Final word on baffles...necessary or not?

[motorpsycho]

I'm on board with you Motorpsycho on this one. My 70cc is heavily modified and goes like a rocket and is relyable to. I regularly do 300kmer runs and have clocked up almost 3000kms to date. The motor has been striped down and the internals look excelent. Because of the mods I run 25-1 oil mix. I agree these engines lend themselves to heaps of mods. Years ago I was involved with drag racing so I guess I'm up with the tricks required. The only mod I have'nt done yet is a jack-shaft shifter kit which I'm just about to start on, need to work out what gears I'll need for the rear casset and I reckon I can get this little sucker to kick 80-100kmph. Drop me a line on your mods I'd like to swap some ideas.


Old petrol-heads never die they just loose their cubic-centimetres

i too was a drag racer in the 80's and i have done a ton of engine work / mods. in my life. as for what i have done to my littel 50 c.c.:
so far, i've added an expansion chamber with no baffle / muffler/ silencer, a high flow air filter, and a boost bottle.
over the winter i plan on porting & polishing the intake and exhaust, and milling the head.
My motor is on a 20" frame and i do not / can not install a shift kit / jackshaft kit...so i have to get the most that i can out of a single speed.
As of right now, my bike has topped out at 38 mph, and i weigh 155 lbs.
I liike more for short bursts of high speed rather than constant crusing speeds.
the plan next summer is to take it and run it on an 1/8 mile drag strip against my friends 24" bike with an 80 c.c. motor on it.

 

[oldsalt]

My experiance with my RAW '80cc' motor is that it was so rich that something had to be done. I was going to solder up the main jet and redrill but decided to look at the inerds of the big sausage muffler [obviously a muffler, not a tuned pipe]. I was astounded by a reverse flow pipe and all manner of baffles in there! All I could figure was that the enginner's mother was scared by a loud moped before he was born. So, in an effort to lean out the top end I removed about half the junk. That leaned out the upper end enough so that it did not run constantly in a 4-stroke mode. Took the pipe off again and performed a complete baffle removal. Now the engine will run most of the time in a 2-stroke mode. At wide open throttle it reverts to the over-rich condition and starts 4-stroking, I can live with that.

Now to the point of all this: If you are already lean on the mid and/or upper end leave it alone. Do some carb work, then consider gutting the muffler. It your bike runs fine then be prepared to richen up the carb if you gut the muffler. By the way, the noise increse, with the gutted muffler, was not enough to write home about.

 

[fourfeathers]

Hi Motorpsycho,
nice to hear of your shared interest in drag-racing, heaps of fun ah!.
Have spent all day tuning and re-configuring a velocity stack for my modified carby.
Heres a little tip I've never seen mentioned anywhere on the forum.
When you take the jug off you'll notice that the bottom of the cylinder sleeve protrudes and partially covers the intake end of the transfere ports. By cutting and grinding this restriction/ configuring to the shape of the transfere port increases fuel flow no end with a marked improvement to performance. Make sure inside edges are re-beveled or you'll have trouble getting the rings into the cylinder again.

Catch yer later. Have fun.

 

[Frogz]

i was riding 1 day, for some reason my bike was being kinda loud
evedently the bolt fell out of my muffler and the end was hanging out(amazingly, i didnt lose it)
bought a new bolt(hex head) to replace it with, the bike ran fine without "any" backpressure, the end was fully off however