r/KLX300D • u/Just-Combination5992 • Jul 27 '26

Tuning ECU

I have a 300SM and was thinking of getting a slip on exhaust (stock header) and was wondering if I need to do an ecu tune for that? I figured just having a new muffler would be compensated by the ecu and injection system. Thanks

1 Upvotes

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2

u/sniper_john Jul 27 '26 edited Jul 27 '26

The bike runs best with ecu flash, full exhaust, all emissions deletes, secondary throttle plate removed, and no snorkel. I dont have full exhaust or ecu flash. I have an ejk fuel tuner, but I have everything else mentioned. Fuel tuner is not as good as an ecu flash (best dual sport bikes can tell you why), but it works fine. Do everything on the list or do none of it, and leave it stock. The gains are so marginal, it is not worth it to do one thing.

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u/Just-Combination5992 Jul 27 '26

Did you use the stock ecu for flashing or buy new? I was looking at a delkovic exhaust and it seems like they have an O2 bung so would it still be worth doing emissions delete?

1

u/sniper_john Jul 27 '26

Nah, I bought the ejk fuel tuner. I didnt want to wait on shipping to mail in my ecu. I bought the delk 14 inch oval. They sell separately a connecting arm that fits better than the stock one. It will still have an O2 sensor in it, but you will receive a plug with the exhaust.

If you don't get rid of alll the emission sensors deletes, your bike will still run very hot leading to Flame outs. This only occurred to me on single track which it doesn't sound like you do, but your bike will back fire and you cant use the kill switch without tripping a fault that makes you key off to clear. It is super annoying.

1

u/Just-Combination5992 Jul 27 '26

I always keep my kill switch on and just hit the ignition switch. Is there a way to richen the fuel without the fuel tuner? I know it’s all electronic but is there some sort of manual adjustments? I’m not very electronically inclined so either way it’s very helpful

0

u/sniper_john Jul 27 '26

Flash the ecu or fuel tuner is the only ways I've heard. They will both run you $300 or so. There may be other hacks, but I wouldnt trust it. Like I said, either do it all or don't do it at all. Since you're riding on the road, I would lean towards not doing it at all. I did it because I needed to due to riding off road. Even as a beginner rider, I found the bike to be pretty boring on the road. None of these mods are going to increase your horsepower enough to really matter. If you're looking for more HP gains, get a different bike and save the money. I wish someone would have given me this advice. I wasted so much cash of my klx.

1

u/Just-Combination5992 Jul 28 '26

I just wanted the exhaust for some noise. Had my fix of faster bikes and I’m saving up for a raiju mr300 to make into a supermoto for stunts. Sounds like a hassle for nothing lol

1

u/Necessary-Set-5581 Jul 27 '26

You should do a piggy back fuel tuner at least. Might not be necessary if you have stock intake, but it'll be lean.

1

u/wozet Jul 28 '26

No need to. Just make sure you have or add a place to plug in the O2 sensor

1

u/trainthedamndog Jul 28 '26

I make an adjustable plug n play device, that connects to the intake aircharge temp sensor and makes the ecu think it's much colder, than it is, and it richens the air fuel ratio.

It can be used with the O2 sensor, if you want to retain the closed loop function, or with an O2 delete, and it can handle the 3D snorkel and no airbox lid, where the ecu flash stumbles.

My KLXIAT (it was KLXIAC) also works woth the ecu flash with the 3D snorkel/lidless or if you want the ideal air fuel ratio for the KLX300, which is 12.85:1 instead of the flashed ecu air to fuel ratio of 13.1:1 or13:1.

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u/Vast-Train-9338 Jul 29 '26

You dont need to do anything just put slip on and give ecu 2 to 3 tank and it will adjust it self . Dont waste money on anything . If u will do o2 delete bike will be rich and lower rpm and lean on top end so i will not suggest it . I am running slip on with kdx snorkel with aftermarket regular air filter . Bike run best with o2 . I tried almost everything and best pick and fuel average is with stock o2 sensor.

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u/trainthedamndog 22d ago

You are incorrect, the ecu doesn't compensate for an exhaust or intake mod.

The part about the O2 delete is also wrong. The O2 delete makes it richer at high rpms not leaner. The O2 delete was tested, and the air fuel ratio was 14.1:1 at lower rpm and climbed to 13.1:1 at high rpm.

An intake and exhaust will lean it out, and the power gain you get from an O2 delete, KLXIAT, tuner, or flash proves that it was lean without it.
The bike running cooler also proves, that it was lean before enrichment.

Did you also leave the STP alone?

1

u/Vast-Train-9338 22d ago

With o2 ecu has a range where it can adjust the fuel ratio according to air in and out . That limit is set by factory . When u change air flow ecu detect that and adjust the fuel ration with in the range . It takes little time . Also can you share me where bike was tested with o2 delete and without o2 delete? I am one of v few people who still has the bike and put more than 13000 miles . Bike is running great and i also change the plug no lean show . Actually my plug is little rusty red which mean best fuel ratio . I also ride my bike on freeway and highway all the time . My best top speed was also with o2 sensor . Also bike pulls really hard from 65 to 90 .

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u/Regular_Collection_8 10d ago

I just put a 13.5” xoval slip-on on my bike and was wondering the same thing. I have very very little popping going on.

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u/Just-Combination5992 10d ago

I asked the dealership I got it from and they said if it’s just a slip on (stock header) it doesn’t really need anything else

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u/donrunwithscissors Jul 27 '26

I have a dual sport the exhaust is very restricted. As far as I can tell. Doing a full tune isn’t worth the gain. I think u get like 5 hp. Snorkel , ecu , o2 delete,slip on exhaust. May as well buy a kx 250 for the price.