i have a standard mc18 r2j and i was hoping to derestrict it. i have read about what needs to be done but i was wondering about, what kind of jetting modification needs to be done?? the bike is currently running standard carb settings.

Jetting is only discussed in the members section. But when you have derestricted your MC18, stay on standard carb setting, ride the bike, see how it runs, do a plug chop and see how that looks. If it feels / looks like jetting changes are required, then that's the time to subscribe and post a question in the members jetting section
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Rich
MC21 Track Bike / RS250 NF5 'Spencer', NX5 'Cadalora' & NXA 'Aoyama' / RS500 / Two Brothers Racing RC30

thanks i'll try that

Just to quickly touch on the 'plug chop' topic

My understanding is, flat out out in 6th, turn everything off, pull the clutch in, come to a stop, pull the plugs and check

This would be a 200km/h run. Can you use a shorter gear to check ?
Obviously, you want max load on the motor. Could you substitute 6th gear, with say 3rd going up hill ?
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What i do is run 3rd gear up a hill full revs and rear brake to keep revs at 10000rpm and full throtle

80XAR wrote:Obviously, you want max load on the motor. Could you substitute 6th gear, with say 3rd going up hill ?

If you then went up that same hill in 4th gear (with your 3rd gear plug chop jetting) the motor would be under more load and in danger of seizing
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i put the motor under load with the rear brake so it wont accelerate any more

i cant drive my bike flat out in sixth on these west cork roads, i would be lucky to make third gear so i think i'll bring it to a dyno instead.

nsrjb wrote:i cant drive my bike flat out in sixth on these west cork roads, i would be lucky to make third gear so i think i'll bring it to a dyno instead.

there's a spot in east cork,where flat out in fifth will destroy a motor .Do you know JOG Tuning in Kerry?,you could do a dyno run there,not sure how good he is with 2Ts though.

i presume you know from experience. it will be a while before i get the carbs set up properly, as i am in the middle of restoring the bike. i'm not working at the moment and that does not help either i am getting new tyres this week next will be breaks then i'll have the carbs done. if i sell my cbr 250 i will have plenty of money to spend on the bike.

What fuel will you be using when you do a plug chop ?
Be aware that the dyno route will give a different jet size compared to the road , unless you can apply load to the motor while on the dyno .

so the plug chop would be the preferred method? i'm not sure of fuel as there is only 1 grade of petrol in ireland as far as i know.
i also tried removing the power valve restriction on my mc18 r2j and took it for a short spin about 1 km after warming up and the bike runs alot worse with this done in higher rpm. i presume this happened because it would have leaned out the mixture more.
i am going to increase the main jets 2 sizes and see how it runs then.

Over the years a number of people have accused me of being either a little insane or rather brave to run WOT in 6th for such a length of time for a plug chop... normally the former!

The thing is where I live there's a nice quiet 1 mile straight ("The Plug Chop Straight") that's flat for 2/3 of the run, then dips very slightly (nice to just boost the revs a bit more!) and finishes with a slight incline that's perfect for loading the motor up! You hit the 30mph speed limit sign just after you've rolled off and killed the ignition and roll into the bus stop! Perfect!

It gives a superb reading on the plugs, but I admit that for some that length of run can be rather intimidating. Regardless though, in my opinion you do need to run flat out for long enough to both clean and then "colour up" the plugs to get a good reading. 10 seconds sounds like a lot, but most standard bikes will need something approaching that kind of time just to get to peak RPM in 6th gear!

As Fontyyy says, a motor in 3rd or 4th won't be under anywhere near the same kind of load as one in 6th. Trailing the brake is OK I guess, but I doubt it will be very consistent. If it works for you though, then great.

Although they seem to be rather fuel inefficient, the MC18 motor seems to be quite efficient in its operation! Derestricting the ignition and airbox on an otherwise standard bike will generally not effect the jetting much, if at all. The MC18's tend to not need the airbox opening up quite as much as the '21 either.
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Maybe we should say what colour the plug must look like if he is running unleaded vs the colour of leaded fuel

i will be running unleaded. i definitely need to up the jetting in my carb, because i have tried the plug chop in 3rd flat and cylinder 1 was running lean cylinder 2 seemed good. i presume the factory setting need altering because i have r5k pipes on my r2j.

i have new plugs and main jets arriving tomorrow so i am going to try them out
and see how it runs.