Morpheuz Posted March 24, 2012 Share Posted March 24, 2012 Hi, Just thought I'd mention this as its slightly different to all the other dragstars I've read about. I have drilled holes in the intake letting air float in there more easily, but its kept its standard air filter, as I dont think its that restrictive without the narrow rubber in there and in being drilled at the back of the sheild. The exhausts are circle cut out at the back, and I'm running the needle higher by one notch, and the main jet is a #101 size. The highest I've seen, is a 100 jet, and AFAIK, no one has touched the needle. Is this ok, for what mods I've done because the plugs are fine, no coking or soot. I'm guessing, it should be still fine if I decide to go 2 teeth up on the front sprocket? No lugging if its on the rich side? Thoughts and comments welcome, I like an open audience when I'm pondering something. Thanks. Link to comment Share on other sites More sharing options...
Paulwhite Posted March 24, 2012 Share Posted March 24, 2012 the best thing to do would be to do a plug chop to check the mixture then adjust accordingly. as to the 2 teeth up front, go for it! it dont take much to change it back if your not happy as to jet size you can get higher just search for mikuni main jet and you will find them. but to be honest you dont want to go too high as its a small engine and the bottom end seems to be a week point in the xv / xvs 125 range. Link to comment Share on other sites More sharing options...
Morpheuz Posted March 24, 2012 Author Share Posted March 24, 2012 Well, now I've circle drilled the cans, it feels lean again, I know I can go higher, I just didnt think it would take it that lean, I cant believe its burning the extra fuel I'll be putting in, the air intake hasnt changed, just the exhausts, so why would it feel like it wants the needle in its highest position, and a 105 jet. I suppose what I'm asking is, am I burning this fuel as power, or is it flowing out the back, the plugs are fine, I've chopped them, but it still has delays, until the rpm is high enough... then I get some pull.... I just dont want to be wasting fuel, but at the same time, if Its giving me power and stopping my engine burning, then I'm all for it... Its wierd, its like the draggy likes to be asphyxiated.... no matter how big the jets are. Link to comment Share on other sites More sharing options...
Moderator Cynic Posted March 24, 2012 Moderator Share Posted March 24, 2012 To give you an idea just how finely airboxes are designes respective to volume, induction harmonics yada yada zzzzzzzzzzz. When my gsx was tuned by TTS they expressly left the airbox on they will only remove it from a direct order from the customer. With the tining they did:- Vernier timing gear (absolute valve timing accuracy) Reset valve timing /overlap for performance Fitted custom dynojet kit (the centre carbs had different carb settings to the outers) Full race 4 into 2 into 1 remus pipe and double exit shotgun can (superb would reccomend to anybody) 4 deg ig advance K+n race filter It took over 30 dyno runs to tune the carbs and the bike was 15-20bhp up which is HUGE and a power/torque curve to die for. Nearly 90bhp at the rear wheel, at the time it was a lot. ESP for the old teapot. Oh yea the point..... On the GSX airbox there is a rubber tube thing to direct the air, initially they took it off. Crap engine didn't like it, they ended up trimming it a little at a time over 4 dyno runs to get it perfec. That bike was and still is shocking to ride, no other 600 bandit or gsx compares from 4000rpm to 13500 it rocks, the best 1400 quid i ever spent (included the exhaust). Sack of shit from tick to 4000 due to the valve overlap being performance biased. Flames out the back on overun lol. Oh and fuel economy going from 180miles per (3gal to res) tank to 100, i managed under 60 miles from full to reserve on the iom. Nearly there..... It took several recognised experts with a lot of experience and kit over 4 dyno runs to trim less than an inch of rubber from the inlet trumpet onthe inlet of my bike. That handfull of holes you have drilled may very well ruin the carberation. The biggest restriction on 4 strokes is the exhaust carb combo, thats the key the combo. The rest of it is that mess of whizzing metal ruining a perfectly good motor (not a 2 stroke is it). The head sets the performance of a 4 stroke in stone. I'm not saying don't do it, god knows i messed with enough of my kit over the years but the airbox alone is not the place to find horsepower or drilling holes. If you have fitted proper sports/performance exhausts maybe. Link to comment Share on other sites More sharing options...
Morpheuz Posted March 24, 2012 Author Share Posted March 24, 2012 Yeah I know, I got a stock Huoniao chinese rubbish bike, from a realistic top speed of 55, to 80mph, I just gave it a free flowing air filter, and a free flowing exhaust, did the sprockets, gave it a bigger carb and bigger jets and that was it, but it never wanted as much as this dragstar is wanting, and this dragstar is more confined in the intake, and exhaust, and it still wants more, I just find it hard to believe it burning the fuel, I've seen the stream from the main jet up the needle when the box was off, and the fuel delivery is pissing out like a tap and it still feels lean.... It just goes against all 125's I've seen. If anyone knows of a higher jetted 125 I'd love to hear it, I'm just worried that it may take fuel all day without burning it and it flies out the back. Link to comment Share on other sites More sharing options...
Moderator Cynic Posted March 24, 2012 Moderator Share Posted March 24, 2012 If anyone knows of a higher jetted 125 I'd love to hear it, I'm just worried that it may take fuel all day without burning it and it flies out the back. Easy de restricted tzr125 uses something like a 240 main With a 170 kit your up to 280's, bigger with porting. Link to comment Share on other sites More sharing options...
Morpheuz Posted March 26, 2012 Author Share Posted March 26, 2012 I'll keep my eye on the plugs, and I'll adjust it accordingly, I just find it hard to understand how it can run leaner by opening the exhaust, when no extra air has been added. The intake revoloution, and the exhausts revoloution, are seperate, its not overlapping like 2 stroke. Link to comment Share on other sites More sharing options...
Moderator Cynic Posted March 26, 2012 Moderator Share Posted March 26, 2012 I'll keep my eye on the plugs, and I'll adjust it accordingly, I just find it hard to understand how it can run leaner by opening the exhaust, when no extra air has been added. The intake revoloution, and the exhausts revoloution, are seperate, its not overlapping like 2 stroke. I'll have to use my addenoids (trainspotter voice for this). The exhaust on a 4 stroke is tuned much like a 2 strokes, the only real difference is the lack of an expansion chamber. Aside from that rather obvious difference they work the same. When the exhaust valve opens there is a pressure wave that travels down the pipe pulling the gas with it, the bike will be 'in the power' when the 'tuned length' of the pipe harmonises to a particular RPM to create optimum gas extraction. This is because there is a reflection from the end of the pipe back to the engine which reduces the efficientcy of the exhaust. Not as drasticly as a 2 stroke as the gasses are being pumped out but there none the less. That is why multi cyl bikes have primaries all the same length, if they weren't it would cost power as they are effectively 4 engines bolted together if one is out of tune its like a bad carb. By messing with the silencer you are messing with the reflection, this will now be out of cync with the carb/airbox where exactly the same happens. Only the system is now out of wack slightly as the airbox will be most efficient when the exhaust isn't and vice versa. Its why most 125 tuning feels like its worked because you lose some midrange spread so you 'feel' a power surge. Your cheap copy chynyoung thigimy dodah probably had bad exhaust and carb set up and you put it right getting better power, chances are yamaha have done a much better job and there won't be a lot of losses to get without some grinding. I hope i've explained it clearly. Link to comment Share on other sites More sharing options...
Morpheuz Posted March 26, 2012 Author Share Posted March 26, 2012 Thanks, youve brought me back to earth.. however, the huoniao, was a single cylinder, single exhaust valve, dual exhaust setup, and was indeed shit, by opening it up like I did, didnt that just make it a straight through, as it pretty much was. Whats the deal with straight throughs? If I give my yammy a straight through, and open the intake completely up, then tune the carb to deliver enough fuel, it should be better power at high rpm right? Mid acceleration should be ok, with the needle higher than stock. However I have no idea where the idle mix screw is. It may stall on decel.. Cheerz for this btw. Link to comment Share on other sites More sharing options...
Morpheuz Posted March 26, 2012 Author Share Posted March 26, 2012 Easy de restricted tzr125 uses something like a 240 main With a 170 kit your up to 280's, bigger with porting. Thats a 2 stroke too, obviously its going to have bigger jets. Link to comment Share on other sites More sharing options...
Moderator Cynic Posted March 27, 2012 Moderator Share Posted March 27, 2012 Thanks, youve brought me back to earth.. however, the huoniao, was a single cylinder, single exhaust valve, dual exhaust setup, and was indeed shit, by opening it up like I did, didnt that just make it a straight through, as it pretty much was. Whats the deal with straight throughs? If I give my yammy a straight through, and open the intake completely up, then tune the carb to deliver enough fuel, it should be better power at high rpm right? Mid acceleration should be ok, with the needle higher than stock. However I have no idea where the idle mix screw is. It may stall on decel.. Cheerz for this btw. I'm no engine tuner but i'll try. Straight throughs are just as they say but the reflections are reduced, every collar, bend and weld in the pipe will affect the way it removes gas. Straight throughs have very little and will therefore be easy to tune. Is this some sort of technical exercise, can't see there being a lot of horses in that v twin, more so they don't respond to revs. Paul's goes well apparently as he used the trusted, ' if its not absolutely vital its gone' approach. Every KG counts. As a slightly off topic example, friend of mine had a 1200bandit and weighed 18stone, i had a tweaked 600 suzuki and weighed 13 stone, apart from me topping out on the limiter earlier there was no difference in our bikes performance. If we swapped bikes though, ha i was G_O_N_E. Link to comment Share on other sites More sharing options...
Morpheuz Posted March 27, 2012 Author Share Posted March 27, 2012 Roughly 13hp in my bike, with straight throus and better intake, hopefully I can cruise at 70 without devvo and his mates overtaking me. Link to comment Share on other sites More sharing options...
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