Ideal exhaust size for lifan 125cc

Discussion in 'Lifan' started by CraigKapo, Nov 6, 2015.

  1. CraigKapo

    CraigKapo New Member

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    I'm curious what would be considered the ideal exhaust diameter to run on a Lifan 125cc?
    I have one that I just swapped into a ct70 clone. I currently have a homemade exhaust on it made of 3/4" tubing and a briggs mower type muffler.
    I was attending a vintage bike night a few days ago and thought I would switch over to the original exhaust because it looks nicer. It is basically a CT70 copy, but I can see that the inner diameter is a little wider than the real CT70 exhaust I have on my '92.
    When I switched I went from a top speed of 54 mph down to 45 mph.
    Now I am looking to order an aftermarket exhaust setup, but I don't want to get something too small. I'm not trying to spend a fortune so I'm looking at some setups on ebay. I just don't want to put something on that's going to kill my top speed like the ct70 exhaust did.
    Is there a certain size tubing I should be looking for?
     
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  3. OLD CT

    OLD CT Well-Known Member

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    None of the cheap copy $65 exhausts will be any better than a real ct70 exhaust. Cheapies floww less. There really aren't any worthy pipes on ebay, to fit the bill right now. I would not buy anything from drct70411 on ebay as the guy is a jerk from what I've heard by many on here. So what I am saying is you are going to have to spend more than 100 bucks for a free flow pipe. Diameter size will be bigger, as it's needed. I don't have any specs for you. Here is a stainless $300 to your door free flow that is quiet also. Sucks, when your exhaust costs more than your L 125 engine!! :26:
     

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  4. CraigKapo

    CraigKapo New Member

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    I'm sorry. I wasn't real clear on what I'm looking to buy. I don't plan to buy another ct70 copy exhaust. I plan to get something that looks aftermarket too. I just wondered what tubing diameter I should be looking for. I just don't want to loose an power.
     
  5. OLD CT

    OLD CT Well-Known Member

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    How do you like this Craig? It's a $125 or so. Minimoto is the brand with a removable baffle. Purchased both from Japan web!ke. The Minimoto measures 1 inch, with the baffle removed.
     

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    #4 OLD CT, Nov 6, 2015
    Last edited: Nov 6, 2015
  6. CraigKapo

    CraigKapo New Member

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    I like that alot. That's exactly the sort of thing I'm looking for. On mufflers with a removable baffle, is it just for noise or does it free up some power removing it?
     
  7. OLD CT

    OLD CT Well-Known Member

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    I can't really comment on that as I never had the removable baffle type till now. I guess it would give you 3 mph faster removed if I had to guess. If there is no difference, quiet would be my choice. It does seem nice to have a choice of quiet when you want, and loud though.
     
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  8. CraigKapo

    CraigKapo New Member

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    Alright. I'll have to look into that some more. But I appreciate the information you've given me. Thank yoy.
     
  9. racerx

    racerx Administrator
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    A properly setup L125 should be good for a top speed close to 60mph, with high 50s being pretty typical. For that, gearing, carburetion and exhaust need to be optimal. Your home made pipe is obviously a lot less restrictive than the inexpensive feebay knockoff of the stocker. Those feebay cheapies are pretty restrictive even compared to the OEM exhaust; they're designed to meet strict noise limits - when fitted to 49cc-powered bikes. Exhaust tuning can get pretty involved. I'll spare you the longwinded tech dissertation. Your exhaust port ID is probably close to 25mm. Your cheapie muffler outlet ID is closer to 15mm, far smaller than OEM stock. You're asking the motor to exhale through a soda straw, IOW...a HUGE flow restriction.

    Changes in exhaust flow can affect air:fuel ratios, so be aware. This can negatively affect top speed, throttle response and peak engine temp. A bit of carb tweaking may be needed, following an exhaust swap, to realize optimal results.
     
  10. CraigKapo

    CraigKapo New Member

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    I am working with a brand new carb that is supposed to be a Mikuni copy. Its 24mm and so far has done really well as far as starting, idling, and running all the way up to 3/4 throttle. 3/4 - full throttle the engine begins to surge and bog randomly, almost feels like something is slipping. If I back off to 3/4 throttle again, i continue to accelerate up to the mid 50s.
    Ive ran new plugs and killed the engine at full throttle a couple of times now and my plug is usually darker brown in color. Ive also ran full throttle and used my hand to slightly cover my open air filter and the engine bogs almost instantly. This all leads me to believe that my main jet is rich. This is why id like to get a permanent exhaust taken care of now so I can get some jets ordered and begin getting the main jet tuned to my permanent intake/exhaust setup. I just wanted some feedback as to what diameter exhaust I should looking for so I dont order too small.
    Carb tuning is still very new to me. Ive built and rebuilt engines of all sizes on numerous occasions, but ive never actually dealt with tuning a carb. Does it sound like im on the right path?
     
  11. racerx

    racerx Administrator
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    Yes, sounds like you're heading in the right direction. It's overrich. Going from the current pea shooter muffler to something that's adequate should lean-out your mixture, especially as the revs build. Only way to know exactly what the new exhaust will do is to bolt it on.

    Better, imo, to start from the rich side then go lean, in small stages, until you reach the point where the engine will just rev-out cleanly under full power/WOT. That will get you within 1-2 steps of ideal and keep peak combustion chamber temps down. Typically, Lifan engines run very hot until broken-in.
     
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  12. kirrbby

    kirrbby Well-Known Member

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    I have a link and maybe some info for you. I have a cheapo Chinese pipe that I tried on my 125. It came with a removable baffle, otherwise its just a big open pipe. Nothing inside to quiet the noise etc. It's also very short. The baffle was a restriction but it would quiet the noise considerably. Without the baffle it was super loud. I drilled some holes thru the baffle for better flow but that did make it somewhat louder. It's a crappy pipe for quieting a big motor any way you shake it. I just used it for a temporary stint till I could mount my good pipe. See pics in the link for that baffle modification. You can look more into that thread for my exhaust info with that bike.

    Check post #86 the thread I linked in the next post.

    Then I mounted a Mizumoto pipe, nice pipe, that I bought from fatcaaat. It was missing the removable baffle but it has some sound damping built in. The pipe was loud but not too loud. Sounded good but I needed to quiet it at least a little for my situation. Fatcaaat found the baffle for me. He had modified the baffle similarly to what I had done with the cheapie pipes baffle. When I installed the baffle it did exactly what I needed it to. Quieted a little with little restriction. So, I'd say pick a pipe that has some sound damping and a removable baffle. Then you can still make modifications to the removable baffle, IF that's even necessary. Somewhere in the above thread there are links to a couple videos of the bike running both exhausts that I mentioned.
     
    #11 kirrbby, Nov 7, 2015
    Last edited: Nov 7, 2015
  13. CraigKapo

    CraigKapo New Member

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    Okay awesome. Ill do some shopping today and decide on an exhaust and get it ordered. Then decide what to do when I get it and put it on.

    I appreciate all the advise guys.
     
  14. kirrbby

    kirrbby Well-Known Member

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  15. kirrbby

    kirrbby Well-Known Member

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    Well apparently I clicked dislike on this post. How do I change that?? Seems I can like it, dislike it, and thank for it. But I can't undo any of them. Wonder if I've disliked any others that I don't know about?
     
  16. CraigKapo

    CraigKapo New Member

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    I thanked myself for the post earlier. LOL. But its not showing up now so I must have hit the back button enough that it didnt go through.

    I like the style of that short pipe you installed. I would just be worried about the amount of noise it makes since I do have a neighborhood nearby. Im certain I could get away with it since I do live outside city limits, I just dont want to become known as "that guy on the obnoxious minibike" when I do go by the neighboorhood or when I drive into town.
    Does that pipe have any other baffles or chambers inside other than the removable baffle you modified? I would think it would have to in order to provide enough back pressure, but there again I am still learning about these motors. Is just a header pipe enough back pressure to not risk burning valves, or whatever else to little back pressure could damage?
     
  17. kirrbby

    kirrbby Well-Known Member

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    That short pipe is empty other than the baffle. That might make it easy to fill with steel wool or other diy noise suppression. It is a pretty nice lookin setup tho.
     
  18. Sapes

    Sapes New Member

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    I know I am late to the party but I just got a new pipe for Lifan 125 on my CT70. It's a Phatmx underneath pipe. I bought it second hand for a $100. The orginal owner fitted it to Z50 but didn't like how it looked. My Lifan has a Mikuni VM22 with it's orginal jets which I am not sure what size they are. From my limited research I need a 20 for my pilot and for the main some are running low 100's to 160's. So I will fit the pipe and I will report back. Here's a photo of it mounted on a CT70. https://encrypted-tbn2.gstatic.com/...gUGMGabnsGsx_6KXs_yBAVb9qqIlhs4_4GhZVYLfYjPik
     
  19. TNStreamerDreamer

    TNStreamerDreamer New Member

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    So did you get your jet sizes figured out?
     

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