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Post Info TOPIC: Hesitant just above idle.


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Hesitant just above idle.
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As above, my TTR starts and idles very well, i can even get it to idle very slowly and it ticks over lovely. But just above idle it seems slightly hesitant, this will be a pain when riding off road. Other than this it revs cleanly through the rev range as it should. Iv'e put the standard exhaust back on incase this was causing a problem but it's still the same. 

Anyone got any ideas from these symptoms ? 



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It could have to do with the Accellerator pump timing. Or, have u tried adjusting your fuel screw at all? ( not to be mistaken for your idle screw).

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Sounds like a blocked or partially blocked pilot jet. They are very difficult to clean thoroughly and, even after putting through an ultrasonic cleaner, they still sometimes need a careful poke with a bit of copper wire.....



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The pilot jet was my first thought as this was blocked when i first got the bike and have read other posts regarding the difficulty with cleaning. I'll have the carb off soon and have another go at at it . I'll also give the carb another check over and give the airways a blow out with compressed air.


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Well i removed the carb today to have another look. Removed the float bowl and the pilot jet and gave it another clean, i spent a fair bit of time makings sure it was clear. The thing that puzzled me was the float bowl had a lot of debris in the bottom and i only cleaned it out a few weeks ago ! Then while i was messing with the carb on the bench i could hear a trickle, i looked round and there was petrol running from the fuel tap and it was in the off position ! I set about taking the fuel tap apart and was shocked to find what a state it was in, it was full of like a sticky tar substance and other debris. The easiest thing to do is to fit a new tap, iv'e had poor results with repair kits over the years.

Sent you an email Brian regarding a new fuel tap.

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That seems odd bearing in mind the plastic tank confuse

I can only think a previous owner had filled up from cans and wasn't particularly careful with cleanliness!

Don't forget to check the little white plastic "hood" filter above the float valve coz that may have collected debris as well.

Brian

PS Email replied to!



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I looked for a filter in the carb but couldn't find one ! How do i get to it ?

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With care! It's under the float valve assembly as indicated in the pic below. Be very very very careful removing the float pin as the support posts are fragile. 

If you can blow through and there is a good airflow them maybe best left alone.

Location of float valve filter.jpg

 

It's the small white plastic filter middle top in the following photo.

Needle_valve_set.jpg

 

Brian



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Whats the best direction to get the float pin out ? Either ?

I will blow through first and if ok i'll forget about that filter.



-- Edited by locky on Saturday 24th of January 2015 11:53:08 PM

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Think iv'e cracked it, got the bike running with a remote tank (it's what i use for carb balancing) and it ran well without any hesitation above idle. A proper ride will confirm. There must have been something still partially blocking the pilot jet. biggrin Also adjusted the pilot screw, 2 turns out seems best.

20150125_122321.jpg

 

 



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Excellent news!

Neat idea with that little remote fuel tank wink



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I fitted a new pilot jet today as i still wasn't sure that it was running as smooth as it could just above idle. Should have done it earlier, it runs smooth and crisp now like it's never done.
I don't think it's worth faffing about trying to clean these pilot jets as you never know if it's 100% clean.

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Time to get it dirty now then??!!smile



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Pete. South Somerset, England.



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Yes I'm off work tomorrow and need to get a few miles on it to bed the new piston rings in.

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Pics to follow then heybiggrin



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Pete. South Somerset, England.



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Naturally, I've just been working out what local trails will be rideable . My favourite one will be a no no due to a very deep water crossing.

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Did you end up modifying your air box?

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Pete. South Somerset, England.



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No still all standard but I have everything to do the mods if I decide to .

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I thought i'd sorted this but it's still there, if i hold the throttle slightly above idle it's still slightly hesitant. It's only in this throttle position that it happens.
 When the engine is hot and i give it the slightest amount of choke it runs perfect. Any ideas ? Would it be worth raising the needle ?



-- Edited by locky on Friday 27th of March 2015 06:35:05 PM

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Locky,

I have that exact issue. Thats one reason I discovered this site. I had to replace the accelerator pump plunger/diaphragm in my carb. The bottom of it started cracking and breaking apart. It wouldn't hold pressure anymore. I thought about coating it with RTV sealant but decided to order another. $24. Check the two O rings in the pump assembly, they may need replacing too. This was also the cause of my extremely hard cold starts. Most of the time I had to use starting fluid. The bad news is that I haven't gotten to ride it besides around the yard in 1st.. That work was done last weekend. I know it fixed the hard starting problem and probably will fix the hesitation. I pretty much have been riding it with little to no acceleration pump! I love your graphics BTW!! I hope this helps and will let you know when I get a chance to stretch it's legs.

 

Brandon



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I should have updated the thread. I had the carb off last weekend and gave it another thorough clean out again. it now seem to be running perfect and ill test it on trails in a few days .
Renewing all the rubber parts in the carb would have been my next step.

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Good luck...nothing worse than an intermittent carb issue.


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Well my carb trouble came back again, i noticed it while riding a few local trails a few weeks back. It's just the same as it was at first !
I stripped and cleaned the carb again last weekend, it all seemed nice and clean but it ran the same when i put it back together.
I decided to order a new diaphragm and the carb side plate 0 ring that turned up today (thanks again Brian).
I installed these tonight but it runs just the same. I'm now at a dead end !!
Just to explain the problem again, when i hold the throttle just a tiny bit above idle it will run eneven and sort of hesitant. On the very odd occasion it will backfire through the carb.
It idles very well and i can turn the idle down quite low and it ticks over like a sewing machine. It revs through the gears as it should and pulls well.
The problem is just above idle. HELP :)

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Hi Locky

Sorry to hear you still have problems. 

Apologies if you have already told us but have you checked that the timing chain and sprockets are 100%? I have had it where the chain is one tooth out and the TTR will run pretty well apart from some fluffing and hesitancy.

I am suspecting it is not the carb at fault although the only way to tell for sure is to fit a carb from another TTR that is running perfectly........

Brian



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I'm sure I got the cam timing correct when I rebuilt the top end but will check it again to make sure.

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Heres a pic of the cams lined up, whats your thoughts ?

20150415_170218.jpg

 



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Looks about right to me. That's not the cause of your problem then.....



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I thought the same but worth a check, iv'e also rechecked the valve clearances while the top was off and they are all fine. The problem is just above idle and apart from this it's perfect, but when slow riding it becomes a pain. Not sure what to check next ! Off to put the rocker cover back on and whip the carb off again. Iv'e got real quick at carb removal now :)

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Ran it again after another carb check (nothing found) . Been thinking how to describe how it runs just above idle, i can hold the throttle slightly open and it sort of runs rough, hesitates and will eventually backfire through the carb if i hold the revs the same. If i just rev it from idle its fine and it idles very well. When it backfires through the carb it cuts the engine. 

Carb off again and also removed the rubber inlet to check it. It was fine when i rebuilt the engine. This is what i found 

20150415_182944.jpg

Yes the rubber has come away from the alloy ! But has this been caused by it backfiring through the carb or is this whats causing my problem ? 

Ive ordered a new inlet but also repaired the old one incase its the backfiring through the carb that blew the inlet apart .

Ive used this to repair the old one 

http://www.dortechdirect.co.uk/window-installer-tools/dow-corning-895-structural-glazing-silicone-sealant.html?gclid=Cj0KEQjwmLipBRC59O_EqJ_E0asBEiQATYdNh474w5pFpBVA_7e1I7lFY7ao1gI1jBXdY1xEDXw4ggUaAg9a8P8HAQ

It's a bit like the sealant they use to bond car windscreens. 

I'll refit the repaired inlet tomorrow and see how it runs, fingers crossed hmm

 

 



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Just been thinking that the inlet could be the fault. It has got worse over the weeks and it never use to backfire through the carb.

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Fitted the repaired inlet rubber and it ran just the same ! It does seem a good repair with that sealant i used but will still fit the new one when it arrives just to be on the safe side.

So at this point i was 100% out of ideas. Stripped the carb yet again just to see if id missed anything, blew everything out with the airline and refitted, guess what , it ran just the same!!!furious

I have the jets incase i decided to do the airbox mod (52.5 pilot and 140 main Mikuni) so i thought id fit the 52.5 just to see if it made any difference, and guess what, it now seems to run perfect with no hesitation and no backfiring through the carb biggrinbiggrinbiggrinbiggrinbiggrinbiggrinbiggrinbiggrinbiggrin . I can't believe that it's made such a difference, but i wonder if it will run a bit rich ?

The pilot screw also seems to make more of a difference when wound in or out compared to before.  

 



-- Edited by locky on Thursday 16th of April 2015 07:07:56 PM

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Just wondering, i fitted this air filter when i rebuilt the bike
www.ebay.co.uk/itm/Yamaha-TTR250-2000-to-2006-Hiflofiltro-Air-Filter-HFF4018-/281564045398
Would this have caused it to run much leaner ?

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I don't reckon it will run rich locky, just check the plug after a bit of a rag aroundsmile



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Pete. South Somerset, England.



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Yes Pete i think it should be fine . Ill test ride it tomorrow if i have time. I still find it strange that its been running lean.

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Fitted the new rubber inlet tonight and tested how it starts with and without choke from cold. It still needs choke so thats a good sign. Ill take it for a ride tomorrow to see how it runs but im expecting it to be fine.

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Looking good locky?

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Pete. South Somerset, England.



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Since my last post ive not been out on it , just been to busy with work and other stuff. When i go out on it next ill post my thoughts.

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Managed to get out on it for an hour today, what a difference a jet makes biggrin . Very smooth running now and seems to pick up a better from idle. 



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That's good that that niggling issue has gone now huh, look forward to more pics on the next outing locky, come back sun!

 

I'm guessing the plug is looking a nice tan colour? Not too black...

 



-- Edited by peteBLUEttr on Saturday 25th of April 2015 07:07:38 PM

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Yes had a look at the plug and it's a nice browny colour so it looks like it's all good and sorted but what a pain it's been !
Still a bit puzzled as to why it needed a bigger jet when most TTR's run well with standard jets !
I guess if i ever wanted to do the airbox mod i'd have too go up to size 54/55 ?



-- Edited by locky on Saturday 25th of April 2015 07:50:05 PM

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If your going to stick an exhaust on at some point it might even work without touching anything. As to the reason why your bike was running lean, I'm not really sure, you still got the restrictor in the back of the header?

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Pete. South Somerset, England.



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No restrictor Pete , it had been removed when i got the bike .

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