DFI engine & exhaust — full removal & refit

DFI engine & exhaust — full removal & refit

Watch the walkthrough

Watch on YouTube ↗ · Jetboard Australia — "Jetsurf DFI Engine and Exhaust Removal, How to save you Hassles" (~38 min). Timestamps below follow the video's own time.

This is the long-form version of the job — a full teardown and rebuild filmed on a late-model DFI, with a conversion to the newer quieter exhaust along the way. It maps to JETSURF's own Engine & exhaust removal and Engine & exhaust installation guides, but with far more detail on the connectors, the coupling, and the exhaust valve.

Tools

• Long-nose / pointy pliers
• Side cutters
• 4 mm socket-head Allen key + a 1/4" drive ratchet + an extension with a pivot/knuckle joint (for the engine-mount Allen heads)
• 5 mm Allen key (M6 engine bolts)
• 2.5 mm Allen key (earth lead)
• 3.5 mm Allen key (silencer screw — has a brass washer)
• JetSurf spark plug tool (a long one helps)
• Hooked screwdriver (to draw the exhaust valve back)
• Small cable ties
• Lanox spray (lubricant / protectant)

Remove the fuel tank — 0:43

1. 0:45 — Engine cover off, set aside.
2. 1:04 — Undo the Velcro strap.
3. 1:04 — Release the fuel-line connector — press the button on the inside of the connector.
4. 1:16 — Unclip the fuel-pump wire below it — tiny clip, catch it with a fingernail.
5. 1:27 — Pull the hose clear (it gets in the way).
6. 1:33 — Release the rear breather tube — pull the fitting towards the tank and slide it out.
7. 1:44 — Lift the tank out.

Engine-mount bolts & spark plug — 1:44

8. 1:52 — Four engine mounts, tight under each side. Each can be undone by its nut or its Allen head — the Allen heads are easier. Use the 4 mm socket-head Allen key with the pivoting extension and small ratchet.
9. 2:26 — Undo the first mount screw — it has a big washer, keep it for reassembly.
10. 2:41 — Undo the mount at the other end.
11. 2:58 — Remove the spark plug retainer and push the spark plug cap off (two fingers). The plug has to come out to clear the engine anyway.
12. 3:21 — Undo the far-side mount using the long extension + swivel head to reach the Allen key.
13. 3:52 — Remove the spark plug with the JetSurf tool; tap to loosen. 4:13 — Inspect it (a darker centre is normal on a two-stroke), then replace it as part of the job.
14. 4:32 — Remove the last engine mount at the back. (On this board there's an aftermarket intake sock over the intake — pull it to reach the mount.)

Disconnect the ancillaries — 5:13

15. 5:19 — Throttle position sensor — simple clip, unclip.
16. 5:24 — Fuel injector connector — press-clip, release.
17. 5:31 — Cooling lines — push-snap connectors: pull the ring back and they come off.
18. 5:37 — Nip the exhaust cooling tube off with side cutters. Keep every offcut and cable tie out of the engine bay — debris ends up inside the engine.
19. 6:01 — Remove the two exhaust springs with long-nose pliers — there's a lot of load. The centre O-ring slides off later.
20. 6:43 — Remove the earth lead at the starter — 2.5 mm Allen key.
21. 7:08 — Release the two low plugs: the timing-sensor plug (fingernail on the clip) and the starter-motor plug (harder to reach, same clip). A small O-ring holds the pair together — keep it with them. See Setting the timing sensor.

Engine cradle & throttle cable — 7:40

22. 7:46 — Undo the two front engine mounts (4 mm Allen key) so the engine cradle can come out.
23. 8:00 — Undo the mount under there; loosen the high-pressure fuel hose at the injector.
24. 8:11 — Disconnect the throttle cable at the front bracket (larger Allen key) and move it clear.
25. 8:57 — Note the two coupling collars/sleeves — they're different. The one with the bigger flange goes on the end where the throttle-cable outer sits. Remember this for reassembly.
26. 9:17 — Snip the last cooling tube; keep the cable tie out of the bay.

Separate the coupling & lift the engine out — 9:27

27. 9:35 — Free the exhaust and the coupling — O-rings on the exhaust side, give it a wriggle. The coupling pops out: a three-leg coupling with small white cush drives — keep them in place.
28. 9:52 — Tip the engine on its side and slip the throttle cable off.
29. 10:03 — Carefully lift the engine out.

Remove the exhaust — 10:14

30. 10:20 — Remove the rear silencer — 3.5 mm Allen key on the internal screw (it has a brass washer — don't lose it). The silencer then pulls off; O-rings each end.
31. 10:44 — Remove the retainer flange holding the exhaust-valve assembly.
32. 10:51 — The exhaust valve is an end cap with an eccentric that sets the position between the exhaust valve and the jet-pump inlet. Inside: a ball, a spring, and a lip seal.
33. 11:16 — Inspect: grooves / melting / distortion on the ball or valve = overheating. Check the lip seal for wear, splitting, or corrosion. The plastic housing is designed to melt as a warning — replace it if it's distorted.
34. 11:46 — With the flange off, that section of exhaust slides back through into the board.
35. 11:58 — Pull the exhaust through — big O-ring on the rear, wriggle it loose and it pops out.

Inspect the exhaust & driveline — 12:15

• 12:21 — Check every O-ring is in place; check the silencer hasn't melted (it's sacrificial).
• 12:33 — Rattle test — early boards have an aluminium centre that corrodes and breaks up; newer ones are stainless.
• 12:40 — Check joints for corrosion and leak marks.
• 12:47 — Pipe colour: black is healthy; chocolate brown means it's been overheated — inspect it hard.
• 13:00 — Blow compressed air back through the cooling line — an overheat means the exhaust / engine cooling system is blocked.
• 13:18 — With the engine out, spin the driveline — smooth, no end play = driveline and jet-pump bearings are good.
• 13:36 — Check the small cush drives (don't pull them right out — they spring loose and are hard to refit).

Clean the engine compartment — 13:53

36. 13:59 — Wipe the bay down. If it's full of sand and grit, wash it out — grit gets drawn through the intake and dents the cylinder.

Fit the new exhaust — 14:24

37. 14:52 — Lube with Lanox spray around the front and around the valve at the back.
38. 15:03 — Slide the exhaust into the big cavity. Orientation matters — exhaust tube and clips facing the right way, with the MSR (or JetSurf) symbol at the top.
39. 15:28 — At the back, align the valve with a finger and wriggle it in. Wrap the throttle cable into the tank strap to keep it out of harm's way.
40. 15:44 — The lubricated big O-ring slides home — you'll feel it seat. MSR symbol up, valve at the back in position (it may need to draw back a little further, next).

Set the exhaust valve (eccentric) — 16:03

41. 16:09 — Draw the valve back into the board a couple of mm — flush with the end of the board — so the silencer fitting seats neatly. Use a hooked screwdriver, hook it in and pull gently.
42. 16:28 — Check the pipe is home on that end (the O-ring catches — push it through).
43. 16:46 — Hands off. Unscrew the little valve cap; the spring comes out.
44. 17:13 — Remove the shipping safety cap and fit the original eccentric cap instead.
45. 17:24 — Fit the ball and spring — don't let the ball drop into the spring or the valve won't close. Stretch/tweak the spring slightly so the ball sits square.
46. 17:51 — Fit the original end cap (light spray on it) — very fine thread, don't cross-thread. Tighten firmly and tap it up hard against the board.
47. 18:15 — Fit the eccentric with its O-ring — O-ring seated, light spray, then the eccentric with the indent inwards and the silencer cavity outwards. End cap on with a little spray.
48. 18:55 — Don't tighten the eccentric screw yet — it has to turn to line everything up.
49. 19:12 — Silencer: two O-rings, one each end. Fit it, then rotate the eccentric until it all lines up.
50. 19:38 — Once aligned, snug the eccentric's Allen screw (thread-lock optional), then tighten the ring on the eccentric.

Reinstall the engine — 20:14

51. 20:34 — Throttle cable first. Turn the engine on its side — ball-and-slot fitting, like a motorcycle. It seats down behind, with the correct spacer (big ring vs small ring — the ring retains the cable). Route the cable behind the little tab that keeps it out of the gear. Get this wrong and you pull the engine again.
52. 21:36 — Spray the O-rings on the exhaust and the coupler.
53. 21:42 — Check the engine turns — free one way (one-way bearing), tight the other (turning the starter gear) — confirms the starter clutch works. See Starter removal & installation and Freewheel removal & installation.
54. 22:10 — Line up the three-leg drive coupling, the exhaust, and the two exhaust-spring tabs against the tabs on the motor (that's what the MSR-at-top orientation is for).
55. 22:40 — Wriggle the engine into place — it takes some pushing.
56. 22:52 — Reconnect the cooling quick-release fittings (push forward, slide in, confirm locked). Fit the new exhaust tube. Zip small cable ties on the tube joints — low pressure, just so vibration can't walk them off. Fit the telltale cooling line (the flow indicator that also bleeds water through the head).
57. 24:14 — Refit the engine cradle. Get the angle right; the notch for the fuel-injection hose faces the throttle body, kinked that way. Fuel-injection hose clip at one end; the flanged spacer holding the throttle cable at the other.
58. 25:05 — Working under the engine, keep the throttle cable positioned, keep the fuel-injection hose-clamp tab in place, feel for the thread and screw it in.
59. 25:30 — Other end: the spacer without the flange, spigot to the arm, onto the cylinder-head end. Bolt in — not super tight.
60. 27:07 — Refit the fuel-injection line on its clip (rubber slides over).
61. 27:20 — Engine bolts — M6, 5 mm Allen key. Start each bolt into the engine bracket, lift the engine, line up the thread. Don't tighten anything until all four are started. Then torque them down.

Reconnect the ancillaries — 28:43

62. 28:48 — Throttle position sensor — push back into place.
63. 28:55 — Throttle cable at this end — locate the cable in its groove and fit the screw. Don't overtighten — it squashes the cable and stiffens the throttle. Firm only. 29:38 — Check the throttle returns smoothly.
64. 29:50 — Starter-motor plug first (it's at the back) — listen for the click, then tug to confirm.
65. 30:11 — Earth lead — back through its O-ring, tiny screw, steady it with the cable, line it up, not too tight.
66. 30:54 — Fuel injector — wait for the clip, fit the cover. Don't pull the sheath too far (the end frays).
67. 31:19 — Spark plug — fiddly, work the angle. JetSurf spanner, not too tight. Fit the retainer.
68. 31:56 — Exhaust springs — patience. Long-nose pliers hooked behind with room to move, clip in. The bottom one is the awkward one. Both springs are identical — either side.
69. 32:53 — Spark plug cap and boot — dry, no oil, grease, or salt water (salt can arc). Push in from both ends; the small cap goes over the plug nut.
70. 33:34 — Fit the intake sock (aftermarket splash cover). Cable-tie it between the two grooves on the throttle-body end, sock positioned upward — splash comes from below.

Refit the fuel tank — 34:47

71. 34:53 — Breather tube — push in, pull the little ring back to lock.
72. 35:06 — Watch the back strap — don't trap it between the fittings or it kinks. Tube behind the back strap; front strap against the motor.
73. 35:31 — The rubber knob seats into a cavity in the tank and holds it. Strap set, tank vertical, drop it in and wriggle it onto the knob.
74. 36:02 — Fuel-pump wire first (it's at the bottom), then the fuel-injection line — wait for the snap. See Fuel tank removal & installation.

Test start — 36:18

75. 36:24 — Lanyard in — the ECU initialises, green light flashes = ready.
76. 37:04 — Key in again — it fires within about three seconds.
77. 37:16 — To stop: let it time out (green flashes, bilge pump runs 3–5 min) or put the key to the LED to power off.