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Sum

Exhaust pipe pop

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Hi all,

I am new to a trial bike and a 2 stroke engine with a carburetor. 

So, little education would be greatly appreciated.

With my new 2020 GasGas TXT 280, I hear pipe pop or bang periodically at idle.

I have been trying slow maneuvers and when I try it without clutch at the idle speed, the bike is pushed forward with every pop, which makes it difficult for smooth operations without using the clutch.

The symptom becomes better a bit as the engine warms up but still there at idle speed especially with the slight up hill (thus the engine is slightly loaded).

I guess my question is, is it what it is or something I can solve by carburetor setup.

I would appreciate your advise.

thanks,

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You will get used to constantly riding the clutch and the brakes, it is the easiest way to get control for your slow riding. The 280 was always seen as the ‘experts’ bike of choice so it could have something to do with its state of tune.

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From your description it could be that the fuelling is slightly rich, this is difficult as already suggested it might be a characteristic of this model. Ensure no carb breather pipes are kinked, trapped or incorrectly routed...see manual for guidance. What fuel/oil mix ratio are you operating with? If you make any adjustment to the carb make small incremental adjustments as an example turn any screw no more than a quarter turn, listen carefully to the way the running engine reacts...you are trying to achieve the smoothest slowest engine idling. Depending on the state of the engine...no air leaks, clogged exhausts, incorrect fuel/oil ratios, crank seals effective etc, air filter clean and unrestricted...you might just get down to eighth of a turn settings. I haven’t mentioned carb float height as you say it is a new bike so bear this in mind, it may need checking. Usually popping in the exhaust occurs on overrun, banging indicates fuel igniting in the exhaust which indicates either an air leak or too rich mixture. Happy twiddling. One screw will be the slide adjuster for idle speed setting, one will be fuel mixture which might be three and a half turns out from full in...screw in very gently until stopped then back out, but this needs to be done engine off. Its a base setting to work from. There will be another screw which is the idle mixture screw which works up to about quarter throttle then there is a transition from idle mixture to main jet and needle, once you are past quarter throttle its the main jet and needle all the way to TWO. As you are in the States altitude will play a greater part on carb fuelling the higher in altitude you go, this needs to be considered as a part of the equation.

Edited by section swept
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Thank you all.

I watched few YouTube video of TXT and at idle they also seem to have pipe popping every second or so.

This one below sounds very similar, even the way it is reluctant to start😄. Mine has hardly any smoke coming out, though.

As long as it is not abnormal, I can live with that. My KTM also has some but not this much pronounced and because the TXT is so light, it is propelled at each pop, which I was not familiar with.

Because it still has the gas filled by the dealer, I don't know the fuel mixture. Carb setting is something I need to learn. Maybe I will start with the idle mixture (is it the same as the air screw?) .

 

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2 screws, one raises and lowers the engine idle speed by lifting lowering the carb slide, other is the mixture/air screw which alters fuel and air mix from idle to around 1/8th throttle.

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Thanks.

I searched through Internet and found this description; "rider is experiencing rich pipe bang, it's a deeper sounding bang and the bike lurches forward on each bang". 

This is exactly what I'm experiencing and, thus, probably the rich pipe bang.

Because it happens only at idle, would you suggest me to try the air screw, letting more air to come at idle? Or should I try the idle jet?

I suspect this is, to some degree, a normal behavior and maybe I should not worry too much about it....

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I also had pipe bang. By all means start with the air screw.  It is free and you don't take the carb off.  I had to richen my mixture.  If you can't improve with the air screw, then take the carb off. You have not put fuel in it yet?  I have found these bikes need a fairly high octane fuel.  I am running 102 octane and 80 / 1 Oil mix.  Adjust the carb after you buy the fuel you intend to use.  Have fun.

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Thanks Tshock250 and Jeff,

Looking at YouTube, I have seen some are similar to mine and some seem much less.

It doesn't bother me that much but some practices require "no clutch" slow operations, which are quite hard with the bangs at low speeds (they disappear with little rev).

If I can tame it down a bit that'd be great. Played around with the air screw a bit but I must agree that the factory set (1 - 1.25 turns) is the best.

I'll try high octane for the next fuel. 

thanks,

Edited by Sum

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Go to your Gas Gas dealer and get 1 tooth smaller on your counter shaft sprocket. The gas gas always had too tall of first gear for tight sections.

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Go to your Gas Gas dealer and get 1 tooth smaller on your counter shaft sprocket. The gas gas always had too tall of first gear for tight sections.

 PS who is your dealer. You should have a 46 to 48 pilot jet.

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The manual says the idling jet is 45. A smaller sprocket is actually a good idea, because if I can rev just a bit, it goes away.

A dealer near me started to sell GasGas from this season. I'm very lucky because it's only 30 min away.

Otherwise, the closest one (Beta) used to be 100 miles away.

Bad news is, this is the first trial bike they ever sold and I don't think they have much experience....

It seems some KTM dealers in US start to sell GasGas.

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