YX with 30mm Molkt carb Tuning Question

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yes mate, valve clearances can have everythign to do with a motor running hot. they will also be hard to start, feel like they have no or lost compression, and be a bit rattly around the head area...
i'm going to do a thread on these purely for minis with big pics and step by step hints in the next couple of days... i'll post in the How-to section...
Doing the valve clearances sounds scary, but is quite a simple process once you have done it once. not half as scary as it sounds, and is very difficult to do any damage... if it's wrong, the bike will be hard to start, but not a great deal of engine damage can be done..
Trial and error is your friend. :)
 
I found this YouTube - ooracing.com how to set your Valve Clearance
Quite good, just he says to adjust them different, the firing stroke valve he says to adjust to .01 and the exhast to .015 ?? everyone on here says .004 for both?? Confusing!!
My bike is very easy to start, not like it was when it was new nor like the other bike which seems to have more compresion i suppose, kicks back and harder on the ankle to start.
 
in the ooracing vid, was he talking mm or inches?
.003'' and .004'' for inlet and exhaust respectively is pretty much the accepted standard.. i can see why you find it confusing...
I would have thought .01 and .015 would be very large gap clearances, if he's talking inches..
if your bike is easy to start, valves may not be the issue, in which case it's back to carby issues...
oh, and have you pulled both yours, and your missuses bikes carbies apart, to see if they are running the same jets?

if you can tell us what jetting specs you are running, we will have a lot more chance helping you out, and getting it right.. :)
 
That Ooracing guy is talking in hundredths of a millimetre ... .01 mm is close to .004" aka 4 thou and .015 mm is close to .006" aka 6 thou ... So he's spot on ... he's providing a safety margin to protect against the valves over heating and sticking in the guides ... Which results in the symptoms that mountain describes has happened to his YX 4 Valve heads ...

When you run a higher lift cam the clearances should be set on the higher side ... higher lift = a longer valve stroke which in turn also = higher stem to guide friction ... and since the valves are open for a longer duration than stock ... they also get less chance to shed heat thru the valve seats ... The exhaust valves are the ones most likely to seize in the guides ... that's why he's added extra exhaust valve clearance ...

Slightly noisier tappet rattle at idle is better than a permanently quiet engine with a windowed piston ...
 
^^^ see this is why we have Cactus. we blunder through suggestions, then he comes on and makes sense of everything...

:)
 
Nah havent had a chance, was gana pull my carby appart saturday, haha i dont like the idea of touching hers, its running well and i would NEVER hear the end of it if i pulled hars appart and then it wasnt running quite the same, haha i copped it the other day after doing an oil change for her, turned out she didnt have the fule swithed on haha lol!
The reason i was thinking valves is because it was running nice (while i was running it in) and then it sort has just gotten worse since, and as i said the other day it melted my oil lines. The only real difference is that after it was broken in and as i get better im riding it faster and a bit harder.
Iv had bout a total of ooooh round 10 - 12 hours, done an oil change after the first 2 and then after bout 6, and then again the other day.
One thing i was testing the other day was full throttle, it gets to about 3/4 and it seems to then flattern out and be a lot louder and sound really weird, like its running way to lean, and blows a bit of smoke out the air filter. WOT doesnt run like it should.
i had a spare 20m the other day so i dropped the e-clip down one notch but havent been able to test yet cos i havnt got my cables yet.
Was going to also pull the carby appart to make sure float level is correct and that it has no crap built up in it, will look at my main jet size then. What should it be? between 95 and 105?
 
haha lol, yeh. well a stuffed motor would be alot quieter than a working one!
think ill stick to that then .004 and .006
 
yeah around 95-100 sounds close. from what you've just said, it sounds like your main jet is a bit out...
 
Hmmm so ill pull my carb appart first sus everything out in the jet size ect, make sure floats good and that there are no blockages, will test run if still not running right after checking all that and assuming the jet size is correct then it will narrow it down to one thing i guess. The valves!
And by the way i havnt actualy opend it up to full throttle while riding yet, just while its in netral, weather that makes any sort of difference.....?
 
if it's coughing and spluttering in neutral, it will probably be exacerbated when running in gear with a load on the engine...
the carby you have, is that one of the butterfly choke valve models?
them suck a bit to tune..
 
they also have a tendency not to open properly under heavy load... makes the bike pop and cough. bit like a junkie really. sell it, buy an OKO. lol
 
it idles fine, it just seems that half throttle in 1st and 2nd it gets a hiccup and in 3rd when im the same bout half throttle and i back off it kind of grumbles a little, and as i said full throttle just kind of sounds really weird, like its running lean but yet a small amount of fuel comes out the overflow.
Not sure i know what you mean by butterfly choke?
 
if you pull your air cleaner off you will see a round disk (butterfly) it closes when you pull your choke on.
that is what sometimes gets pulled on by the engines vacuum.

also you mention something about blowing smoke out the carby sometimes, can you describe that a little better.

only way to get to the bottom of this issue is doing it in these stages..
1.. check valve clearances
2.. pull carby apart and post what size pilot and main jet you have and tell us where the e-clip is. and also check your float level.

once you have posted your carb info on here then you will get the correct info about setting the carby up.

it would probably take you all of about 10-15 minutes to take the carby apart but do the tappets first.
 
if you got your bike from atomik, chances are it's not a 30mm molkt but a 26mm molkt like mine, Also they are jetted pretty close from factory with a 102 main, you will probably find you just need to change the needle clip and you should be good to go as the atomik mechanic suggested. I think moving the clip one down should ease a lot of your problems.
 
i have moved the clip down one but cant test at this stage, will hopefuly get the new oil leads tomorow.
When im playing with it i will pull the air filter off and see if the butterfly closes when the throttle is wide open.
I duno if i can describe it any better, its just as i said, its only a small amount comes out of the air filter when the throttle is wide open, i have read that if its to lean it can spit hot fuel back into the carby causing the carby to leak and yeh well blow smoke from the air filter.
 
Where i live there arnt any stores that sell parts for the chinese pittys. Would a normal store like kawasaki, honda ect sell new carbs and if so whats a good price for what, just they tend to be pretty usless down my way!
 
try DHZ for a carby. an OKO 26mm or 28mm, but again your still going to be back to where you are now.. (you will need a full kit if going an OKO.. carb, manifold adapter and aircleaner and a jet kit)
no carby is a direct fit and run...
they all require setting up and tuning...

and also you maybe be replacing something for nothing.....check your tappets...

surely by now you must see how important your tappet settings are since nearly every1 here has been going on about them....

and i spose you could also swap carbs on both bikes and see if the problem follows the carb...
 
Thump*140's valve clearance info is right for a general use engine though ... It all depends on how you're treating it and what you're using it for ... remember , that Ooracing guy is RACING ... so he's setting the valves to live with constant high rpm usage in mind where everything gets a lot hotter than normal ... In the case of hard usage , it's better to have more clearance than less ... that allows you to have peace of mind between valve clearance checks ... If you run the minimal clearances , you just need to check them more often ...

I can remember when CRF Hondas first hit the scene ... they had rapid valve recession problems ... A guy and his wife over in the US who had been the champion desert racers for donkeys years were persuaded to switch over to Hondas with full factory sponsorship ... mechanics and all ... They both made to to the 400 mile point and their engines died in the ass ... The valves lost clearance and the engines stopped ... as a result they both failed to even finish the race ... The last thing I heard was they were going to sue Honda ...

Now IF the Honda "Engineers" had anticipated the wear rate of the valves beforehand ... they could have increased the clearances sufficiently for those two people to finish the race and win their classes ... but they didn't and got sued ... LOL ...

Yes ©orza™ ... I'll bet your inlet valve has lost clearance and you're getting blow-back thru the inlet tract (aka reversion or pumping losses as Mack "the greatest tech mind on MR" calls it) ...

When an engine won't rev out up top it's usually the result of the jetting being too rich ... If there's reversion happening ... air flows in past the jets picking up fuel ... reverses back , picks up more fuel , then heads in again picking up even more fuel ... So it can exhibit the symptoms of being too rich even with the correct jetting ... The answer is to correct the leaking inlet valve first and in a lot of cases the engine will run right again ... But since people mess with the original carb settings in an attempt to fix the symptoms , that doesn't always happen ...

Get ready ... because the same symptoms will hit your missus's bike when the valves sink into the seats ... Wear a helmet and ear plugs at all times while working on her bike to avoid rolling pin and screaming damage ... shoulder pads might be a good idea too in case she misses your head ...

Thump*140 has actually tuned a lot of carbs so he knows from first hand experience that these engines require smaller jets than what a lot of people used to claim ... especially on Planet Minis ... There were some ridiculous and laughable jet spec claims from supposed experts ... which didn't quite add up to reality ... I notice that NOW ... their jetting info has started to become more realistic ...
 
Yeh i can see that, and im not just going to replace it if its fine, but if the vacume is pulling the butterfly valve shut then its usless! ill just be throwing money away on new oil leads all the time and hair re-groath cos im pulling it out in frustration lol.
will check all those things on saturday, just trying to find out as much as i can.
 
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