wild foamy Posted January 2, 2009 Share Posted January 2, 2009 hi everyone. i think i may need to up-jet my carb, how easy is it to change the jets and how can i do it? thanks, steve Link to comment Share on other sites More sharing options...
JUST ME! Posted January 3, 2009 Share Posted January 3, 2009 hi everyone. i think i may need to up-jet my carb, how easy is it to change the jets and how can i do it? thanks, steve Geday again mate, I have tried to establish before just what "big bore" size you went for, but am still none the wiser! Without knowing this and exactly what the bike is doing in the various rev ranges, it would be difficult to suggest a starting point. If the bike is running lean, Eg engine overly hot,plug too light,then do not ride it until jetting is commenced. Working on the assumption that the engine is still under 70 cc, as a starting point go up 2sizes on the main jet,lift the needle one notch. Ride bike at say a consistent 30 mph for a couple of miles, pull clutch in and hit the kill switch at the same time,roll to stop. Wip the plug out and have a look at it. Does this make the bike run sweeter or worse? Trial and error until you get it somewhere in the ball park! As i have said before ,in my opinion large capacity increases in relation to the original bore sizes,fitted to the original crankcase,does not produce the same relative power gains. Plus produces new balance problems. Having said that push on with this mod and see how it goes! GOOD LUCK! Link to comment Share on other sites More sharing options...
Madison Motorsport Posted January 3, 2009 Share Posted January 3, 2009 One question springs to mind - Why are you bothering on a 50? The amount of money you are spending and are looking to spend, you may as well just go out and buy a bigger machine. Link to comment Share on other sites More sharing options...
wild foamy Posted January 3, 2009 Author Share Posted January 3, 2009 One question springs to mind - Why are you bothering on a 50? The amount of money you are spending and are looking to spend, you may as well just go out and buy a bigger machine. Im 16, 50cc is all i can ride. i am running a 60cc big bore (still marked as 49cc on the barrel) and its mainly at full throttle the engine starts to slow down and can't produce the power that it normally does. and at lower RPMs' it just doesnt have the grunt, so once you change from 4th into 5th it will just die and drop back to 30-35mph tomorrow i'm off work and dont go in again until next saturday, so will pull the carb off tomorrow morning and see what size jet i am running, then go into probike in town and see if they have any jets available in the size i need. if not i will order them from motocarb.co.uk but how do i find the jets in the carb? - Steve Link to comment Share on other sites More sharing options...
Moderator Airhead Posted January 3, 2009 Moderator Share Posted January 3, 2009 but how do i find the jets in the carb? - Steve Jets?...no Jet, singular , main jet theres only one, its in the middle below where the needle is. Link to comment Share on other sites More sharing options...
wild foamy Posted January 3, 2009 Author Share Posted January 3, 2009 hmm, okay, would i need to take the carb bowl off to get to it and change it? i thought there were 2 or 3 jets (Main jet, pilot jet, needle jet?) Link to comment Share on other sites More sharing options...
Moderator Airhead Posted January 3, 2009 Moderator Share Posted January 3, 2009 hmm, okay, would i need to take the carb bowl off to get to it and change it?---Possibly if there isnt an access cover in the float bowli thought there were 2 or 3 jets (Main jet, pilot jet, needle jet?)----There are but you wont be changing them, only main jet You wont be able to plug chop until youve run in your new barrel, so just put the bigger jet in, start at two sizes up and also try lifting needle one notch, then when its run in you can plug chop to see if its right Link to comment Share on other sites More sharing options...
wild foamy Posted January 3, 2009 Author Share Posted January 3, 2009 okay, will have a tinker with the carb tomorrow and go up a couple of sizes on the jet, is there anytihng i can do about the low/mid-range lack of power?, or is that just because the big bor eis new? Link to comment Share on other sites More sharing options...
Moderator Airhead Posted January 3, 2009 Moderator Share Posted January 3, 2009 okay, will have a tinker with the carb tomorrow and go up a couple of sizes on the jet, is there anytihng i can do about the low/mid-range lack of power?, or is that just because the big bor eis new? that is why youre lifting the needle a notch as well Link to comment Share on other sites More sharing options...
wild foamy Posted January 3, 2009 Author Share Posted January 3, 2009 ah kk, will try that tomorrow, thanks Link to comment Share on other sites More sharing options...
JUST ME! Posted January 4, 2009 Share Posted January 4, 2009 ah kk, will try that tomorrow, thanks Geday again, I take it this little jigger has a mikuni on it, you don't have to take the carby off to change main jet. Just remove throttle slide, loosen clamps,rotate carby 90 degrees.On some mikunis you have to remove the bowl,some have a large plug that scews out allowing you to remove jet with a socket.From memory it is 8mm. Along time since i have tinkered with a mikuni. From memory some of the main jets on some styles of carbs had an o-ring around them. If it is that style of jet,ensure that o-ring is in good shape. I tend to think this one will be the plain short style. The jet size will be stamped on the bottom or side of jet! If you have a contact at the bike shop, sometimes they will allow you to swap jets. You are doing the right thing getting the top end of the range in tune first and it is essential that you don't allow the bike to run lean,it will pick up the bore and you will be back to square one. Plug checks will be a good indicator, run in or not. As far a messing with a 50cc goes, good on you! Learning about this stuff has got to be better than playing the pokies or doin drugs.Go your hardest! Warning, Jetting can be tedious. Be patient and you will get it just right. oh yeah, is this little jigger pre-mix or auto lube? There is other jets that may have to be played with! The main jet is the one you need to be concerned with first. Get the top end working well and we will go from there! I assume all of the carbon was thoroughly removed from the exhaust port! Link to comment Share on other sites More sharing options...
wild foamy Posted January 4, 2009 Author Share Posted January 4, 2009 well i got out there this morning, took the carb off and took the carb bowl off, sure enough the little main jet was right there looking at me. the main jet is a size 94 (88 stock) and the big long one it was sat on was an 80 i think. will probably try a 105 and 115 to get a good idea of where abouts it needs to be, then fine-tune it your right about tinkering with 50s', its good fun and it is indeed an autolube engine with a mikuni carb, the whole barrel was changed so the exhaust port is brand new, much like the rest of its internals Link to comment Share on other sites More sharing options...
wild foamy Posted January 4, 2009 Author Share Posted January 4, 2009 Had a quick look around for jets, the one already in my carb is hexagonal and the head is aobut 3mm deep on it. most other ones ive found are either Round,or have a much longer hexagonal head. can anyone reccomend a good jet that would fit? my haynes manual shows the same hexagonal head that is already on my carb :S Link to comment Share on other sites More sharing options...
wild foamy Posted January 4, 2009 Author Share Posted January 4, 2009 bad news... went to Bikex to get a new jet, only to find that they hadn't got any. and on the way back it died whilst going up a hill. no coughs, no nothing, just there on minute and the next it had completely cut out. that was possibly the longest walk i have ever done, and even with a small bike its hard to push it the remaining 3 miles home. took the head off when i got home and there were no signs of lean running, the plug was wet with fuel, with a dark brown colour on the cylinder head and piston (no obvious signs of overheating or internal damage). it has compression, fuel and spark so im not sure what to do now. sometimes whilst attempting to start, it will backfire (and when in a closed garage on your own, scares the sh*t out of you if you arent expecting it) so it is atleast firing, just not constantly and in the right direction. Lesson learnt, will put the original bore back on tomorrow. - Steve Link to comment Share on other sites More sharing options...
JUST ME! Posted January 5, 2009 Share Posted January 5, 2009 bad news... went to Bikex to get a new jet, only to find that they hadn't got any. and on the way back it died whilst going up a hill. no coughs, no nothing, just there on minute and the next it had completely cut out. that was possibly the longest walk i have ever done, and even with a small bike its hard to push it the remaining 3 miles home. took the head off when i got home and there were no signs of lean running, the plug was wet with fuel, with a dark brown colour on the cylinder head and piston (no obvious signs of overheating or internal damage). it has compression, fuel and spark so im not sure what to do now. sometimes whilst attempting to start, it will backfire (and when in a closed garage on your own, scares the sh*t out of you if you arent expecting it) so it is atleast firing, just not constantly and in the right direction. Lesson learnt, will put the original bore back on tomorrow. - Steve Don,t give up until you have dialed in the big bore,you have nothing to lose! Link to comment Share on other sites More sharing options...
wild foamy Posted January 5, 2009 Author Share Posted January 5, 2009 big bore kit is a loss, some deep scratches down the side of the cylinder on the exhaust side and it doesnt seem to want to run. whilst putting the original bore back on i snapped one of the piston rings, so now i need a new set of rings and have a piece of piston ring inside my engine which has jammed the crank too cold to mess around with it tonight, Link to comment Share on other sites More sharing options...
JUST ME! Posted January 6, 2009 Share Posted January 6, 2009 big bore kit is a loss, some deep scratches down the side of the cylinder on the exhaust side and it doesnt seem to want to run. whilst putting the original bore back on i snapped one of the piston rings, so now i need a new set of rings and have a piece of piston ring inside my engine which has jammed the crank too cold to mess around with it tonight, Sorry to hear that mate, playing with 2 strokes can really test youy patience! Try and get the ring out without splitting the cases. Put her back how she was and treat it like you stole it. Don't get too disheartened , everybody who tinkers has had their share of screw-ups. If you are having difficulty keeping rings compressed while fitting the barrel, You can remove the piston, introduce it part way it to the bore, then hold the whole assembly over the rod whilst you fit the gudgeon pin. Make sure piston is right way about. If your using your original piston, make sure you use new clips! HOPE IT ALL GOES WELL! Link to comment Share on other sites More sharing options...
wild foamy Posted January 6, 2009 Author Share Posted January 6, 2009 would i be able speed up the oil supply to give it a bit more lube?, just a thought as it may help when breaking in the new rings Link to comment Share on other sites More sharing options...
Moderator Airhead Posted January 6, 2009 Moderator Share Posted January 6, 2009 would i be able speed up the oil supply to give it a bit more lube?, just a thought as it may help when breaking in the new rings It shouldnt be necessary Steve, that has never been a part of running in even a brand new engine, the crucial things are that you did a good engineering job when you assembled it and as has been said many times jetting and mixture is set correctly, if you are putting your old 50cc pot back on i suppose youre jetting must me somewhere near as its as it used to be, just make sure the air mixture screw is set right Edtt You should wipe round the bore and piston with two stroke oil upon assembly On first starting your bike you should force the pump stroke to maximum without opening the throttle to maximum briefly to ensure oil is there immediately. Link to comment Share on other sites More sharing options...
wild foamy Posted January 6, 2009 Author Share Posted January 6, 2009 On first starting your bike you should force the pump stroke to maximum without opening the throttle to maximum briefly to ensure oil is there immediately. i did take the nescessary precautions when installing the kit, and got it well lubed up for the first run. the old 50cc pot is back on and running the original jet how do i force the pump stroke to its maximum? Link to comment Share on other sites More sharing options...
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