Yamaha TTR 125

[Three44s]

I have a TTR 125 Yamaha (motorcycle).

When I bought it, it came with a FMF power core 4 pipe.

I believe the carb needs re-jetting. It has standard jets right now. The main is a “105” and the pilot is a “15”.

As it stands right now the bike is a total pain to start and run.

I ran the carb disassembled several cycles through a ultra sonic cleaner and many more struggles through it with the pilot jet. Before the bike sat too long it had the same problem, that of very tedious hard cold starts and a pain to keep running even when warm.

My question is this: Who has experience jetting this model with an after market pipe that enhances air flow? What number jet should I order each for the pilot and the main?

Three44s

[mnewcomb59]

We bought one with a mouse nest in the air box for cheap. My dad wanted to uncork it a little bit so he put a few small holes in the air box to let some air in and put some washers between the baffle and muffler to let some air out. I think with those mods he went up 1 step on the main jet but I will check with him later. I know that he changed sprockets and that was the main improvement. Before 5th gear topped out around 35 mph and it was not out of power, just out of gear. Now it will comfortably cruise dirt roads around 40 mph a little over half throttle.

[mnewcomb59]

Dad says he went to 110 and 17.5. You might want to go a little larger if your aftermarket pipe really flows. Once I bought a DR350 with FMF pipe. I bought it for cheap with the carb in pieces. I had to go up about 3 steps on the main before it would start easy and pull in the upper RPMs.

[mnewcomb59]

Also we recommend ethanol free gas for all the toys and small engines. Around here at the places that have it is labelled Rec 90. This gas keeps longer and doesn't gum up carbs. All our small engines get Rec 90 with fuel stabilizer for the winter months and I haven't had to clean carbs in about 4 years.

[popper]

Is the needle adjustable? And float set correct?

[WheelgunConvert]

Try a 0.005 or 0.010 washer beneath the E clip on the needle. The kind at hobby stores for RC cars usually fits.

[Three44s]

Thanks for the suggestions thus far.

I read the comments from a You tube video the other day and the maker of it went through the wringer with the same pipe on the same size and model of bike and found that a 110 and a 17.5 were his jets of choice so that runs concurrent with mnewcomeb59’s suggestion of what his father determined. Thank you!

I have not adjusted the needle setting yet, it may be raisable still. The pilot is not adjustable of course except by way of the air screw.

The float is not adjustable because it’s a plastic one.

I really do think that both jets need up sizing though because the bike is so far “out of it”. I am not looking for a lot of power as this is an irrigation cycle but total reliability and no foolish behavior is what I am seeking.

Thanks

Three44s

[mnewcomb59]

The bike is extremely cold blooded. It has the same case and quantity of oil as the bigger TT-R and needs choked for at least 15 minutes. All that oil takes forever to heat up with the small bore, BUT the large quantity of oil adds a degree of reliability and lengthens maintenance intervals. You can ride the thing for 15 minutes and the case is barely warm to the touch where other bikes are HOT after 5 minutes. Also the choke likes to turn itself off so I think dad replaced something so it would stay choked. Other guys put a small vice grip on it so it stays choked. It is actually an "enrichener", not a "choke". It doesn't restrict the air to richen the fuel:air mixture but it adds fuel to change the fuel:air.

[Three44s]

Thank you for that added insight!

I am thinking that a bit lighter oil viscosity is in order, not because of the lean fuel mixture but because of the relatively low oil temperature. This bike will be running spring, summer and fall so 2/3 of the run is cooler weather.

I knew that the “choke” is actually a fuel enrichener. We have had to run with it on continuously and in working sprinklers etc. it’s a lot of stop and go so the engine temp is even lower as a result.

Best regards

Three44s

[1006]

My Suzuki has the same issue when it sits too long.

The jets varnish and start to close up. A mechanic turned me onto an acetylene torch cleaning tool. I use it to gently clean the jets, and it works. Then I make sure to run a high dose of Sea Foam fuel additive once each year. The bike runs great as long as it gets the Sea Foam.

[fastdadio]

Thank you for that added insight!

I am thinking that a bit lighter oil viscosity is in order, not because of the lean fuel mixture but because of the relatively low oil temperature. This bike will be running spring, summer and fall so 2/3 of the run is cooler weather.

I knew that the “choke” is actually a fuel enrichener. We have had to run with it on continuously and in working sprinklers etc. it’s a lot of stop and go so the engine temp is even lower as a result.

Best regards

Three44s

Having to run it with the enrichiner open is a sure sign of fuel starvation, as is hard starts. Likely dirty/plugged jets. Replace them as mentioned above.