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I had several blow-backs into the air box resulting in a blown seal to the manifold which in turn led to a high idle. I have a tuneECU map and exactly the same pipe as a buddy of mine and he does not have the problem. Anyone else had this issue?
 

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2008 RC8 / 2007 690
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I had several blow-backs into the air box resulting in a blown seal to the manifold which in turn led to a high idle. I have a tuneECU map and exactly the same pipe as a buddy of mine and he does not have the problem. Anyone else had this issue?
valve not closing and allows charge into throttle body.
 

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I had the same problem once we installed the Cometic head gaskets and increased the compression. I added a motion pro catch can with two hoses to purge the oil and keep the airbox clean. I was able to route the catch can in the same spot as the evap canister in the subframe assembly.
 

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Blocked PCV vent? Breather hose top rear cylinder ignition side. Follow it, maybe canister is gunked up and clogged.

If top end was never apart I dont believe it would be valve related or timing related. Unless your tensioners are about to fail ( COULD HAPPEN!!)
 

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I suppose a collet or spring may have broke on the valve.

Usually valves get tighter as they age dont they?? I suppose depends what wears, the valve seat, or the finger follower on the cam.

Yours sounds loose if its backfiring, which is bad for guide seals and the seat surface. Its winter, pull the valve cover and check them.

Does it only do it on cold starts? As te engine heats the valves and metals expands, at different rates. Titanium intake, SST exhaust valves, aluminum heads, and DLC fingers all expand at different rates.

Good news is that shims are chea. Not KTM shims mind you, but Harley davidson 10mm shims are a perfect fit in the RC8 for a 1/10 the price.
 
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