Honda TL125 Information Page

This page lists general information on the Honda TL125, as well as maintenance and troubleshooting information. If you think something should be added here or want to correct any information please go to the feedback page.

Identifying Various Year Models of the TL125

ModelYearSerial noGas tank
accent color
TL125 (K)1973Frame TL125-1000003 onwards
Engine TL125E-1000001 onwards
Tahitian Red
TL125 K11974Frame TL125-1100001 onwards
Engine TL125E-1100001 onwards
Tahitian Red
Candy Sapphire Blue
TL125 K21975Frame TL125-1200001 onwards
Engine TL125E-1200001 onwards
Tahitian Red
TL125S 761976Frame TL125S-1000417 onwards
Engine TL125S-1000001 onwards
Shiny Orange

Generally the TL125 engines can be divided into one-piece-head (1973 to 1975) and two-piece-head (1976). In the latter the cylinder head breaks horizontally into two, camshaft in between.

Main Differences Between Year Models

ModelYearMain Difference to Previous Year
TL1251973First production year
TL125 K11974Pretty much the same as 1973, some minor differences. Right engine cover slightly different (carries different Hoda part number).
TL125 K21975New front forks (Showa).
TL125S 761976Two piece head, 0.5mm larger bore diameter.

Engine General

YearBore & StrokeDisplacementCRHP
1973 - 197556.0mm x 49.5mm122cc8:18 @ 8000 rpm
197656.5mm x 49.5mm124cc8:18 @ 8000 rpm

Some TL125 Tune-up Information

Engine oil capacity
1.0 liters1.0 U.S. qt.
Front fork oil capacity (reassembly)
130 - 140 cc4.4 - 4.7 fl. oz.
Valve clearance (I&E)
0.05 mm0.002 in.
Spark plug
10.8 - 13.2 kg/cm2156 - 187 psi

Gear Ratios

In TL125 the 1st, 2nd and 3rd are very low and close for off road work, 5th is as long as could be accommodated in the space available and 4th just bridges the gap. Unfortunately, Honda had to change the order of the gears in the cluster and reduce the size of the flywheels to cram it all in. Any major long stroke crank mods will foul 5th gear (I believe you can do about +10mm max, Powroll crank kit is +9.5mm).

Because the gears are reordered, it isn't possible to mix and match gears between TL and it's siblings except in very limited ways. The whole cluster must be replaced as a unit. The TL and CG type clusters will not interchange with the later XL125/185/200 5 or 6 speed internals without using later cases as well.

Thanks for Mark Worsfold for the ratio info.

Final Drive
Front15 teeth
12, 13, 14, 16, 17, 18, 19 also available
Rear60 teeth
40, 49, 52 also available
Chain428 - 120L

Carburetor and Jetting

All TLs have a 20mm Keihin roundslide carburetor (18mm slide). Jetting is slightly leaner on the 1976 S model, I prefer the earlier jetting. But as always with jetting you just have to try and figure out what fits your engine.

1973 to 1975 TL125
Main jet: 95Part #99114-246-0950, Honda code 0173336
Idle jet: 38Part #99124-089-0380, Honda code 0185884
1976 TL125S
Main jet: 92Part #99101-116-0920, Honda code 0426072
Idle jet: 35Part #99103-355-0350, Honda code 0426080

I'm pretty certain the idle jet is Keihin jet type N424-22 and the main jet is Keihin jet type 99101-116 (jet size is added to the end so #35 idle jet would be N424-22-35). I would appreciate if anybody could confirm this.

Replacement Screw Sets

Most of the engine "bolts" in the TL are 6mm Phillips screws. They will get messed up in no time, and are generally just very unpleasant to work with. Following is a list of hex socket head cap screws I have used to replace almost all the Phillips screws in my bike. Sizes are given as dia x length, all threads are "standard metric". Note that there are different number of screws in different year models, quantities below are selected based the highest number required (so don't worry if one or two are left over).

Head Assembly & Ignition
2 pcs4x8 Socket head cap screw
2 pcs5x12 Socket head cap screw
2 pcs6x25 Socket head cap screw
2 pcs5x20 Socket head cap screw flat head
Clutch Side Cover
11 pcs6x40 Socket head cap screw
1 pcs6x50 Socket head cap screw
Magneto and Countershaft Cover
6 pcs6x30 Socket head cap screw
10 pcs6x50 Socket head cap screw

Some good resources on maintenance and tuning:
Back to TL125 homepage

Last modification February 16, 2003
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Honda TL125 Information Page