some questions about 72cc bbk

[br4inl3ss]

hi all.
after weeks of awake nightmare ( bought 81cc thatc annot be used, mroe than 3 weeks to order anything, and so on , and impossible to find problem with 81cc bbk ), i can finally get my hand on a quality 72cc bbk ( went 81cc because it was available in less than 3 month ...)

so questions are....
is the 72cc really almost trouble-free ? 
is it true the engine life is very good with this bbk ?
i know its not NEEDED, but will a big valve head make a good difference instead of stock head IF magic happens and one is available ?
what AFR should it run to at idle , cruise, fullt hrottle ? ( i have my glowshift wideband installed )

also, i own this scooter since a year and NEVER had any engine problem ( beside this nightmare of 81cc bbk ) but i have some connecting rod play on the crankshaft ( not in a pull/push motion, and not right/left.. only slide from left to right ). is this normal
no crankshaft nosie at all even with the 81cc when testing it. i dont think its a bad play then ?

will i need double base gasket with the stock head ? ( minor material removed to lower compression with 81cc, but i see no difference back in stock form )

since those engine been run by alot of people to 10k rpm bone stock with no problems up to 35 000km, can the same be acheived with 72cc or it must be lower to stay on the safe side ? ( just wondering for downhill. not planning to rev it that high for no reason ).
thanks

[GrumpyUnk]

Oh: "i have my glowshift wideband installed"

Well that explains everything. The sensor is blocking exhaust flow. You have too much back pressure.
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I lied. Actually, it may cause back pressure in the exhaust. That could possibly cause some funny carb operation upon acceleration. Never have used double base gasket, or 'correct' cylinder head, or 'oversize valve' head. What ever it came with, new piston/rings/cylinder, and back together. Have an A9 cam on the shelf, and have use slightly up-size carburetors.
tom

[br4inl3ss]

Jun 3, 2022 8:47:01 GMT -5 GrumpyUnk said:

Oh: "i have my glowshift wideband installed"

Well that explains everything. The sensor is blocking exhaust flow. You have too much back pressure.
...
..
.
...
..
..
I lied. Actually, it may cause back pressure in the exhaust. That could possibly cause some funny carb operation upon acceleration. Never have used double base gasket, or 'correct' cylinder head, or 'oversize valve' head. What ever it came with, new piston/rings/cylinder, and back together. Have an A9 cam on the shelf, and have use slightly up-size carburetors.
tom

bro are you the only one that connect to this forum ?? 
well i tought about backpressure, so the sensor is spaced out a bit and ONLY about 5mm or less is actually inside the exhaust.

shouldnt cause any issue this way. "shouldnt". had some problem similar to this on my heavily modded 1999 dakota and i fixed it the same way ( also giving false reading and need recalibration every week ). to help me stay away of problems, i even throw the bosch sensor in the trash and bought a ultrapower ( for a honda ) from rockauto. 10 time cheaper and 20 time more reliable. trouble free since 8 years on the same damn sensor.

for the A9 cam, are all "performance" cam the same or it must be specified A9 ? it was planned to have a A9 cam from day one. but yeah i had some problems lately as you know 

[GrumpyUnk]

I was waiting for someone to poke their head up. Finally said WTh and posted. The down pipe on a 50cc is not much larger than my thumb(well, it is larger) so using a regular O2 sensor could block off a lot of the area and cause some back pressure. Dunno about wideband sensors.
As far as I have read, there are/were several cam versions with numbers around '9'. You may be able to find reference on site. You can't change lift in these, so must only be fattening the curve so they lift earlier and later. To a point. I wonder if the cams labeled as such are actually that different. There was a pretty big thread on site within the last four? years where comparisons were done, but I am not going about buying cams to test and actually am selling my herd. Well plans are to sell most. Do not feel my balance is good enough any more for larger machines, sold one yesterday, and the other to go on FB soon. Followed by the scooters that I have made functional once again. And the pit bike I can never ride(too heavy)... and so it goes.
tom

[br4inl3ss]

that sucks you have to sell all those things.

ive seen the thread you're talking about. but its a bit misleading.