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Discussion Starter · #1 ·
So my buddy gave me his YFZ450 to see if I could fix/sell it for him. He said it was "running rough". It had been a few months since he had tried starting it once I got it. The battery was dead so I tried charging but turns out it was bad. I replaced the battery. Now its turning over fine but won't start.

I checked the gas and it was definately yellow. Stunk and pretty much turned to crap. So I drained the tank, cleaned the carb and all the jets and put new gas in it. Main jet was pretty bad so I think thats why it was "running rough". Float needle was stuck so that may be why it wasn't starting. Now I reinstalled the carb and still am not getting it to start.

I checked the fuel inlet nozzle and carb cleaner came through fine so I dont think there is any blockage. When I spray a bit of cleaner through the carb inlet while starting it wants to start and even did once or twice for a quick second when giving it some gas but immediately stopped.

Any suggestions?
 

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i would scrap those jets and replace them with new. your local shop/dealer should have some in stock. jets never seem to completely clean out once clogged. also pick up a couple inline fuel filters since the tank was pretty bad. you'll probably have to swap the filters out a few times.
if that doesnt work try checking timing. not hard to do and will take around an hour.
 

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Discussion Starter · #3 ·
So I finally got around to working on the quad again (actually this was a couple weeks ago) . tomconnell95 it did end up being the timing. It was off about a tooth. Not much but enough to keep it from starting. Started right up and after adjusting the fuel screw about a half a turn it idles perfectly. Give it a little gas and it sounds great. Starts popping about half throttle and will completely cut off if I go over half throttle.

This I am going to pin on the main jet which is probably shot. I could not find the size on the jet to know what is currently in it. Previous owner put a fatboy 4 exhaust system on it which comes with a jet kit so I assume it was one of those.

What size main would you guys recommend? I was thinking of trying a 175 main.

05 YFZ 450
Fatboy 4 complete exhaust system
K&N air filter with lid off
 

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elevation?
 

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45p, 165-168m, 3rd clip. That should get you close.
 

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Discussion Starter · #8 ·
I went with 168m and 45p. The bike starts up nice with choke on but when i take the choke off it cuts off after a second or two. After it warms up a bit it revs a little high while choked. Anyone have any ideas on why this might be. Really trying to get this thing running since Spring is right around the corner.
 

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It wouldnt hurt to swap the plug now that it actually runs. Could be a bit fouled. Advanced auto parts or auto zone should have one. i know advanced can actually look up what plug you need for the yfz. Make sure its a ngk.
 

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What's your fuel screw at?
 

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It should idle up with the choke on, it should idle back down with the choke off.
 

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then it sounds lean on the pilot, try a 48p or your idle might be set too low.
 
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