I'm at ropes end trying to sort out a very fussy 2017 e4 gas gas txt 125, bike only has about 5 rides on it by my 13 y/o daughter and it is safe to say that it is impossible to start for her. To her credit, the count of experienced adults who either can't start it or have extreme difficulty getting it lit, is now 5. For some reason I seem to be able to kick it over briskly enough to get it to fire, but this is not a very workable solution as if she's not with me she's stuck with a dead bike. If I'm with her then riding consists of perpetually needing to park my bike to get her sorted everytime she falls or stalls. A ma:jor pain generally.

So, here's what I know so far:

1) Spark is very weak, unless you spin the motor very quickly (plug out and with hand or foot on kick lever) Anything less than rapid movement gives zero spark.Comparing this with my 280 of same year shows how weak it is, 280 shows a very nice spark with just a modest movement of kick lever with hand.

2) naturally, have replaced plug, platinum tip etc, made sure high tension lead is making good contact etc.  Have swapped cdi *and coil *with the 280 with no difference which led me to the  conclusion that the stator must be bad,  wrong!!  My first rate dealer, Dave of Gas Gas pacific quickly expedited a new hydria stator to me and I thought must  have the problem beat but alas it's essentially the same.** As a side note, coil is the same part number between both bikes, CDI is a different #, obviously different mapping but functioned to give a spark (weak mind you)

3)Of course I've checked the carb, thought of trying a 55 pilot but the bike once running is perfect and besides, I'm already convinced the weak spark is the culprit.

I'm hoping we can get to the bottom of this because it just isn't right and I'm about to pull my already thin hair out!!

Thanks for any knowhow offered,  Cheers

 

 The Gas Gas pro model has always been hard to start. It takes a technique, you cannot just kick it over and over again. One of the issues, it only has a partial kick start gear shaped in a half moon. In fact my last Gas Gas was bought from a guy that could not start it and he makes his living riding bikes hundreds of miles a week.   

 The 55 pilot is a step in the right direction. Helps to get the piston to top dead center, then a very quick short kick, You also always need to make sure the kick start gears are engaged or the gears will chip.

Edited January 18, 20197 yr by lineaway

Just a thought, If the parts from the 280 when in the 125 are as poor, maybe its the return (earth side) half of the circut that is the probleme

I am not familiar with the Hydria system, but if it is functionally the same as the Kokusan, then there would be a ground wire from the HT coil to the chassis, check to see if the connection is a good one. Use an ohm meter for continuity, HT coil ground/earth to the motor, it may be just relying on the coil mounting bracket to the frame. Bye, Peter B.

Thanks guys, I'll go through the coil grounds (to frame) maybe adding an additional ground wire.  May even try my 280 stator and even the big flywheel, not very likely but has been suggested that the small 125 flywheel might not have strong enough magnetism. Somethings gotta give, never been so frustrated with a bike, especially a new and shiny one!

check earths. Check the cdi plug in is dry and making good all connections. Get someone who has had a gasser for a while try start it and if theyve got good technique as above it'll point you one way or another. Stators on gas gas arent usually a problem.

Edited January 18, 20197 yr by nigel dabster

 Check all thd pins in the cdi connection. We have seen a few that were out of place, not making a full connection.

Had a weak/eventually no spark issue on my 18 250. It just decided it wasn’t starting again, then spent ages chasing a spark, checked earth, tang through wiring etc.  Turned out the issue was a faulty CDI unit. 

Apologies for the bad fag packet sketch, and if I’m telling you how to suck eggs, I’m not a fan of anything electrical. If stator/ignition setup is the same as my 18 it may give you some figures from a good stator/wiring to comapare with.

Final confirmation for me I was seeing around 12v up to the cdi when cranking it over, dependant on arm strength, then less than 3v out to the coil. CDI had signs of splitting around the potting so I suspect moisture was the culprit.

 

Edited January 19, 20197 yr by dan929

Thanks to all the folks who have offered their insight, it's very much appreciated. Still no resolution, I've gone back to the original stator since it proved to make no difference with the new one. I've made sure the coil is perfectly grounded to the frame tabs by filing all the paint off and using conductivity paste. As well, just for certainty, added an extra ground wire from coil to engine. Running an 18 thou plug gap now and have confirmed all pins and connections are good (apparently). No noticeable improvement and spark still appears pretty feeble.  Have the #55 pilot coming in tomorrow which won't help the spark but I pray it helps.  Dealer has ordered a new harness which will be tried next as a long shot.  

still hoping and will update thread at first sign of anything positive.

Thanks again all!

In the 5 years since this post went cold, has there been any development on improving poor starting?

Assuming there is not an electrical problem, making the starter jet richer can help.

Does it have a Dellorto?  If so, they have replaceable starter jets.

When I did not want to wait for jets to arrive for my old TXT321, I just enlarged its original #60 starter jet hole from 0.023 inch to 0.028 inch (making it approximately a #70).  Much easier to start!

Figured I had nothing to lose, as I could just solder up the hole and re-drill to original size if it made things worse.

The jet number is the approximate diameter in millimeters, so a #60 would be about 0.60 mm in diameter.  When I drill a jet, I obliterate its original markings so the next guy is forced to measure.  But I also always supply a full set of note with any bike I sell.  

 

There always seems to be a focus on fuelling and I recognise there's been some success with playing with it but I don't know what it is particularly but I like the idea of weak spark being a culprit. Especially in this case where the OP has gone to great lengths to prove it (apparently never solving it tho).

I fully understand the fuelling has to be right, and 2 strokes are renowned for clogging jets etc so I get where the focus on fuelling is coming from. But the fact gassers are so well known for poor starting even on very new machines would point to something else at least not helping.

Went to the Reg Bowker yesterday and watched in awe as the riders jumped on their bikes after refuelling and with just one kick we're off again! Even gassases! No magic dance or superstitious routine. So it is possible to achieve. 

Start it in neutral is the obvious one as Pro clutches have a tendency to drag no matter what type of oil or ATF you put in. If the bike has a KEIHIN PWK 28 then take the Jet metering block off and clean the tiny holes you see of any gunge then  put a new jet block gasket in before putting it back on. Make sure the jetting is not too rich as it just soots the plug if you are not thrashing the motor regularly causing bad starting/running. In my experience the standard plugs are better than the NGK platinum in the 125 and they are better with a bigger gap like 0.7. Do not over oil the air filter and 80:1 in the tank is plenty of oil , you do not need more to be safe unless you are running it in a trial with lots of road work. Take the reed block off and put some new standard reeds in to make sure its all as it should be and be scrupulously clean while doing all the work and make sure gaskets seal properly.

Edited December 16, 2025Dec 16 by Tr1AL

I think you can get a clear float bowl for that carb, makes it easier to diagnose 🤓