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Similar Forum Topics
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By Bobbywolf
I am working on a basket case for a friend. It is a 98 Big Bear (YFM350FWB). It came with a parts machine which is a 96, which I am coming to find out is VERY different from his machine.
Anyway, first thing is first. I checked compression, 150psi. Valves are set correctly, and the engine is in time. I cleaned the carb, and there was some junk in the passages. It is a chinese carb, which I figured from the lack of markings or lettering altogether.
The bike runs. It idles ok, but breaks up badly under acceleration. Pulling a new spark plug shows it is running lean. White strap, with no black whatsoever. So I have the carb adjusted with the mixture screw out way too much (about 5 turns), and the diaphragm needle lifted to the top slot. It is still not getting enough fuel (or too much air). It backfires through the carb, and cannot get above idle without carrying on. The carb boot is in good shape, so it isn't pulling any air there. I did test this as well by spraying ether around the boot when running, looking for intake leaks.
Anything big I am missing here? I am starting to believe that this chinese carb is the issue. This quad came with the original carb, which I would like to rebuild and use, but the mixture screw is totally stuck, and stripped way down in its recess.
Thanks for any assistance.
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By p5200
I'm assuming, it's alright to test the engine after adjusting valves without the rear axle installed? Can someone please verify this? I'm waiting on axle parts and wanting to get that done while waiting. Thanks! 🙂
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By Werewolf
My wheeler originally had a fuel leak.But on trying to start it no spark. Took front end off, when I try to start it I get one spark then nothing. Come back a while latter one spark,replaced coil and cdi box no help?
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By WyattLemke25
Working on a 2016 Sportsman 570 and it has a new battery and spark plug. No codes, fuses all look good. It cranks for a while and when it starts it will only run for a few seconds before stalling. At one point it was running at 3000 rpm with no throttle input, then it dies. Not sure where to look besides messing with the throttle cable, so suggestions are appreciated, Thanks.
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By 97kingquad
I have been rebuilding some ATVs in my spare time and teaching myself along with the help from the internet how an engine works and getting bikes running again is quite enjoyable. I even built an arctic cat 300 4x4 from two parts bikes the had seized motors and missing parts. It was pretty enjoyable.
So I am now working on a sazuki quadrunner 300 1992 which had a whole list of issues when I got it. I have fixed almost everything I need to in order to get this bike running. But something is going on inside the head or crankcase.
I had to replace the timing chain because it was very stretched due to the previous owner.
What the issue was, the timing chain was off the sprocket inside the engine due to it being stretched it slipped off. So the previous owner rebuilt the top end thinking it would fix it which it may have temporarily, but when doing so they welded an extra inch onto the tensioner to hold the chain tight. Which as you can imagine caused a dozen other issues.
So that stretched the chain to the point where I could remove the cam with the tensioner in.
It beat the sliders all to hell. Destroyed the cylinder housing and obviously ruined the tensioner.
I didn't realise all of this until after I rebuilt the engine. I noticed wear where the timing chain runs through the cylinder. I found the cam had no retaining chair, or clip whatever you want to call it so the cam was beat to sh** also. It had almost an inch of play side to side.
So I pulled the head off of my parts bike and fixed all of it. Then put it together and went to pull it over and found it was not on the sprocket (this is when I realised that all that damage and the welded tensioner was because the timing chain had been off the sprocket)
So I pulled the stator cover off and pulled the flywheel (which I should add to get at the stator cover I have to remove the rear tire and a arm as well as remove the bolt through the front of the engine. And the exhaust system has to be removed to pull the cylinder as the exhaust guard is bolted to the side of the timing chain tensioner. Stupid setup. Glad the king quad doesn't have that.
So I got everything apart and the flywheel off. New timing chain (nice and tight now) put the head back together and flywheel but it is quite hard to turn the engine over. I can but with difficulty. When the valve cover was off it seemed to spin much more freely. Before I tear everything back apart and start again any ideas on what it is?
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