M2R YX140 ( w/ Molkt carb ) PROBLEMS!!

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mason2race

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Hi mini riders I have got some problems with my brand New pit bike from funbikes.co.uk in the uk.

Bike came already built up(PDI) btw!

So, first & foremost before first engine start removed the plug out(Denso...btw) was sooty black!! Banged in a fresh NGK cr7hsa plug ..then continued to kick the bike over a couple times on choke but no start so then I took choke off n kicked it and it started! I let it warm up for 10mins then took it out for its hour run in...that went all according to plan. Was feeling very happy until i came back to it hours later...the bike would not start at all...very unhappy at this point! So i decided to take the plug out to find the New plug all sooty black just like the Denso!?! Cleaned it up to looking all New again & refitted! Then the bike started...whoop whoop :) let it warm up,then done the oil change to New Silkolene comp 4 oil ( the best I'm advised ) started the bike again & let it sit for 10_15 mins then hit the kill switch! Job done!

The next day.... after a few tries the bike started,warmed it up as per then set off for a ride....INSTANTLY i noticed once shifting into 2nd gear about 1/4 to 2/4 on throttle the power disappears while backfiring & popping,nearly throwing me off the bike once power returns at half throttle all the way to fully open! This happens in every gear if the throttle is below the bog point!

I've called Funbikes about this and they say its a possible idle/air mixture adjustment needed so tried that no difference.... so before i call them back to vent my frustration at i would kindly ask for you're advice as to getting my bike running perfect!

Thanks
 

motorman

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Could be a couple of things mate.

So it wasn't having issues the first time you rode it after you finally got it started?

It sounds like your air/fuel mixture is still off. A good starting point is to wind all the way in and then wind back out 2.5 turns.

Otherwise your jetting will be out. Have a search around the site as there are a lot of threads on how to jet your bike.
 

my67xr

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Welcome to Miniriders,

The Molkt carbys seem to be a bit hit a miss
They can suffer from sticking floats, which can cause the carby to flood.
Try tuning it, start with the mixture screw at 1.5 turns out.
Start the bike and let it warm up, then raise the idle speed a little,
then turn the mixture screw in or out till you hear the revs rise.
You want it running at the highest smoothest rpms, fine tune it.
And when you are happy with it, drop the idle speed back down to normal again.

Take the bike for a test ride and see how it goes


With the NGK spark plug in it, was the original Denso one a Resistor plug ?
We run then in Australia with a C7HSA, using a resistor drop's the power output at the electrode.
I f you have a multimeter, set it to 20.000 ohms and measure the resistance of the spark plug cap.
It unscrews off the end of the coil lead, place on lead from the meter to the thread where the lead screws in and the other to the part that clips onto the spark plug
You should get a reading close on 5,000 ohms (5K ohms)
If you get that, then you don't need a resistor spark plug as the resistor is built into the spark plug cap.
If you get a reading close to 0 then you do need a resistor spark plug.


With the popping, do you have the air filter oiled up with filter oil?
If not it causes the engine to run lean.
If it is, then i'd try moving the needle clip down a notch on the needle to richen it up a little
 

ringo

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Can fix all your problems in three easy steps!!

1) Remove the molkt carby

2) Place molkt carby in disposal unit

3) Purchase and fit 24 or 26mm oko carby, happy days!!! :D
 

mason2race

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Thanks for the advice guys...i did have a tinker but no real difference!On a positive note the people I bought the bike from sent me another new molkt carb which I have installed with a new heat spacer & gasket! So here I think lies the problem. The bike now starts within a few kicks everytime wen cold,instantly wen warm and is smooth on throttle & ideal wen idle! But soon as I get to quarter throttle wen riding it starts to splutter until past half throttle as such!? This has gotta be a main,pilot jet issue?? P.s the main jet is stamped 102,no idea what the pilot is!
 
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my67xr

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Have you tuned the new carby to suit your engine?
Has your foam air filer been sprayed with filter oil?

If the carby hasnt been adjusted to suit then that could be part of the issue.
Start the bike and warm it up,
Raise the idle speed a little, then adjust the mixture screw in or out 1/4 of a turn and let it settle for 5-10 seconds.
listen to the way it runs, you want to find the spot where it runs at the highest/smoothest rpms.
Keep adjusting it out till the engine starts to run a bit slower
Then adjust it back in while listening for the smooth/high revs.
once you think its close then drop the idle speed back down to normal again
Take the bike out and give it a try.

Does the engine rev smooth and without hesitation when you blip rev it?


The other thing woth a new engine is the valves might need their clearances adjusted.
OORacing have a good video on youtube that explains how to do it.
 
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mason2race

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Hi sorry for the late reply! So the new carb is running spot on I think, rev is smooth when bike is idling,blip to wide open is fine but soon as I set off in 1st gear & so on as turning the throttle is loses power around 1/4 then comes back at about 1/2 throttle and even feels like it's hitting a limiter (chugging,spluttering) at wide open throttle in each gear! I called funbikes yesterday and they said they've never come across this issue but have decided to send me out a new CDI unit as they think this could be the issue with the loss & regain of power..not presenting the rite curve as such!! 3 carbs later so that can't be it,there's something else! What do you guys think?
 

my67xr

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Have you tuned the new carby to suit your engine?
Has your foam air filer been sprayed with filter oil?
 

8r3nd0

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Lift the needle up/drop the c-clip down a notch, sounds like it needs richening up and also check you don't have and exhaust leak.


Sent from my iPhone using Tapatalk
 

my67xr

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With the chugging up top i reckon it's running too rich ^, so you could try moving the clip up on the needle to the top notch.
If that help's then you need a smaller main jet.
If it was lean it would feel flat.

Either that or there is too much oil on the air filter, but i have asked that question a couple of times now with out a reply
 

8r3nd0

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Says its losing power at 1/4 turn and has a big bog like feeling so from my experience with this on multiple bikes it's always been not enough fuel but no worries your never wrong I guess lol.


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mason2race

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Hi sorry for the late reply been soooo busy!! anyways im glad to say that the problem is now sorted... the new CDI unit was the culprit!! not sure how as they are sealed units but i fitted it then took the bike out & it was bang on the button,everything is how it should be... 140 animal!!! :) :) :)
 

mason2race

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With the chugging up top i reckon it's running too rich ^, so you could try moving the clip up on the needle to the top notch.
If that help's then you need a smaller main jet.
If it was lean it would feel flat.

Either that or there is too much oil on the air filter, but i have asked that question a couple of times now with out a reply

sorry fella i completely forgot to add...yes the filter has been sprayed with silkolene filter oil!! thnks for your help :)
 

my67xr

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Good to hear it's running sweet
Thanks for the reply :thumbup:
 

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