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The TTR250 FAQ web pages -> TTR250 -> Repairs and maintenance -> Fitted a FMF Q-4 silencer - do I need to more the needle up or rejet?
Post Info TOPIC: Fitted a FMF Q-4 silencer - do I need to more the needle up or rejet?
matador


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Fitted a FMF Q-4 silencer - do I need to more the needle up or rejet?
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Time for me to ask the dumb question, I brought a FMF Q4 silencer (not sure why now) it was a bit noisy but I fitted a piece of perforated stainless pipe with a blanked off end inside the  back of the silencer and it works fine but I suspect I need to change the carb settings (although the bike runs ok). Any ideas on needle position or jet sizes needed?

Years ago I tuned up a bike and ended up buying a box full of jets to set it up, so cost quite a bit, so to save buying a selection of jets and constantly having the plug out to colour test, I would be grateful for a few tips.

Many thanks in advance.

 



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TTRfan


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If you have increased the back pressure with an insert then there is every chance you are OK with the standard jetting.

A more open silencer usually weakens the mixture. If you take the cover off the airbox and it still just about runs OK then you are in with a shout wink

Brian



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matador


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Many thanks Brian, it's tips like yours above that are worth a lot.

Yep I ordered the Q4, then spotted your post on trying to quieten one down but loosing power that made me think it's not a good idea.

Anyway, I removed the rear insert with the spark screen inside and noticed inside the main body is a perforated tube, so working on the old silencer theory of the surface area of the holes must equal the diameter of the pipe. I used an old baffle from the XTR (the other one shot out when riding) which is perforated,  cut 3" off the screen pipe (leaving the screen) and as luck would have it, the XTR baffle tube slipped inside the screen pipe (but couldn't drop inside the silencer) so when assembled it looked the same but has two perforated tubes at the back now, but alot quieter. I could have blanked the screen pipe and drilled 50+ small holes in it to achieve the same, double baffle = a lot of fiddling.

My son said it has a deeper sound of a larger bike. I still want to use the original silencer for Horse events.  

Have a good weekend - not too many 'Grockles' on the beaches for you.



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The TTR250 FAQ web pages -> TTR250 -> Repairs and maintenance -> Fitted a FMF Q-4 silencer - do I need to more the needle up or rejet?


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