Kubira Posted July 7, 2009 Report Share Posted July 7, 2009 i have noticed recently, my bike has a slightly noticeable splutter at around 6k'rpm when WoT thru the gears, just before the ole poweband kiks in, she just sorta , clears her throat' for lack of better explanation.. no flat spot, there doesnt seem to be a problem with power delivery,, but im worried this is what its eluding too. Im thinking a replacement of spark plugs and a carby tune may alleviate my issue. Rolling Eyes Any ideas appreciated cheers Link to comment Share on other sites More sharing options...
cagimaha Posted July 7, 2009 Report Share Posted July 7, 2009 What sort of bike is it? Two strokes (especially parallel twins) often have a bit of a rough patch before the powerband. Over the years many things have been tried to alleviate the problem. Some work better than others but boost bottles, balance pipes, reed spacers and airbox mods have all been used to good effect and may be worth looking at. Also (this one depends on the bike) but normally I'm not on full throttle untill in the powerband. I try to sort of wind it on progressivley until its in the take off zone. If this is a new problem that has recently developed then a clean and synch of the carbs will probably sort it. If plugs are cheap then I'd probably replace them too cos they do get a bit of a hard time in a two stroke. Link to comment Share on other sites More sharing options...
cagimaha Posted July 7, 2009 Report Share Posted July 7, 2009 Yeah that's the purpose of a boost bottle, or YEIS isn't it? Whey bring on the 80's four letter acronyms! Yeah as I understand it its an inherent resonance problem found the majority of two strokes that they use these techniques to mask. A lot of people blame the K&N style filters with the chrome caps because they reflect a lot of pulses back down the inlet tract. Link to comment Share on other sites More sharing options...
Kubira Posted July 8, 2009 Author Report Share Posted July 8, 2009 Whey bring on the 80's four letter acronyms! Yeah as I understand it its an inherent resonance problem found the majority of two strokes that they use these techniques to mask. A lot of people blame the K&N style filters with the chrome caps because they reflect a lot of pulses back down the inlet tract. whats Yeis? Thankks a lot, im pretty sure i wind the accel. as youve described, probly should have worded it better but you know what i mean(flat knackers) The bike is an NSR 250, yep good guess Cagi, twin 2T indeed, mc 21 se mediocre mods, there's a few holes in the air lid, and 150 jets whereas 128's are stock.. It has definatly only just arisen, it is barely noticable tho. Flicked the oil tank, and running premix, im used to this style, ie motor cross bikes Im really not tuned up to what it really is, it seems like it could be a few things, as mentioned.. Well a carby tune and some new plugs are gonna be thrown in, see what happens then.. bout it.. Link to comment Share on other sites More sharing options...
cagimaha Posted July 8, 2009 Report Share Posted July 8, 2009 YEIS was a system yamaha came up with back in the 80's for their RD125LC if I remember right. Might have been the TZR125. Basically it was an air reservoir/chamber connected to the intake between the carb and the reeds which smoothed out any resonance coming up the inlet tract towards the carb. Did the problem start when you changed to premix? If so then I think I may well have the answer to your problem. When you use premix it actually leans out the mixture. You have compensated for this by increasing the main jet size but that only alters the mixture when on large throttle openings. The mixture at part throttle will be leaner which could be the cause of the hesitation. To alter this try raising the needles a notch and see if this improves it. Hope this helps, Ben. Link to comment Share on other sites More sharing options...
Kubira Posted July 8, 2009 Author Report Share Posted July 8, 2009 Ive been running mix for the better part of the 3 months ive had the bike, and ive just noticed it last week or so. Bike does have the chambers between carbs and reeds.. The 150's were installed when i got it also. HOwever, it could be a lean issue, the plugs are a lil dry i think.. Link to comment Share on other sites More sharing options...
Kubira Posted July 10, 2009 Author Report Share Posted July 10, 2009 id like to clean the airflow tube out, any idea where the other end is? Link to comment Share on other sites More sharing options...
cagimaha Posted July 10, 2009 Report Share Posted July 10, 2009 That goes into one of the myriad of internal airways in the carb bodies. You can clean it a fair way by soaking it in carb cleaner but the only way to get it properly clean would be to get the carb ultrasonically cleaned either by a specialist or with one of the DIY kits off ebay. Just another thought... Are you using a castor based oil? Hope this helps, Ben. Link to comment Share on other sites More sharing options...
Kubira Posted July 11, 2009 Author Report Share Posted July 11, 2009 yeah souds like the go, ill carefully strip sown each carb, get some carb cleaner. finally got 2 days off to work on my bike, wooo hoo - im using tts racing fully sythetic gear Link to comment Share on other sites More sharing options...
cagimaha Posted July 11, 2009 Report Share Posted July 11, 2009 I only asked about the oil because the NSR world site and honda themselves recommend the use of a castor based oil which is reknowned for gumming carbs up but that isnt the problem here. Link to comment Share on other sites More sharing options...
cagimaha Posted July 14, 2009 Report Share Posted July 14, 2009 If you think about the fuel going through the jet at a constant throttle opening and constant revs then the amount of fluid flow is constant too. If you run an oil injector system then there is just neat fuel going through the jet. If the mixture is correct in this scenario then you switch to pre-mix then some of the fluid coming through the jet is now oil which means there is less fuel getting in causing a leaner mixture. It dosent matter which circuit is being used in the carb the mixture will be leaner. Often when converting to premix or tuning a bike people will sort the main jet out so that the mixture at full throttle is ok but neglect the rest of the circuits. This is normally ok for engine longevity but often causes stuttering or hesitation lower down in the rev range. If you see what I mean... Link to comment Share on other sites More sharing options...
fontyyy Posted July 15, 2009 Report Share Posted July 15, 2009 and 150 jets Slightly richer than all these people put togeather. Link to comment Share on other sites More sharing options...
cagimaha Posted September 26, 2009 Report Share Posted September 26, 2009 Yeah thats what I was commenting on, that you need to put bigger jets in when going from autolube to pre-mix and also if drastically changing the mix ratio. Kubria did this get sorted in the end? Link to comment Share on other sites More sharing options...
Kubira Posted October 7, 2009 Author Report Share Posted October 7, 2009 Morning, bit o neglect on my part, apologies. Ive not altered anything in the carby since going to premix accept the for-mentioned, thorough cleansing, and gone to standard jets (did i mention that?) @ 128's, However... A bigger and bolder and a much more exciting issue carefully removed, has seen any issue i've had before totally vanish!! Basically i bought the bike 4 months ago, and been going thru all the systems and components as you do, when you feel the need to tear something apart / clean and re assemble. So i came across the power valves and had a deep and meaningful turns out the servo wasn't affecting the powervales at all due to wear on the rod and P/V butterflies. Funnily enough i already knew about this from pretty much day 1, as i recall poking them thinking, hmm they're a bit loose.. I can safely assume they were merely 'Going with the Flow', if you catch my drift. After unsuccessful (so far) attempts to source powervalve rods, ive simply used a few (extra) decent washers to secure a nice grip between the butterfly and the rod, and set them up meticulously to hrc spec. You might well imagine the grin on my face as i climbed from 8 to 13000 revs (no strange choking anywhere)in the blink of an eye on my first outing. mmm, vales operational This was done around 3 weeks ago now i suppose, been keeping an eye on the plug colour, and servo/power-valve operations. All seems fine Link to comment Share on other sites More sharing options...
racerd Posted October 15, 2009 Report Share Posted October 15, 2009 whats Yeis? Thankks a lot, im pretty sure i wind the accel. as youve described, probly should have worded it better but you know what i mean(flat knackers) The bike is an NSR 250, yep good guess Cagi, twin 2T indeed, mc 21 se mediocre mods, there's a few holes in the air lid, and 150 jets whereas 128's are stock.. It has definatly only just arisen, it is barely noticable tho. Flicked the oil tank, and running premix, im used to this style, ie motor cross bikes Im really not tuned up to what it really is, it seems like it could be a few things, as mentioned.. Well a carby tune and some new plugs are gonna be thrown in, see what happens then.. bout it.. yeis means yamaha energy induction system Link to comment Share on other sites More sharing options...
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