My 2 cents ...

O2 sensors on ATVs (especially sport quads) are a great tuning tool for EFI or Carbed quads. Think of the 02 sensor itself (not the electronics) as a wear item. You'll get about 40-80 hours of test time out of a sensor (using leaded fuels), and they usually cost less than $80 to replace. So, yes, I agree with Mark, dont leave that in there if there is no testing going on.

I am against 02 sensors (especially sport quads) being put in the new EFI quads as a way to regulate the A/F ratio. They need to stick by the tried and true method of barametric pressure and air temp sensors. Too many sport quads use leaded fuels.

 

Thanks Doc, I agree that its strange. It might be the mild cams building to much midrange pressure. Its only going through the midrange that I get ping, so if I had more cam it may not show up.

DuneMe & Redstone, Thanks for the heads up. I was always only going to use it as a tuning tool, not leave it in. Its the NGK and does not lend itself to a permanent installation. I really like that I can now just add a bung for the sensor and use it on any vehicle I have.

Well, off to Lakeport and find some Toluene.

Thanks everyone.
Scott

 

you also need to know that running race fuel, or a mix of pump and race even, can and usually does change your a/f mix and jetting. I am running a much smaller jet with 110 octane leaded Sunoco fuel that I ever dreamed I'd be running.
Just keep that in mind, if you are rich now and go up to a race mix you will probably be even richer. or depending on what type of fuel or additives, maybe the opposite.

 

Doc, I ended up getting Trick Tek TT111 (Cheveron/Phillips) from Hillside Honda for $6.50 a gallon. Piedmont had Toluene, but its was $18.95 as gallon!

I'm running around 20% 111 octane race gas with 91 octane pump gas for about 95 octane. No signs of any pinging.

I ended up with the following settings at 90 degrees with 13% humidity at 2,750ft elevation:

162.5 Main(True Mikuni Jet, not DJ)
-98 needle on the top notch.
50 pump
30 pilot with 3.5 turns out. Think I will go to a 25.

I truly can't believe how fast my DS is. I can't even imagine what you guy's DS with the big builds run like. With the fine tuning I did today its got a great power band and with my 22x11x9 All Traks I can't get it to hook even in 5th on our dry fireroads. I had to go to our of our paved roads to do my testing.

Thanks for all of you input and look forward to see you at the dunes someday.
Scott

 

Good deal!!! Glad you got it running good!!!! You must be about the only person in the county with a DS Bomb. I have yet to see one on the trails on Cow or Elk.

A bit of advice I'm sure you already know. Keep reducing the mix until you hear detonation again add a bit more mix and write that mix down. Set your jetting (like Hightower said) and your done. Run that same mix over and over.

One thing also to remember is that if your that close to pump gas it should only take a few ounces of tolly/ gallon to stave off detonation. This way you only have to carry a gallon or two to mix with instead of gallons of race gas. You might be surprised at how little tolly it takes to slow the burn.

About the dunes. The car owner that I drive for wants to go to Samoa on the 23rd for a race. I won't have my quad up there, but you could come up there and watch some good races and ride some sand.

Again Congrats!!!

 

I have been to the Somoa dunes a couple of years ago. I didn't even know about the drag strip there until I was unloading and heard some runs. Its been a long time since I was at the drags. I can't make the 23rd. Someday I want to take my SHO there and see how it runs.

I will start backing off the race gas till I get a ping and then go back up a little. I will wait until I'm at sea level again where I will need the most octane.

You know its funny, I have never been to Cow or Elk. Lived here all my life, and have only rode on on our ranch on Cobb. But I will be trying it out one of these days, my sister's boy friend has a XR400 and keep promising to show me around.

I have never seen another DS650 in the county, kinda a rare bird.

 

When you installed the new piston, what was the deck height?
For bests results you should have been between .035 and no more than .060.
If deck height is below .035, piston may hit head and if over .060, you have no quench and thus detonation may happen.

OMR

 

OMR, I remember the specs were per JE, but I can not find where I wrote down the exact number.

I just learned from MrHorspower that he has cc'd these new JE shelf pistons and they are really a 13 to 1 piston. So now I know where my problem is.

Learning this I'm going to bump up my race gas ratio, he recommends a 50/50 mix like Dragon did, so I will be going there,

Scott

 

great news, glad you're getting it allswaured away.
remember, if/when you step your mix up to 50/50, you will need to rejet. and then like Doc says, stick with that mix so your jetting won't be effected.

wow, a 98 needle on top groove. yes your pilot is definitely rich if you got the idle screw 3.5 turns out - when you drop the pilot and turn the screw in I am curious if that will force the needle up a notch.

 

Highttower,
My bad I have a 97 needle. I think I will be going back to your recommended setting of second notch and starting over.

I'm going to tune the idle and needle by how its running and the main with the O2 with the 50/50 mix..

Its just a bit of a learning curve.
Scott