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CheGuevara

650L manual decomp

12 posts in this topic

Can manual decomp be retrofitted to the XR650L? Would it be as simple as buying the assembly from an XR600 and popping it in?

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Let me guess, aftermarket camshaft? Try it with just e-start first, you don't need decomp!

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Aftermarket cam, yes. I'm still building the motor, but I also have the 675 Wiseco kit (10.25:1 comression), so there is concern it may be difficult to start. The motor is in a TZ250 chassis, and as such I may need to use a smaller battery as well - I'm guessing anything I can do to make it easier to start will be a plus.

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The motor is in a TZ250 chassis, and as such I may need to use a smaller battery as well - I'm guessing anything I can do to make it easier to start will be a plus.

that should make for a fun ride - pics?

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Ask and ye shall receive:

d376.jpg?ph2dxOCB50y83CGJbb50.jpg?ph2dxOCBY5i93BXGb6a9.jpg?ph2dxOCBvRGhef3F1a50.jpg?ph2dxOCBQLQ65WyE68f9.jpg?ph2dxOCBx3izI7TW4e04.jpg?ph2dxOCBrEbWvBRt

It's actually a bit further along than the pics show - I just havent had a chance to take any more current (these are mostly as of Dec.).

So anybody know about the manual decomp? Lots of smart people on this board and I'm betting someone has my answer. :)

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If anyone's interested: The head was ported and rebuilt (new valves, springs etc) by Jay Wright of Barebones Machine (he actually said it required very little -mostly just cleaning up the ports), 675 Wiseco kit, rebuilt crank, every bearing in the motor has been replaced (believe me, that wasn't cheap!), will be running the Hotcams Stg 1 cam, carb to be determined but I may try an HSR Mikuni (42?) and the exhaust is yet to come but will consist of 1.5" primaries into a collector with about 2" outlet followed by a reverse-cone meg -no muffler (at least initially) so I'm sure my neighbors will love me.

I'm hoping I might get close to 50HP with that. Anyone know if that's realistic or am I smoking crack here?

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Did the Domi have a manual decomp? I'm thinking that it might be as simple, I would look at pre 95 DR 650's too, very similar and it has a decomp.

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I am almost positive that the XR600R head is the same as the L. The only difference between the two bikes is the stroke I think, besides e-start. Might be worth trying to get a used head off of e-bay and test fitting. The Ls head has all cast features of the decomp, they just didn't mahcine it.

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Can manual decomp be retrofitted to the XR650L? Would it be as simple as buying the assembly from an XR600 and popping it in?

You do not need it.I built my engine it cranks better now then it did when it was stock.If anything the decomp makes one harder to start.Without it when the engine comes up on the compression stroke it will fire right up.I have a Wiseco 10.25 piston,Hotcams stage one cam,Mikuni flat slide and we did a three angle valve job.I am happy with the bike and have had no problems with it starting.

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