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Tommy D

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  1. Tommy D

    Decel Backfiring - Jetting?

    Kasuyaho, I'm in Sydney, Have had CO2 censor up the pipe on the dyno and all was good, plug looks fine, Dyno run was done at Sydney Dyno in Kensington, HRC Kit installed by Dirt Bikes R Us, Vortex information is from Nick at Teknik Motorsport. Nick builds the XR650's that race in (and win) the Australian Safari, so i trust him (a bit, he's still trying to sell me something though). His labour is expensive but he does really good work, he did my suspension too and it's perfect. Update: Took out the fuel strainer and reserve tube and used a larger fuel hose. Magic, atleast half of the backfiring has gone away. It's down to 3 or 4 pops when going from about 6000rpm down to 2000rpm into a corner and not virtually no loud bangs. This i can live with. Now i'm going to try and go back to the 68s pilot and original pilot screw setting to see if it gets worse again. Will also try a 180 main jet as spoke to Teknik the other day and he says that the Aus safari bikes run on a 178 to 182 depending on temperature. So you're probably right about the 185 being a bit fat.
  2. Tommy D

    Decel Backfiring - Jetting?

    Basically XR Stamm you've got it in one. . . The noise is driving me crazy. I'm not talking about one or two pops here, but a flurry of loud bangs. None of the other bikes on the track backfire on decel (except one suzuki), and most of them have aftermarket pipes, pistons, cams etc. So i'm pretty sure it can be tuned out some how. I'm also not completely convinced that it's not hurting the engine/exhaust. That being said, i blocked the air cut off. Still backfiring. I turned out the pilot screw. Still backfiring. I changed the pilot for a #70. Still backfiring. I rechecked the exhaust and intake for leaks. No leaks. Got onto a new line of thought while testing it though. The backfiring mainly happens after getting on the gas for a bit and then backing off the throttle. Or when i am nearing an empty tank of fuel it gets really bad. So i'm thinking maybe the float bowl is draining and then leaning out. I think i'm going to try taking out the reserve petcock and mesh filter and put on a new piece of fuel hose too. Might be wrong, but it's cheap and easy and i think my only other option is to buy a new pumper carbie and exhaust to be sure i get the problem. Atleast it still goes fast. It's just the noise that's shitting me, it brings a little bit too much attention from the police when you have an illegal exhaust on the bike.
  3. Tommy D

    Decel Backfiring - Jetting?

    When (and if) i get it, i will definately put it on the dyno for a comparrison run against the last graph. Supposedly, the vortex offers 4 to 7 horse power increase on a stock XR, but really comes into it's own on a bike with high comp piston and high flow parts right through (carb, cam, exhaust etc). But you also need a damn good spark plug too, the ones that came in the HRC kit are $80 (aussie) each here. And you need to lighten the flywheel to get the gains down low too. So it's not as easy as bolting on a CDI and getting 10 horsepower. But then again salesmen always make "qualifications" to their estimated horsepower gains.
  4. Tommy D

    Show your PIG

    Don't knock the scooter. . . it's got less chicken strips than the CBR600RR behind it!
  5. Tommy D

    Show your PIG

    Not a good photo, but it's not about how good the photo is.
  6. Tommy D

    Decel Backfiring - Jetting?

    Haven't got the air fuel graph on the computer, but heres power/torque. I've been told that a Vortex Ignition will get me another 6 to 10 horsepower, but i'm not sure if i really need it. Good point on doing one thing at a time, i'll do the cut off valve first, the pilot screw then pilot jet. Blue line is pilot at 1 1/2 turns out, red line is pilot screw at 1/2 turn out.
  7. Tommy D

    Decel Backfiring - Jetting?

    Thanks for all the advice, looks like i have some work to do this weekend. I have ordered a #70 pilot and will try it out. I do know of the mod to block the deceleration softener, but i haven't done it yet (for some reason i was thinking it would make the backfiring worse?). I'll do that mod too. The fuel screw is set at 1/2 a turn out, this was set when it was on the dyno. It made about 30% less power at the bottom end with the fuel screw set at 1 1/2 turns out. Now i'm confused cause this would mean that the pilot is too rich? But then again the dyno run was only done on acceleration, not deceleration. I have got the HRC needle and needle jet installed so theoreticaly they should be right. And it never backfires when cruising along at mid throttle, only when i shut the throttle off completely at mid to high revs. I may as well recheck the exhaust and intake joins again. I used a gas torch (not lit, and listen for increased revs) to check for intake leaks, and a match (lit, to see if it gets blown out) to check for exhaust leaks. Is there a more accurate way to check for leaks?
  8. I have an HRC kitted 2000 XR650R, converted to supermoto. Ever since installing the HRC kit, along with a full exhaust system, filter, air box mods etc. The bike has been backfiring on deceleration. . . a lot. I have checked the obvious things like exhaust and intake leaks, had it on a dyno to check the fuel mix (a lovely 13:1 to 15:1 all the way through the revs). But it still backfires. It's backfiring mainly at mid to high revs but only when i close the throttle completely, if i open the throttle a little it stops. Problem is, being a supermoto, i need the compression of deceleration to brake into corners. So i can't just raise the idle to get rid of it. I am now thinking that the problem is that it's running too lean when the throttle is closed (or there is a problem with the spark plugs, but i'll try that one last cause the HRC plugs cost a fortune here). So my question is (finally, sorry for the long babble), will increasing the pilot jet size richen my mix with the throttle fully closed and hopefully stop the backfiring? And, if it does richen the bottom of the rev range, will this kill the power at low revs and take off? I'm currently using a 68s pilot and a 185 main, and i have tried 3 jet sizes either side of the main with no success. Any help is greatly appreciated, i've just about run out of ideas to fix this. Tom.