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Would Full Exhaust Install Include Rejet?

Discussion in 'Modifications and Projects' started by WheelsLegman, Nov 14, 2012.

  1. For my birthday my bf got me a new full exhaust system for my bike. Would you assume the mechanic would adjust the jetting to suit as part of the install?

    My partner said he mentioned the jetting to the guy and he said "dont worry we'll take care of it."
    It seems to pop a little bit when decelerating, not a loud pop but its there. My partner noticed the header pipe get really hot when he rides but I didnt notice it as I wear cordura pants he wears normal jeans..apparently can be a sign of running lean. Seems to run better than before tho..

    I emailed the place just before so hopefully they get back to me. I was just wondering, in your experience would a mechanic install something and leave it in a state where it could potentially damage the bike? If they didn't adjust the carb in any way should I not ride it till I have the time and money to adjust the jets? I really dont want to damage the engine its a brand new bike...

  2. If the new exhaust headers are same diameter as old, probably no need for anything else. If different, probably yes. But jets are not adjustable, they are changed for bigger or smaller ones, as required. If the makinik changed them, I presume it should show on the invoice?

  3. Yes I am aware of what jets are thanks...perhaps alter would have been a more suitable word. Anyway its not rocket science...

    Well I checked 2 Brothers website and they say a re-jet isn't necessary but would be good. Maybe the header pipe is the same diameter as stock.

    I spoke to the mechanic and he said changing the main needle would be a good idea as i did get a full system. Now i'm thinking should I buy a whole stage one or stage 2 jet kit and get him to install that for me? This whole air fuel ratio thing seems tricky to get perfect..
  4. I wasn't trying to be condescending but genuinely helpful. And since you don't seem to understand the difference, I'll leave you alone. Have fun with it.
  5. Does sound to be running lean. Best way to check is to take the bike for a decent run (ie high revs), then as soon as practical shut it down and check the sparkplugs. A lean fuel mix will show up as a white/grey colouring on the plug tip.

    If your bike has Mikuni carbs (like most do) there's basically three different throttle positions that can be altered. Idle mix is for 0-1/4 throttle, needle position (clip height) is for 1/4 to 3/4, and changing the jets is the only thing that will affect 3/4 to full. So yes, definitely change the jetting. Adjusting the carbs will mask the symptoms at lower throttle but if it's running lean flat out there's a very real risk of doing serious damage to the engine.

    There's a lot more to gas flow velocity than just the diameter of the pipe it's flowing through.
  6. Yes it will flow more gas, yes the jetting should be changed. How much is a guesstimate or an analysis depending on how finite you'd like it to be. Dynojet offers jet kits as you'd know, I remembered some people have good results on their bike, others dont like the characteristics. I guess it's always a problem, esp for jetting which suits a certain atmospheric condition, and that the more performance oriented you make it for one condition the worse it is for every other, hence why jetting is a compromise on street bikes.

    Check out the kawiforums, supermotojunkie, advrider, thumpertalk, it's been done to death and then a few times more. I did a quick search and turned up a bunch of results (e.g 124-128 MJ up from stock but everyone's local relative air density is different!). Did your mechanic do anything? You'd have to ask them - and then verify it.

    here's a few things you may have already seen: