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Discussion Starter #1
My Yamaha 2008 YFZ-R1 has done 26,000 km or 16155 miles. Its running really rough, starts on 3 cylinders, the fourth (unsure which one it is) cylinder fires up every now and then when riding and it feels ok when its firing, but still slightly under powered. At all other times it just runs on 3 cylinders and feels like garbage.

Pulled the ignition coils out on the weekend thinking it could be them that's causing the problem. The ignition coils are made by Mitsubishi, found these spec for them on this web manual: Electrical Specifications - Yamaha YZFR6X(C) 2008 Service Manual [Page 43] | ManualsLib
Model/manufacturer: F6T568/MITSUBISHI
Minimum ignition spark gap: 6.0 mm (0.24 in)
Primary coil resistance: 0.85–1.15 Ω
Secondary coil resistance: 5.01–6.78 kΩ

When I tested them with my multi-meter, I got the following readings (left to right across the head):
Cylinder 1, 2, 3, and 4:
Primary 1.4 Ω (either 1.3 or 1.4 across each primary)
Secondary 5.7 kΩ (either 5.65 or 5.7 kΩ across each secondary)

When taking the rubber boot off the bottom of the 4th coil, the plastic shielding underneath cracked off really easily (so now i have to buy at least one more).

Looks to me like ALL the primaries are reading out of spec (resistance too high).
Zero resistance would indicate a shorted coil while a high resistance reading would indicate an open coil.

Would this high resistance reading be causing the coils to malfunction? or not deliver the right voltage to the spark plugs and in turn be causing my issue?
All the readings on the secondary seem fine! If one of the coils was arching to the motor, would you be able to hear this like a ticking sound?
 

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You have to add the test lead resistance which is usually around .2 Ohm. I would say they are all in spec.

Mark
 

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Discussion Starter #3
I swapped out the coils, serviced the injectors, checked spark plugs, still had the issue. Tested the compression the other day (admittedly the engine was cold), got the following results:
Cyl1 - 150psi
Cyl2 - 140psi
Cyl3 - 0psi !!!!
Cyl4 - 150psi

All low readings and Cyl3 was alarming. Pulled the engine out, head off and found I've been struck by the same old valve issue lots of people experience with the 07-08 R1's.. check the photos out. The bloke at Harris Engines here in Perth, Australia said he hadn't seen one that bad on any engine, very lucky it didn't drop the valve.
Apparently all the intake valve guides are chewed out to some degree. So I need to replace all 8 intake guides and valves. YAY!.. jokes. These parts aren't cheap.

Once having new guides put in and the valve seats re-cut, has anyone found they experienced the same problem again in a few thousand kms or is this just a case of a bad batch of guides going through the factory back in the day during production of the VIN range.
1014469
1014470
 
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