Keihin CVK Pilot Jets for Carbureted Triumph Twins and Triples
The pilot jet (also called the slow jet or idle jet) meters the fuel for the pilot circuit of a Keihin CVK carburetor. That circuit controls starting, idle and the first part of the throttle opening, from closed throttle to roughly 1/4 throttle, including the move from idle onto the needle circuit. Fit new pilot jets to replace clogged or damaged originals. Or go up a size to cure cold-starting problems, a lean stumble off idle or popping on deceleration after fitting a freer-flowing exhaust or air filter. Each jet is sold individually and fits one carburetor.
Fitment
For Triumphs with Keihin CVK carburetors, including:
- Bonneville and Bonneville T100 (air-cooled, carbureted)
- Thruxton 900 (carbureted)
- Scrambler (carbureted)
- America and Speedmaster (carbureted)
- Keihin-equipped triples: Adventurer 900, Legend TT, Sprint 900, Thunderbird 900, Tiger 885, Trident 900 and Trophy (later models with Keihin carbs, not earlier models with Mikuni carbs)
Not for: fuel-injected Triumphs, or triples fitted with Mikuni BST carbs. For those, use our Triumph Pilot Jet for Mikuni BST Carbs.
Stock pilot jet sizes and tuning guide
- 790cc and 865cc Bonneville, T100, Thruxton and Scrambler: most use size 40 as standard. Size 42 is the common upgrade with aftermarket exhausts and a free-flowing air filter.
- America and Speedmaster: size 42 as standard. Some riders go to size 45 with open exhausts.
- Triples: usually size 38 or 40. Check the size stamped on your old jets.
The size is stamped on the jet. Bigger numbers give a richer mixture. If your bike starts and idles well on stock exhausts, keep the stock size. A pilot jet one size larger is the usual cure for hard cold starts, a lean stumble off idle and exhaust popping on deceleration, especially after an exhaust or intake change. Always make pilot circuit changes alongside the pilot (idle mixture) screw setting and main jet changes, not on their own.
Signs you need new or different pilot jets
- The bike starts only on choke, or won’t idle without the choke after warming up
- The idle hunts, is uneven, or the engine stalls when you close the throttle
- Hesitation or a stumble just off idle
- Popping in the exhaust on deceleration (usually lean)
- Problems after storage: a pilot jet clogged with old fuel is the most common cause of poor idle on a bike that has been sitting
Installation and cleaning tips
- Remove the float bowl. The pilot jet is reached from the float bowl side of the carb. Remove the carbs as described in your workshop manual, then remove the float bowls.
- Use the right screwdriver. Use a screwdriver that fits the jet’s slot exactly. The brass jets are soft and easy to damage.
- Clean, don’t ream. To clean an old jet, push a single strand of copper wire through the fuel passage, then flush it with carb cleaner and compressed air. Tip cleaners can enlarge or scratch the jet and cause erratic fuel flow.
- Check the air holes and taper. Keihin pilot jets have small air bleed holes along the side, so make sure they’re all clear. Also check the taper on the end of the jet and the seat in the carb body. A poor seal here causes a rich, unstable idle.
- Don’t overtighten. Screw the jet in until it seats, then nip it snug.
- Set up after reassembly. Set the pilot (idle mixture) screws, then synchronize the carbs.
See every Keihin CVK circuit explained step by step in our Constant Velocity Carburetor Cleaning and Tuning Tips & Tricks guide.
Parts and tools for the job
- Triumph Main Jet for Keihin CVK Carburetor PN Main-Jet-CVK: rejet the main circuit at the same time
- Triumph Carb Repair Kit for Keihin (1) Carbs PN MBI-182457: a float needle, slotted pilot screw and seals for a full rebuild, at a saving over buying parts separately
- Triumph K&L Float Needle for ’93–08 Keihin Carbs PN MBI-188953
- Motion Pro Carburetor Synchronizer PN MBI-SYNC: balance the carbs after any jet change
- Motion Pro 08-0229 90° Hex Driver Set with D Bit PN MBI-35-7820: turns the original D-head pilot screws. Find it in our workshop tools collection.
Reviving a bike that’s been sitting? Read Resurrecting a Ran-When-Parked, Barn Find, Carbureted Triumph.
Save money with a Keihin carb repair kit.
For main jets for Keihin CVK carbs, click here.
Need a float needle? Click here.
Other Keihin carb parts are available here.
Additional Items to Complement the Pilot Jet:
- Triumph Main Jet for Keihin CVK carburetor
- Triumph Carb Repair Kit for Keihin (1) Carbs
- Triumph K&L Float Needle for ’93-08 Keihin Carbs
This item is not available for sale in nor shipment to California. The California Air Resource Board (CARB) prohibits the sale of this item per California Code of Regulations, Title 13 § 2220 et seq., California Code of Regulations, Title 13 § 2470 et seq., California Vehicle Code §§ 27156 and 38391, and California Health & Safety Code § 43151 et seq. CARB Enforcement Advisory
The product images shown are for illustrative purposes only and may not be an exact representation of the product received. Manufacturers occasionally make minor cosmetic changes to items, such as color, finish, label, or design. These changes do not impact the item’s function or compatibility. Please contact us if you have specific concerns regarding appearance.
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Frequently Asked Questions
What does the pilot jet do on a Keihin CVK carburetor?
The pilot jet meters fuel for the pilot circuit, which controls starting, idle and the first part of the throttle opening, from closed to about 1/4 throttle. It also feeds the transfer ports that bridge idle and the needle circuit.
What size pilot jet does my Triumph Bonneville use?
Most carbureted 790cc and 865cc Bonneville, T100, Thruxton and Scrambler models use a size 40 pilot jet as standard. The America and Speedmaster use size 42. The size is stamped on the jet, so check your originals before ordering.
Should I fit a 42 pilot jet after installing aftermarket exhausts?
Size 42 is the common upgrade for Bonneville, T100, Thruxton and Scrambler twins with freer-flowing exhausts and an air filter, especially if the bike is hard to start cold, stumbles off idle or pops on deceleration. If the bike starts and idles well, the stock size 40 is usually fine.
Does a bigger pilot jet make the mixture richer or leaner?
Richer. A higher number has a larger metering orifice and flows more fuel through the pilot circuit.
How many pilot jets do I need?
One per carburetor, and the jets are sold individually. Order two for a twin, three for a triple, or four for a four-cylinder Trophy 1200. Always run the same size in every carb.
Can I clean my old pilot jets instead of replacing them?
Often, yes. Push a single strand of copper wire through the fuel passage, check that the side air holes are clear, then flush with carb cleaner and compressed air. Replace the jet if the slot is damaged, the taper is marked, or it was cleaned with a tip cleaner, which can enlarge or scratch it.
Do I need to remove the carbs to change the pilot jets?
On most carbureted Triumphs, yes. The pilot jet is reached from the float bowl side, so the carbs normally come off the bike to remove the float bowls. Follow your workshop manual, and synchronize the carbs after reinstalling them.
Should I adjust the pilot screw after changing the pilot jet?
Yes. The pilot (idle mixture) screw fine-tunes the pilot circuit. Reset it after any pilot jet change, then set the idle speed and synchronize the carbs.
Will these pilot jets fit Mikuni BST carburetors?
No. These are Keihin CVK pilot jets. Earlier Triumph triples with Mikuni BST carbs need Mikuni pilot jets, which we also stock.
Can I buy these pilot jets in California?
No. Under California Air Resources Board (CARB) regulations, we can’t sell or ship carburetor jets to California.
