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Discussion Starter · #1 ·
I'm riding in the Bighorn Mountains this weekend, my sled is lean on the pilot circuit. What is the maximum I can turn out the fuel screws? I have them 3 turns out now and it's still lean.
 

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after 3 turns out i would get bigger pilots. i normally try to stay between 1.5 and 3 before i change size on pilots
 

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i am thinking the same as you are Joel, my lowend is pretty lean with about 820 degrees F at 6000rpm, seams like the sled is somewhat irreatic and bogs, but stops as i give it a juice with the choke plunger or encrease the speed and rpm`s , i havent ridden the sled as slow as this before, but as the the little lady was riding a supersport 550, the speed was a bit lower as i am used to.. thats how i noticed this condition..
 

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What elevation are you having problems at?

When you go to the mountains what elevation will you be at?
 

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Discussion Starter · #7 ·
I am riding between 7 and 10K feet. I have the fuel screws out 3 turns and it's still lean from about 3K RPM to 4200 RPM or so. I know it's the pilot circuit because if I flip the choke on 1/2 and go WFO from a stop, the sled pulls hard out of the hole but then obviously the power dies off in the midrange and at full throttle because it's rich with the choke on.
 

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I am riding between 7 and 10K feet. I have the fuel screws out 3 turns and it's still lean from about 3K RPM to 4200 RPM or so. I know it's the pilot circuit because if I flip the choke on 1/2 and go WFO from a stop, the sled pulls hard out of the hole but then obviously the power dies off in the midrange and at full throttle because it's rich with the choke on.[/b]

I'm missing something, a prox is rich on the idle circuit at sealevel from the factory, so at 7k' it should really be rich.

What has been changed, what pilots are in it?

I agree that 3 turns is about as much as you want to go, but something doesn't seem right here.

Pilot air setting to big?
 

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Discussion Starter · #9 ·
I figured it would be rich on the pilot circuit too. I'm using the stock pilot jets. I haven't changed the pilot air setting at all.
 

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The Manual says up to 5 turns out then go to a different size pilot.
 

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I'm missing something, a prox is rich on the idle circuit at sealevel from the factory, so at 7k' it should really be rich.

What has been changed, what pilots are in it?

I agree that 3 turns is about as much as you want to go, but something doesn't seem right here.

Pilot air setting to big?[/b]
I'm not sure about the big blocks but I know on our 600's they were pretty lean dowm low and would idle high after they were warm and mainly after long pulls. so we had to crank out the screws a little to get the idle down and stop the lean detination
 

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I'm not sure about the big blocks but I know on our 600's they were pretty lean dowm low and would idle high after they were warm and mainly after long pulls. so we had to crank out the screws a little to get the idle down and stop the lean detination[/b]

after richening it up with the fuel screw, where you experiencing any loading up at take offs?? i know the 600's have some lean spots down low, but it seems if you try to turn the screws out and let it idle for a short period of time it tends to load up and you have to play with the flapper instead of just gunning it.
 

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after richening it up with the fuel screw, where you experiencing any loading up at take offs?? i know the 600's have some lean spots down low, but it seems if you try to turn the screws out and let it idle for a short period of time it tends to load up and you have to play with the flapper instead of just gunning it.[/b]
yeah mabye a little its not bad though and if your gonna race some one you just need to hold it justbefor engagment for a little bit then it seems so clear out
 

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I am riding between 7 and 10K feet. I have the fuel screws out 3 turns and it's still lean from about 3K RPM to 4200 RPM or so. I know it's the pilot circuit because if I flip the choke on 1/2 and go WFO from a stop, the sled pulls hard out of the hole but then obviously the power dies off in the midrange and at full throttle because it's rich with the choke on.[/b]
The fuel screws only affect idle. Once you crack the throttle, it is on the pilot and PAJ. As you open the throttle further, it transitions onto the needle. Instead of talking rpm, talk throttle position...idle,1/8,1/4, etc. Where is your needle?
 

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Discussion Starter · #15 ·
The bog is at less than 1/4 throttle. My needle is set in the 2nd clip. It runs perfect once you get up past engagement RPM. It shows in the manual that the fuel screw effects the mixture just past idle, almost to 1/8 throttle. The 3rd day of riding it was cold and the sled was hard to start without the choke, this also tells me that it is lean from idle to 1/4 throttle.
 

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You running a tempaflow or ATACC? The fuel screw "technically" can affect up to around 1/8 throttle, but it tapers off very fast. It's not doing much there. I only ever use it to tune idle and response off idle. Once that is right, I'd look elsewhere for adjustments, or you will end up with a rich idle trying to tune a bog out at 1/4 throttle with it. I don't have any experience tuning sleds at elevation, but I know I've seen more than once where mountain guys INCREASE the pilot and pilot air jet...Don't know if it's due to the weaker signal in thinner air? I've seen it mentioned on SnoWest several times.
 

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Discussion Starter · #17 ·
Yes, I am running an ATACC. I used it for the first time during this trip(Bighorn Mountains). When I was in West Yellowstone last year, I did not have to change any pilot jet or fuel screw settings. But I did read in the ATACC instructions that it may slightly lean out the pilot jet circuit so that is probably why. I noticed it leaned out the pilot mixture at low elevation too. I had to go from 1.75 turns out to almost 2.25 turns out at low elevation to get the normal idle back.

I have also read that the pilot circuit needs to be richened at high elevation, I never even thought about that until after we got out there.

I am thinking about trying size 50 pilot jets and turning the fuel screws all the way in for low elevation riding and then turning them out as needed for high elevation riding. Maybe that won't work though.

I have always used the fuel screw to tune idle and throttle response right off idle too. This is where the dead spot in the throttle is at. Pretty much right after I open the throttle there is a dead spot, it is a surging and very irregular increase in RPM when the throttle is applied.
 

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Have you tried the air screw adjustment? It affects to a greater throttle opening than the fuel screw alone. In some cases, when you lean the mains, and needle for high altitude, you need to richen the pilots. Your ATACC is leaning it ou tof course. Have you tried putting the needle back in #3? On the initial throttle transition, you may need to increase the amount of fuel flowing at low end, pilot.fuel screw/air screw. Similar to in some cases when grass dragging, and the mains are reduced greatly, you need to richen the needle/pilot to not have a lean bog off the line. For reference one of the extreme cases I ran across of this was grass dragging a 95 Mach 1. The mains had to be reduced more sizes than other sleds for the same temp (13 sizes from stock if I remember right), but the needle had to be put in the richest clip, not to have a lean bog. It ws so rich on the needle that it would slobber when idling, or on the line, but hit the throttle, and it responded instantly. The 700 twin mods wer ran back in 01 in Yellowstone also needed richer pilots to not have a lean bog off the line.
 

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Discussion Starter · #19 ·
No I have not tried the air screw adjustment. I have not tried putting the needle back in #3 slot either. Anytime I've ever rode the sled above 4000 feet elevation the needle has always needed to be in the #2 slot because it would bog really bad in the midrange otherwise and I'd have horrible gas mileage.

but the needle had to be put in the richest clip, not to have a lean bog. It ws so rich on the needle that it would slobber when idling, or on the line, but hit the throttle, and it responded instantly.[/b]
I am not a carb genius by any means but I definitly know my way around them and what changes effect what. I don't quite understand how a rich needle setting would make the idle mixture rich....doesn't the needle always completely block off the main jet when the sled is idling?
 

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That sled had the big 44 mikunis on it, with the needles that way you could see the fuel spraying out the carbs a lot more than the stock needle setting.
 
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