Scooters - 50cc > Like 50 2T

Pressure test, Honda Bond, temperature gauge, tachometer

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Mark James:
My two-year saga of my bbk seems to finally be over.   My first try was the Naraku which seized up and scratched/pitted the cylinder head.  Malossi was next which resulted in the piston and rings toasted (head still salvageable with only 1 small scratch in it.   After going through 2 bbk kits ($$$$$) I decided to put the original back in which led to soft siezes and me pushing the bike home several times.  Gave up on it last fall and started thinking (and watching youtube videos) about pressure testing.  Finally pressure tested it 2 weeks ago and found my problem was the reed cage gaskets were leaking (which I replaced during the 1st BBK) causing the extreme lean/heat conditions.

I got a new Malossi piston (why do they make their pistons a little shorter than the standard size? and wtf with their circlips?) and reassembled the head using hondabond (in addition to base gasket, no hondabond on o-ring gasket).  In addition I used hondabond on the reed cage.  Pressure tested and it held 5 lbs for 40 minutes so I was confident the problem was solved.  Next was an install of temperature/tachometer gauge to monitor the cylinder head temperature.  Used 245Luigi’s posts (ty) for jetting the original carb, added 2 capfuls of oil to gas tank and turned up the oil pump to maximum and I was ready to go

The engine was running a little hot  (350-375making me nervous) so I switched to heavier rollers (6.5 slider to 8.5 roller I had laying around).  Still a little too hot so I had to reinstall the black plastic air flow restriction (that came with the bike) in the air intake and that makes the bike a little slower with less rpms so it runs a little cooler (300-325 with one time today at 350 in a hilly area.   

Have a 92 main jet right now and when I upjetted to 95 it just ran hotter so I stayed at 92.  I hope I can find a solution to the heat so I can get rid of the air flow restriction.  Top speed without the air flow restriction was mid 40’s, 41 with it.  I think that speed is the bike’s maximum because of the gearing.

My advice to anyone doing the bbk, pressure test, Honda Bond, temperature gauge, tachometer.  Hope this helps someone the same way I have been helped by this forum.

Stig / Major Tom:
Very nice write-up Mark!
Thanks for sharing your experiences and expertise.

Stig

Mark James:
New Carb.

Still was having heat problems (350ish) in hilly areas and i noticed that at wot the temperature was fine.  As I backed off the throttle it heated up quickly and also at 1/2-3/4 throttle it was running hotter than wot.  Started thinking about the needle.  Since the needle clip is not adjustable in the original carb (no room for shims either) I bought a 19mm $25 chinese carb on amazon.  Still ran hot with needle clip in #3.  Tested and moved it down, again down and ended in position #5.  Same hilly area and the temperature hasn't gone above 300 degrees.  Still want to get rid of the air restrictor but I am happy with the performance.

Main jet 92, Idle jet 38, needle clip in position 5 (closest to the point).

I am mixing 50:1 (2.6 ounces/gallon) now in addition to the oil pump.  The engine sounds different when I premix and I am sticking with it.

245luigi:
Glad to see my posts helped. Is the Keihn carb a PHBG clone? If its not I am not too much help. If it is my jetting is different because I have the 2t atomiser setup in there. See if you can jet the main that it hits 330 in the hilly areas. Seems to be the sweet spot. Hitting 350 is close to bad. I soft seized once and it was right when I hit 370. I run 330 all day no worries.

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