Carburettor, fuel tank & throttle cable service

Carburettor, fuel tank & throttle cable service

Watch the walkthrough

Watch on YouTube ↗ · Jetboard Australia — "Ultimate Guide to Jetsurf Carburettor, Fuel Tank, and Throttle Cable Service" (~42 min). Timestamps below follow the video's own time.

A carbureted GP board (go-kart-style carb with mixture screws) that's been sitting: the carb needs an overhaul, the ICU battery is flat, and the throttle is sticky. This covers the lot — and the fuel-tank breather-valve test that catches a very common older-board fault.

Tools & supplies

• 5 mm Allen key on a 1/4" drive, cut to length so it clears the carb screws without removing the engine (Rod's own tool)
• 1/4" drive ratchet; flat-blade and small Phillips screwdrivers; pointy-nose pliers
• Carburettor / combustion-chamber cleaner (engine conditioner) + compressed air
• Mikuni pop-off pressure tester (with a JetSurf carb adapter)
• Motorcycle cable lubricator + insulation tape + a graphite penetrating lube (e.g. Würth Rust Off)
• Lanox spray, grease
• Carb rebuild kit (diaphragms, gaskets, needle & seat, spring) — from JetSurf, only if parts fail inspection
• New carb-mount gasket; small syringe for priming; a spare offcut of breather tubing

Remove the fuel tank & carburettor — 0:44

1. 1:01 — Remove the fuel tank: unclip it, hold the hose up (it tangles), work it out. Pull the little breather valve off the back.
2. 1:53 — You don't need to pull the engine. Use a 5 mm Allen key on a 1/4" drive, cut to a length that just reaches the two carb Allen screws.
3. 2:32 — Loosen and remove both carb screws (one each side — the lower one is tight, but the cut-down tool reaches).
4. 2:51 — Flick the small throttle-cable clip off, lift the carb away. Check the gasket is present and in good condition.

Overhaul the carburettor — 3:14

5. 3:20 — General inspection. Check the butterfly shaft for slop — a worn shaft causes idle problems.
6. 3:38 — Top cover off (flat-blade screwdriver): behind it is the inlet filter and its seal. Wash the filter in petrol / carb cleaner.
7. 4:12 — Split the diaphragm stack piece by piece. The orange/yellow pulse line feeds crankcase pressure in to oscillate the pump diaphragm.
8. 5:03 — Fuel-pump diaphragm & check valves — the little check-valve flaps must sit flush with the body; if they're curled, replace them. Clear any debris. These and the diaphragm are the two most important parts.
9. 5:44 — Metering diaphragm & gasket — this vacuum-carb diaphragm works the needle & seat. Check for holes, distortion, a hard/dried disc, and a bent centre pin.
10. 7:01 — Needle & seat — undo the retaining screw a little (spring-loaded), slide the rocker arm out with pointy-nose pliers, lift the needle. A viton-tip needle always has a small groove — that's normal; replace only for a big groove or tip wear. Replace the needle and seat as an assembly.

Set the mixture screws — 8:25

11. 8:25 — Before removing them, note where they are. The plate on the carb gives the factory settings: high speed 1.5 turns out, low speed 1.25 turns out.
12. 9:12 — Wind them out gently — never seat them hard. The fine needle tip and the aluminium bore both damage if forced, and the mixture will never match the plate again.
13. 9:49 — Check the tip for a groove (a light mark is fine, a groove is not), the small O-ring for condition, and that the screw isn't seized with salt. Clean, fresh O-ring, light grease.
14. 10:34 — Clean the carb: squirt combustion-chamber cleaner down the low-speed and needle-and-seat holes and over the body — it foams and soaks through the tiny progression holes. Leave it to soak ~1 hour.
15. 12:23 — Blow the carb through with compressed air, making sure the small progression holes are clear — a blocked progression hole causes a flat spot, poor throttle response and hard starting.

Reassemble the carburettor — 12:55

16. 13:01 — Fit the needle-and-seat: spring in its hole first, then the needle (clean tip), then the rocker arm — the clevis must go through the clip, and the needle spring must sit in the ball depression on the arm. Slide the axle in, hold it, fit the retaining screw — firm, not tight.
17. 14:15 — The metering valve arm must be exactly flush with the carb body. Too low: bend the arm up and tap it to settle. Too high: hold the needle end and push it down. Get it dead flush.
18. 14:56 — Rebuild the diaphragm stack. Line up the dowel pins and the moulded "bump" on each layer so everything registers. Order: metering diaphragm + gasket → fuel-pump diaphragm with check valves → its gasket → top casting. Reuse parts that pass inspection; fit a JetSurf carb kit if any failed.
19. 16:53 — Screws back in — firm enough to seal, not super tight. Keep the settings plate next to its screws.
20. 17:43 — Refit the filter the same way round (there's a locating groove), filter first, then the seal, then the cap. Fit the cap facing the tank — opposite the mixture screws — or the tank won't go back in.

Fit the mixture screws & pop-off test — 18:48

21. 18:54 — Lanox in the holes, light grease on the O-rings (keep it off the tips). Wind each screw in until it just seats gently, then out: high speed 1.5 turns, low speed 1.25 turns. Fine-tune on the water later.
22. 19:52 — Pop-off test with the Mikuni tester + JetSurf adapter. Pump up slowly: the needle & seat should hold steady (a dropping gauge = a leaking seat). It should pop off at roughly 12–16 psi and settle back to just under 12 psi, holding there. It must hold below ~10 psi. This also leak-tests the filter gasket and every lamination.

Refit the carburettor — 23:00

23. 23:04 — New gasket on the two dowel pins, with the pulse-line hole lined up (gasket to carb to manifold).
24. 23:36 — Slide the carb onto the dowels. Start the top screw hand-tight to hold it, then the lower one, then tighten both with the cut-down tool.

Free & lubricate the throttle cable — 24:30

25. 25:02 — Unscrew the cable bracket at the cylinder; the clamp can stay. Ease the cable back through — if it snags in the gears, remove the clutch/gear cover (two small Allen keys) to see what's going on.
26. 26:27 — Wrap a little insulation tape around the cable end so it seals in a motorcycle-style cable lubricator, then clamp the lubricator on.
27. 27:29 — Use a graphite penetrating lube (Würth Rust Off or similar) — it lines the cable, and breaks down rust and corrosion. Hit it, catch the mess with a rag; it pressurises the cable.
28. 28:57 — Keep working it in from both ends and rotating the assembly until lube comes cleanly out the far end — that means it's reached all the way through.

Refit & adjust the throttle cable — 30:58

29. 31:05 — Feed a draw wire (speaker wire) through the route first — under the washer on each lower seal-assembly bolt (holding the cable away from the gear and against the crankcase), between the pulse-line tube, onto the carb arm. Tape a loop on the cable end and pull it through.
30. 33:19 — Push the cable end onto the carb arm with a flat-blade screwdriver; check it's seated.
31. 33:44 — Fit the cable into the bracket. The thin side of the bracket goes against the cylinder, the thick side against the fuel tank, cable on the top side.
32. 34:29 — Set the free play: pull the cable almost tight, then check the throttle. You want near full throttle with the tiniest bit of play at idle.
33. 35:01 — Don't overtighten the clamp — it squashes the cable and the throttle stiffens and won't return (the carb return spring is weak). Just firm. Test it returns cleanly.
34. 35:39 — Refit the clutch/gear cover (covered separately) and the carb cover.

Test the fuel-tank breather valve — 36:24

35. 36:30 — The Achilles heel of these tanks: the breather valve blocks with salt and corrosion, so air can't replace the fuel being used. The tank sucks in, pressure drops, the carb can't draw fuel, the board stops. (On the water: pull the cap and you'll hear it suck.)
36. 37:07 — Bench test: push an offcut of breather tube onto the valve and blow — air should pass into the tank. Then check it doesn't leak fuel back out.
37. 37:44 — While you're there, check the filter floating in the bottom of the tank — if it's manky, undo the rear Allen screws, pull it, clean it, reassemble on its gasket. Every tank (carb or injected) has this same valve — check it.

Refit the tank, prime & test start — 38:22

38. 38:28 — Fit the breather tube (pull the collar back, push in, check it's tight). Route the tube behind the rear tank strap so it can't kink. Tip the tank up, press it onto its rubber mount, do the Velcro.
39. 39:05 — Priming trick for carbureted boards: take a small syringe of fuel from the tank (about a thimble) and squirt it down the carb — a dry carb takes a while for the little fuel pump to fill.
40. 39:55 — Lanyard in — bilge pump runs, green light flashes. Key in to fire. It may take a couple of goes on a freshly overhauled carb while the pump pulls fuel through. Run it out on the hose once it catches.