4 stroke upgrade question

Discussion in 'Performance Mods' started by cj6jeep80, Feb 22, 2015.

  1. cj6jeep80

    cj6jeep80 New Member

    Hello.....I currently have a HS 49cc................ SBP air cleaner........ SBP shifter kit ........My bike runs really well, but after putting on my SBP air cleaner I have had to adjust my idle screw to the point where it is almost falling out.....after setting this screw wide open the bike seems to run just fine.....quick on take off ....responds well to throttle.....and a top speed of 35 or so.....never satisfied, I read how it's possible to drill out the jet to a larger size, thinking this may add more power or at least allow me to set my idle screw in a better position.....so I tried drilling out my jet a little bigger(size 72 drill bit)....but i'm afraid I might have screw it up somehow as my bike starts and runs fine, but with a little throttle the engine starts to sound a little rough.....Haven't been for a test drive yet as we are presently over loaded with snow at the moment.....I can only assume the bike would run poorly after hearing it running rough at half throttle in my garage...Funny but it idles quite nicely.....I am wondering if this is because I need to make a exhaust upgrade?....or have I drilled my jet too big?.....Or am I better off leaving the stock jet size and have my idle screw wide open?...........Any help would be appreciated.......Can you please tell me if it is necessary to have a exhaust upgrade with a SBP air cleaner and a enlarged jet or is the exhaust optional?.....Thanking you in advance.....Rick

  2. msiert

    msiert Member

    I believe the stock jet size in the HS is a #75 bit. Might have jump to much by going to a #72. I heard you could solder the hole and re drill it. I would recommend to try a #74 and see how that works before going to a #73.
  3. darwin

    darwin Well-Known Member

    Are we talking about the idle jet seated below the black plastic idle rpm adjustment screw? If so get a Honda idle jet from Honda and it will cure that issue.
  4. cj5jeep80

    cj5jeep80 New Member

    Thx....No....I am referring to my main jet in the carb.....Will have to try drilling a smaller hole....Any advise on what I should be doing with my exhaust?... Frankly, I like the stock exhaust, as it is quite......but if a exhaust upgrade will make the bike perform better after putting the SBP air cleaner and re jetting, I would be willing to put up with the extra noise.....Thanks again
    Black Beauty.jpg
  5. KCvale

    KCvale Motorized Bicycle Vendor

    Dumping the can muffler for a real one helps regardless of the air cleaner.
    I just use a spare 2-stroke muffler, preferably the Non-Cat ones.



    Or you can get a 'semi-poo-poo' pipe.


    And there are multiple full poo-poo's but they are bit more restrictive and pretty much just for looks.
    They are all just about as quite, less restrictive, and don't blow out at your calf in front of you.

    If you want nice little boost for $8 put an NGK 7544 (CR7HIX) Iridium spark plug in it.

    It's a bit longer than stock for bit more compression, they make one heck of a spark, and it should last the life of your engine.
    I put them in all my HS 142F 4-stroke builds.
  6. cj6jeep80

    cj6jeep80 New Member

    hey ....thx for ur help.....bike looks great.....wow...I will certainly try that spark plug you recomend....I think I will try these 2 stroke mufflers then...NON CAT?..........I had no idea you could use them on a 4 stroke.....As you can probably tell, this is my first bike.....so I'm rather new at this...........Is there a huge difference in noise after changing the muffler out?....and is it easily connected to the engine?.....Thanks everyone for the help..
  7. KCvale

    KCvale Motorized Bicycle Vendor

    You are very welcome, and thanks for the kudos ;-}

    If anything a new pipe is quieter, especially when riding.
    The non-cat or small cat pipes have better flow.
    The epa pipes have a bigger cat, a bit less flow but better for the environment.

    The 4-stroke has a cocked exhaust port, but the pipe work fine coming down on the right side.
    A 2-stroke has a level port, the pipe comes down on the left.
    The semi-poo-poo is especially for 4-stroke and comes down on the left as well.

    If It's a little off, you can just elongate the mount holes on the mount flange so you can twist it a bit.
  8. cj6jeep80

    cj6jeep80 New Member

    Hey thanks again......Just tried to order a black exhaust from bikeberry but they are out of stock in black.....I think those are the ones you are referring to......Great advice ....Thx
  9. cj6jeep80

    cj6jeep80 New Member

    Hello KC.....I have ordered a black 2 stroke exhaust online.....but when I went to remove the stock exhaust , I am having trouble removing the old exhaust studs from the engine......Also wondering how you went about mounting the new exhaust?Will I need new bolts and gasket?.....Do the old exhaust studs unscrew from the engine?......Thank you ...Rick
  10. KCvale

    KCvale Motorized Bicycle Vendor

    Yes the exhaust studs come out, just use vice grips (or double nuts) to get the stock exhaust studs out and use some nice bolts to hold the new pipe on, I like grade 8 Allen's but hex bolts will work.
  11. cj6jeep80

    cj6jeep80 New Member

    Just wanted to thank you KC....Just change my spark plug to Iridium....Then bolted on my new black 2 stroke exhaust (allenwrench bolts) like you recommended.. I did have to heat the pipe and bend it in a vice somewhat, but very little....fit on very easily...It was like a breath of fresh air for this little engine.......Purrs like a kitten....and no extra noise, real quite.....Couldn't be happier after following your advice.....Thank you....Rick
  12. KCvale

    KCvale Motorized Bicycle Vendor

    You are very welcome Rick.
    I'm happy to share those easy cheap little upgrades you can actually feel when you ride, that's why I do them on most everything I build from the get go ;-}
  13. rockrtboy

    rockrtboy New Member

    will this give any boost in mid-range power? I need a little extra for hills.