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Discussion Starter · #1 ·
You guys have been a lot of help on this project and i am hoping maybe you can do it again. After a fresh rebuild and fixing some other problems i finally got it running and it seems to be running great except for one thing.
It starts great(one pull) and idles great(1500rpm's). But when i put it on a stand and rev it up(very snappy) It doesnt want to rev down below 4000 rpm' unless i choke it and then it goes down and idles normal. if i ease into it slowly(2000 or more rpm) and let off, it gradually climbs back up to around 4000 again. It seems to be running lean somewhere between 2000 and 4000 rpm. Is there a good place to start?(carburator wise?) Hopefully its not sucking air from somewhere its not supposed to be.
 

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Did you change pilots?
air screws?
reeds?

Stock timing?
 

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Discussion Starter · #3 ·
Stock timing
Stock air screw settings
Didn't change reeds
pilots were just cleaned, nothing else
 

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Start with the basics, check to make sure everything is hooked up properly. Check your throttle adjustment, are the slides closing? I had a throttle cable act up and the slides would not return to idle position.

Also make sure the carb boots don't have cracks and that the clamps are tight.

Edit: Also make sure the throttle linkage on the rack is not hanging up on anything.
 

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You guys have been a lot of help on this project and i am hoping maybe you can do it again. After a fresh rebuild and fixing some other problems i finally got it running and it seems to be running great except for one thing.
It starts great(one pull) and idles great(1500rpm's). But when i put it on a stand and rev it up(very snappy) It doesnt want to rev down below 4000 rpm' unless i choke it and then it goes down and idles normal. if i ease into it slowly(2000 or more rpm) and let off, it gradually climbs back up to around 4000 again. It seems to be running lean somewhere between 2000 and 4000 rpm. Is there a good place to start?(carburator wise?) Hopefully its not sucking air from somewhere its not supposed to be.[/b]
A lot of XCR 8s did the same thing. I think the best fix was one size bigger pilot air jet if I remember correctly. The 8s had a .9 pilot air jet and going to a 1.0 helped it idle down without the sled loading up. The 99 XCR7 was basically an identical motor with a smaller bore so I would start there.
 

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Start with the basics, check to make sure everything is hooked up properly. Check your throttle adjustment, are the slides closing? I had a throttle cable act up and the slides would not return to idle position.

Also make sure the carb boots don't have cracks and that the clamps are tight.

Edit: Also make sure the throttle linkage on the rack is not hanging up on anything.[/b]

This is good one. Throttle cables that are too tight will cause this too. Happend once to me. I got a little over zealous when syncing and adjust the carbs. Remember that you should have some free play in the flipper.
 

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A lot of XCR 8s did the same thing. I think the best fix was one size bigger pilot air jet if I remember correctly. The 8s had a .9 pilot air jet and going to a 1.0 helped it idle down without the sled loading up. The 99 XCR7 was basically an identical motor with a smaller bore so I would start there.[/b]

I think you ment .8, going to 1.0 will make it leaner. It will suck more air less fuel. .8 will suck less air more fuel.
 

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You guys have been a lot of help on this project and i am hoping maybe you can do it again. After a fresh rebuild and fixing some other problems i finally got it running and it seems to be running great except for one thing.
It starts great(one pull) and idles great(1500rpm's). But when i put it on a stand and rev it up(very snappy) It doesnt want to rev down below 4000 rpm' unless i choke it and then it goes down and idles normal. if i ease into it slowly(2000 or more rpm) and let off, it gradually climbs back up to around 4000 again. It seems to be running lean somewhere between 2000 and 4000 rpm. Is there a good place to start?(carburator wise?) Hopefully its not sucking air from somewhere its not supposed to be.[/b]
After you've confirmed that you have no external air leaks, pull airbox and raise throttle slides. Carefully inspect the carb slides for corners being broken off. This will cause the problem. You should replace the junk stock slides with the new black aluminum ones anyway. Check other threads in this forum for info on this.

Good luck.
:div20:

You never stated why the engine needed rebuilt. Maybe this was the cause.
 

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Discussion Starter · #9 ·
Ok..........So i will start in the beginning.
The Motor had 3800 miles on it when it blew up. This is when i bought the sled. I had the crank all gone through(rods,pins and whatever else it needed) Then i had the PTO end cyl. replated and it got a new piston and rings and the rest of the cylinders got a hone job and new rings on the original pistons. I replaced all gaskets,seals and o-rings. Checked everything over when putting back together.
The cause of the blow up i think was the PTO end cylinder oil line to the carb boot was plugged. Everything else seemed to be fine.
I checked the adjustment on the throttle cable( it has some play in the cable)
I couldn't see anything broken off on the slides(although i will do a search on here about that and find out about the Black aluminum ones)
I think i will start with the pilot jets(although it always idled fine bofore it blew up???)
Could something else in the carbs be plugged?
 

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I think you ment .8, going to 1.0 will make it leaner. It will suck more air less fuel. .8 will suck less air more fuel.[/b]
Actually people were changing to the 1.0. I am assuming this made the sled easier to tune with the fuel screw with the bigger air jet?
 

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Discussion Starter · #11 ·
Can i turn the fuel screws out a little and will that help? I can't find any air leaks. But i havn't bought any pilot jets yet. Should I?
 

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First thing is first - make sure your carb is seated on the boots well. For some reason, when you have the motor apart for a long period of time, the carb boots will get out of form or shape. Dont ask me why it happens in that way but it does. I have seen it happened to me once and couple of times on other sleds. This is what I did to get it fixed - dont clamp it down - just a snug for a time being, if you do tighten it, it will pushes your carb off the boot and cause you to have air leak. First, run the sled slowly, let it get up to a good operating temperture. Ride it slow. (keep your eye on the carb and make sure it doesnt come off) If you run her a while enough - the carb boots will start to get back to an orginal form or shape and the clamps will set on without pushing the carbs off. Once you got the clamps on and its seated good - then mess with the fuel screw to get your idle to where you want you idle to be at. Anyone? WL.
 

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Pockets - tell me more about this brass restrictor in the oil line - What's the down side if it's not there??? I built an XCR800 Tripple Edge and now can't remember if I remember seeing that in the oil line.

Thanks,

XCR5
 
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