Exhaust mod = performance boost

Discussion in 'Performance Mods' started by dzdaz, Mar 8, 2007.

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  1. dzdaz

    dzdaz Guest

    It finally got warm enough(above 35) to have a nicer ride here today. Still wasn't getting very good top end so I did the exhaust baffle cut off mod. WOW! I got better performance all around, better power, about a 5 mph boost, and less bogging at wide open. It did bog a little but then pushed through it and actually started to pick up more speed. Didn't really notice it being much louder, just a bit deeper at lower speeds. Reading thru this site has really been helpful. Thanks to everyone. I'll definitly be doing some more modifications to my bike in the future. e.g. sprocket, plug/wire, better oil/gas, etc... Anyone know where I can get a gas cap that doesn't seep or are they all pretty much the same? Mine came with the 70cc kit I got from dacscommm.

  2. azvinnie

    azvinnie Guest

    glad to hear ya riding in better weather, as far as the caps for the gas tanks, some leak and some don't, we just got a kit from dax and the carb dosen't work. i lent him my spare carb and his bike fired up and stayed running. kind of crappy but wtf can you do.....anyway im building a trike and might have a spare cap that l can send ya when im done going through all my parts that l have............you taker ez dz
  3. Guest

    Guest Guest

    Are you returning the carb, or are you going to try to get it working first?
    Set the needle clip in the middle. Make sure the carb is getting fuel....that the float is letting fuel in.
  4. azvinnie

    azvinnie Guest

    when i held the carb in my hand i felt alot of rattleing, l open the bottom of the carb and noticed the throttle hole pin wasen't even screwd in(part#47on grubes diag). the other prob was that the cilinder (with the needle) that goes into the carb was getting stuck in the carb. i switched it with a spare carb and it worked fine. thank god for spare parts!!!!!
  5. dzdaz

    dzdaz Guest

    I'm gonna keep the carb, and try that needle washer adjustment.
  6. mrsaxman99

    mrsaxman99 Guest

    how much of the baffle did you cut out? I cut the ~6" tube that is connect to the end cap off, and got an increase in power, but it cuts out at higher rpm due to bad backpressure
  7. Guest

    Guest Guest

    It's not cutting out due to bad back pressure- it's cutting out because now it can run faster and is running out of fuel. put the next larger sized jet in and set your clip in the slide to the middle notch.

    If you don't have access to a larger jet, then you CAN drill the main jet out. Find a drill bit that almost fits in it and turn it in with your fingers....then pull it straight out and some of the jet material will come with it. no more than that though. If you aren't confident in trying this, then buy a bigger jet....your dealer/seller may be able to help with this.
    dchevygod likes this.
  8. gone_fishin

    gone_fishin Guest

    'joe...it seems most of these chinese carbs have 4 slots on the needle.

    most of them run best on slot 2 from top, (me: gutted muffler w/cap on, #2 slot, cut-out at top-end) are you saying try #3 slot for a bit more fuel? i have and it hasn't improved performance, but i've been considering boring the jet a tad. after your post, i'm confident it's worth doing.

    i'm sure others agree with me when i say i appreciate your layman's info 8)
  9. Guest

    Guest Guest

    FYI the idle mixture screw adjust the idle mixture to about 1/4 throttle. The needle covers from 1/4 to about 3/4-7/8 throttle, the main jet is pretty much for WOT.
    TheBaldKiwi likes this.
  10. mrsaxman99

    mrsaxman99 Guest

    we (me and augidog) don't have idle mixture screws...along with most of the rest of us. We have an idle screw...that just sets the lowest the idle will go...has nothing to do with mixture.
  11. Guest

    Guest Guest

    Well, you know someday I'm going to have one of these then I can speak with great authority instead of just passing along general engine knowledge and diagnostics! :grin:

    Seems strange that the carbs don't have an idle mixture screw...is there maybe one under a cap? Can someone post a big photo of each side of the carb?

    Anyhow, let me know if you find an improvement in the top end when you enlarge the main jet.
  12. mrsaxman99

    mrsaxman99 Guest

    our only mixture adjustment is through moving the pin that goes into the jet.

    I can take a pic or two tomorrow. I don't know that I'll drill out the jet, that would probably make it run wayyy rich throughout the entire rpm range. It almost seems I need that "5th injector" push...aka a forced fuel induction at higher rpm....if in fact a lack of fuel is what is causing my engine to cut out at high rpm. With all the research I've done, however, it does seem to mostly be due to the fact that the exhaust isn't allowing the proper tumble/turbulance/pressure/whatever-you-want-to-call-it for the correct burn cycle at that higher rpm.
  13. gone_fishin

    gone_fishin Guest

    well, i'm gonna try the jet thingy, because i can always back off one notch on the mixture...i think it's gonna be the solution, tho.

    Bikeguy Joe: srdavo posted an excellent pictorial on the carb, but i'll be danged if i can find it...

    the main needle in slide has 4 slots & a circlip to adjust depth/mixture.

    the idle screw merely seats on an angled slot on the slide, in or out for more or less.
  14. mrsaxman99

    mrsaxman99 Guest

    augi you gonna drill out the jet? I figure at least one of us should? lol
  15. gone_fishin

    gone_fishin Guest

    yes, i've been flirting with the idea all along, now i just need to find the right drill-bit.

    i'm gonna be busy all this week maybe not even get to ride, surely no time to work on it. i'll let you know when i make the leap.
  16. Guest

    Guest Guest

    Alrighty then..... I DO mean to drill the MAIN JET, not the one the needle goes in! These carbs do have a main jet, right?

    I've never seen a carb with no idle mixture adjustment (except for the smallest of two stroke engines- the Cox model plane engines).

    Just thought I'd add that.

    Also augi, you may want to take the jet with you to home depot or wherever you are going to look for drill bits and find one that is close to the opening in the jet.

    I know it's going to be really small, and therefore cheap, so you may want to buy a couple of sizes.

    A reminder to those that will try this- remove only the smallest amount of material from the jet, don't use a bit that is so big you actually have to drill it in there, you should be able to just hold the bit with pliers and turn the jet to get the bit to "thread in" and then gently pull it straight out. don't remove any more than that until you try it.

    Now, can you buy a replacement jet from your "dealer"? Maybe they have a slightly larger jet in stock? That would save the hassle of finding the right sized bit, and playing the "looks about right" game.

    I have done this before BTW, mostly because I'm too cheap to go all the way to the bike shop, find out they don't have the right size in stock, then wait two weeks to pay a rediculous amount for a tiny piece of brass!
  17. Guest

    Guest Guest

    BTW- if you remove the float bowl and look into the bottom of the carb, is there a bigger jet next to the one near the center one where the needle goes?

    That should be your main jet.

    I really need to get one of these things....... :???:
  18. gone_fishin

    gone_fishin Guest

    well, for no pics you're getting it mostly right....

    (note how too much tilt could in fact cause float-binding & false fuel-level. mixture is adjusted by changing the relative position/height of the needle in relation to the slide. on the other side of the slide is the angled slot that the idle-screw acts on)

    yes, the main jet is at the bottom of the "pick-up"...it's gonna be a fairly easy job, i've bored/jetted many a single-barrel/6-cyl chevy in my day.

    actually, when you DO get to look at one, you'll be a be a bit impressed i think, pretty good features thru very simplistic engineering.
  19. mrsaxman99

    mrsaxman99 Guest

    I might bore out my jet just a tad today....I am convinced that my fuel is becoming a restriction...
  20. gone_fishin

    gone_fishin Guest

    i haven't been able to do it yet, but here's what i've learned about mine: it's running as best it can & it runs great. it responds a bit at topend when i apply a tease of choke, so i'm convinced...

    maybe rif has the right drillbit, i could do it this weekend.