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Discussion Starter #1
I’ve recently just purchased a 04 raptor 350. This four wheeler had sat for about 6 months before I got it. It had trouble cranking and had minor issues here and there. I have replaced the a arm, rear bushings/bearings, rear brake pads and rotor, o ring on exhaust valve and gasket on the left casing to the clutch. I have also increased the size of the pilot jet from I believe a 135 to a 145. I have tuned in the carb and had it cranking somewhat okay in 30 degree weather and holding a good strong idle and running good once warmed up. I noticed a very slight ticking from what I was told was the valves when warmed up and it would be okay for a short time. After 2 weeks of testing and double checking all my work I finally decided to take it for a good spin. I rode for 3 hours on and off and eventually my four wheeler began backfiring through the carb. I cut it off and allowed it time to cool down and tried to pick back up but it wouldn’t crank. I eventually killed the battery trying to get it to crank and finally used starting fluid. The four wheeler will no longer stay running at idle no matter how much I adjust the carb and when I’m giving it gas it’s backfiring a ridiculous amount when the rpms rise and come down. Please help me with a proper diagnosis so I can get back on the trails at a reasonable price. Thanks
 

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Welcome to the forum, best bet would be to go back through the carb cleaning all jets again. It's possible debris got in the fuel from sitting for so long.
 

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Welcome to the forum, best bet would be to go back through the carb cleaning all jets again. It's possible debris got in the fuel from sitting for so long.
I agree, you might also remove, drain and flush the gas tank. Replace or add a fuel filter. Run a small copper speaker thru all jets and carb body orifices and then spray cleaner thru.

WELCOME TO THE FORUM.
 

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Discussion Starter #4
Thanks for the warm welcome! I have went through about 2 tanks of gas in the time I’ve been doing the repairs. I will get out there tomorrow and clean the carb and check all jets and air/fuel mixture screws. I will remove and clean the gas tank as well which I haven’t done yet. I forgot to mention before that I replaced the petcock, and the fuel line as well.
 

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Fuel left in a tank, hoses or carb's will start to gum up and turn to varnish in as little as 2 weeks. Once the residue is dried inside the carb and tank it can flake off and plug up again. When the tank is off, put lots of marbles or nuts and bolts to shake around and help with the cleaning. You could also add some Seafoam to the tank.

Why did you change the hose and petcock?
 

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Discussion Starter #6
I replaced the petcock and fuel line because the petcock was old and didn’t want to turn properly and the hose was dry rotted to the connector. I just took it upon myself to replace it all for 20$.
 

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Did you replace the whole petcock assembly? If I recall from doing ours, there is a screen in there right?
 

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Discussion Starter #8
I just got finished cleaning both the carb and the gas tank/petcock. Everything looks shiny, new, snugs up and seats properly. I’m still having an issue with maintaining idle and a little carb backfire. Like I said I recently changed the main jet from a 142 to a 145. I did not mess with the pilot but it ran properly that way for about 2 hours. My next step is to get both a stock main jet and pilot jet which I believe are 142.5 and 22.5. The pilot has no identification and looks like it was overtightened. I checked with the Yamaha shop near my house and they have nothing in stock because it’s a 04. I recently changed the petcock because I had issues turning it to reserve and the fuel line was dry rotted to it.
 

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Discussion Starter #10
I’m still stuck you guys. Spark plug looks good it was new but now it’s slightly brown not black and not wet.it backfires a little less but still won’t crank without starting fluid and still dies out when the rpms drop close to Normal idle level.
 

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Discussion Starter #12
This spark plug had less than 4 hours on it but I replaced this prior to resetting and rebuilding the carb. Any input will be greatly appreciated.
Morph, I went to the page and read up. Thanks for the link, I will be going by those steps from scratch to make sure everything I did is good and I didn’t miss anything else.
 

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Discussion Starter #14
I have not adjusted or checked the valves. I don’t have the proper tools to check the clearance. I’m new to this work and I am trying really hard to learn and do it myself with much studying and learning before touching anything.
 

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I have not adjusted or checked the valves. I don’t have the proper tools to check the clearance. I’m new to this work and I am trying really hard to learn and do it myself with much studying and learning before touching anything.
I think it could may be the problem becuse you try all things with carb and its doesnt help..try to check that out
 

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I would check the rubber manifold for leaking or cracking. A vacuum leak can cause the mixture to lean out and cause backfiring.

Also check cam to crank timing marks. The cam chain may have skipped on the sprocket.
 

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Discussion Starter #17
Sea, the vacuum hose that come from below/beside the air box not connected come up between the gas tank and air box lid. It t’s off to the top of the carb if I’m not mistaken. That hose has been very loose and I would like to know if that is the source of my problems. I’m going to add a image of said hose and how I have it hooked.
 

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I may be getting older, but I refuse to grow up!
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Sea, the vacuum hose that come from below/beside the air box not connected come up between the gas tank and air box lid. It t’s off to the top of the carb if I’m not mistaken. That hose has been very loose and I would like to know if that is the source of my problems. I’m going to add a image of said hose and how I have it hooked.
Can't tell from the picture. If it's a crank case or float bowl vent then it shouldn't matter. If it is a carb body or manifold vent then it can cause a problem. If it has suction or pressure when running it needs to be connected somewhere.
 
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