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Dre907

TT Decompression Plug

7 posts in this topic

Would my 06' YZ450F benefit from the Thunper Talk Decompression Plug, or is it no longer a problem for this model?

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The decomp plug is for the 426 exhaust cam conversion for plugging where the decompression lever once was. You shouldn't need it on the 450 as far as I know.

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You need it also on 450s up to '05,I think they fixed it on '06s.

The reason for this, just to explain, is that on the 450 Yamaha used a plastic decomp plug and it has been known to blow out even thought it is secured with the bolt. The aluminum TT plug will not blow out.

Josh

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The reason for this, just to explain, is that on the 450 Yamaha used a plastic decomp plug and it has been known to blow out even thought it is secured with the bolt. The aluminum TT plug will not blow out.
Actually the stocker wasnt secured with a bolt, that was the problem. The aftermarket ones like here on TT are secured with a set screw. I had one on my WR, it was awesome. It doesnt appear that the 06's need one, at least not that I could see.

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The 06 does not require the plug, the head no longer has the hole for the decomp assembly in it. The 03-05 need the plug, as does any 426 with the decomp removed- the stock Yamaha plug is a joke.

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The '06 YZ450 head has eliminated the entire boss where the decomp shaft used to go. The plug is no longer needed, just like Dave said.

The earlier YZ450's, and the '03-'05 ('06?) YZ250F's, had the afore mentioned cheesy plastic plugs that you could shoot at track officials by pinching the breather hose and twisting the throttle. Like black_n_blue_thumper said, they were held in by voodoo, which would periodically fail and leave you with a big ol' hole in your head.

The decomp bore was retained so that the engine could be back-fitted with manual decompression if desired. That's why the lock bolt is was still there. This was occasionally needed early on by guys fooling with cam timing and throwing the auto system out of sync.

As an alternative to the pricey but cool TT plug, I sometimes use an 18mm steel or brass expansion plug. Pull the seal out, drive the plug in with a little sealer on it, and stake it. Problem solved for $1.50.

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