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Race tuning a TTR250 engine
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Most of us use our TTRs for trail. track or road and therefore the requirements are very different to those of a race-tuned engine.

I have been contacted by a kart racer who is using a TTR250 donk in his kart and has asked about tuning it to the max.

This was my reply:

Regarding the carb, the standard TTR carb that you have fitted is a pumper in that it has a round slide with an accelerator pump. This will shoot a spray of fuel every time you hit the throttle. This raw fuel helps the engine to rev up faster so that the engine does not have a spot where is wants more fuel but can't draw it yet from the jets. It can be problematical jetting replacement carbs but if you join the TTR250 forum and do a search you will see that some owners have fitted a Mikuni and given suggested jetting.

There used to be a guy in the Midlands that would get extra oomph out of TTRs by boring the carb but I can't find any contact details. He was called Phil Manning but hasn't advertised for years. Phil would also bore out the exhaust port to give more bhp and quicker pick up.

The usual way of getting more power from a 4-stroke engine is to increase the compression but I am not aware of anyone that has done this. It is worth checking out the CRs quoted by the manufacturers of replacement TTR pistons such as Wossner and Wiseco. It might be possible to skim the head using some Plastigauge to make sure that the piston does not make contact with the valves after the work has been done.

The head could be gas flowed but some tuners warn that making the inlet tract too smooth can make the mixture flow too smooth and thus the petrol and air don't mix as well as they would if there was turbulence.

Depending on how deep your pockets are, it is possible to get hot cams from the States - see http://www.webcamshafts.com/mobile/motorcycle/yamaha/yamaha_ttr_250_(99-06)_dohc_4v.html although I haven't had any feedback from anyone that has tried them so it might be a bit of a chance. Hot cams make an engine less tractable for road or trail use and are only suitable, in my opinion, for race applications but that is what you are doing with your TTR engine so probably OK.

Race engines are usually fitted with light flywheels to enhance pick up with less weight to get moving when you crack the throttle. The TTR flywheel is really heavy so there might be scope for lightening it. Again, I haven't heard of anyone doing this as most TTRs are used offroad where extra weight means improved tractability - something you don't need on the race track.

Further gains could be had by running a total loss ignition system and taking the charging coils out of the equation. Weight could be reduced with a smaller battery and taking the rectifier/regulator and associated wiring and connectors out of the circuit."

Has anyone tuned their TTR to the max and can give some first-hand advice please? Or do you know anyone that has?

What have I missed?

Brian 

 



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Can he run E85 ethanol fuel or av gas ?
The E85 will run a lot cooler so he should be able to lean the jetting out and get a few more HP .
That is if its available and or allowed in the classes he races


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Super Guru

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I know I am resurrecting a really old thread but am interested to know:

1. Has anyone heard of or have contact details for Phil Manning in the Midlands?

2. Does anyone have any experience of boring the TTR carb?

3. Has anyone tried the hot cams?

Brian



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Exeter, Devon, UK

http://www.ttr250.com  - The one and only dedicated TTR250 FAQ! 
 

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