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Strange running!
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Hi All,

New to the forum.. hope you're all well.

I recently picked up a 2006 TTR250. It was not running but I've managed to get her going.  There's a strange problem that I can't work out. When I start it cold, with the choke on she runs quickly to high revs then settles down to lower RPM after a few seconds.  After a couple of minutes I take the choke of it idles well and I can rev her up slowly but if I give it a fist full it bogs down and wants to stop.  What could this be?

 

thanks,

Gavin



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Sounds like it needs a good carby clean 

 



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Yeah thanks.. I did pull it apart and gave it a clean but no difference. 

What are all the hoses to and from the carby and airbox for? If they are mixed up of not connected can it have a impact on how the bike runs?



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The hoses are the carb breather and overflow. They won't affect the running. More than likely you have a clogged pilot jet/passage. Most people think the pilot jet only controls idle but it actually effects how the bike runs all the way up to about half throttle. What's happening when you are cracking your throttle open is you are leaning out your mixture causing the bog because of your pilot circuit not providing enough fuel. I would bet if you got on and rode it you would have a mean lean decel pop coming off throttle.

I've done quite a few carb rebuilds. Taking it apart and blowing it out with cleaner just doesn't cut it most of the time. My process is this:

1. I always purchase a rebuild kit because of the chance of lost parts ect while working on it. I also like to replace everything while I have it apart because if you are going to take the thing off the bike why not freshen her up.

2. I take the carb apart and boil it in in acidic water. Remove all the plastic bits you can get to.  You can probably leave the slide in but definitely remove the float as you can ruin it. You can do this with lemon juice, vinegar, whatever. About half vinegar, water mixture. If you have a ultrasonic cleaner this is better but most people don't. This loosens the deposits / varnish inside the carb passages where you can't see or get to.

3. Blow out all the passages with compressed air. For the pilot jet listen to where the air is escaping and alternate plugging those holes with you finger to clean out everything.  Some people will try to run thin wires into the passages.  I've never had to do this after boiling.

4. Reassemble with new jets, needle seat, gaskets from the kit. I like putting new jets in because they are sensitive to contamination. A jet can be dirty and cause poor running and it is hard to tell just looking at it.

The carb guide on here can get you through all the specifics.

One more thing. If your engine to carb boot isn't tight tight it will run lean and you will run in circles rebuilding your carb trying to fix an issue that isn't the carb. Make sure that boot is really snug.

I re-read you post and your issue may also be caused by incorrect float height.  Check that too.

 



-- Edited by Rooster on Thursday 20th of September 2018 02:52:46 PM



-- Edited by Rooster on Thursday 20th of September 2018 02:58:40 PM

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good on you rooster and ttboof!  sound like another carby rebuild.. for a sanity check before I do so, I uploaded a video from this morning to show the problem.  

 

https://www.youtube.com/watch?v=iP_aqQtcgRg

 

what do you think???



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I'm still staying with carby as Brian said the pilot jet is in play first third or so of throttle opening 

Also low float hight also not as common can cause a bit of grief 

It's a bit rare but the accelerator pump not working can cause a lag or flat spot but not that bad 

 

Just follow Brian's steps also be super careful if taking the float pin out I tend to use brake cleaner and compressed air to avoid taking the pin out 

Too cautious maybe 

 

Once all clean and back on the idle mixture screw should be at its best setting around one and a half turns out (if it's way off that now try setting it at one and a half turns out and try it first ) 



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I watched the video.  The accelerator pump isn't in play until about 1/2 to 3/4 throttle.  It looks like your issue is at around 1/4 to 1/2.  I'd just go ahead and do a full rebuild and inspect everything.  There about a dozen different problems that can cause issues in that throttle range unfortunately.  Top of the list is dirt idle circuit though.  A thorough rebuild inspecting everything and setting back to factory spec should solve your issue. 

I had an issue similar to this on a Bayou 300 ATV.  When I did my carb rebuild I changed the float angle accidentally.  It would run great wide open and at idle but bogged under acceleration and died easily.  It's hard to explain with out pictures but what happens is the fuel needs greater vacuum than it would otherwise when the float height is set too low.  Think of the engine as drinking out of a straw.  Harder to suck through a longer straw than a shorter one.

 

I concur with ttboof that your issue could be also caused by bad idle mixture screw setting.  Try turning it out a bit.  If you get past about 2.5 turns and it starts running better you have a dirt pilot jet/circuit.

 

 



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What Rooster said - get the All Balls carb kit and especially be sure you replace jets.

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Hi guys - thanks for your comments.. after a full rebuild I'm unfortunately still in the same boat, actually it's worse now than before.. she started with a choke on first kick after the rebuild without even a shot of thottle. Was super happy for about 10seconds. Then as it got slightly hot it started to die, same as before - but as I said it's worse now, dying sooner and not even able to start after it's hot... Can it be the air breather hoses running in from both sides? The airfilter has been replaced... Any other suggestions?

cheers..

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Partially blocked strainer in the fuel tap 

Might be flowing enough to fill the carby bit but maintain it once it starts 



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