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YX with 30mm Molkt carb Tuning Question

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©orza™

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Hey All,
Ok what yas all think. Both me and my girfriend have 140cc bikes with Yx motor and Molkt 30mm carbs. Her bike seems to be a little bit smoother than mine in the lower gears and a fraction bit more responsive, mine in the low gears 1st and 2nd at low revs tends to hiccup a little, also when in a higher gear and i release the throttle i tend to get like after burn gargle, bit like you hear on a V8 with exhaust kit after you put your foot flat on the pedal and take it off real quick.
If i adjusted in the fuel screw on the carb to lean it out a little would that help?
 

DvDRip

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sounds like you're already running lean, with the bike running adjust the air mix screw until it revs cleanly. there's a tuning guide in the tech/help section. also raise the needle in the slide by one notch (clip down one) to see if you can get it to stop crackling in the higher revs
 

©orza™

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Hmmm ok, i would have thought that would have been caused by to much fuel. Will turn the air mix screw in a little then.
Recon it might be a good idea to see how it runs with the choke out then? Iv never had to use it before, always starts easy without it. Guess i never figured it was running lean to try that though...
 

©orza™

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Ok so i adjusted the air screw in thismorning about 1/3 of a turn (clockwise), couldnt realy take it for a spin cos my yard is to small, but crused around just in first. Didnt seem to hiccup like it did before, might need a slight bit more ajusting, will have to wait till tomorow when i give it a proper run.
I did howerver try using the choke, When i did the motor stalled, way to much fuel, tried again with some throttle and i keept it running but was cracking like a bitch and blowing smoke, is that normal for the choke, should it be pumping in that much fuel?
 

thump*140

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once a motor warms up, it will cough and crackle a bit on choke... the choke is designed (on any vehicle) for the motor to run from cold. Once it warms up, the choke, or the chokes purpose, is no longer required, and will adversely effect the motors running, hence the reason you have to use a little throttle to keep it ticking over..
I would imagine the root cause will most likely be needle clip setting.. popping usually means it's a little on the lean side, so if you lower the clip one groove, effectively raising the needle, this may go some way to alleviating the issue.
 

©orza™

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Yeh i dont think i need to adjust the clip, its quite smooth in the top gears, my exhaust does just seem to be a little more throwty compared to me misses. I think it might be pretty close where it is, maby if anything just need to turn the air mix 1/4 more of a turn, wont know for sure till tomorow though.
 

sean01

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gears have nothing to do with yr needle clip settings...
as does the main jet at idle...
what i mean is there is a particular part of the carb to be tuned for each part of the throttle opening...

screwing your mixture a little at a time isnt doing anything...
with the engine warmed up and at a comfortable idle start screwing the mixture screw in till its about to die. now from there slowly screw it out till it reaches its maximum clean idle.

one thing tho is you mention popping...
are your sure its popping and not crackling
popping means lean and crackling means rich

i suggest you read the carb tuning guide a couple of times to get a good understanding as to what part of the carb needs to be altered for the issue your having

let us know how ya go
 

©orza™

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Ok well i was riding on the weekend and it busted an oil cooling leed, melted the silicon around it, i fixed it with gaffa tape and gasket silicon and got it going again, then the other one melted and started to leak, so you would think the bike is running lean rite. So why is my spark plug a dry black? im guessing thats why it may be running a bit rough but that doesnt explain why it would be getting hot enough to melt and break the oil cooling leads, as when the spark plug fouls it mean running rich.... Any ideas on that???
 

sean01

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maybe the spark plugs black cause you run with choke on.
i was wondering that from reading some of his previous comments but thought to myself...surely couldnt be true...

corza..what colour is the front of your pipe where it comes out of the head?...and have you ever seen it glow red?

and as for the oil lines...there can be many reasons for them to break....1st thing that comes to mind is quality and other is how close there running to the exhaust and there position...
 

thump*140

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yeah melting oil lines is a bit sus... they *should* be high-temp lines... and would require the oil to be VERY hot indeed to melt them... perhaps quality of the lines was the issue, rather than oil temperature..
put new oil in it, and check to see how quickly it goes from being clean and honey coloured, to black crap...

Corza, can you pull the carby apart, and tell us what sort of jetting you are running? so far no one has asked, and you havent specified your jetting...
let us know what you've got, and we can probably sus it from there if it needs looking at, but you mentioned it's running pretty close to spot on, so the issue may be elsewhere..
 

©orza™

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maybe the spark plugs black cause you run with choke on.
I know your just putting it out there, but no im not that stupid lol, and if you read the comment before you would have read that my bike wont run with the choke on. So can rule that out of the question.

As for pipe no, neva seen it glow red!! I wouldnt say that the oil leads are that close to the exhaust pipe, and the other bike doesnt seem to have this problem? i would have thought if they got that hot the motor would cut out, well at least before it melted the silicon coating on the leads..... They are just the standard ones that came on the bike so im guessing very cheep, and maby just duds.
Am going to go to Enzed and get some good quality ones made.
 

©orza™

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Answering you question thump, have spoken to the mechanic at Atomik and he has told me that the jetting should be correct, but he suggested to first look at the float level in my carby, if thats at the right level then to adjust the slide down one notch, and also get a NGK spark plug as the one in it is a DENSO?? Was supposed to be NGK in it already!!!
 

thump*140

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yeah might be worth trying what the mechanic from Atomik suggested. I'm actually astounded that someone from Atomik was helpful !!! ;) A decent plug gapped properly may be of some assistance with the issue, but i'd say it's in the needle clip setting, and possibly valve clearances..
 

©orza™

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Think i just got some dodgy oil cables, im useually pretty unlucky lol.
When you say valve clearances what are you refering to??
 

thump*140

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all fourstroke engines run valves for the purpose of controlled induction of fuel/air mix, and the expulsion of burnt exhaust gases. In the case of china horizontal motors, (that's whats is in your mini), the valve clearances are adjustable, via adjustable rocker arms.
To run correctly, the valves need to have a specific clearance between the rocker arm, and where the rocker arm touched the valve cap. This gap is .003" and .004" respectively for the intake and exhaust valves.
To check them, there is a thread in the "How-to" section, and generally a lot of issues involving the poor running of minibike engines, are attributable to the valves not being adjusted correctly, and having poor valve clearances...
have a look through the thread below, which although it's for a vertical engine, the procedure is the same for the mini engine.
If you find your valve clearances arent accurate, or within specification, they will need adjusting, and may actually sort out your carburettion issue. And yes, even on new engines, valve clearances can be set all wrong...
http://www.miniriders.com.au/motor-tutorials/20425-good-guide-adjusting-valves.html
 

DvDRip

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my oil lines melted when my pitpro was brand new, got replacements from pitpro and it never happened again. I think I tuned the fuel screw and lowered the needle by 1 clip. so it's probably not dodgy cables.
your engine can run lean in one part of the rev range but rich in another. which explains why your plug is black.

and if atomik says your jetting is correct then it most probably isn't ;)
 

©orza™

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my oil lines melted when my pitpro was brand new, got replacements from pitpro and it never happened again. I think I tuned the fuel screw and lowered the needle by 1 clip. so it's probably not dodgy cables.
your engine can run lean in one part of the rev range but rich in another. which explains why your plug is black.

and if atomik says your jetting is correct then it most probably isn't ;)
Haha lol, possibly, but me and me misses have the same and hers runs fine, iv been told to turn the air fuel mix screw all the way in and then turn out 1 and 1/2 turns as a starting point, lower the clip and check the float level, will try all this Saturday and let yas know how i go. Brought new cables hopefuly will be here by the weekend. And brought a NGK spark plug which may be of some good as well.
 

DvDRip

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before any of that do your valve clearance. also it would be a good idea to open your and the missus carby and see if they run the same jet size
 

©orza™

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Would the valve clearences have anything to do with the bike running hot, what are the symptoms usualy, im guessing if mine are out they are to loose! have looked at that thread and read how to do them, its a good example, still bit nervous bout doing it lol, looks easy enough just hate screwing with things im not familiar with!
 

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