Carb clearance, intake length and muffler

MinimumVK

Member
Local time
3:31 AM
Joined
May 19, 2023
Messages
75
Location
Slovenia
Hello fellow builders! If you dont like reading skip to the next paragraph. So to start i decided to try taking off the muffler end cap to see what it would be like on my stock YD100 motor. Took it off and the low end torque was increased ALOT which i liked but the bike 4 stroked after 40km/h. Put the cap back on but took it back off again the same day since i got used to the extra torque and hill climbing ability. For the life of me i couldnt find jets for the BoFeng that would ship to me. Looked everywhere in a few different cities but no luck. Was looking around AliExpress and found a Dellorto clone for 8 euros shipped! Ordered it and it arrived a few days ago. One of the reasons i got it is because i can get emulsion tubes and jets from my local Tomos moped parts store. The quality of it was decent and i cleaned it up and put in a 60 jet that i had and tried it. The bike still had good torque if not a bit better, idled better and it started 4 stroking at 45km/h this time so i will have to jet down a bit more... One problem is that i dont have enough clearance to fit the cone air filter (ziptied the stock filter without the red plastic for testing) so here are my questions:

1st: Making the air filter fit i wanted to either modify the stock intake. Read about how extending it with a hose would make me lose some top end power. Would it make that much of a difference on my stock motor and if re-jetting the carb would fix it?
If not that i would try to make a flange out of PVC hoses to put the air filter somewhere in front of the rear fender (3rd picture). Another thing is if intake length from carb to air filter impact performance in anyway?

2nd: As said above i took and kept the exhaust end cap off the muffler because its nice having a bit more low end torque. Anyway the bike is now a lot louder and i dont want unwanted attention drawn at me so could i weld an extension of the header pipe that would go to the rear of the bike and weld a muffler there without losing that low end torque? Also saw some people on here running those really long exhausts (again read somewhere that increasing header length of the stock exhaust increases torque but decreases top end) (4th picture).

3rd: I have a 36 tooth sprocket laying around and thought of using it in combination with the longer intake and exhaust to keep the bike at low revs where the torque is at but also having a good enough speed (about 50km/h) as it was before.

Main thing i want to fix is the noise so some idea about the muffler would be nice. I can live with the zip tied air filter for now and the carb just needs a bit of more tuning.

Wanted to do a lifan 125cc build but i bought another project car so dont have much time or money for all of that on top. But i am planning to make a 3rd bike with an LD100. I helped my friend build a bike with the same kit and his has good torque and still goes about 55-60km/h with the stock 44t sprocket and Bofeng carb. Shame the YD100 doesnt have the same power...

Thanks in advance for the help and sorry for the long write up.
 

Attachments

  • 20240308_201449.jpg
    20240308_201449.jpg
    250.8 KB · Views: 75
  • 20240308_201458.jpg
    20240308_201458.jpg
    173.1 KB · Views: 63
  • 20240308_202611.jpg
    20240308_202611.jpg
    231.7 KB · Views: 55
  • muffler extension.jpg
    muffler extension.jpg
    186.2 KB · Views: 63
And for the noise, cut the tube out of the muffler cap and holt the cap back on. It will be quiter, but still a bit more powerful than stock. A 36t should work good for you
Yeah i cut off that pipe since i built the bike, didnt notice that much of a difference in power just a bit more noisy.
 
Want decent power and more low end torque with very little fab work then the dime a dozen MZ clone pipe like this


With this muffler basically shoved in the end (or you could weld it on and do it kinda the right way).

Is actually a decent, cheap, and easy to source combination that does make a good improvement in torque and power in the rpm range these engines operate in.

Are they ideal? No. Do they still work? Well enough.

You will need that muffler to keep the noise from being ridiculous, aka the cap off your stock exhaust loud without said muffler.

You can find a few videos on youtube with that combo, this is an example of one.
 
Links to Amazon may include affiliate code. If you click on an Amazon link and make a purchase, this forum may earn a small commission.
As for not finding jets for the Bofeng. Did you search for 99101-124 jets?

Also sold by Honda (can usually order form any Honda Motorcycle dealer).

For the Honda jets you can order them as 99101-124-XXXX. The X's being a place holder for jet size. A 65 jet would be 0650, a 70 jet would be a 0700, and a 75 being 0750. So if you wanted a 65 jet you would be looking for a 99101-124-0650.
 
Want decent power and more low end torque with very little fab work then the dime a dozen MZ clone pipe like this


With this muffler basically shoved in the end (or you could weld it on and do it kinda the right way).

Is actually a decent, cheap, and easy to source combination that does make a good improvement in torque and power in the rpm range these engines operate in.

Are they ideal? No. Do they still work? Well enough.

You will need that muffler to keep the noise from being ridiculous, aka the cap off your stock exhaust loud without said muffler.

You can find a few videos on youtube with that combo, this is an example of one.

I bought a couple of those pipes for 80 CDN last year. They do work well as a one size fits all. Now, they are hard to find at 80 each. They are stupid loud without an additional muffler on the end.

The BoFeng jets are 6.5 / 7 mm Aliexpress and Amazon have them. I think these will work.
 
Links to Amazon may include affiliate code. If you click on an Amazon link and make a purchase, this forum may earn a small commission.
The BoFeng jets are 6.5 / 7 mm Aliexpress and Amazon have them. I think these will work.
Amazon.ca
This kit is not very viable if your trying to go with smaller jets...The stock jet in the BoFengs carby's is a #70 jet...All the sizes that kit has are only larger sizes, none of the smaller sizes are in that kit and many folks need to go down a size or two.
 
Links to Amazon may include affiliate code. If you click on an Amazon link and make a purchase, this forum may earn a small commission.
Yes that is right. I didn't look close enough, just looked at the diameter of the threads not the actual size of the jet itself. My bad.

Most will need from 65 to 70 at the most.
 
Back
Top