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ghoti

Comments, advices, opinions XR650L re-build.

6 posts in this topic

It's getting to be time to freshen up the L. It's an 04, 21,000 miles, E series can with stock head pipe, Uni, de-smogged, de-snorkled, carb mods. I am happy with how it runs and the gas mileage so I would like to keep those in mind during the re-build. As a minimum I'm thinking rings, cleaning up the ports, maybe a polish on the exhaust side, thinner base gasket and of course a thorough inspection. Opinions on a hotcam or high compression piston upgrade. Do you need a bigger head pipe and carb to realize a difference? Would you have rathered done something less radical? Gas mileage? Anyone know of a 9:1 or so piston for the L?

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You can't do a thinner base gasket on the L, it throws off the timing.

A high comp piston is the way to go. Easy to do and worth it.

Hotcam changes the engine completely. Wants to rev much more than stock.

If you do both these mods the stock carb is crap, vacuum slide is slow to react and not a good match for the engine. I could not jet mine to work well after the mods. At a minimum, you will need a flat slide, best to get a pumper, Edelbrock or FCR.

Exhaust header is probably not needed unless you want every last bit of topend.

Stock comp ratio is 8.3:1, Wiesco is 10.25:1, JE is 10.5:1. I have heard Thumper Racing make a 10:1.

My mileage is roughly 45mpg. My temp dipstick doesn't get over 225F even at 90 mph on the highway.

MGS

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You can't do a thinner base gasket on the L, it throws off the timing.

A high comp piston is the way to go. Easy to do and worth it.

Hotcam changes the engine completely. Wants to rev much more than stock.

If you do both these mods the stock carb is crap, vacuum slide is slow to react and not a good match for the engine. I could not jet mine to work well after the mods. At a minimum, you will need a flat slide, best to get a pumper, Edelbrock or FCR.

Exhaust header is probably not needed unless you want every last bit of topend.

Stock comp ratio is 8.3:1, Wiesco is 10.25:1, JE is 10.5:1. I have heard Thumper Racing make a 10:1.

My mileage is roughly 45mpg. My temp dipstick doesn't get over 225F even at 90 mph on the highway.

MGS

They sell high compression gasket sets??? What timing is thrown off, cam? Can you explain how.

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As a minimum I'm thinking rings, cleaning up the ports, maybe a polish on the exhaust side, thinner base gasket and of course a thorough inspection.

Your original post stated you were looking at a thinner base gasket. They don't make this nor can you do it without slotting the cam sproket.

When a thinner gasket is installed (or the head is decked) the distance between the crank and cam changed. The timing chain is a fixed length, so by reducing the crank to head distance, you throw the timing off by a few degrees. To get the engine timed correctly, you need to slot the holes in the cam sproket, XRs Only offers this service.

A high compression piston, hotcam, pumper carb, and exhaust is the way to go. I have 5000 miles on mine.

MGS

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Yes, this is right, if you lower the head relative to the crank then this retards the cam timing. It can be easily dialled out by slotting the cam sprocket (I did mine myself with a drill + rotary burr) You need to be careful setting the timing cam afterwards of course

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