garethr Posted February 25, 2009 Report Share Posted February 25, 2009 I've added a thicker clutch plate and dropped the gearing on my sons TXT 50 Boy, which have transformed the little bike but still isnt quite there! I've seen quite a few older TXT 50 Boy' in various trials and they seem to have much better low down power and seem to cope with the low rev tight stuff much better than my sons. I dont like the auto clutch to be honest! It seems like you have to pick the revs up quite high for the thing to bite and start moving at which point it shoots off at quite a rate! I may be exaggerating a bit here but this is to try and explain what is going on. It has improved with time as I think the clutch springs have weakened a bit and the bike starts moving at lower revs than when it was brand new. Hopefully it will keep improving as a TY80 is much easier to ride at low revs in the tight stuff. My question is... has anyone added any flywheel weights to the bike, is this possible, is it advisable!? Quote Link to comment Share on other sites More sharing options...
laser1 Posted February 26, 2009 Report Share Posted February 26, 2009 It doesnt look like there are too many boy 50 experts around. I have no experience with them but my little boy rode a ktm50 centrifical clutch and it initially had very poor low end response. I eventually improved it with proper jetting. I know people do an airbox mod to the boy50's that supposedly helps them run better (along with the mods you have done). Another thing I learned was to clean the carb on a regular basis. The pilot jet passageways are so small in those little carbs that ther are very suseptable to blockage. I was always amazed at the difference a 1/4 turn of the airscrew would make on those little bikes. Good luck - I hope you get some advice from experienced boy50 owners. Quote Link to comment Share on other sites More sharing options...
nigel dabster Posted February 26, 2009 Report Share Posted February 26, 2009 done it on the manual 07 50. Quote Link to comment Share on other sites More sharing options...
p@ul250 Posted March 10, 2009 Report Share Posted March 10, 2009 My kids have had txt 50 boys for the last five years between them. The best mod you can make is fit a 60 tooth rear sprocket (from Talon Engineering) this seems to allow the bike to move off slowly with the clutch biting sooner and less aggresively. Persevere with the trying of different thickness of steel plates. In one of our bikes we have one thick plate and two thin and the other bike one thin and two thick. Another mod I would recomend is to open out the inlet to the air box.If you remove the air box lid and turn it over you will see a small square hole. cut away the plastic towards the back of the hole until it's about double in size. This allows the engine to breath at higher revs and seems to cure the boys tendency to bog down at low revs. I hope this is some help. the TXT Boy is a great little bike when sorted. Quote Link to comment Share on other sites More sharing options...
garethr Posted March 26, 2009 Author Report Share Posted March 26, 2009 Would a gunked up carb cause the plug to get black and sooty? My lads bike spits black oil out of the exhaust quite a lot and is covering everything. It picks up well from low revs but doesnt rev cleanly at mid to high revs it misses coughs and splutters. I'm in the process of cleaning out the carb and air filter and replacing the plug. Does anyone know the correct number of turns for the air screw? I was also thinking about dropping the needle (i.e. lifting the clip up) one notch so that it runs leaner at mid revs. There is quite a weak little spark, so I suppose the problem could be electrical? How about the float setting? Is this just a quirk of the little bike and all I need to do is keep cleaning the carb frequently? Cheers Quote Link to comment Share on other sites More sharing options...
camlifter Posted March 26, 2009 Report Share Posted March 26, 2009 years ago when my kids rode 50's we had a few of the tomas 50cc mx bikes, they had the auto clutch that needed to be reved up to kick in. i made great improvements by taking the springs in the clutch and stretching them a little. smothed the bikes out very nicely. Quote Link to comment Share on other sites More sharing options...
laser1 Posted March 26, 2009 Report Share Posted March 26, 2009 Would a gunked up carb cause the plug to get black and sooty?Doubt it - Black and sooty is telling you your jetting is too rich (assuming everything else is working to spec) My lads bike spits black oil out of the exhaust quite a lot and is covering everything. It picks up well from low revs but doesnt rev cleanly at mid to high revs it misses coughs and splutters. Like you correctly thought, try dropping the needle. Maybe need a smaller main as well. What fuel/oil ratio do you use. I'm in the process of cleaning out the carb and air filter and replacing the plug. Does anyone know the correct number of turns for the air screw? I was also thinking about dropping the needle (i.e. lifting the clip up) one notch so that it runs leaner at mid revs. You should tune the air screw according to performance, not a set number. Warm up the bike, Put the bike on a stand. make sure the rear wheel is off the ground (auto clutch). Make sure your idle speed is set to a fairly low rpm, but the bike doesnt stall. Grab a huge handfull of throttle and quickly wack it open to full throttle (twist as quick as you can and release). When the air screw is too lean (too much air) , the bike will bog before reving up. You will want to richen the air screw (less air) untill the bog goes away and the bike revs quickly w/o hesitation/bogging. If you make it too rich, (go too far) the bike will start to burble and wont rev as quick. Too rich isnt as obvious as too lean. I usually find it easiest to start on the lean side with an obvious bog, when you can just make out a very slight bog still, about another 1/2 turn will probably get you pretty close. This is a relative thing though. You should try and develop a good ear for this, as these little bikes like to be optimized according to temp/humidity/track ect - There is quite a weak little spark, so I suppose the problem could be electrical? Maybe - electrical can do all sorts of funny things. Its hard to see the spark on these things though. Use a new plug and try above. How about the float setting? Again, could be, check it when you clean the carb - check the jetting. (im sure stock is too rich) Is this just a quirk of the little bike and all I need to do is keep cleaning the carb frequently? Cheers Quote Link to comment Share on other sites More sharing options...
garethr Posted March 26, 2009 Author Report Share Posted March 26, 2009 Thanks very much for the info laser1... I will give it a go and see how it goes. Like I say the bike pics up really sharply from low revs so I suppose the air screw isnt far off ideal. I will make it a bit leaner and drop the needle too and see how we go. I use 80:1 mix. Thanks again. Quote Link to comment Share on other sites More sharing options...
garethr Posted March 27, 2009 Author Report Share Posted March 27, 2009 (edited) Hmmm! Just gone to clean the carb and move the needle down a notch and it's already on the 2nd notch down from the top. We've had the bike from new so that's how it came from the factory, unless it's been changed by the dealer. If I move the needle down another notch (there are 5 notches in total), it will be on the top notch (i.e. lowest needle position and leanest setting). Is this advisable??? Edited March 27, 2009 by GarethR Quote Link to comment Share on other sites More sharing options...
laser1 Posted March 27, 2009 Report Share Posted March 27, 2009 Its easy enough to try....If the main jet is stock, then it doesnt suprise me. What jets are you running? Quote Link to comment Share on other sites More sharing options...
garethr Posted March 27, 2009 Author Report Share Posted March 27, 2009 The whole thing is standard. I moved the clip to the top notch and put it all back together and wound out the air screw to 3.5 turns. It sounds much crisper and revs like a banshee with no stutter at all. Is there a chance that everything could be a bit to lean now and cause the engine to pop!? Quote Link to comment Share on other sites More sharing options...
laser1 Posted March 27, 2009 Report Share Posted March 27, 2009 You should always check your plug after any jetting changes. Also, Listen to the motor - if you here any pre detonation rattle (lean main) or over lean knocking when you chop the throttle (lean air screw) , then you want to rejet. In this case, it doesnt sound like it since your plug was black before (although that can be misleading). I would order up a leaner main jet so you could put the clip back near the middle. You may want to go even leaner when the hot weather arrives. When jetted and running properly, that little engine should scream pretty good. Sounds like progress. Quote Link to comment Share on other sites More sharing options...
garethr Posted March 27, 2009 Author Report Share Posted March 27, 2009 I really am grateful for all this help you are giving me laser1!!! You obviously know your onions! I'm sure many others will gain from your comments and tips for many moons! I checked the spark on the brand new plug before fitting and it was a bit stronger than the previous plug, but I noticed that the spark jumped about a bit. It didnt spark in the same place. Is this normal? So leaner means cooler running engine? What happens when you go too lean? Does it just drop performance because there isnt enough fuel going through the system or can something more serious happen? Quote Link to comment Share on other sites More sharing options...
laser1 Posted March 27, 2009 Report Share Posted March 27, 2009 I really am grateful for all this help you are giving me laser1!!! You obviously know your onions! I'm sure many others will gain from your comments and tips for many moons!Your welcome - but just remember what they say about free advice! I checked the spark on the brand new plug before fitting and it was a bit stronger than the previous plug, but I noticed that the spark jumped about a bit. It didnt spark in the same place. Is this normal? Set the proper gap on the plug and dont worry about the spark jumping around - the fact that you can see a spark is a good sign. The fact that the bike is ripping along is even better. So leaner means cooler running engine? What happens when you go too lean? Does it just drop performance because there isnt enough fuel going through the system or can something more serious happen? here is a good read for jetting basics: http://www.thisoldtractor.com/gtbender/mg_...orto_manual.pdf Quote Link to comment Share on other sites More sharing options...
garethr Posted March 28, 2009 Author Report Share Posted March 28, 2009 Fantastic read (not finished yet). It's telling me just how much I've taken for granted over the years when my dad used to look after my bikes! Quote Link to comment Share on other sites More sharing options...
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