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The TTR250 FAQ web pages -> TTR250 -> Carb stuff -> New muffler does carb need adjusting?
Post Info TOPIC: New muffler does carb need adjusting?
Forgorin


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New muffler does carb need adjusting?
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So, I put on a new muffler over the weekend and took the bike for a spin.  Wow!  More grunt!  I feel like she has more torque now (able to change gears earlier at lower speeds).

 

I am hearing a bit of backfire when decelerating at higher RPMs.  I am unsure if this is because it is running lean or rich (haven't had time to check the spark plug yet).

 

Any advice?  I don't really want to change jets unless I have too.  Could adjusting the umm.... air mixture screw help?

 

Cheers,

Japan Michael



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pug


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Pop a new plug in an take it for a spin have a look at the plug after 10 miles that should give you a good idea what its running like colour wise should be a nice light brown

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TTRfan


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Hi Michael!

Pug's suggestion is a good one so go with that.

In my experience popping and crackling on the run over is usually caused by an air leak - probably at the joint between the header pipe and the muffler itself.

If you are sure that joint is airtight, can you tell us what the new muffler is like - is it much more open (louder!) than the original? If it is then maybe you need to consider raising the needle a notch to richen the mixture but that depends on the result of your plug chop.

If so, it is unusual that you get more low down grunt as more open exhausts tend to give better top end power but at the expense of the bottom end confuse

The mixture screw is unlikely to have an effect on anything above about a quarter revs and your symptoms occur at higher revs.

Brian

 



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Forgorin


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Sorry to take so long to get back to you guys. Spring break then busy at work!

Well, popped in a plug. Not sure about the colour. I think it might be a lighter than a nice tan colour. I took a photo, will try to attach it.

Also the muffler is a Taira.r.c It is a Japanese brand. The muffler is second hand and about 16 years old. Brian, it is loud!  I haven't messurme it yet but it is a lot louder than stock. I don't really like it.  I bi was able to pick it up for about 60 pounds. I really wanted something to lighten the bike. The seal seems pretty good .Really tight to get on.  Perhaps I should have used some copper grease?

 Plug.jpg

 

Thanks for everyone's help!

Michael .



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Cubber


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The electrode on your plug, Michael, shows a very weak mixture in my opinion. bleh

It should really be a straw colour for optimum mixture.

spark-plug-lean-rich-optimal-640x360.jpg

A tweak of the mixture screw may suffice. confuse

Martyn



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East Budleigh. Devon
TTRfan


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If the plug is really as white as the photo shows then Martyn is absolutely right - you have a very weak mixture cry

How long did you run the new plug for?

It may well be that, if you keep the pipe, that you might have to rejet as the mixture screw may not richen the mixture sufficiently.

However, it is worth raising the needle by putting the clip on the bottom notch and see how that affects the colour reading first.

Brian



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ttboof


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With mine it poped and cackled on decel 

so main jet was ruled out  i went up one size on yhe pilot (richens first third opening )and dropped the needle one notch on the standard jet ( leaned it a bit ) and its a happy bike with a stain tune pipe with australian fuel 

just thr set up that works for me and better cold starts 

 



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Forgorin


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Martyn, Brian, thanks so much for your answers. It's so nice to have a place to go to get answers! I'll try and take the carb apart next weekend and adjust it.
I tried measuring the decibels today. It's over 90. Not really to my tests. Gonna try and repack it.

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TTRfan


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If you repack or put a decibel killer in the exhaust you may not need to adjust the carb.....



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Forgorin


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AH..... OK! Then I will endeavor to do that first. Thanks Brian!



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Forgorin


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Long time in replying. Took the carb off the bike the other day and raised the needle. Now, the bike chokes, at anything over about 20% throttle, sputters and dies. Took the air filter off and left the cover open. Runs fine!? Sigh, I took it apart again and put the needle back to the middle setting. slipped the old muffler back on and now she refuses to start...!

I'm pretty sure I need to put a larger jet in there. On Monday I will take it to the local bike shop. He mostly does custom bike work. He said we can take a look at it together and figure it out.

The fun of trying to do things yourself eh!

Michael

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Benjah


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When you say 'decelerating', do you mean when the throttle is completely off?  If so then it could simply be the fuel screw needs adjusting.

 





-- Edited by Benjah on Sunday 5th of August 2018 12:21:10 AM

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Forgorin


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Benjah, that's correct. It's adjusted now.

Got it all fixed today. Runs great. Turns out the float bowl was a bit low. Learn something new everyday!

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