When I first started the bike I was using an as new OEM CRF50 carb and air filter assembly, the engine started with a few kicks idled and run nice, I like to put a rebuilt engine through 3 heat cycles then retension the head but into the third cycle the engine started to run on when backing off the throttle, went looking and found a few good examples of what can make your bike run rough after it has been sitting around for a while.
The Honda OEM air filter element was less than two years old as I had replaced it when I first bought the bike home, surprisingly it was quite fragile and disintegrating:
DSC02561.jpg
The rubber O ring between the cylinder head and inlet manifold was flat so I replaced it along with the O ring in the insulator spacer and the front face of the carburettor:
DSC02565.jpg
Also lubed the throttle cable just in case it was sticking and the engine was running quite well at this stage with the new parts fitted but it felt restricted and needed some more air.
So I replaced the CRF50 carb with an OEM XR/CRF70 carb and inlet manifold only had to make a small adjustment to the throttle tube for cable slack, the 70 carb makes a lot of difference, will get a video of it running, sounds great with the throaty mid-range/top end roar through the small foam pod air filter:
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Stock jetting as it came out the box, have two of these carbs on my bikes it is one of my favourite 50cc engine upgrades:
DSC02687.jpg
The inlet manifold flange that bolts to the cylinder has had 6mm shaved off it to provide clearance to the frame from when the carb was on my J1, this frame seems to have more clearance so I will be able to get a heat spacer between the head and manifold.
The Takegawa rear shock is spot on for me at 90kg, the kids will grow into it
:
DSC02678.jpg
The Honda OEM air filter element was less than two years old as I had replaced it when I first bought the bike home, surprisingly it was quite fragile and disintegrating:
DSC02561.jpg
The rubber O ring between the cylinder head and inlet manifold was flat so I replaced it along with the O ring in the insulator spacer and the front face of the carburettor:
DSC02565.jpg
Also lubed the throttle cable just in case it was sticking and the engine was running quite well at this stage with the new parts fitted but it felt restricted and needed some more air.
So I replaced the CRF50 carb with an OEM XR/CRF70 carb and inlet manifold only had to make a small adjustment to the throttle tube for cable slack, the 70 carb makes a lot of difference, will get a video of it running, sounds great with the throaty mid-range/top end roar through the small foam pod air filter:
DSC02684.jpg
Stock jetting as it came out the box, have two of these carbs on my bikes it is one of my favourite 50cc engine upgrades:
DSC02687.jpg
The inlet manifold flange that bolts to the cylinder has had 6mm shaved off it to provide clearance to the frame from when the carb was on my J1, this frame seems to have more clearance so I will be able to get a heat spacer between the head and manifold.
The Takegawa rear shock is spot on for me at 90kg, the kids will grow into it

DSC02678.jpg
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