet my moped and I was just wondering if you could help me out..

I have a Speefight 2 with a stock carb, I have a sports covered air filter, a leo vince tt exhaust & a 70cc kit, what jets should I be looking at?

thank you.
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spannermonkey...
Renault 5 Driver



Joined: 20 Mar 2015
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PostPosted: 18:39 - 13 Jul 2015    Post subject: Reply with quote

Not that easy every machine is different. Not a simple bolt on task. you have to feel, listen, look and learn.

You have to set the idle circuit, then the slide/cutaway then look at the main jet.

How does it run will all those bolts on's?

Can you buy different jets and carb parts?

What is happening from idle to 1/4 turn throttle? 1/4 to 1/2 and 1/2 to 3/4 and 3/4 to flat out.

From that you can start to address the carb issues. If you struggle to get the carb to work it may need a bigger one. Have you played with port timing and shape?

If the engine run in first before you open it flat out and wreck the rings?
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andys675
World Chat Champion



Joined: 08 Feb 2007
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PostPosted: 22:43 - 13 Jul 2015    Post subject: Reply with quote

did the standard exhaust have a catalyst?

as they had an even smaller jet as standard, best to go much bigger as running rich only foul's the plug, running weak holes the piston
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stevo as b4
World Chat Champion



Joined: 17 Jul 2003
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PostPosted: 16:21 - 14 Jul 2015    Post subject: Reply with quote

Pay for a set up on a dyno with proper gear.
Or if you know someone with a similar bike, and similar mods/same parts fitted etc, then use their set up and see how it works.

You can't successfully home tune and set up the fuelling etc on a bike with messing about with plug chops etc. I've been there myself many times.

Also people think auto tuning is easy, but there's lots to consider.

You need the jetting to be close to be able to spec the roller weight and clutch engagement speed etc, but then you need the transmission set up so that you can ride at the load/speeds where you need to optimise the jetting.
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