expansion pipe problem - motorized bicycle

[bajaracer1]

I bought a stock expansion pipe off a 2003 Suzuki RM65 off Ebay for $25. cut my stock exhaust about 3-4 inches from the header, and welded the expansion pipe to it. then welded the silencer to the end of the expansion pipe to quiet it down.
I also got a dellorto clone carb (SHA) with a .68 jet.

problem: the bike is not really any faster! I didn't get this big jump in power after i went over 3-4k RPM. It's still a smooth acceleration. There is no coming on the pipe. It just feels like stock!

whats the problem???

 

[BigBlue]

The problem - the pipe wasn't designed for your engine and isn't tuned. Some members have been successful adapting other pipes to the HT. Do a search. Download a copy of Two-stroke Tuner's Handbook from Gordon Jennings.

Good Luck,

Chris
AKA: BigBlue

 

[bajaracer1]

So there's nothing I can do to make this work?

 

[culvercityclassic]

I say remove that restrictive so called silencer and use the one made for that pipe. See what happens then....

 

[culvercityclassic]

One more thing... Did you port or clean up the intake and exhaust port? Trim the piston skirt? Break the motor in with a couple tanks of gas and do the things I mentioned. Hope it helps

 

[dodge dude94]

Looks like the pipe is just flat too big to me. Not enough backpressure.

 

[bajaracer1]

I broke the motor in with 4 tanks of gas before I installed the pipe. I didn't port anything though. or trip the piston. I ran the bike without the silencer for a few days. It was so loud that I herd ringing for a few hours after, but it wasn't any faster!

 

[culvercityclassic]

Ok...I will step back on what to do...cuz I have become a Four Stroke Tuner...

 

[bajaracer1]

anyway the bike for sale $535

 

[Venice Motor Bikes]

A reed valve, '3 port'-port job & a better intake & carb will make a lotta difference.
(& get rid of that stock muffler like CCC said)!!

& while you're at it, get some good front brakes!!!

 

[bajaracer1]

But do you think all that would give me that crazy all of a sudden power boost once I get up to RPM? They call it "coming on the pipe".

also what carb, and reed valve would you recommend?

 

[mew905]

for speed, go with arrow and stuff your crank case, also get a bigger, tunable carb (Dellorto SHA clone, AKA Runtong or DaxRT, isn't a great carb tbh, I didn't notice anything but better idling). a 19mm-20mm Mikuni or Dellorto PHBG carb are fully tunable, and will provide the flow the motor is demanding. Also because that pipe is rather short before the expansion chamber, odds are you may not see "coming on the pipe" until higher RPM's, maybe around 6000. Reed port the piston, boost port the intake, raise the exhaust 1mm, and widen it to 30mm (ROUND THOSE EDGES! you could break a ring on the first rev if you dont!). That should net you the power and revs to get on the pipe effectively. If you find you've lost some of your low end, get an offset intake (or buy some 3/4" ID silicon tube, its like $2 for a foot), and add around 3-6" to your intake length to raise the power band at the low end a bit. You will need to make some kind of adapter to go from the 3/4" stock intake to the almost 1" throat of the carb.