just installed sbp expansion pipe now problems(maybe)

Discussion in '2-Stroke Engines' started by thuginfc, Nov 23, 2009.

  1. thuginfc

    thuginfc Member

    ok i ordered and instlled the expansion exhaust from sick bike parts instantly i noticed huge torque gains but it is now reaching a max rpm and staying there i can pull the clutch and try to rev more but it barley revs out anymore its topping out at maybe 20 mph but then sometimes ill be cruising along and then it gets extra grunt like it should be running like and will rev out fully and top out at about 33mph ill bring it down and then its running crappy again

    things i tried

    Clean air filter
    replace cheapo plug with ngk bh7
    upgrade to msd plug wire and boot
    ported out carb a little bit and removed that stupid air robbing ring in it (this actually made a good difference in accelerating)
    sealed carb on with gasket sealant
    adjusting chain (thinking it might of been too tight)
    adjusting clip in carb though all the positions but stock was best as per the plug color
    60 psi tires

    does anyone know what could be causing this? i would like to get it worked out before my new sprocket comes in

    my bad on title spelling just installed*** not unstalled
    Last edited: Nov 23, 2009

  2. motorpsycho

    motorpsycho Active Member

    did you tune the pipe? The sbp pipe is tunable by cutting the pipe that comes out of the cylinder. Depending on how long / short that pipe is, will alter when the engine breathes the best. It could be that you are reachng the peak power band of the pipe sooner than you were reaching it with the stock exhaust. when the motor "comes on " the pipe, it will give you a supercharged effect and you will feel it hit the powerband. But, i'm thinking that if you are reaching the powerband before the motor is reaching it's peak rpm, then maybe the motor is fighting the pipe because it has passed the powerband?
    I could be way off base on this, i'm just guessing.
  3. thuginfc

    thuginfc Member

    no it is hitting the power band sometimes thats when it takes off and smoothes out real nice and yea i tuned the pipe i cut about 3/8 -1/2 inch of the pipe in 1/4 inch ingroments till it hit the best rpms

    when i first put it on i rode around the block a few times and i seemed perfect till the bike warmed up i guess
  4. spad4me

    spad4me Member

    What ring did you remove from the carb?

    I installed a tuned pipe from another supplier.
    I selected an initial length of twelve inches from the manifold to the beginning of the fat part of the chamber..
    This is a good place to start.
    I kept the twelve inch pipe as fine for me.
    The jet needs to be re drilled.
    Trial and error.
    I drilled it bigger .
    Then soldered it closed and used successively larger holes until it ran very good.
    About ten or so tries.
    I finally removed the pipe and re jetted the carb.

    The Arizona laws changed, requiring less than twenty miles per hour OR ELSE.
    I figure a thirty percent increase in hp from my tuned pipe.
    Another ten percent for port matching, and exhaust and intake porting . Grinding for greater flow.
  5. Ghost0

    Ghost0 Guest

    Intermittent problems are typically carb or ignition related. Whenever there is a sometimes it does this or sometimes it does that, this is usually the problem. Definitely check for air leaks. Most of our customers report the need to lean the engine out after installing the chamber, most can get away with just lowering the needle all the way by putting the clip on the top notch. Some however need to change jets or use the solder and drill method. How many miles do you have on the engine? If it is not broken in yet this may be contributing to your issues.
  6. 210061741

    210061741 Guest

    I noticed with mine if the gasket in between the Intake Pipe and the Intake port on the Engine blocks the intake port at all my bike runs like ****.
    Use some aluminum cookie sheet to cut a matched gasket.
    assemble the intake.
    Remove it and you will have a nice impression of where things seal and are open.
    Trim the gasket re-assemble and your good to go.
    Also make sure you grind the exhaust gasket to match the port as close as possable.
  7. thuginfc

    thuginfc Member

    the ring i removed was the one just inside the intake if you take your filter off youll see what im tlking about

    i will try leaaning it out again and see what happens my motor has about 300 miles or so. im guessing its broke in

    i opened up the exhaust gasket and the intake gasket
  8. spad4me

    spad4me Member

    Is the ring you removed the choke?
    Kind of like a washer with a lever attached.
    Remove the cover to the magneto.
    Dry it out with a hairdryer , heat gun or just leave the cover off for a day or so.
    After it is dry seal the wire's where they leave the magneto housing with silicone.. seal the magneto housing .
    Remove the kill switch run the wires ,blue and black directly from the magneto to the cdi.
    Cap off the white wire.
    Turn off the fuel petcock.
    Remove the two screws holding the bottom of the carb on.
    Look for junk in the bottom of the bowl .
    Turn the petcock on to see fuel freely flowing from the needle and seat.
    Gently push up the fork that the float pushes against.
    Fuel flows then stops.
    Carefully remove the jet and push a needle through the tiny hole in it
    You need fuel spark and air.
    After every thing is back together..
    Start the engine.
    Spray any thing even windex.
    On the intake manifold , and carb to check for leaks
  9. thuginfc

    thuginfc Member

    no the ring removed was actually part of the carb casting it clearly slows the irfloow though

    tried a stock carb, ran worse.
    the carb is completely clean removed the jet and every part and soaked it overnight in carb cleaner.
    it ran better leaned out a little more but the plug didnt seem right color and motor seemed running too hot so i got it second from top notch nowbut isnt running as good as it was leaner

    is it safe to run it on the highest clip?

    i too thought it might have something to do with magneto took cover off cleaned everthing out it all looks brand new inside there
  10. thuginfc

    thuginfc Member

    also tried running it without the kill switch no different so i hooked it back up
  11. Ghost0

    Ghost0 Guest

    I run mine with the clip on the top groove and have a .62 mm jet. Stock jet is around .7 mm.
  12. thuginfc

    thuginfc Member

    so your running way leaner than stock, i will move my needle back to the leanest position and try it again but it seemed to run pretty warm

    i figured opening the the carb and adding this exhaust would alow for more airflow and would lean it out i am an auto mechanic and usually when you add more airflow you have to add more fuel but i guess its diff on a 2 stroke

    other than getting this thing tuned in right i love yalls exhaust i can now pull wheelies on this thing (until i get my 36t sprocket atleast)

    gonna run this thing foras many miles as i can upgrading it when money permits me and look for a nice frame for my next build and will def get a shift kit on that thing
  13. Ghost0

    Ghost0 Guest

    You would think more flow means you can use more fuel but how the expansion chamber works is it actually uses a pressure wave to force your exhaust port closed before the piston closes it. This increases the amount of fuel in the combustion chamber which is why the expansion chamber adds more power. Since it is keeping more of the fuel/air in the combustion chamber it tends to make the engine see a rich condition which is why leaning it out tends to work. The pressure wave is also why you can adjust the pipe, the trick is to get the pressure wave to do its thing at the right time to increase horse power, expansion chamber design, tube diameter all effect how the pipe works but changing the header length is what makes the biggest difference. Shortening the header means the pressure wave takes less time to travel the distance it needs to do its job. So it provides more power in the higher rpm range because the timing of the pressure wave corresponds to the rpm. If you lengthen it then the pressure wave takes longer to travel and corresponds timing wise better at a lower rpm.
  14. thuginfc

    thuginfc Member

    after trying multiple carbs, multiple needle settings, stock exhaust diff plug and wire ,diff magneto diff cdi....I FINaLLY FIGURED IT OUT!!!!

    well it was 2 things i replaced the fuel filter, noticed that the line had tiny crack in it pulled it off plugged the end and blew through it sure enough air blew out, replaced line and took off running great get down the road a little and it starts bogging reached down and grabbed filter and it took off like a bat outa ****

    rode a lil more and looked down to find the filter full of bubbles went home ziptied filter to frame and took off again running better than ever passed a little cop radar box it said 38mph(prob not very acurate but its all i got right now) thats on a 44 tooth my 36 is scheduled for delivery tommorrow WOOOHOOO!!!

    still got questions though:

    whats the best way to keep fuel line from bubbling?(noticed its still doin it a little)

    also should i seal the slide opening/throttle cable opening on the carb (not leaking but still for good maitnence)

    how much top end should i gain with my new sprocket? (i heard 7-10mph)
  15. thuginfc

    thuginfc Member

    still having a problem at wot

    when i acellerate it runs good no bogging or anything until i get to around 27-30 mph it just stops reveing and bogs down a little i can roll off the throtle and it starts picking up again until i hit WOT and it bogs again

  16. Ghost0

    Ghost0 Guest

    Still sounds like a fuel mixture problem to me. All I can say is try going leaner. If that doesn't work try going richer. Since your issue is at WOT, the only way to achieve this is by changing the jet. There is another possible explanation. You may be out revving your gearing and port timing. With stock port timing these engines have kind of a built in rev limiter. You could try going to a smaller rear sprocket to take advantage of the optimum power band of your engine. You could also try shortening the pipe to see if you can move the power band a little higher in the rpm range.
  17. thuginfc

    thuginfc Member

    i have changed to a 36 tooth rear sprocket and it doesnt sseem any faster than it was before maybe a little bit i know i could get it faster cause its not reving no where nearas high as it used to if i could just get through the bog soetimes if i feather around on the throttle when it bogs i can get it to rev out a little more

    ima try to open up the intake tube a little to lean out the fuel a little more

    also how much is the intake tube gasket restricing the motor stock havent had it off to look yet
  18. AussieSteve

    AussieSteve Active Member

    I agree with Ghost0. The bogging sounds like your mixture is still too rich.
    I had heaps of trouble in this area and now run the slide needle on it's lowest setting for mid-range and changed from an 0.79mm main jet to 0.73mm for high throttle openings. Made a huge difference.
    What colour is the plug?

    Heaps - it's worth cutting your own or trimming a stock one.
    Rock Solid Engines sell a laser-cut inlet gasket that perfectly matches the port opening, if you don't feel like messing around cutting one. I bought one of these - wish I'd bought a few. Next order.

    ... Steve
  19. 210061741

    210061741 Guest

    If you get that pipe tuned right that lil motor should roar.
    But timing or "header pipe length is key".
    I actually made a larger dia header pipe which is 1 pc going from the manifold to the j shaped pipe.

    The sound wave created in the chamber needs to arrive at the exhaust port opening at the right time.

    Otherwise it lets fuel air out the exhaust or lets exhaust back in.

    You want the wave to hit and compress the fresh air fuel charge.

    My Grubee will rev to 8000 rpm with the stock carb and this pipe.
    I sacrifice some of the low end though.

    Keep playing when that pipe Comes therell be no doubt about it.
  20. thuginfc

    thuginfc Member

    well i got the pipe to hit right before it starts to bog and would be exactly where i want it(if it didnt bog) ive tried the leanest settings on the carb but it ran way slower gettting up to speed

    sorry if i made this thread seem bad about the exhaust cause the exhaust is actually great heaps more low end power and im sure once i getmy carb tuned right it will scream

    it didnt bog with my 44 tooth sprocket just kinda sputtered at WOT but would bust out of it after a few seconds.

    ive drilled the jets on my pocket bike before just dunno where all my ity bity bits went to but i would like to get a jet pack if anyone sells jets for theese carbs but i cant find any