reducing engine capacity 300 to 200cc

[geordabroad]

Hello, I live in China and it took a lot of work to get my TXT300 Pro shipped over here. At the time it was the only bike I saw that was for sale near my parents house in the UK and fit within the time frame I had to get it shipped. As I am a beginner the more I ride the bike and the more I talk to others the more it becomes blatantly obvious that what I need is a lower capacity bike.

My question is (disregarding cost for the moment) is it feasible to replace the 300cc piston and cylinder head with a 200cc piston and head? I have a flywheel weight and a spacer on the top of the cylinder to reduce compression but I think a radical change to 200cc would suit me better. I realise I might also have to change jets in the keihin carb as well.

The cost issue... shipping another bike out is out of the question as I'm only likely to be here for another year, and it would be expensive!

Any thoughts you might have on whether this is possible and what might be needed, warmly welcomed.

Cheers

Ian

[benz19]

200 uses a 125 crank which is different to 250,280 and 300.

you would need ,crank,ignition,head barrel piston ect ect ect. = EXPENSIVE!!!

Benz

[german munster]

You say, you have a Keihin carburetor (30?). Normally the GG 300 TXT has a Dell'Orto PHBL26BS, it works more "softer" and would be the cheapest solution. But I'm no GG rider, perhaps other GG riders can help you more in this question.

German Munster

[geordabroad]

200 uses a 125 crank which is different to 250,280 and 300.

you would need ,crank,ignition,head barrel piston ect ect ect. = EXPENSIVE!!!

Benz

Thanks Benz

would changing to a 250 be easier then? and is a 250 that much different from a 300?

Also, as I have a Keihin carb, would changing to the standard delarto help?

Ian

[copemech]

The standard 250 with a Dellorto is gentle and easy to ride.

If you throw the kiehin into the deal, you may well find someone willing to exchange the complete topends and carbs.

May be a good deal for both ends! Put up an ad in the classifides!

[geordabroad]

Thanks copemech. Someone has been in touch who's interested in just what you suggest Cheers, Geordabroad

[beatabeta]

Probably the easiest and cheapest thing to soften the power initially is

1: flywheel weight (might already have one)

2: head spacer

3: have the head ground out a bit (poss best to have done professionally depending on your skills/knowledge) this will make a huge difference.

then I'd maybe look at getting a 250cc kit and finally if you're still not happy swap the Keihin for a Dellorto. Personally I dont think the carb will help in softening the power noticably

The Keihin is a great carb and I personally would keep it. Luckily for you the Dellorto also works perfectly on Gas Gas.

Good luck

[sting32]

Probably the easiest and cheapest thing to soften the power initially is

1: flywheel weight (might already have one)

2: head spacer

3: have the head ground out a bit (poss best to have done professionally depending on your skills/knowledge) this will make a huge difference.

then I'd maybe look at getting a 250cc kit and finally if you're still not happy swap the Keihin for a Dellorto. Personally I dont think the carb will help in softening the power noticably

The Keihin is a great carb and I personally would keep it. Luckily for you the Dellorto also works perfectly on Gas Gas.

Good luck

hope I am too late, but if you can get a base gasket (gasket under cylinder base/bottom) ordered that is thicker than what you have, you will lessen the power, do one or the other but that head spacer looks to be a way to go.

The kehin carbs are NOTICABLY quicker on the bottom end, not sure why... but the problem here is that swapping to delorto means you need the other reed block assemby(?), throttle cable?

I'd try the slow throttle maybe and the 10 tooth sprocket on front, this and the suggestions from BETABETA could definitely soften the bike, make it easier to ride. Plus as you get better you can undo these mods.

You should have your finger on the clutch slipping the clutch 70-80% of the time you ride a section, even more when you need to go slow or have more "control of the bike" so if you can cause yourself to learn this technique faster, the bike wont seem "so big" IMHO.

[peterb]

Hello Ian,

I remember your posts a long time back, I think because you were(are) a Geordie in China.

The 250 is quite a snappy motor compared to the 300 and may not be so easy to ride. The Keihin, when set up with a GJH needle carburates better than the std DelOrto, and provides better low end throttle control, in my opinion. The DelOrto I find is a more racy carb at low revs.

To get around your problem cheaply and effectively, I would try the following:

Install 2 or 3 extra base gaskets, 0.8mm thick.

Retard the ignition by slotting the holes on the external pick up sensor mounting bracket so you can then rotate the sensor counter clockwise, slot the holes as far as possible to give you a range of adjustment, try to end up with a sensor to flywheel clearence of approx 8 thou as if it is a Ducati ign, they work best at this sort of gap - bad starting with a greater gap when hot.

As said previously, best to run with a 10T gearbox spkt.

Ta ra, PeterB.

[steveo]

The best mods I have used to settle them down and give a more gentle response is,

1. A Dell'Orto PHBL26BS with a standard induction manifold from a 250. This will give you the biggest reduction from the aggressive response the 28 Keihen generates. When changing from a Keihen to a Dellorto a small spacer fitted at the end of the outer cable where it goes into the neck of the carb top works nicely.

2. Slow response throttle tube. (black)

3. Hebo Gas Gas flywheel weight.

4. 10 tooth sprocket.

All things that are quite easy and reversible if you are looking for more grunt later as your skills improve.

Steveo