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I am currently running a modified (by previous owner) stock exhaust on my TTR 250. I'm happy with the performance and sound but it is on it's last legs. BTW I believe the modification removed some of the internal baffling to make it more free flowing. Recently I purchased an after market exhaust to replace the ageing stocker. After fitting it I noticed a reduction in low and mid range power. Power didn't really come in till the revs really built up. I've since swapped it out for the stock exhaust. 

The maker of the new exhaust has kindly offered to modify the pipe free of charge to improve it's performance. My question is, based on the symptoms, what needs to change? Too much flow, to little flow ? Any suggestions would be welcomed.

Cheers



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I have found generally the better the exhaust flows the better the bike goes, but at the expense of noise. You have to find the happy medium with the noise and performance...
Change too much and jetting will be effected and need adjusting.
Uncorked, ie baffle in the header, airbox and throttle stop with a free flowing exhaust really wakes up the TTR.

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Okay I tested the new muffler against the modded stock one back to back today and this is what was immediately apparent. The new muffler gives more power in the upper rev range at the expense of low end torque, and vice versa. I prefer me some low end grunt for trail riding so it's back with the modded stock muffler. Maybe the new muffler is too free flowing and doesn't provide sufficient back pressure? 



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Can you pack it out and try to reduce the free flow?



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You mentioned the manufacturer is happy to modify it. What do they recommend? How loud is the new one. Often they come with inserts that are removable on the ends that change the flow/noise/power delivery.
What brand muffler is it.

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I would but the new exhaust doesn't have any packing. After emailing the manufacturer of the exhaust again they suggested that playing with the needle height and fuel screw would likely bring back the missing torque. I've played with the needle height before and it only seemed to run properly on the middle setting so I might have a play with the jetting. The fueling on the main jet seems really good so I'll try going up a size in  the pilot jet. Currently I'm using a 50 so 52 it will be. I've previously opened up the airbox and installed a twinair filter so 52 sounds reasonable to me.



-- Edited by Benjah on Wednesday 27th of June 2018 11:51:54 PM

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Kaos wrote:

You mentioned the manufacturer is happy to modify it. What do they recommend? How loud is the new one. Often they come with inserts that are removable on the ends that change the flow/noise/power delivery.
What brand muffler is it.


 The exhaust is from a company here in New Zealand called Motorworks. I believe it's just one guy making them and he seems really good about helping customers get to a point where they are 100% happy. No inserts etc.. just re-engineering back at the factory.



-- Edited by Benjah on Wednesday 27th of June 2018 11:55:03 PM

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let us know if you find genuine 52 pilot jets, i need one aswell

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I bought some dodgey cheap ones from eBay. Certainly not genuine but based on the photos at least,  they look the same to me.

 

 



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Got a link Benjah?

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Link to cheap pilot jets:

**Note these probably won't work** 

https://www.ebay.com.au/itm/10Pcs-Set-Slow-Pilot-Jet-for-PWK-type-CVK-type-PE-10Pcs-Carburetor-Main-Jet-Kit/152990329939?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

When I select 2003 ttr 250 it says the part is compatible and since all the TTR250 jets are interchangeable.

** This Pilot jet apparently does work**

I've also just ordered a Mikuni VM28/486 52.5 pilot jet from Rocky Mountain ATV, will give that a try too. Using this jet was bought up in http://ttr250.activeboard.com/t49951533/carb-jetting-information/

So many jets...



-- Edited by Benjah on Friday 29th of June 2018 10:59:33 AM

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Furthermore,

I've also ordered a #52 pilot from sigma6. I'm using the scattergun approach to buying a pilot jet. I'll write up the results after I've tried them all.

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Please let us know how you get on as the 52 is discontinued from Yamaha.

Cheers

Steve



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Great look forward to your results

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The #52.5 Mikuni work well. My low end torque that went missing after installing a new pipe has returned. Still a little funky sometimes  in the upper mid RPMs so I think I'll play with the needle height.  The sizing of the cheap Chinese  knockoffs was not even close. Still waiting on the Sigma6 jet.



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Thats great.

I was hoping they still fit (I'm sure I remember reading of lots of people fitting them) I was lucky enough to get a couple of yamaha #52 pilot jets and have dropped the clip down one notch on the needle. Runs really well through all throttle positions. Have the airbox opened up and an aftermarket TK exhaust. 



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Leigh.
I also run the tk.
Any chance u have a 52 u would sell.
Cheers

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Hey I don’t, sorry Kman. I would just use the 52.5 Mikuni - if I didn’t have a Yamaha 52 I would do that for sure.

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**UPDATE**

Finally the bike is running like a champ. The final piece of the puzzle was the needle height, which ended up going down 2 clips (i.e leaner) which was not what I was anticipating at all. It pulls smoothly and with authority from any point in the rev range. A clue to the needle height was in the engine temp. My digital speedo ( a trail tech striker ) takes a temp reading from a sensor connected to one of the exhaust header studs. With the stock exhaust, it read around 160 deg C at a steady mid throttle speed. With the new pipe this dropped to 130 deg C, which suggested to me that the bike was running rich. With the needle dropped 2 clicks the temp is back up to 160 deg C. 

The needle height adjustment together with the larger pilot jet (52.5 Mikuni) has completely cured the bikes fuelling issues. All the lost low and mid range power is back (and then some) and the top end is much improved over the stock exhaust. Ultimately, the best part is I'm no longer fretting about the TTR not been all it can be when I ride it.  



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