Carburetor and Jetting Guide
The carb your build actually needs, the jets we stock for it, and the tuning process we have used on our own kits since 1995. Honda, Kawasaki, Yamaha and import engines.
One Carb.
Three Jobs.
Start here
A slide carburetor meters fuel through three overlapping circuits, each covering a slice of the throttle range. That is why “it runs bad” is not enough information. Where in the throttle it runs bad tells you which jet to touch.
- Pilot jet and air screw. Idle to about 1/4 throttle. Starting, idle quality and the first crack of throttle.
- Needle and clip. About 1/4 to 3/4 throttle. Where you ride most of the time, and where most rideability complaints live.
- Main jet. About 3/4 to wide open. What the plug chop reads, and the circuit that protects the piston.
Which circuit feeds the engine
fuel vs throttle
The circuits overlap. A pilot change moves the bottom of the needle range, which is why they get tuned in order, bottom to top.
Pick
Your Bike
Which carb for which bike
Bigger is not better. A carb that is too large for the engine drops air speed through the venturi and kills throttle response. These are the pairings TBparts builds its kits around. When in doubt, take the smaller of two sizes.
Honda 50cc and 70cc carbs
The stock Keihin on these engines is tiny and jets in tiny steps: a single size is a real change. For a stock or lightly modified engine, a fresh AFT reproduction carb with the right main is often all it needs. For an 88cc to 117cc bore kit, the TB 20mm is the carb TBparts has built these kits around for over fifteen years. It reuses the stock intake stack on most models, so the install is bolt on.
- Stock and mild engines: 16 to 18mm stock or AFT carb, mains 50 to 67 depending on model
- 88cc to 117cc bore kits: TB 20mm, mains 75 to 115, pilots 30 to 42
- TB 20mm stock jetting is an 89 main and a 35 pilot
- Race heads and ported heads: 22 to 24mm Nibbi PE with the matching intake
Stock replacement3 mains included
AFT Carburetor Kit, Z50R / XR50 / CRF50 '79 and up
Reproduction of the stock carb, close to original, with throttle cable and three main jets to fine tune. The stock main is usually right on an unmodified engine.
$48.99
20mmRace / ported headMost popular
AFT 20mm Performance Carb Kit 2, All Models
Carb, intake for race or ported heads, heat stop, gaskets, hardware, air filter and an adjustable throttle cable. The go to carb for 88cc and up bore kits.
$119.99
Need a jet kit for the TB 20mm?
Mains 75 to 115 across three kits, pilots 30 to 42 across two. The stock 89 main suits most 88cc to 110cc builds.
KLX110 and Z125 carbs
Kawasaki shipped the stock Keihin with five different main jets over the years (72, 75, 78, 80 or 82), so pull the bowl and read yours before ordering anything. A pipe and filter usually want one or two sizes up, and that is the cheapest power on the bike. For a stock bore KLX110, the Nibbi PE22 kit is the one TBparts calls the best carb kit to run. For 143cc and larger, step to a 26mm.
- Stock carb rejet: mains 75 to 115, pilots 38 to 42
- Stock bore with pipe and filter: Nibbi PE19 or PE22 kit
- 143cc to 178cc bore kits: Nibbi PE26 kit or Mikuni VM26 kit
- Race head builds: Nibbi PE28 race head kit
OEM Keihin18mmStock replacement
Keihin 18mm Carburetor, Stock OEM, KLX110 All Models
Genuine Kawasaki replacement with the flat blade adjustable air screw. Bolt on and go. Best price available and free shipping.
$149.99
22mmStock boreBest seller
TB Carb Kit, Nibbi PE22, KLX110
TBparts' pick for stock bore KLX110s. Hard anodized Nibbi PE22 with the TBparts manifold. Does not reuse the stock airbox.
$139.99
26mmBore kits
TB Carb Kit, Nibbi PE26, KLX110
The 26mm kit for 143cc and larger builds. Nibbi PE26 with TBparts manifold, all year models. Polished slide and air passage for consistent power.
$159.99
Rejetting the stock KLX110 carb?
Two main kits cover 75 to 95, the large kit runs 100 to 115, and the pilot kit is 38 to 42.
KLX140 carbs
The KLX140 also left the factory with a spread of mains (90, 92, 95, 98 or 100), so start from what is in the carb. The bike responds well to a simple rejet with a pipe. When you go to a bore kit, the VM26 is six millimeters larger than stock and TBparts pairs it with a billet manifold for an airbox delete, which is where the KLX140 picks up power everywhere.
- Stock carb rejet: mains 82 to 115, pilots 38 to 42
- Bore kits and pipes: genuine Mikuni VM26 kit with billet manifold
- See the KLX140 VM26 install PDF in the Tech Center
Genuine Mikuni26mmAirbox delete
TB 26mm Carb Kit, Mikuni VM26, KLX140
Genuine Mikuni VM26 with a proven record of performance and easy tuning, paired with the TBparts billet manifold for an airbox delete setup.
$222.99
Stock carb6 jets
Main Jet Kit, KLX110 and KLX140, All Models
Sizes 82, 85, 87, 90, 92 and 95 for the stock Keihin. Covers most exhaust and filter changes on either bike.
$11.99
TTR110 carbs
The TTR110 stock carb takes a wide spread of mains, and Yamaha's factory jetting is on the lean side. TBparts sells the 130cc big bore kit with the pod filter and jets included for exactly that reason: the carb needs both when the displacement goes up. On a stock bore with a pipe, start one main size up and plug chop from there.
- Stock carb rejet: mains 95 to 115, pilots 12.5 to 20
- 130cc bore kit: buy the kit with filter and jets included
- Big bore plus pipe: consider a 24 to 26mm Nibbi with the matching intake
130ccJets includedPump gas safe
TB 130cc Big Bore Kit, Air Filter and Jets, TTR110
55.5mm high compression piston kit, as big as the TTR110 goes without boring the cases. Comes with the dual stage pod filter and the jets to run it.
$209.99
Stock carb5 jets
TB Main Jet Kit, TTR110
Sizes 95, 100, 105, 110 and 115 for the stock TTR110 carb.
$13.99
Stock carb4 jets
TB Pilot Jet Kit, TTR110
Sizes 12.5, 15, 17.5 and 20 for the stock TTR110 carb. Fixes off idle stumble after a filter or pipe change.
$15.99
CRF110 carbs
The 2013 to 2018 CRF110 ships with a 68 main, which is lean even for a stock bike, so a 75 or 78 is the usual first move with a pipe. For anything over stock displacement, TBparts calls the Mikuni VM26 perhaps the best carb to run on Honda four strokes above 100cc, and pairs it with the 132cc big bore kit as the best combination on this bike.
- 2013 to 2018 stock carb: factory 68 main, kit covers 75 to 85
- 132cc and 147cc bore kits: TB 26mm Mikuni VM26 kit
- The VM26 works on a stock bore too, but shines with the bore kit
Genuine Mikuni26mmBest with 132cc kit
TB 26mm Mikuni VM26 Carb Kit, CRF110 2013 to 2018
Genuine VM26 with the intake to fit the CRF110. Works great on the stock bore, best with the 132cc kit. The carb TBparts recommends for over 100cc Hondas.
$209.99
Stock carb4 jets
TB Jet Kit, KLX110 and CRF110 2013 to 2018
Mains 75, 78, 82 and 85. The 75 or 78 is the usual first step up from the CRF110's factory 68 with a pipe.
$11.99
TRX90 carbs
The TRX90 is one of the easiest machines to jet because TBparts publishes both stock sizes: an 82 main and a 40 pilot. The TB 20mm kit is built to reuse the stock airbox and intake manifold, so it drops in as a replacement for a tired OEM carb and picks up power with a pipe or bore kit.
- Stock carb: 82 main and 40 pilot from the factory
- Stock carb rejet: mains 82 to 95, pilots 35 to 45
- Worn carb or performance build: TB 20mm kit, reuses the stock airbox
20mmJets includedStock airbox
TB Carb Kit, 20mm with Jets, TRX90
Replaces a worn OEM carb or unlocks more power. Reuses the stock airbox and intake. Comes with an extended throttle cable and jets.
$114.99
OEM carb6 jets
TB Main Jet Kit, TRX90
Sizes 82, 85, 87, 90, 92 and 95 for the OEM carb. Stock is an 82.
$11.99
OEM carb5 jets
TB Pilot Jet Kit, TRX90
Sizes 35, 38, 40, 42 and 45 for the stock N424-74C carb. Factory is a 40.
$17.99
Import engine carbs
Most import engines arrive with a Chinese copy of a Mikuni or Keihin. Those copies are not stamped with a model number, and genuine Mikuni jets do not fit them. The fix for tuning headaches is usually a real carb: a Nibbi PE26 on a 125cc to 160cc, an OKO 26 as the value option, and a Nibbi PE30 or Mikuni VM28 only on the 190cc four valve engines and race builds that have the head to use it.
- YX125, YX140, Lifan 125 and 140: Nibbi PE24 or PE26, or OKO 26
- YX160, ZS155 and 190cc engines: Nibbi PE26 to PE30 depending on head and cam
- Nibbi PE jet ranges: mains 78 to 135, pilots 32 to 40
- Confirm your intake spigot size before ordering a bare carb
26mmAnodizedBest value
Nibbi PE26, 26mm Performance Carburetor
Hard anodized with a polished round slide and smoothed air passage. The splash guard keeps it steady on rough ground. The best value 26mm on the market.
$83.99
26mmValue pick
OKO 26mm Performance Carb
Less expensive than the VM26, reliable and easy to tune, with a full range of TBparts main and pilot jets behind it. Needs a kit intake on most models.
$92.99
30mmRace builds
Nibbi PE30, 30mm Performance Carburetor
For 190cc four valve engines and race builds. On a mild engine a 30mm is a step backward, so match it to the head and cam.
$89.99
Jets for Nibbi PE17 through PE30
Small main kit 78 to 92, standard kit 98 to 122, pilot kit 32 to 40. Also fits the AFT 24 and OKO 26 main kit range.
Bare carbs, any application
Buying a carb on its own makes sense when you already have a TBparts intake from a previous kit, or you are building something custom. The catch on most bikes is the intake: the VM26 and OKO 26 will not fit a stock manifold. Genuine Mikuni VM carbs are stamped with a model number, which is how you know the Mikuni jet kits will fit.
- Mikuni VM24 (512): 88cc to 150cc, 35mm spigot, ships with a 40 pilot and 210 main
- Mikuni VM26 (606): the carb behind every TBparts 26mm Mikuni kit
- Mikuni VM28 (418): flat slide, for engines with the head and cam to feed it
- Nibbi PE22 and PE24: anodized, budget friendly, 22 and 24mm
Genuine Mikuni26mm
26mm Performance Carb, Mikuni VM26
Genuine VM26 606. Will not fit the stock intake on most models; see the model kits above for the correct manifold. One of the best performing carbs on the market.
$142.00
Genuine Mikuni24mmStock jets published
Mikuni Carburetor, VM24
Genuine VM24 512 series for 88cc to 150cc mini bikes. Fits 35mm spigot manifolds. Factory installed jets: pilot 40, main 210.
$186.00
Genuine Mikuni28mmFlat slide
Mikuni VM28 418, Flat Slide 28mm
Mikuni's TM series flat slide: faster, smoother airflow than a round slide. For strokers and race heads.
$155.00
22mmAnodized
Nibbi PE22, 22mm Performance Carburetor
Hard anodized, polished slide, splash guard. The right size for stock bore KLX110s and mild Honda bore kits.
$79.99
24mmAnodized
Nibbi PE24, 24mm Performance Carburetor
Same construction as the PE22 in a 24mm bore. A good fit for 88cc to 125cc builds with a matching intake.
$83.99
Mikuni VM jet kits, genuine carbs only
Mains 140 to 185 and 195 to 240 fit the VM20, 24, 26 and 28. Pilots 15 to 27.5 (VM20/26) and 10 to 30 (VM24/28).
Rich
Or Lean?
Read the engine
Nearly every carb complaint sorts into one of these two columns. Decide which one you are in before you touch a jet, because the fix for one is the opposite of the fix for the other.
Running lean
Not enough fuel
- Pops and bangs on deceleration
- Bogs or stumbles when you snap the throttle
- Hard to start cold, runs fine once warm
- Surging at steady throttle, better with the choke partly on
- Runs hot, pings under load
- Plug is white or light gray after a chop
Fix: air screw in 1/4 turn, then pilot up, clip down, main up. One step at a time. Rule out an air leak first.
Running rich
Too much fuel
- Blubbers and smokes, cleans up when you open it
- Fouls plugs, sooty black deposits
- Hard to start hot, idles rough when warm
- Flat and lazy at wide open, will not rev out
- Strong fuel smell, wet plug after a failed start
- Plug is black and dry, or black and wet
Fix: check filter oiling first, then air screw out 1/4 turn, pilot down, clip up, main down. One step at a time.
How We
Jet A Carb
The method
Change one thing. Ride it. Read it. Change the next thing. Bottom circuit to top, because each one moves the one above it. This is the same sequence TBparts has used on its own carb kits for two decades.
After a bore kit
Ride a session on the new top end, then set valve lash again. Tight valves after break in mimic a jetting problem and no jet fixes them. TBparts spec on its heads and cams: 0.003 inch, intake and exhaust.
1
Check the basics
Fresh high octane pump gas, race gas not needed. A clean, lightly oiled filter, not soaked. Ground wire tight on bare, unpainted metal. Petcock and fuel line flowing. Exhaust gasket in place and the pipe tight. Half of all jetting complaints are one of these five.
2
Confirm the intake stack
On 20mm carb kits the order from the head is: cylinder head, gasket, plastic heat stop, gasket, intake, carb. A missing gasket or a reversed heat stop is an air leak, and an air leak reads as lean no matter what jet you fit.
3
Set the air screw baseline
Back it out 1 3/4 turns from lightly seated. Warm the engine, then adjust in 1/4 turn increments for the cleanest idle and off idle pickup. On the TB 20mm most bikes end up in the 1/2 to 3/4 turn range from there. Past 2 1/2 turns out, the pilot is too small. Under 1 turn, it is too big.
4
Sort the pilot circuit
With the air screw in range the bike should start easily, idle steady and take throttle off idle without a stumble. Stumble that clears with more throttle: lean pilot. Popping on decel: lean pilot or an exhaust leak. Fouled plugs and a rough hot idle: rich pilot.
5
Set the needle
Ride at steady 1/4 to 3/4 throttle. Flat or surging midrange that improves with the choke partly on is lean: drop the clip one notch to raise the needle. Blubbery midrange that cleans up when you open it is rich: raise the clip one notch. Start in the middle groove.
6
Plug chop the main
Fresh plug. Long stretch at wide open in a high gear, kill it at full throttle, coast to a stop, pull the plug. Light brown or tan is right. White or gray is lean: main up one. Black and sooty is rich: main down one. Repeat the chop after every change.
Jet Sizes We
Stock, By Carb
The reference
Every range is the span of jets TBparts sells for that carburetor. Where a factory stock size is published it is listed, because the right starting point is the jet already in the carb, not a number from a forum. Jet numbers are not interchangeable between families: a 110 in a Mikuni is a different orifice than a 110 in a Nibbi.
| Carburetor | Main jets | Pilot jets | Stock size | Notes |
|---|---|---|---|---|
| Mikuni VM20 (273) and VM26 (606) | 140 to 240 | 15 to 27.5 | not published | Genuine Mikuni only. Main kits 140 to 185 and 195 to 240. |
| Mikuni VM24 (512) | 140 to 240 | 10 to 30 | Pilot 40, main 210 | Factory installed jets are published on the VM24. Pilot kits 10 to 17.5 and 20 to 30. |
| Mikuni VM28 (418) flat slide | 140 to 240 | 10 to 30 | not published | Same jets as the VM24. |
| Nibbi PE17 through PE30 | 78 to 135 | 32 to 40 | not published | Small main kit 78 to 92, standard 98 to 122, plus the 85 to 135 kit shared with the AFT 24 and OKO 26. |
| TB 20mm carb | 75 to 115 | 30 to 42 | Main 89, pilot 35 | Drop to 75 to 80 on 72cc and smaller. Go to 100 and up with a bore kit and pipe. |
| AFT 24mm carb | 85 to 135 | 35 to 48 | not published | Shares the 85 to 135 main kit with the OKO 26 and Nibbi. |
| OKO 26mm and TB 28mm | 85 to 160 | 38 to 44 | not published | Standard main kit 85 to 135, large kit 140 to 160. |
| Stock Keihin, KLX110 and KLX110L | 75 to 115 | 38 to 42 | Main 72, 75, 78, 80 or 82 by year | Read the jet in the bowl before buying. |
| Stock Keihin, KLX140 | 82 to 115 | 38 to 42 | Main 90, 92, 95, 98 or 100 by year | Five factory sizes, same as the KLX110. |
| Stock Keihin, CRF110 2013 to 2018 | 75 to 85 | n/a | Main 68 | Lean from the factory. 75 or 78 is the usual first move with a pipe. |
| Stock carb, TRX90 (N424-74C) | 82 to 95 | 35 to 45 | Main 82, pilot 40 | Both stock sizes published. One of the easiest to jet. |
| Stock carb, TTR110 | 95 to 115 | 12.5 to 20 | not published | The 130cc kit is sold with jets and a pod filter for this reason. |
| Stock and AFT carb, CT70 K0 to '77 | 58 to 67 | 35 to 40 | Pilot 35 | Pilot kit fits the TBparts CT70 carb only. Main kit fits AFT and OEM K0 to '77. |
| AFT carb kit, Z50R, XR50, CRF50 | 57 to 61 | n/a | not published | Replacement mains for the TBW9156 carb kit. |
| Stock Keihin, Honda 50 and 70 | 50 to 59 | n/a | not published | Small carbs jet in small steps. One size is a real change. |
Jets are non returnable. Every kit page lists exactly which carbs it fits. Genuine Mikuni VM carbs are stamped with their model number (273, 512, 606, 418); the Chinese copies on most pit bikes are not, and Mikuni jets will not fit them.
Symptom
To Fix
Troubleshooting
Work top to bottom. The cheap, mechanical causes are listed before the jetting causes on purpose.
| Symptom | Most likely cause | What to do |
|---|---|---|
| Hard to start cold, fine once warm | Lean pilot circuit | Air screw in 1/4 turn. If it wants less than 1 turn out, pilot up one size. |
| Hard to start hot, fouled plug | Rich pilot, or an over oiled filter | Clean and lightly re oil the filter. Air screw out 1/4 turn. Past 2 1/2 turns, pilot down one. |
| Bogs when you snap the throttle | Lean off idle, or an air leak | Confirm the intake stack and gaskets first. Then air screw in 1/4 turn, then pilot up. |
| Stumbles or surges at part throttle | Needle clip position | Clip down one notch (richer). If it gets worse, go back and raise it one instead. |
| Flat on top, no pull past 3/4 | Main jet too small | Plug chop. White or gray plug: main up one. |
| Blubbers and smokes at wide open | Main jet too big | Plug chop. Black plug: main down one. |
| Pops and bangs on decel | Exhaust leak, or lean pilot | Reinstall the exhaust gasket and tighten the pipe. If it persists, air screw in 1/4 or pilot up. |
| Runs great, then fades and stalls | Fuel delivery, not jetting | Petcock, fuel line, tank vent, float level. A blocked vent starves the carb after a few minutes. |
| Runs like a carb problem, plug looks right | Electrical | Ground wire on bare metal and tight. A bad ground mimics a carb problem so often TBparts lists it first. |
| Knocking after a bore kit | Cam timing or clutch nut, not the carb | Cam lobes down toward the piston with the marks aligned. Clutch nut torqued with a clutch nut socket. |
Elevation,
Weather, Mods.
Why jetting drifts
A carb meters air by volume; the engine burns it by mass. Anything that changes air density changes the mixture. That is why a bike jetted at the beach runs rich in the mountains and a bike jetted in July runs lean in January.
Going up in elevation
Thinner air, so the same jet runs richer. About one main size leaner for every 2,000 to 3,000 feet is the usual starting move. Above 5,000 feet the pilot often needs to come down a size too.
Cold weather
Denser air, so the same jet runs leaner. Winter usually wants one main richer than summer, and the choke sees more use.
Exhaust and filter
More air needs more fuel. A pipe is often one main up. A pod filter one more. Small changes, but they stack.
Bore kit
A bore kit with a pipe is a different carb size, not a jet change. The stock carb becomes the restriction. See the carbs by bike above.
Carburetor
Questions
Get some answers
What size carburetor should I run on a pit bike?
Match the carb to the engine. Stock 49cc to 72cc engines and mild bore kits run best on 18 to 20mm. Bore kits from 88cc to 117cc on Honda cases run 20 to 24mm. The 130cc to 147cc KLX110, TTR110 and CRF110 kits are built around a 26mm, usually the Mikuni VM26 or Nibbi PE26. Only strokers, big import engines and race builds benefit from 28 to 30mm.
How do I know if my pit bike is running rich or lean?
Read the spark plug after a plug chop. Light brown or tan is correct. White or gray means lean; black and sooty means rich. Symptoms help too: lean engines pop on decel, bog off idle and run hot; rich engines blubber, smoke and foul plugs. The rich or lean comparison on this page lists both columns.
What is a plug chop?
Fit a fresh plug, ride at wide open throttle in a high gear for a long stretch, hit the kill switch while still at full throttle and coast to a stop. Remove the plug and read the color. Because you killed it at full throttle, the plug shows only what the main jet was doing.
Where should the air screw be set?
TBparts starts every carb at 1 3/4 turns out and adjusts in 1/4 turn increments once the engine is warm. If the best idle is beyond about 2 1/2 turns out, the pilot jet is too small. If it is under 1 turn, the pilot is too big.
Do Mikuni jets fit Chinese carbs?
No. TBparts Mikuni jet kits fit only genuine Mikuni VM carbs, which are stamped with a model number: VM20 273, VM24 512, VM26 606 and VM28 418. The copies that come on most pit bikes use different threads and orifice sizing, and no pit bike ships with a genuine Mikuni. Jets are non returnable, so check before buying.
What main jet comes stock in a KLX110?
Kawasaki used five different sizes over the years: 72, 75, 78, 80 or 82. Pull the float bowl and read the number stamped on the jet before ordering. The CRF110 from 2013 to 2018 ships with a 68 main, the TRX90 ships with an 82 main and a 40 pilot, and the Mikuni VM24 ships with a 40 pilot and 210 main.
Why will the Mikuni VM26 not fit my stock intake?
The VM26 uses a different spigot and bolt spacing than the stock carb on most models. TBparts sells it in complete kits that include the correct intake manifold for your bike. Buying the carb alone works only if you already have a kit intake.
My bike knocks after installing a bore kit. Is it jetting?
Almost never. The two common causes are the camshaft installed with the lobes facing up instead of down toward the piston, and a clutch nut that was not torqued with a proper clutch nut socket. Fix those before touching the carb.
Shop carburetors by bike
More from the Tech Center: spark plug chart, engine build specs, big bore kit guide.
