Motorbike's rpm slowly increases on its own? Very strange,

[Horsley6]

Hi, ive got a Peugeot XPS 50cc. As soon as i kick start the bike the rpm stays as a pretty reasonable rate for about 5-10 seconds, then the rpm starts to increase, as if i was slowly turning the throttle to full. I CANT kick start the bike and let it idle, The rpm just increases to full throttle on its own.

This hasnt just started happening to the bike either. Its been re-built and hasnt even ran in the new 50 kit. The carb that is on is a 21mm TNT carb if it helps.

I have adjusted the idle screw and that hasnt made any difference at all. I adjusted the mix screw aswell to see if that made it better or worse. Still no change. The slider in the carb is working fine, it isnt stuck or anything. I think the bike is running too rich aswell because the plug is always a dark oily colour.

Whats causing the bikes rpm to slowly increase on its own ?
P.s, The little pin inside the carb is on the 2nd notch down. What would changing this do ?


The problem - https://www.youtube.com/watch?v=abKnKvoR1cA&feature=youtu.be

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EDIT:- Heres the picture of my slider, ive adjusted it so its all the way down but it still looks to me like its open too much. I kicked the bike up and the problem is still here.
https://i45.tinypic.com/23rvl78.jpg

[russell210276]

generally a airleak course idle to raise slowly what happens wen the idle is going up and you rev it a little does the engine revs hang then drop a little.

also check your throttle cable adjustment and make sure it isnt getting snagged anywhere.

is it a 2 stroke? as you said you have a rebuild what about the crank seals was they replaced?

[Horsley6]

Hi, just went outside to have another look at the bike, and as soon as i kick start it up it just got to maximum rpm within a few seconds. No waiting about it, i had to turn it off straight away. Throttle cable is fine its got plenty of slack, and yes, its a 2 stroke and yes crank seals was replaced.

[russell210276]

mine had a similar problem where it would rev straight up but that turned out the needle and slide needed adjusting and wasnt sitting correctly.

the only other problem is a air leak your gonna after spray around the carb manifold and airbox and the head and base gasket with eva wd40 or easystart the engine note will change if theres a leak but first just have a visual inspection especially around the carb manifold look for cracks, splits, tears. can you put a vid up of the problem?

[Horsley6]

Here's a vid of it:- https://www.youtube.com/watch?v=abKnKvoR1cA&feature=youtu.be


As you can see, as soon as the bike is kicked i dont even have to touch the throttle and the rpm is already sky high. Im turning the key the stop it revving on full for a long period of time (the piston hasnt been ran in yet)

[russell210276]

thats what mine did remove the throttle linkage on the carb and re seat it see if that cures the problem your needle sounds to be stuck open.
if not.

look for airleaks as i said and if you cant find anything look into the crankcase seal even tho its had a rebuild people put the seals the wrong way

[Horsley6]

re-seat the needle ? what notch should i change it to ?

[thomp1983]

he's not saying change the notch just take the slide back out of the carb and refit it checking it is in properly, only 2 things are likely to be causing your issue, a massive air leak or your throttle isn't closing properly allowing more air in, try refitting the slide with the throttle cable disconnected and see if that helps

chris

[Horsley6]

Right cheers chris, ill take a look tomorrow

[russell210276]

yer remove the cable and put the slide in on its own if you have a philips screw near the top of the carb undo that and make a note how far the slide drops in on its own then refit the cable and needle see if it matches if not the needle is open slightly and you need to adjust your throttle cable.

how many miles have you done since the engine rebuild?

[Horsley6]

0 miles since the re-build. Its been a slow re-build and this is the closest its been to "running".

[russell210276]

did you do the rebuild your self? the seal seems to be the culprit im afraid if everything checks out with the carb.

it will be leaking air in the crankcase best bet is a leak down test just to make sure

[Horsley6]

Not me personally, a friend of mine who race's dirtbikes. He's done his fair share of bottom end rebuilds. He's had ALOT of experience with bikes. He's re-build loads of bikes. My guess is that its something to do with the slider not closing propperly. Like i said ill strip carb down tomorrow and get to the bottom of this.

[Matt-]

I had the same problem with my NSR

it turned out to be a number of thing's,

Slider needle was not correctly fitted and also the throttle cable had seen better day's

Have a good Carb inspection, clean out the carb " again ", take a out slider check it, put it back in, check there's no leak's from the carb and fire it up
____________________
RIP jack (wheelie king), you will never be forgotten.
Current Bike's - Road Legal TZR 125 Pitbike, Aprilia SR50R 2010

[RobertT800]

I Also happend to have this problem on my NSR the throttle cable had snapped whist at full throttle pulling a wheelie it :/ check that?
____________________
1998 NSR 125 (SOLD)
2000 CBR f4 (Crashed and sitting in a garage while i decide what to do with it)
2000 R6

[Matt-]

[Horsley6]

ive found the problem. The splitter is lifting bottom end of the throttle cable causing the slider to raise slightly.