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Old 9 Oct 2006
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1984 TT600 auto decompression question

Hello, I'm new to your forum and I have a question about the auto decompression on a 1984 TT600. I have adjusted the decompression cable freeplay to .5 mm as instructed in the original Yamaha manual with the engine at top dead center. The valves are also adjusted correctly. The bike has a ton of compression and runs very well but it is very hard to start because the auto decompression only works some of the time. Its as if the decompression lever pulls back at the wrong time during starting. Any ideas? I just purchased this bike and its in great shape except for this problem. Has anyone here had this problem? Thanks.
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Old 9 Oct 2006
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Hi pkoval
just looking through the Clymer manual for you. (hope i have not sent this twice as i just had finger trouble... bit early for me!)

remove spark plug to make turning engine with socket easier
remove both the exhaust and inlet valve covers
remove timing covers from the left hand crankcase cover
use 19mm socket and wrench on alternator nut and rotate counter clockwise until at TDC on the compression stroke. to check you have this right do the following.

align the T mark on the rotor with the crankcase timing mark.
make sureboth sets of rocker arms have free play (in other words all valves are shut)
in one of the sets of valves is not shut then rotate the rotor an additional 360 degrees and match the T mark up again. should now be TDC.

measure freeplay at thetip of the decrompression cam lever to the right gap. 0.5mm (0.02 in)

i hope that this is of some help to you. i found that taking the time to do this accurately made starting the XT600 i have much easier.

also make sure that you are taking a full swing on the kick start, if not you will miss the benefit of the de-compression.
another tip i was given was to ease the kick start round until you hear a definite "click" from the decompression lever. this means that the lever is in the right place to start your full blooded swing on the starter!

Good luck.
Many thanks, Grub
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Old 9 Oct 2006
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The easy way

Start the engine, move back the deco lever till you feel the exhaust rocker hitting it (be tender!). If you have to move the lever more than 0.5 mm, adjust the cable.

As to kickstarting: make sure to, after each attempt, to let the kickstart pedal move entirely back to it's rest position.
Then the kick:
Move your foot and the lever slowly downwards till you feel resistance. This is the moment that the correctly adjusted and functioning deco system lifts the valve. Then, push forcefully down rather than kick down.

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Old 9 Oct 2006
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Manual decompression setup

Thanks for the tips and info. Does anyone know if a manual decompression lever can be adapted to this bike? Such as whats on the early TT and XT 500s.
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Old 25 Oct 2006
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Originally Posted by pkoval
Thanks for the tips and info. Does anyone know if a manual decompression lever can be adapted to this bike? Such as whats on the early TT and XT 500s.
My TT600 has a manual decompression lever, and I'm damn sure it's either an 83 or an 84. Works like a charm, and much more useful than the auto. I actually transplanted it onto my XT600 frame, I liked it so much.
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Old 26 Oct 2006
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You sure you didnt adjust this at BDC and not TDC.

The T mark lines up at both of these cycles. Use a small screwdriver or similar tool and poke it down te plug hole to feel that the piston is at the very TOP of its stroke.
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