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banana4monkey

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A guy in my Army unit wanted me to do some work on his Yamaha XS650 a while back. He wanted some mechanical and cosmetic work done to this bike. It had some oil leaks and it didn’t run right (he thought it was something to do with the carbs. He had an aftermarket exhaust to install and he wanted me to relocate the foot pegs. He also wanted me to chop the front fender and give it a gloss black base clear paint job. I really wanted to do this job for more painting practice. First thing I did was an overall inspection on the bike to see what needed to be replaced in addition to the assumed workscope. I ran the bike to get an idea of where the oil leaks were coming from and also did a compression test. More to follow on this.

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Bike as received
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oil leaks
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More oil leaks

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start investigating oil leaks

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Compression test



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banana4monkey

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This bike wasn't running right when the owner bought the bike so I had to do some checking. The bike sat for awhile since the last time it was run so with todays gas I disassembled the carbs and fuel strainer in the tank. Todays gas tends to leave reside after 3 months if the fuels not stabilized. This can cause partial or complete blockage of the carb jets that can lead to a lean condition or if completely blocked can cause the bike not to run at all. It is important to know what the factory carb specs are to make sure you have a good baseline for tuning if someone made the incorrect changes. This bike has a dual CV (constant velocity) carb setup. After the carbs are cleaned I move on to synchronizing the carbs, setting the valve clearance, and checking the timing.

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Checking the strainer in the tank

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carbs off the bike

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float bowls off and jets out

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Carb components out. Check the needle and seat, diaphragm, and clean jet passages.

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A little residue in the bottom of the float bowl

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Carbs assembled and ready for installation and synchronization.


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MR. X

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Looks like fun .
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Sometimes you have to stop pedaling and just coast for a little while.
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banana4monkey

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Before I do the carb synchronization I want to check the valve clearances and the ignition timing. The valve clearance is important so that the valves will operate properly when the engine is running. The valves have a cold clearance to make up for the expansion in the metal due to a rise in temperature when operating. Too much clearance and the valve timing is off and the valves get noisy. Too little clearance and the valves stay open when they should be closed. If the valve doesn't close fully it will not transfer the heat to the head and can burn or melt. To set the valve clearance on this bike you put the piston at top dead center on the compression stroke and check the clearance between the rocker and the valve with a feeler gauge. You can typically find top dead center by lining up the "T" on the flywheel with the marking notch in the case.  The clearance is adjustable with the threads on the end of the rocker arm. You loosen the jam nut and turn the threads to adjust the clearance. Once the clearance is set you tighten down the jam nut. I always recheck the clearances after a few times after they are set to re-verify. Clearance specs are obtained from the service manual.

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Tools for setting the valve clearance on this bike.

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Inspection cover is off and checking the intake clearance with a feeler gauge.

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On to checking the exhaust clearance.

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banana4monkey

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Next I checked the ignition timing. For this you hook up the timing light to the battery and the #1 cylinder spark plug wire. Then you start the bike and maintain the RPM per the service manual . Squeeze the trigger on the timing light and it will flash every time the spark plug is fired. You aim the timing light at the flywheel which has timing marks on it. The timing marks on the rotating flywheel will line up to one stationary point on the case. Timing is usually set in degrees and for this engine it just has a mark where the timing should be at idle.  The timing was right on so there was no need for an adjustment. Again I like to do the following when troubleshooting suspected “tuning issues”

-          Compression test

-          Check for spark on all cylinders and check spark plugs

-          Use new fuel

-          Clean carb and fuel tank strainer/filter

-          Check carb specs – float bowl height – jetting – mixture screw adjustments

-          Check for proper fuel flow

-          Check  ignition timing

-          Clean air cleaner/filter

 

Next step is carb synchronization.

  P1010087.JPG  P1010088.JPG 


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banana4monkey

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Below are some pictures of the finished bike. It turned out good but would have been better if the frame was painted. Again the client did not want to pay for this. Also rear set pegs were used and the shifter and brake levers were modified accordingly.

bike.JPG  bike2.JPG  bike3.JPG  bike4.JPG 

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