I had an EFI KQ that refused to rev over 2500rpm, after wasting days on checking the fuel system, I took the cam cover off and found the cam had seized on the LH bearing, and the cam and followers were shot as well. Being unable to find a used head, we got a new cam & followers and machined out the cam bearing, fitting a bush on the new cam. I did wonder why the cam had gone, but assumed the owner had run it short of oil. Anyway the new set up soon started to rattle so have stripped it again and found it had been running dry. So oil isn't getting to the head. Could be a blocked oilway, the pump weak, or the pressure relief valve is stuck open. I'm not sure where to start as the pump is in the RH engine case, the relief valve in the left case, and checking galleries involves removing head and cylinder. Anyone had this problem?

 

Wish I could help you man! But never heard of this problem...Zuks are pretty rock solid. Most likely lack of maintenance. Have you googled the issue? Come up with anything? It may be as simple as no one changing the oil and filter. I got an ATV in the other day...2006, never changed the oil/filter or inspected the air filter. Engine knocks...LOL

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I went for the pump first and found it to be spot on, no scores or wear. Tried the oil galleries next, Suzuki have made the system very complex. Oil is fed to a channel between the clutch outer and inner case then back up the two RH head bolts. The front one just feeds the oil across under the exhaust port, presumably for cooling, but the back one feeds the centre bearing of the cam and up one of the cam cover bolts to the inlet rocker shaft, which dribbles oil onto the cam lobes. The front rocker just gets splash lubrication, and quite how the outer cam bearings get oil is a bit of a mystery. Anyway blew the galleries out with an air line, spun the engine on the starter, and oil started to flow up that rear bolt hole. So with new cam and followers, and checking I got oil through at every stage of the assembly I put it back together. The "boss" tried it today and recons it has more power than the one we had for sale a few weeks back, but he has been using a 2WD 300 Honda since we sold the Suz as our stock of used bikes has been very low lately. He will run it around his farm for a few weeks to make sure the oil is still circulating before selling it on.

 

Well, thats great! So what fixed it....new cam and followers? Blowing out the oil galleries...just curious....maybe it was ran low on oil for a while? And here to learn about this one. Anyway, glad its fixed for ya!

 

The cam had not been getting any oil since the first rebuild, it had only done a few hours and the trough under the cam was bone dry, except for blackened metal paste. After I blew the galleries out I removed the clutch cover, poked round in the channel between the clutch cases and found a drip of silicone sealant, just big enough to have blocked the passage to the rear head bolt, which is only about 2mm diameter. It could have been this. I am fairly careful with silicone as a rule, but am going to trust to the paper gasket on 400 manual clutch covers in future if a tiny blob of silicone can do this much damage.

 

I use the RTV very very sparingly as well. I use a very thin coating on the engine case side to ensure no leaks and gasket adhesion.....then I use a really lite film of grease on the cover side of the gasket..for sealing and it prevents the gasket from tearing if the cover were to be removed again. RTV is great.....when used sparingly. Glad she running like its supposed to!