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The TTR250 FAQ web pages -> TTR250 -> Carb stuff -> Opinions Please.... Confused Jets Popping Exhaust
Post Info TOPIC: Opinions Please.... Confused Jets Popping Exhaust
Archershome


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Opinions Please.... Confused Jets Popping Exhaust
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Hello yes its another question on jets... I am confused and have read other forums.

Ok TTR250 04 plate, fitted new twin air filter and FMF Q4, snorkel still fitted as gone in some big puddles, bike seems a little sluggish in comparison  to a friends with similar set up. I have a 14/52 sprocket set up and would think it should pop up front wheel easy but it takes some work!

I get a lot of popping on the overrun on deceleration, and quite a lot of black shoot has started to appear in the exhaust to a point it comes out some times, see it on number plate.

I have had a look the jets, and it says 50 pilot and 147 main no idea what make these are. Oh and clip is on position 3

Thoughts and ideas be greatly received. biggrinbiggrinbiggrin

I may post some pictures later

 

 

 



-- Edited by Archershome on Monday 19th of May 2014 07:20:58 PM

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TTRfan


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!47/50 jetting is common on UK blue TTRs and they will be the standard Yamaha TTR jets.

Leaky valves can cause popping on the over run and black soot (especially if its not "powdery") can indicate that the engine is burning oil.

If your TTR has done a lot of miles, or you don't know its background, then it might be possible that you are down on power because of low compression - possibly a combination of poorly seated valves and worn piston/rings.

If you rebuild a tired engine, the increase in performance is very noticeable. 

Just thinking out loud.....

Brian

 



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Archershome


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Hi Brian, thanks for the reply.

What about the possible running lean / rich ideas...

I will borrow a compression tester, and check this at some point soon, and look to see if powdery or liquid

On millage 64000 approx... Is this allot for a TTR? I would not know if its on original parts?

Cheers

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TTRfan


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As you have the right jets fitted and, assuming there are no faults with the carb and you have a clean air filter and a standard exhaust, I would have thought the mixture should be spot on.

It would seem unlikely that the POs would have done 64,000 miles with the wrong carb settings unless the last owner fiddled with the carb before the TTR was sold confuse

If the engine hasn't been opened since new then I would have thought that, at the very least, new rings and valve stem oil seals plus a decoke were in order wink

Brian



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TT-R250M


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It would help to have more info like elevation, country, climate, etc. but I will try to explain rich and lean conditions as best I can.

Rich

The carb will pop/backfire on deceleration, this is because of the un-burnt fuel that now has not enough air to mix properly. When the slide is shut down all of a sudden it shuts the air off, if it is slightly rich it will pop because it does not any way of taking in more air to counter react the rich problem.

It may also be sluggish and not rev out very easily.

It may stall when letting off the throttle quickly and backing down to an idle when stopping.

Spluttering when accelerating.

Black soot on the spark plug.

If the throttle is closed after WOT for some time, it will loose revs rapidly and may stumble or miss. This is called the roll-off test.

Lean

Backfiring on acceleration is due to a lean condition. The reason for this is that the engine does not have enough fuel so when you apply the throttle and the slide lifts up, it backfires on acceleration. Much like my WR400 does when low on fuel.

Over-heating or a glowing red header, the reason for this is that the fuel helps to cool the cylinder, if there is not enough fuel to cool it down it will obviously get hot.

Lacking power, obviously from running on the wrong fuel air ratio.

Flat spot when accelerating.

Pinging valves.

White deposit on spark plug or clean spark plug indicates a lean condition.

If the throttle is closed after prolonged WOT it will pick-up in revs (roll-off test).

................

There are more symptoms than this but these are the most predominant.

Your jets seem to be standard, I can only guess that you are either from the UK or AU/NZ as these are the standard jets for these countries.

Hope that helps.

Jarrah

 

>frowns at editing below but needed to add info blankstare<

 



-- Edited by TT-R250M on Tuesday 20th of May 2014 12:24:43 AM

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TTRfan


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Jarrah's post highlights how helpful it is for members to at least put in some basic info on their profile blankstare



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Archershome


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That's an awesome reply, added location now in profile...

Few things to look at, enjoying my new project learning a lot.

I have got to say there have been some really helpful people on here. What an excellent site. Keep up the great work Brian.

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TT-R250M


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Keep in mind that popping/backfiring in the exhaust can also be due to an air leak at the head or where the header pipe meets the silencer.

When I fitted my FMF Q4 I used some exhaust sealant to help seal it (as it says on the fitting instructions).

Valves not sealing or out of spec can also cause backfiring due to a lean condition so this is best checked if nothing else helps.

Jarrah



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