Major Help Needed kymco 50cc 4t

Discussion in 'Scooter Tuning' started by Scootboy87, Nov 1, 2018.

  1. Scootboy87

    Scootboy87 New Member

    Messages:
    13
    Hey all I have a 50cc agility 16+ and I have some problems I need addressing.

    I have replaced exhaust with a technigas silent pro, I brought it brand new and couldn't see any restrictions.
    I have replaced the carb with a 17.5 or 18.5mm naraku. I am currently running an 88# jet.
    I have a derestricted CDI.
    I have an unrestricted boss and a multivar variator.

    My MAXIMUM SPEED on a flat is 31mph
    1. Does this sound correct.

    2. When I reach that speed and only that very top speed I start getting a gurgling from my exhaust at the muffler, what could that mean?

    3. I took out the large rubber grommet from the airbox, since I upjetted and replaced a new exhaust, to increase airflow but here I am having problems, the airflow is EXTREMELY SENSITIVE , I mean just from covering up 30% of the the inlet at the front of the airbox with some tape, makes a difference of 10kmh top end, and the bike running from ok to running terrible, should my airflow be this sensitive? Or is it because my oversized carb etc?

    Thank you all.
     
  2. 4strokelover

    4strokelover Active Member

    Messages:
    375
    Rides:
    Longjia Raptor 200
    Im not sure about this one. It could be because your still running it as 50cc with all those upgraded parts. I could be wrong but ts somthing to thin about.
    Someone will come along with better info than me aha
     
  3. scubabiker

    scubabiker NITROJUNKIE

    Messages:
    7,321
    Measure the intake part of your airbox. If its over the 18mm of your carb venturi its maybe a little too big.
    But I would say you have missed a restrictor somewhere.
    Like a hall effect sensor in the trans.
    Or a limiter wire going into the cdi box.
    Both do the same thing, cut the sparks over a certain rpm, even if the cdi has no limiter
    If you follow what I mean?
     
    Scootboy87 likes this.
  4. Scootboy87

    Scootboy87 New Member

    Messages:
    13
    I have a derestricted CDI, so I do not think that's the problem, I also installed the original CDI and the bike ran slow, so I removed the purple loop wire in the CDI plug and the bike ran exactly how it did with my unrestricted CDI, so it doesn't seem to be the CDI problem, I don't think there is a sensor in the trans cutting spark at high RPM or what woukd be the need for a resteicted CDI? Do you mean in the CVT?

    I have another question, my fuel tank is at the bottom of my bike, and I cannot see a fuel pump, the fuel line runs up to a a vacume petcock, I'm guessing this is just a vacume activated petcock as opposed to a vacume fuel pump, because when I took the outgoing fuel line off the petcock and cranked the engine over no fuel came out,

    1. Does this mean that my carb sucks fuel itself from the fuel tank below it?

    I bypassed the petcock in question and attached the fuel line directly to the carb, and the bike ran for a few minutes and then cut out, I eventually got it working again by reattaching petcock, and laying the bike on its side and cranking it with no throttle for a few minutes it barely started to tick over and would cut out at the slightest hint of throttle so I left it BARELY ticking over on its side for a minute and it slowly started working ok again.

    2. Did I probably flood the engine and foul the spark plug a little?

    3. If indeed I don't need this petcock, and my carb does just suck fuel from the tank below it, and I did just flood the engine the reason I flooded it I'm guessing is because, I am using the original factory cylinder but with a 18mm carb and 88 main jet, as opposed to the factory 12mm carb and 80 main jet?

    4. The reason i have such a big jet and upgraded carb was because the bike was struggling with speed, now I'm wondering if this petcock had something to do with it, Can I try jetting the carb down to an 80 and bypassing the petcock again, or is there another reason the bike stopped after a few minutes and refused to start when I by passed the petcock, I left the vacume hose attached so it shouldn't have nothing to do with that.

    5. If my petcock does have a problem and when I bypassed it the engine was receiving the right amount of fuel, but fouled the plug and flooded, could it have something to do with my timing or spark? This could also make sense has to why the bike was and is running slow in the first place?

    6. With or without said petcock, no fuel comes out of the fuel line when I crank the bike over, HOWEVER when I attach the fuel line to the carb the bike does run, is this normal? Or do I have a faulty pump, that I can't see, or in fact is this petcock a pump, and it's not getting enough vacume to work, or it's blocked etc?

    I have attached pictures, thanks for you're time.
     

    Attached Files:

    Last edited: Nov 5, 2018
  5. scubabiker

    scubabiker NITROJUNKIE

    Messages:
    7,321
    Yeah I would say this sounds like your vacuum pump is playing up, thats what that is. A vacuum pump, it works on the vacuum pulses from the intake manifold.
    3 pipes,
    1. line from tank into pump.
    2. Line from pump into carb.
    3. Vacuum line from pump to intake manifold.

    Check the vac line for breaks.
    Also when was your last service/valve adjustment?
     
  6. Scootboy87

    Scootboy87 New Member

    Messages:
    13
    It seems line 3 was loose on the manifold I put a clip around it and checked fuel output I'm getting a decent amount of fuel.

    Bro, now I have nearly tried EVERYTHING, I've completely changed CVT, tried different springs, clutch, weights, belts etc, there's a few kmh in it.

    Tried larger carb with different size manifolds and spacers and jets.

    Tried different air intake, stock, stock derestricted, freeflow.

    Tried 2 different exhaust, original and technigas silent pro.

    Mixing and matching all these parts has got me to 50kmh, this bike should do 65, 60 being a minimum.

    There's CLEARLY another problem, it could be the gearing because it was originally restricted to 25kmh, but if it was extremely short gearing the acceleration would be pretty fast right, but it's not.

    At this point would I be right to think the culprit can only be, Head gasket, Piston/rings, bad cylinder and or head, bad valves or bad valve timing crankshaft or something wrong with spark timing?


    At has a flat spot around 42kmh and after a few seconds starts accelerating again if that's any clue, not an obvious flat spot but it seems to stay at 42kmh for a few seconds before it starts moving again SLOWLY up to 48. Thanks again man
     
  7. scubabiker

    scubabiker NITROJUNKIE

    Messages:
    7,321
    Check your valve clearances see how they are.
     

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