hi need help with top speed 66cc 2 stroke engine.

[Rin]

hi, how are you all, if anyone can give me some advise, that would be awesome.
just setup my 66cc 2 stroke to my mountain bike, bought it off ebay.

it has decent acceleration/torque up to around 40km then just stops there, it feels like its hitting a rev limiter or something.
is there a way to improve the top speed without sacrificing torque because i need the hill climbing. i want it to hit 60km top speed, is that possible for these engines? i am only 60kg.

also theres a lot of black oily stuff spitting out everywhere? i am running 16:1 oil to fuel ratio, using 2 stroke semi-synthetic penrite oil, and 95unleaded.

thank you

 

[FNTPuck]

They recommend the first two tanks of premix should be ran with that extra 16:1 oil ratio for break in. After that, you should lower the oil in the mix which will help pick up power. Some like a bit more oil and run 25:1 after break-in, some 32:1...anywhere between there should be OK. If you are on your first two 16:1 tanks still, then reduced power is normal and you shouldn't be flogging it that hard anyway during break-in. There will always be SOME oil residue coming from the exhaust but due to the high amount of oil during break-in there will be more.

60kmh is pretty fast for a bicycle but definitely possible but be sure to make sure your bike has been upgraded to support those speeds since it won't last very long otherwise. Replace clamshell spoke mount with hub adapter sprocket, replace motor hardware with quality parts, loctite pretty much everything, good brakes, etc. If you are only doing 40 now, 60 is quite a long ways off so will definintely need a gearing change which will hurt your hill climbing tq.

While there are different performance tricks to help different rpm ranges like more powerful/remapped CDIs, extended intakes, reed valves and ported pistons, etc, the biggest and simplest noticeable change will be your gearing but you can't have it both ways. You can gear for more low end at the expense of top speed or vice versa. Everyone's needs are different due to where they ride(hills, flat long roads, city, etc), bike and rider weight(heavier bike needs more tq to get moving), and how they ride(always WOT for long periods or stop and go?) so there is no perfect one-size-fits-all gearing.

TL;DR: Finish break in without beating on it too hard and switch to a standard lower oil ratio. Drop a few (I would start with -2 since you said you need the climbing power) teeth on the rear sprocket and test again, to see if the extra speed is worth the loss of TQ/acceleration for you. Nobody else can answer that questions for you. Look for power mods to help get the bike moving against the higher gearing like jaguar CDI, extended intake, CNC head, and a ported piston+reed valve.

I'm sure some of the more experienced members will chime in with some tips as well...there is TONS of great information on this forum and lots of very experienced members to learn from.

 

[crassius]

yes, finish break in before trying to tune much

you may be too rich and 4-stroking - quickest way to tell is ride uphill and see if at some throttle setting motor sound changes and it starts to pull harder