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2008 YAMAHA BIG BEAR 400 4X4 rough idle and hard start

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Got the bike brand new in July of 2009. ran great, snorkeled it and tuned the snorkel so no mixture adjustment was necessary. it wasn't long before the bike was difficult to start. it will not start now without hitting the gas. even after the motor is nice and hot it won't start without getting on the throttle. then it idles rough once it starts. it sounds like the timing is off. There's a very faint black smoke from the exhaust, and the plug was black, so it appears as though it has been running rich. HOWEVER, I can take the airbox lid off and take the air filter out and it makes no difference. still has that black smoke and sputtering idle. it runs perfectly when you're riding it. no sputtering, no lack of power, nothing.

side notes: the idle adjustment screw got really hard to turn, I have to use pliers now. the idle is sporadic, it's either about to stall or it's revving at 3000rpm. the choke only seems to work about half the time. could the choke be sticking and causing a rich condition at the carb?

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called a service center because we have an extended warranty and they said they'd try to get it covered, or bill for something to cover it. it turns out the choke was rusted. they had to replace the whole carb. warranty covered $170 and we had to pay $160 out of pocket. could have been much worse.

so my next question is how should I go about getting all of the water out of the carb after we swamp it? obviously draining it doesn't cut it. if we turn it up on the rear rack would that dump it all into the airbox? do I need to blow it out with air or vacuum it out after we get home? suggestions... other than the obvious "don't get water in the carb."

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First off, this thread belongs in the YAMAHA forum, so I will be moving it there. Don't know it that was a site glitch, or if you mistakenly posted in the Kawasaki forum. I have noticed a few wierd things in the forums today.

Anyhow, I think the obvious "don't get water in the carb" advise is the best, have you ever seen a hydrolocked motor? It isn't pretty, water will not compress like a nice air/fuel mix does. If you do suck a bunch of water into your carb, and don't bend your rod or break a piston or something. I would take the carb off and take it apart, and blow it out with compressed air. I would also check for sediment in the rest of the intake track, just in case a bunch of crap makes it throught the filter with all the water.

I included a pic of the aftermath of a good hydrolock for your veiwing enjoyment.


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very nice! thanks a bunch for the info. I can take a motor apart and put it back together but I have never messed with carbs.

when we do have an accident and swamp it, we've gotten pretty good about shutting the bike off or at least letting off of the throttle so that water doesn't make it all the way into the chamber. we immediately drain the airbox, then dry out the air filter as much as possible on the trail, then drain the carb, then check the oil and make sure there isn't any water in there. if there is water in the oil, we don't even attempt to turn it over. someone's getting towed back to camp for an oil change. (we all have extended the crank case breather hose and made loops around the air filter and that has saved our butts from getting water in the oil about 75% of the time.) however, despite this routine the carb must be holding water that doesn't drain and is not being held in a place that is crucial to performance. because in less than a year we're replacing the carb due to rust.

so would turning the bike up on the back rack help to dump the water back into the airbox until we can get back home and do the maintenance you spoke of, or would it make no difference?

Edited by coupedehille
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Turns out the service manager who told us what the problem was didn't exactly have the story straight. he said there was water "in" the carburetor. I was thinking he meant where the fuel is. it was in fact a problem with the linkage. the inside of the carb was fine. (he gave me the old carb) looks like we've been doing a satisfactory job of draining the water out and keeping it clean. the little side cover where the idle adjustment screw and throttle spring and such are enclosed had water inside and was rusted. the choke was stuck and that was the main problem. looks like I'll need to remove that cover after each ride and hose it down with some WD-40 as well as the choke. 3 screws, that's no biggie. my buddy had the same problem on a honda foreman. so if you ride water, remove the outer covers on your carb that house the mechanical parts of it on a regular basis, you could be holding water in places you don't realize.

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  • 2 years later...
  • 1 year later...

Sounds exactly like what mine is doing, except mine has never been run through water. In fact, its barely been run at all because its always fouling spark plugs and leaving me sit 10 feet from the garage when I do want to ride it, but the shop I bought it new from tells me there isn't anything wrong with it.

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  • 3 weeks later...

to time the big bear take your cam sprocket cover off and line the line on the sprocket up with the mark on the head(youll see it) then take the little plastic plug out under the h/l/r shifter, top left side of crank case and you should see the little t on the flywheel if you dont turn your motor over by hand(pull start removed) untill you do, if that line on the sprocket is a link off mark a link and spot on the sprocket remove you cam chain tensioner(big bolT THEN SMALL 2) remove sprocket and move your sprocket clockwise or counter clock wise as many links as it was off from the mark(this is why you need to mark your chain/sprocket. then put sprocket back on , check timing make sure it now lined up, put chain tensioner back in(2 small bolts then big one(this is important)) check again make sure timing marks all line up, then put cover and plug back on, good idea to check valves at this time to line up cam line with marking on head pop off your valve covers, check intake is between .002-.004 and exhaust is between .006-.008, if not adjust them....this is assuming you have a feeler gauge and know how to set valves

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