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Discussion Starter · #1 ·
Hey guys, I've seen several posts around an nothing has made a difference.
So, my atv starts great, idles fantastic.
Mid range, the bike falls on its face an back fires horribly.
WOT - from dead stop itll lift tires up (never did this before lol so something is right or way wrong)

I borrowed my atv to a buddy to plow his country drive an very bad idea. Blades bent, brakes r f'd an doesn't run right now.
Also, last year I ran into a problem, out riding (looking for mud) an riding in a creak an found a deep spot, started to drop killed atv, got pulled backwards an looked at air box didnt take water on, fired it up an was good ever since it really hates a the shallow creek. (May not be pertinent but thought I'd throw it out there)


✅Cleaned carb 3 times, 2 cans of carb cleaner, compressed air.
✅Adjusted an verified float level to 13mm using my caliper, from mating level of bowl to very top of the float
✅verified the fuel level out bottom of carburetor roughly 4.5mm from steam of carburetor to top of level of fuel
✅Verified all jets are clean clear, verified diaphragm for vacuum is good (had a small pin hole, ordered a genuine yamaha part an installed)
✅Put a new spark plug in, an verified gap with die-electric grease
✅Removed my in-line filter I installed. (Just to say it's not that
✅Sprayed starting fluid around seals/boots for intake (bike doesn't have noticeable climb on rpms)
played with fuel screw doesn't seem to phase it at all? (It has the spring, washer, an o-ring)


I did install an all-balls carb kit about 2 years ago bike is completely factory, no mods.

If anyone could lay some insight I'd be grateful, riding season is here an it's not ready ??
 

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Has the valve lash ever been checked, and the valves adjusted?
I have done other 660's and around 1000 miles they all needed adjustment, and were popping like yours. Doing this will also let you confirm the timing is on.
 

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Cleaning a carb with carb spray, air hose, and a small piece of wire in every passage you can get at can be hit or miss. After trying this many times finally solved my carb problem that idled ok but spit and sputtered under acceleration. Soaked the carb in Napa Mac's 6402 carburetor cleaner with dipping basket 1 gallon can for $25. Also check your needle and seat if the seat is brass install a new oem needle and seat. Somewhere around 2007 they switched to a new style seat that was chrome platted less problems with stuck needles. Also when done riding turn off your fuel valve and let run until out of gas.
 

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Discussion Starter · #5 ·
So, I've reached out to a friend of mine from a local dealership. Hes taken my carburetor to his shop, an going to use an ultrasonic cleaner on it. An, the needle an seat have been updated to the chrome plated version. I think I'm going to try an tackle the valves after I get the carburetor back so I know what "fixed it".

If this ultrasonic cleaner works im definitely going to the store to buy one that's for sure!
 

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Discussion Starter · #6 ·
Hey guys, so I adjusted the valves intake to .006 an exhaust to .008 very tight (lose .007) Carburetor was cleaned using ultrasonic cleaner, another new spark plug. Good blue color. New air filter, ran compression test came out to 90psi with throttle closed an 130 psi when open. However I do have a fuel leak from the guy who cleaned an made an adjustment to my carburetor, he said he adjusted it with the carb at an angle putting slight pressure against my needle spring to 13 mm, an now I have a leak out bottom of carburetor,

The proper way to do this is have it sit level on a bench an adjust the float height to 13mm. From the surface where float bowl mates to very top of carburetor, atleast that's what I'm Gathering from the manual an what everyone else has said.

An still same situation, backfires at just off idle to WOT. But idle an WOT are great.
 

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Did you ever solve this problem, I’ve got the same issue…not sure what it could be. Hope someone knows. Thanks!
Welcome from Colorado.
This thread is all over the place, with too many parts/systems being worked on.
Start a new thread to focus on your problem and what you have done so far.
Popping through the intake or exhaust is a sign of valve lash needing adjustment.
 
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