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2003 Yamaha Warrior performance issues

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Somebody help !!! I have an 03 Yamaha Warrior 350 and everything was running great up until a few days ago when I cranked up for a quick run around the yard and it won’t do anything but idle. It starts easy, idles ok, but the second I touch the throttle it starts bogging and backfiring etc and dumping a mist of raw gas back out the air inlet side of carburetor.

I’ve pulled the carburetor apart now three times checking things out and unfortunately don’t know enough about these small carburetors to tell if something’s worn out. No visible damage or anything. But one thing I did notice was that the needle has some wear where it runs through the slide, but like I said, I don’t really know what the wear limits are as I cant find info on that stuff anywhere.

The ignition timing is right on the money, I checked the valve clearance and they were ok, the coil checks out good, etc. But wonder if it could be the CDI breaking down under load or maybe the same thing with the stator?

Cylinder compression was also check and came out above average at about 125 psi.

I’ve talked to a few ATV mechanics that say it’s still the carburetor based on what I tell them. You can definitely tell it’s running way rich at idle due to the strong smell of unburned fuel.

One thing that does strike an interest is with a timing light on it at idle, the fire is strong and consistent. But when you try and give her a little more throttle the fire is intermittent right along with the miss in the engine. The spark plug is brand new, but the one I just removed did have noticable soot on the electrode and beneath the threads.

It's done this a few times before, but only for a few seconds or until I get it warmed up halfway decent. Then it reved fine and hauled a**s as usual.

I have debated on buying a new carburetor, CDI box, etc… but that combined is about 600-700 bucks, and I just don’t want to start throwing parts at it.

I have even pulled the side cover to make sure the stator and such weren’t damaged.

I am pretty much at a stand still and dont know where else to look. Could it really be the carb?

Please tell me there's somebody out there who has had the same issue and figured it out????

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The thing that stands out to me is that you say it is blowing raw fuel back through the carb, that indicates that the intake valves are still open or aren't sealing properly during the compression stroke. I would start by checking the timing chain and tensioner. Make sure the timing chain hasn't jumped and make sure the tensioner is holding the chain tight. It might also be a good idea to check the valve lash too. If that is all ok then we can work from there.

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Here are some areas to troubleshoot..right from a warrior manual (notice what DD said...as a possibility with the valves):

If timing or Firing incorrect:

Spark plug dirty, broken, or maladjusted

Spark plug cap shorted or not in good contact

Spark plug incorrect

Ignition coil trouble

Fuel/air mixture incorrect:

Main jet clogged or wrong size

Jet needle or needle jet worn

Air jet clogged

Fuel level in carburetor float bowl too high or too low

Bleed holes of air bleed pipe or needle jet clogged

Air cleaner clogged, poorly sealed, or missing

Air cleaner duct poorly sealed

Water of foreign matter in fuel

Carburetor holder loose

Fuel tank air vent obstructed

Fuel tap clogged

Fuel line clogged

Compression low:

Spark plug loose

Cylinder head not.sufficiently tightened down

No valve clearance

Cylinder, piston worn

Piston ring bad (worn, weak, broken, or sticking)

Piston ring/land clearance excessive

Cylinder head gasket damaged

Cylinder head warped

Valve spring broken or weak

Valve not seating properly (valve bent, worn, or carbon accumulation on the seating surface.)

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The timing chain and cam are all in good shape and in the correct position. I have checked the ignition timing with the engine idling and is right on the "F" mark referenced in the manual. Compression was also checked and is good at 125 psi. I'm leaning towards the carburetor or the ignition pick up module. It starts and idles too good to be a major mechanical issue. The presence of fuel spraying back is either an indication of A: the engine is getting too much fuel due to carburetor failure or misadjustments or B: the ignition isnt producing enough power to sufficiently burn all of the fuel being delibered.

I talked to another ATV rider in my area and he had even heard of the ground wire at the reverse lever being the cause of such a problem. The only way I see that happening is if Yamaha decided that's where the system ground for the CDI unit is terminated. Possible I guess, but not likely in my opinion.

Gentlemen, you both have given me some very useful info and I greatly appreciate it. However, everything suggested has already been checked and in most cased double checked. I have this puppy stripped down to the bare engine and frame so I can see what the heck I'm doing, so the air cleaner has been completely removed. New spark plug gapped per Clymer manual. Fresh gasoline and even changed the crankcase oil and filter. I have unplugged all ignition and related connectors and cleaned with a premium electro-contact cleaner. Everything was running great until Monday evening when this happened. It has happened a couple times before, but cleared up in a few seconds and only when it was cold. I have taken the carburetor completely apart, and I mean COMPLETELY apart, blown through all ports, jets, and passages with compressed air and carb cleaner to make sure there is no foreign materials stuck in areas where there shouldnt be. However, there is indication of wear on the needle where it passes through the slide. But I dont know what too much wear would be. It isnt posted in any of the literature I have or have been able to find.

Any thoughts now?

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I owned a 2000 yamaha warrior 350 and it was doing the same thing when i purchased it. I was told it was the carb. valves and the timing was off. I installed new valves, rejetted the carb on to find out it wasnt the problem. I decided to take it to a local dealer and it took them maybe 2 mins to fix it. The parking brake was stuck. Right next to the clutch lever you will see a black piece going into the parking brake. Remove it and release it then put it back in and the quad will be just fine. If it doesnt work make sure the parking brake itself is pushed all the way out.

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Firts off, let me appologize for not reading your first post more thoroughly, I missed several key pieces of info that you stated. I have heard of several strange wiring and switch issues with these machines like the one your friend was telling you about and like what the last poster mentioned. It is certainly a possibility that something like this could be your issue. I also think that you may have something with the idea that there is too much fuel trying to run through the carb which could be a float adjustment issue. If the float is not adjutsted properly, fuel will continue to fill the float bowl and flood through the main jet and run back into the airbox. There should be instructions in the Clymer manual for adjusting the carb float. Also check for holes in the float, if it fills up with fuel, it won't rise up and push the seat into the fuel inlet. What you mentioned about the timing being inconsistent seems very significant to me. That problem points toward a CDI, coil, or pickup issue. Most likely CDI imo. I would check the connection between the spark plug boot and coil wire too, unscrew the boot from the coil wire and make sure there is good clean wire exposed at the tip of the wire. You may need to clip a 1/4 to 1/2 inch off the wire to get to some good clean cable. Then screw the boot back on the wire. I would just start by checkint the things that cost little or nothing. I think there is a good chance that your CDI is the probmlem, but you probably want to eliminate the simple cheap possibilities first. Good luck.

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