Increase intake length on 2/stroke

Discussion in 'Performance Mods' started by geebt48cc, Apr 19, 2011.

  1. geebt48cc

    geebt48cc Member

    Hey there,

    66cc Slant is doing everything well, but after I increased the intake length to 9" it lost some of the bottom end torque? (just the opposite of why I did it to begin with?) I've sealed everything on new intake with JBWELD because I new that this would be a one time only fix.

    Well, its still a bit slower starting out, but then pretty much runs the same (bit less torque) than it did before I lengthened intake from stock to 9"? Main problem is when I pull in clutch handle it wants to rev up to very high RPMs? If I nurse throttle slowly, it will idle fine.

    Checking plug after 10/mile run, and its a clean tan burn. I'm confused because if there was a air leak causing revving, then I wouldn't think plug wouldn't look such a good tan (chocolate color) after 10/mile run?

    .............PS: I would be introuble if I didn't have the kill switch when it starts revving so high at idle?

    Any other ideas?

    Thanks very...............Glen:confused:

  2. jaguar

    jaguar Well-Known Member

    Plug readings are less reliable on these little weak engines.
    Did you find the air leak yet?
  3. geebt48cc

    geebt48cc Member

    Hey there Jaguar,

    Wellllllllllllllllllll? It's not the head or base of engine. I resealed intake to Jug (I know it looks like alot of black sealant, but just wanted to make sure at first it can't leak) I've taken everything back apart that does'nt have JB on it, and reassembled. So, I'm going to check today if weather cooperates.

    Appreciate once again you asking.............

    Attached Files:

  4. hi now i can see the picture better i should told you if you stall have the air leak i bet you it at the threads steel and copper don't like to mat good try useing some thread sealet for the threads that y i braze my barb fitting in for my boost bottle and then i jb wald because the threads alway leak :idea:
  5. geebt48cc

    geebt48cc Member

    Good deal Proctor.......

    I used JBweld on the threads + carb. I cut just a bit off to get better fit, and it's right at 8.5" total. Took out today about 5/miles and do believe now it's better than before. lol, See it takes awhile to check preformance because the weather here is so eradic this time of yr. So, hope that 8.5" is the length I want for a 2010 Skyhawk 66cc, cause I can't go back now after using JBweld huh.....

    .............but I do believe I'm on to something here, but checked plug, and now it's a very light tan............I might drop one?

    Thanks for checking out................. Glen
  6. your welcome and let me know how it go's Glen :grin5:
  7. jaguar

    jaguar Well-Known Member

    Yeah, put something on the threads where the hose clamps onto them or else you'll have a leak there.
  8. Ozi

    Ozi Member

    Main problem is when I pull in clutch handle it wants to rev up to very high RPMs? If I nurse throttle slowly, it will idle fine.

    I have similar symptoms to what you describe even with my small extension.. had to do it to clear the frame. You have no leak trust me Ive tried everything. I think the extra length/volume is somehow siphoning fuel out during deceleration .. :confused:

    Attached Files:

  9. DuctTapedGoat

    DuctTapedGoat Active Member

    You can remove JB Weld - just heat gun it.
  10. hi my intake idles fine ozi i bet you have a small air leak :cool2:

    Attached Files:

  11. jaguar

    jaguar Well-Known Member

    If there's no air leak between the carb and engine or at the crank seals then you just need to jet the carb richer. Raise the needle. It's not unexpected that a mod like this would require rejetting, especially if it was off to begin with.
  12. geebt48cc

    geebt48cc Member

    Yeah, Jag I'll tell you more after tomorrow. I believe your right about raising the needle one more slot. Jag, see, I've milled/ported/expansion and now intake length on carb. I'm sure that this might just make it run leaner? I pulled plug after a few miles, and it's tan in color, but alittle to light tan for me. So, I'll pull needle up another slot.

    PS: I'm very interested in your ignition also?!~
  13. jaguar

    jaguar Well-Known Member

    From a research paper I also recently found out that increasing the stock pipes length (from piston at exhaust port to muffler) to a total of 25" to 30" can give a boost at low revs. I just tested 30" and gained 13% speed going uphill at around 3600rpm. But it lost speed at higher revs. The graphs show that 25" would gain at both low and high revs. I'll cut off 5" and try it again tomorrow.
  14. geebt48cc

    geebt48cc Member

    Well, I got my extension on intake done. Works well! I weigh right at 255, but can take the hills here in SW VA. right about 4-7mph better. So, if you see me, you better look fast.............(Cause I'll be gone!~)


    Attached Files:

  15. jaguar

    jaguar Well-Known Member

    There's also the option of using the offset intake manifold which will make the intake length 5+3/4". Adding one inch more with tubing will put the engine in the ballpark of the ideal 6.5-8.5" length.
  16. goodtime65

    goodtime65 Member

    high reving and than slowly coming down is a for sure sign of an airleak