DTR 125 Bottom/Mid range tune up?

[Conner]

Hey all, basically ive got a DTR125 02. the bikes had all the lighting ignition barrel speedo etc stripped off it all it has is a killswitch. im basically looking for ways to improve the acceleration and performance but im not worried about top speed as im using it for enduro/hare'n'hounds so im not likely to get the bike above 60 mph can anyone suggest ways and methods to help me out? ive heard about changing the sprockets to a different tooth setting any thoughts?

cheers

Conner

[jattie]

Conor,

You are right, if top speed is not a factor, changing sprocket ration will creates an improvement in acceleration, but reduce the tope end. The easiest way is to change the front sprocket. They normally come in 13 14 and 15 toth options and bikes normally come out with a 14. Going down to a 13 will increase acceleration. There's also a 12 oth, but very scarce.

There's lots of ways to improve the engine performance if you want to work on the engine. The exhaust makes a huge diffirence and the standard ones are very restrictive. A performance pipe will make a huge diffirence.

If you dont want to spend lots of money, you can increase the compresionby skimmimng the heads.

Hey all, basically ive got a DTR125 02. the bikes had all the lighting ignition barrel speedo etc stripped off it all it has is a killswitch. im basically looking for ways to improve the acceleration and performance but im not worried about top speed as im using it for enduro/hare'n'hounds so im not likely to get the bike above 60 mph can anyone suggest ways and methods to help me out? ive heard about changing the sprockets to a different tooth setting any thoughts?

cheers

Conner

[Conner]

on the topic of reducing the tooth ratio of the front sprocket, how much of a reduced top end would we be roughly talking? also what difference would adjusting the rear sprocket do?

a new silenced dep exhaust is on the list for definite

what sort of engine modifications are there that can be done either by myself or done without having to sell a kidney?

Annnd finally you mentioned skimming the heads? ive heard this mentioned before but im unsure as to what this entails?

[Ryan09]

Id personally put a larger back sprocket and smaller front on, full dep exhaust system and make sure your power valve isnt jammed open as this would make it a night mare on HnH's. I wouldnt bother on having anything skimmed, if you really wanted to maybe bore it out? Again not a lot of point though considering the price.

Depending on which sprockets you choose i recon you will still hit 55mph easily and it would get there pretty swiftly but remember you dont want too much power as it could become a bit of a handful in really tight parts of the course so youll need to find what your happy with.

Good luck with the racing

[Vez]

on the topic of reducing the tooth ratio of the front sprocket, how much of a reduced top end would we be roughly talking? also what difference would adjusting the rear sprocket do?

a new silenced dep exhaust is on the list for definite

what sort of engine modifications are there that can be done either by myself or done without having to sell a kidney?

Annnd finally you mentioned skimming the heads? ive heard this mentioned before but im unsure as to what this entails?

Easiest way is to send the engine to Stan Stephens and ebay a kidney.

If you are feeling mechanically minded, maybe clean the exhaust and transfer ports up a bit. Level the inlet port out a bit, the casting isn't great on DTR's. Polish the piston up every race or so. Source an earlier inlet manifold, or modify yours. And fit a snorkel from a Lanza.

Skimming of the head is having a very small amount shaved of the face that joins the head to the barrel to increase compression.

I would vote for an arrow exhaust system instead of the DEP.

[jattie]

on the topic of reducing the tooth ratio of the front sprocket, how much of a reduced top end would we be roughly talking? also what difference would adjusting the rear sprocket do?

Adjusting the front sproket is easier if you want to play around with rations since one tooth in font does not affect the chain length and adjustment potential to keep it tight enough, otherwise you have to remove some chain links.

The net effect would be a function of the ratio from front to back, for example say you have a 48 tooth sproket at the back and a 14 in front so a ratio of 14:48 i.e. 3.4285. So adjusting one tooth in front smaller you will get 3.6923, that is a reduction of almost 8%. (3.6923-3.4285/3.4285*100)

You will get roughly the same effect by adding 3 teeth at the back, so the top speed will decrease by roughly 8% and the torque/excelleration that you experience by roughly the same amounts.

a new silenced dep exhaust is on the list for definite

what sort of engine modifications are there that can be done either by myself or done without having to sell a kidney?

1. You get high performace reed valves (Boyesen - Fibreglass type) with a shorter lifespan, but increase in engine RPM and overall performance. They can resonate at higher frequencies.

2. Gafflowing in inlet ports, basically polishing the fuel inlets and widening them and widening the holes in the pistons that flows fuel trough the crancase. Make sure the crank case seals are leaktight and does'nt effect the fuel mixtures.

3. Use the Iridium type spark plugs and multispark types.

4. Increase the combustion presure by reducing the combustion chamber size. (skim the head - see below)

5. Build or buy a custom exhaust.

On these bikes every little increase adds up to the overall performance, keep in mind that all these changes also leads to a reduction in engine life and fuel consumption.

Annnd finally you mentioned skimming the heads? ive heard this mentioned before but im unsure as to what this entails?

Skimming the head basically means reducing the cumbusion chamber size. The cyclinder head normally have a little ridge and a gasket. You hace to determine how much room is left for the piston to turn around on the top at speed and take away some of the spare capacity. An easy experiment is the remove the aluminium gasket. A millimeter of part of that make a huge diffirence. Be aware thou that the engine runs hotter and you can burn holes is the pistons if the fuel mixture is to lean.

[Ryan09]

Hi,

Have you entered a HnH before? If not do what you can afford to the bike first before splashing loads of money and you may find it okay as is.

I'd personally sort out the suspension first as I found it really soft and not very responsive for fast pace.

If you like it then maybe up grade to a ktm 125exc or if you have a full liscense a wr or larger exc?

Hope it all goes well and enjoy it, that's the main thing!

[Vez]

Adjusting the front sproket is easier if you want to play around with rations since one tooth in font does not affect the chain length and adjustment potential to keep it tight enough, otherwise you have to remove some chain links.

The net effect would be a function of the ratio from front to back, for example say you have a 48 tooth sproket at the back and a 14 in front so a ratio of 14:48 i.e. 3.4285. So adjusting one tooth in front smaller you will get 3.6923, that is a reduction of almost 8%. (3.6923-3.4285/3.4285*100)

You will get roughly the same effect by adding 3 teeth at the back, so the top speed will decrease by roughly 8% and the torque/excelleration that you experience by roughly the same amounts.

1. You get high performace reed valves (Boyesen - Fibreglass type) with a shorter lifespan, but increase in engine RPM and overall performance. They can resonate at higher frequencies.

2. Gafflowing in inlet ports, basically polishing the fuel inlets and widening them and widening the holes in the pistons that flows fuel trough the crancase. Make sure the crank case seals are leaktight and does'nt effect the fuel mixtures.

3. Use the Iridium type spark plugs and multispark types.

4. Increase the combustion presure by reducing the combustion chamber size. (skim the head - see below)

5. Build or buy a custom exhaust.

On these bikes every little increase adds up to the overall performance, keep in mind that all these changes also leads to a reduction in engine life and fuel consumption.

Skimming the head basically means reducing the cumbusion chamber size. The cyclinder head normally have a little ridge and a gasket. You hace to determine how much room is left for the piston to turn around on the top at speed and take away some of the spare capacity. An easy experiment is the remove the aluminium gasket. A millimeter of part of that make a huge diffirence. Be aware thou that the engine runs hotter and you can burn holes is the pistons if the fuel mixture is to lean.

The inlets should not be polished on a 2-stroke. The surface is similar to a golf ball and reduce friction by trapping a thin layer of air (or mixture) and allowing the mixture to pass over them faster than a polished surface would allow.