Will 87 gas make my bike ping or rattle?

[Joey%B23]

I was far away from home and knew I wouldn't make it back on the fuel I had left in the tank! I always run Mobil 93 super gas in my bike but I had my girl bring me my can ,2 stroke oil,and 2 gallons of gas! She got 87 from cumbies now the bike pings almost sounds like a rattle comming from the kips valve! Do you think that is from putting the 87 cumbies gas in it?

[KDXGarage]

I think so.

You might not want to dump her, but definitely dump the low octane gasoline.

[Goofaroo]

I always run 87 octane. A stock KDX is only around 9:1 compression and certainly shouldn’t need more octane to keep it from pinging. It could be that 93 octane was masking a problem. Too much carbon buildup, timing is off, an air leak, jetted too lean, or engine mods could be causing the pinging.

Either way, if it’s pinging on 87 You don’t want to ride it like that until you find out why. Your KDX should run perfectly on 87. Pull the plug and see how it looks.

[KDXGarage]

I knew you would be first to disagree. :-)

OP, dump it and put high octane it, then come back and report your findings.

[Goofaroo]

I don’t disagree. If he’s gonna ride it without repairing it and it runs without pinging on 93 fuel then go for it. He obviously shouldn’t run it if it’s pinging.

A stock H model is 7.9:1 compression. Unless it has a mechanical issue it should run just fine on any pump gas from 86 to 93 octane.

[Slick_Nick]

I always run 87 octane. A stock KDX is only around 9:1 compression and certainly shouldn’t need more octane to keep it from pinging. It could be that 93 octane was masking a problem. Too much carbon buildup, timing is off, an air leak, jetted too lean, or engine mods could be causing the pinging.

Either way, if it’s pinging on 87 You don’t want to ride it like that until you find out why. Your KDX should run perfectly on 87. Pull the plug and see how it looks.

I gotta ask, why? For the amount of gas the KDX uses, how much money are you really saving by not running premium fuel?

[Goofaroo]

They run crisp and clean on 87. Why would I not?

[SS109]

I use to run 87 on my old '90 200 (RB head and carb, Vforce III, FMF pipe, Dyna-Ring) but after dialing in my jetting I noticed my bike ran quite a bit warmer and even boiled over twice on me. I figured I was running right on the edge of detonation at times, even though I couldn't hear it, so I bumped my fuel to 91. My bike cooled down, no more boil overs, and didn't have any issues after the change.

Now I run 91 in everything regardless of mods or not. Running the higher octane allows you to push your jetting as close to optimum as possible to get the best power and fuel mileage. Lastly, for the 20-30 cents more I spend on a gallon, it is worth just the piece of mind as well.

Joey, I would do like KDXGarage says, just drain the 87, mix up some good 91+ and pour it in, and see if the problem goes away. If it does, you know it was just the low octane or maybe just crap gas.

[Goofaroo]

Fuel choice is like an oil thread. Everyone has an opinion.
My engines are in stock configuration and I have never had overheating issues or any other problems with running 87 octane. Your engine mods and in particular the head mod could very well dictate a bit more octane to tone down the fuel to prevent preignition.

My post was directed to the OP who claimed he always used 93 octane and then found that it pings with 87. If the bike is stock it may have a problem. If it has been modified and he bought it used he may not even be aware of the mods which like your bike might require more octane than a stock motor.

Like I said, an engine that only has a compression ratio of only 7.9:1 compression certainly should burn 87 octane fuel very efficiently. I was simply trying to give the OP a heads up that he may have a problem he’s not aware of.

If he has a stock KDX and has been burning 93 octane fuel for a long time I would suspect carbon buildup in the combustion chamber and the top of the piston is causing it to ping on the more “lively” 87 octane.

[SS109]

I wasn't challenging you on what you run. I was only relaying my experience and why I run what I run. The only thing I suggested was to swap out the low octane (maybe crap gas?) for some high octane and see if the problem goes away. To each their own.

[KDXGarage]

Please stop giving out incorrect information that it is only 7.9:1. It is higher before the KIPS kicks in.

Please stop encouraging people on this site to use 87. That could lead to engine damage for someone, so no need for you to make blanket statements for all owners in all situations.

Thread locked.

[SS109]

Just so the correct info is out there...

RON + MON is the octane rating system we use in the USA ***also take note of what it says in the "CAUTION" box

[Julien D]

Thanks, guys. It is important that we do not allow disinformation on this site, especially that which could cause damage to someones baby. This site is meant to be an informational resource for KDX'ers both new and old, and any information that myself or the moderators see as potentially damaging will be censored.

To state it simply and clearly, It is a fact that the manufacturer specifies a minimum US octane rating of 90. If you run a lower octane than specified, you risk engine damage or failure.