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New exhaust, bike backfiring.. Alot

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Hey all, Just installed my yoshimura rs2 full system and have been having alot of backfire on deceleration and engine breaking. The bike has a 3*3 mod and jd jetting. The kit says to use the 165 vs the 155 if you have full exhaust. Could the issue be having the 155 installed and not the 165? Or could it be a header leak. It looks like the flange on one side is just barely not flush but it will not tighten anymore than it already is. If you think it is a header leak what is an easy way to test that? Im thinking its the jetting, but thats just my amateur opinion. Any thougts? 

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Yes, you have to change the jetting to add the extra fuel to the extra air you are now flowing.  Sometimes just going out (turning counterclockwise) on the fuel screw can richen the mixture enough.  If you back it out and it still pops, needs the jet.

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The only jetting that will change decel popping is the pilot jet and the fuel screw.

When you start the bike for the first time of the day (cold motor), how quickly can you take the choke off and have it run clean?  I've found that if choke can go off in about 30 seconds or less and after another 30 seconds the bike is running cleanly, then your pilot & fuel screw are rich enough and no decel popping.  So if your bike is fine on start up, that might mean it is a pipe issue vs. jetting.

Changing the pilot jet size is a big change, fuel screw adjustments are a small changes.  Meaning, if you have big time popping (due to lean condition) then just twisting on the fuel screw isn't going to fix that, you need 1 or 2 pilot jet changes.  

Is it possible to put your stock silencer back onto the new Yosh pipe?  That way you have not changed the pipe mounting but with the stock silencer you'll be way less lean.  Try that, if you still have the same popping it is probably the pipe install.

Also, a cheater "fix", running a higher idle will give you less decel popping.  Not a real fix, but it is very noticeable. 

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On 8/17/2017 at 6:55 PM, dannyrg85 said:

Hey all, Just installed my yoshimura rs2 full system and have been having alot of backfire on deceleration and engine breaking. The bike has a 3*3 mod and jd jetting. The kit says to use the 165 vs the 155 if you have full exhaust. Could the issue be having the 155 installed and not the 165? Or could it be a header leak. It looks like the flange on one side is just barely not flush but it will not tighten anymore than it already is. If you think it is a header leak what is an easy way to test that? Im thinking its the jetting, but thats just my amateur opinion. Any thougts? 

Try the 165 and see.

What carb you running?

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6 hours ago, Bermudacat said:

Try the 165 and see.

What carb you running?

Stock, going to throw the 165 in tomorrow 

3 hours ago, TX-SANDMAN said:

Try a 27.5 or 30 pilot just with an adjustable fuel screw.  What year is your bike?

2015, where's a good place to get pillows Jets? Jd jet kit only came with the 25

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Nice ... once you increase the pilot you will be very happy.  I run a 30 with my Leovince exhaust.

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Rockymountainmc.com is one good source for drz400s jets.

i tell all my drz400s friends the jd 25 is usually too small.

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3 hours ago, TX-SANDMAN said:

Rockymountainmc.com is one good source for drz400s jets.

i tell all my drz400s friends the jd 25 is usually too small.

 

I ran 22.5 on my pilot and it was perfect. If you're running a 27 its likely your fuel screw is ineffective.

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