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Discussion Starter · #1 ·
So I have a '99 XCR-800 with the Mikuni rack carbs. They have been bored 38 to 40mm.

The only change from stock is the pilot air jet being a 0.9 instead of 1.0 to richen up the low end.
Pilot jet 145
Main 450
Mixture 1.5 turns
Needle clip 3rd slot

I took her for a ride yesterday. The Kuskokwim river is frozen, very flat, and has 4 inches of light powder on it. I drove at 5500 rpm for about 1 mile with EGT temps around 1200* F. Shut down and the plugs looked good. Pistons too new for a wash check, they are still shiney. Then took it to 6000 rpm and the temps hovering around 1275-1300*F, the curved part of the plug that extends over the electrode still looked good, the plugs had been a little wet with oil (I am off adjustment), they were now noticeably drier. When I took it to 6500 rpm, the clutches are beginning to shift, there is a greater load on the motor, and I am going 60 mph. The temps on the EGT's are at 1375*-1400*, at the entry to the danger zone with my probe placement. I am guesstimating I was a little over 1/3 throttle. The plugs were now dry except for a little oil on the end of the rim, the curved portion was not grey, but you could see the beginning of a little color change, no longer that cardboard brown.

I know the oil in the gas-tank for break-in would lean the mix out, and with the oil pump needing adjustment, that would lean it even further.
This morning it is 5* F, so I will struggle with the airbox and getting the oil pump where it should be first off. Next will be turning the mixture screw in 1/4 turn from 1.5 turns out to 1.25 turns out. This will also help the low end mix richen just a little. I think these will work well off idle to about 1/4 throttle. I will compare these adjustments to yesterdays.

Depending on how plugs and EGT's read, I will then move the needle clip down 1 slot to bring the needle farther out of the needle jet. This will richen the 1/3 - 3/4 range. It was suggested to me to move 2 slots, but I want to see how it looks with just one.

The beauty of having that flat river out there is: I can make as many runs as I want, just changing one thing on the carbs to see what the effect is.

I am going to take some spare plugs with me so I can run up to the Pol dealership and show the plugs to the mechanics and service manager for their opinions. Then back down to the river for more testing.[:D]
 

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You are very lean, I don't like going over 1250 on the egt

What I've done for tuning carbs is see if there is a 800 polaris that uses 40mm carbs, get all the info (mains, pilots, mixing tubes, needles, air screw) put all that in and retry and adjust as needed.
 

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Discussion Starter · #3 ·
The normal operating temp for my probe position is 1400* F. I see that when at the end of the midrange just as the main jet takes over.
Reason I am having to do all this is the work done inside the motor, the bored carbs, the reeds, the pipes, and the airbox mods. It is allowing the motor to breathe much more freely, so I am trying to be careful in how I go about this.

I adjusted the oiler yesterday using a dental mirror. I even bought a new throttle cable to make sure everything up to snuff. Found out the old cable threaded part had worn threads, so there was no way to tighten up the nuts to keep the adjustment.

I turned in the mixture screw to 1.0 turns out from a light seat. It fixed the hesitation.
I was going to raise the needle one slot, and as I was holding the clip with the pliers, getting ready to insert it into the slot, it vanished. No joke, the clip simply fell out of the pliers. I know the look on my face must have been priceless. Good thing I was only three miles from the stealership, I hoofed it over and bought five of the little buggers. It was too dark to look at anything by then so I just went home. Today I will do some more experimenting.
 

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Discussion Starter · #4 ·
So the temp today is 0* F, no wind, had another 3 inches of powder snow last night. Total powder on the river is about 6-7 inches.

I have moved the E-clip to the fourth slot on the needle, and this has helped cool the temps through the midrange. I deliberately held the throttle at 6,500 - 7,000 rpms where the clutches are shifting/load increasing and near the end of the midrange. I found I need to adjust my EGT gauges in the pods. I had them so 1375* F. was straight up-and-down. Somehow they are no longer straight up-and-down. I was able to make the temps climb to 1350* - 1375* F, and they began to come back down as the main jet took over. I think before installing an ATAAC, I need to put in 460 main jets, this will by my -20* F. starting point.

I was not following my owners manual on breaking-in a new or rebuilt engine, I was having so much fun varying the throttle, I began to smell burning plastic!!! [Wow] I stopped the sled and opened the hood to see smoke coming from under the pipes where they cross up and over the shock tower. I dropped to my knees and looked into the right side shock recess to see a big bulge, complete with the wrap-marks from my insulating pipes wrap. [Flame1] CRAP!!!

Long and short of it, I had so much heat in the pipes, I melted my tub. Not bad mind you, but I bought some 0.025" aluminum sheeting to make a raised portion over this spot, that the pipe can rest on so it won't continue to melt my tub. Now all I have to do is get the pipes off, and diddle with the "tub protectors".

Other than that? Well, at 60 mph steady speed, I convulsively pasted the throttle and had the skis lift off the ground. I let off the throttle when I realized I still did not have directional control, and I could no longer see since my goggles were bouncing all over my face. This is with the supposedly terrible Xtra-12 suspension, which, by the way, I am still trying to figure out why people say it is a trail suspension. Thsi thing is pretty hard riding, even after I dropped the 243 lb./in. spring in favor of the 123 lb/in. spring on the rear track shock. I think I will have to drop the front track shock spring to the next lowest to have a trailable ride.
[Bevis]
 
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