K&L 18-3720 Float Bowl Drain Screw for Triumph Keihin CVK Carburetors
The K&L 18-3720 is a replacement float bowl (float chamber) drain screw for the Keihin CVK carburetors on carbureted Hinckley Triumphs. These include the air-cooled Bonneville, T100, Thruxton, Scrambler, America and Speedmaster twins, plus the later Keihin-equipped 885cc triples and the Trophy. It replaces Triumph part number T1241034. Fit a new one when the original is stripped, rounded, seized or leaking. A working drain screw lets you empty the float bowls before storage or transport, and lets you check fuel level with the carbs still on the bike.
Why the float bowl drain screw matters
Fuel left in the float bowls evaporates and leaves behind a gummy residue. The tiny pilot jet, emulsion tube air holes and transfer ports in a CV carb are the first passages to clog. That residue is the main cause of hard starting, a hunting idle and a stumble off idle after storage. As our carb cleaning guide puts it, most spring workshop jobs in the 1990s were carb cleanings on bikes parked all winter with fuel in the bowls. We recommend draining the float bowls whenever a carbureted Triumph will sit for more than about three weeks.
A drain screw that’s rounded, seized or weeping fuel makes this simple job impossible, so many owners skip it and pay for a carb cleaning in the spring. A new screw costs far less than a strip and clean.
Fitment
Fits Triumph Keihin CVK carburetor assemblies T1240650, T1240660, T1240670, T1240680, T1240932 and T1245050. On the triples, Triumph switched from Mikuni BST carbs to Keihin CVK carbs partway through production, so check your VIN against the cut-in numbers below.
- Adventurer 900 (after VIN 62507)
- America (carbureted)
- Bonneville and Bonneville T100 (air-cooled, carbureted)
- Legend TT (after VIN 62393)
- Scrambler (carbureted)
- Speedmaster (carbureted)
- Sprint 900 (after VIN 55881)
- Thruxton 900 (air-cooled, carbureted)
- Thunderbird 900 (after VIN 62393)
- Tiger 885 (after VIN 55615)
- Trident 900 (after VIN 55880)
- Trophy (after VIN 29156)
Sold individually: each carburetor has one drain screw. Order two for a twin, three for a triple, or four for a four-cylinder Trophy 1200.
Not for: fuel-injected Triumphs, or triples built before the VIN numbers above, which have Mikuni BST carbs.
How to drain the float bowls
- Turn the fuel petcock to OFF and let the engine and exhaust cool.
- Put a short length of fuel-safe hose on the float bowl drain nipple and run it into an approved fuel container.
- Loosen the drain screw a few turns and let the bowl empty completely. Do one carb at a time.
- Snug the drain screw closed. Don’t overtighten it: the screw and float bowl are small and easily damaged.
- Wipe up any spilled fuel and check each drain for drips before you put the bike away.
Follow the procedure in your Triumph service manual or owner’s handbook. Work in a well-ventilated area away from sparks, flames and pilot lights.
Check fuel level with the carbs on the bike
The drain screw also lets you check float level without removing the carbs. Fit a clear hose to the drain nipple and hold it upright beside the carb. Loosen the drain screw just enough for fuel to flow into the hose, then turn the petcock to PRI. (On California models, turn the ignition on so the float bowl vent solenoid opens.) The fuel in the tube should sit 1.5 mm (±1 mm) above the float bowl gasket surface, roughly 1/16″–3/32″. Triumph’s dealer tool for this, 3880125-T0301, is just a clear hose with markings, and a battery vent hose does the same job. Read the full procedure in our Constant Velocity Carburetor Cleaning and Tuning Tips & Tricks guide.
Related parts and guides
- Triumph Carb Repair Kit for Keihin (1) Carbs PN MBI-182457: a float needle, pilot screw and seals for a full rebuild
- Triumph K&L Float Needle for ’93–08 Keihin Carbs PN MBI-188953: cures fuel overflowing from the bowls
- K&L 18-4645 Keihin Carb U-Ring PN MBI-CVK65953: stops fuel leaks between the carbs
- Motion Pro Remote Fuel Bottle PN MBI-AUX-FUEL: runs the engine with the tank off while you tune or troubleshoot
Bringing back a bike that sat with fuel in the bowls? Start with Resurrecting a Ran-When-Parked, Barn Find, Carbureted Triumph.
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 K&L 18-3720 drain screw fit?
It fits the float bowls of Triumph Keihin CVK carburetor assemblies T1240650, T1240660, T1240670, T1240680, T1240932 and T1245050. These are used on carbureted air-cooled Bonneville, T100, Thruxton, Scrambler, America and Speedmaster twins. It also fits the Adventurer 900 after VIN 62507, Legend TT and Thunderbird 900 after VIN 62393, Sprint after VIN 55881, Tiger 885 after VIN 55615, Trident after VIN 55880, and the Trophy after VIN 29156.
What Triumph part number does K&L 18-3720 replace?
It replaces Triumph T1241034, the float chamber drain screw for Keihin CVK carburetors.
How many drain screws does my Triumph need?
One per carburetor. The screw is sold individually, so order two for a twin, three for a triple, or four for a four-cylinder Trophy 1200.
Why should I drain the float bowls before storage?
Fuel left in the float bowls evaporates and leaves a residue that clogs the pilot jet, emulsion tube air holes and transfer ports. Draining the bowls before a bike sits for more than about three weeks prevents most hard-starting and off-idle stumble problems after storage.
How do I drain the float bowls on Keihin CVK carbs?
Turn the petcock off and fit a hose from the float bowl drain nipple to a fuel container. Loosen the drain screw a few turns until the bowl empties, then snug it closed. Do one carb at a time and check for drips afterward.
Can I check float level using the drain screw?
Yes. Fit a clear hose to the drain nipple and hold it upright next to the carb. Loosen the drain screw just enough for fuel to flow, then turn the petcock to PRI. The fuel level should be 1.5 mm (±1 mm) above the float bowl gasket surface. On California models, turn the ignition on so the float bowl vent solenoid opens.
My drain screw is leaking or stripped. Do I need to remove the carbs?
Usually not. On most bikes the drain screw can be reached with the carbs installed. Turn off the fuel, drain the bowl, then remove the old screw and fit the new one. If the screw is seized, use penetrating oil and a correctly sized screwdriver bit, and work carefully to avoid damaging the float bowl.
Does this drain screw fit Mikuni BST carburetors?
No. It’s for Keihin CVK carbs only. Earlier Triumph triples with Mikuni BST carbs use a different float bowl arrangement, which usually needs an adapter such as Triumph 3880120-T0301 to check fuel level.
Can I buy this drain screw in California?
No. Under California Air Resources Board (CARB) regulations, we can’t sell or ship this item to California.
