2-stroke Jetting

[MarJay]

Hello,

I have just won some SWONA exhausts for my TZR250 on ebay.

I have searched and searched and cannot find any info on TZR jetting.

One site mentioned that (with an RD350) the person in question should go up two jet sizes and then do a plug chop.

Now I vaguely understand what they mean by a plug chop, but can someone go into more detail, and is this a good idea on my bike?

Cheers,

Mark.
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F; Cheap project: CBR900RR FireBlade
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

[gavin]

"Generally" speaking, just swopping pipes shouldnt require any jetting change. a 2-stroke is basically a scavenge pump, the intake and the porting determine how much air it can flow, the exhausts really only determine how and where the power is delivered.

however, if these pipes make it rev higher, or make peak power in a different part of the rev range, you will probably need to tweak the jetting to suit.

doing a plug chop means first starting with new plugs, running the bike up to whatever part of the rev range wot want to check, then killing the engine and checking the plug colour. BUT.....plug colour varies with other factors such as plug grade, oil type, oil ratio etc etc, so you cant take one colour as gospel for perfect jetting.

i would ignore all talk of plug chops at this stage.

go get a selection of larger jets (say upto 5 sizes bigger) and put the biggest ones in. lift the needle as high as it can go. and run it up. it will proably be way too rich and stutter like mad. if it dosent you need to find some bigger jets. if its stuttering, go down a grove on the needle and try again, keep going, repeating this till it smooths out in the midrange, if it dosent, come down a main jet size and put the needle back up to the highest setting. repeat all this untill it pulls cleanly through the midrange without stuttering. it should also pull cleanly at the top end if you have done this right.

THEN do a plug chop. you want a clean, tan coloured ceramic around the centre electrode, and the side electrode should be carbon and deposit free, 1/3 of the way back. Generally speaking.

dont forget the pilot jet also contributes to all throttle openings, sometimes tweaking the pilot screw can sort top end jetting out.

if you were to just chuck a size bigger jet in it and attempt a plug chop, you run the risk of holing a piston. start way too rich, work down.

[Kickstart]

[cagiva gezzer]

Pop up to Aylesbury or give Chris a call at Road and Track.

Their TZR won the "TZR Challenge" and Chris knows everything there is to know about RS's/TZR's/RD's/NSR's.
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"because one stroke isnt enough and four strokes waste two"

[MarJay]

As far as I can tell the engine hasn't been rebuilt for a loooong time. The bike goes well, and it revs, and it has a nice gob of power.

How do I know if/when it needs a rebuild, and will a top end rebuild suffice or is it worth taking the time and doing a full engine rebuild?

Basically I want to make the bike quick and reliable - restore it to its former glory!

Its fun to embarrass porsches on a little 250!
____________________
British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F; Cheap project: CBR900RR FireBlade
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

[MarJay]

[Gazdaman]

Might be worth changing the rings, it's not /too/ much of an issue if it seizes though, spares are so damn cheap for these bikes.

I've got aftermarket pipes on mine, and K&N filters, standard is a 230, I've put a 230 in, but I'll give it more trial and error, considering it doesn't actually run at the moment!

Everyone knows TZR250s are quick on the track, there was one in the fast group at Lydden, on the tracks with few long straights they kick ass.

Gaz