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Inherited 1990 Yamaha YFM250B Quad, mostly fixed up but now stuck, PLEASE HELP!!!

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So my Father-In-Law has a few 4 wheelers and one of them is a 1990 Yamaha YFM250B. When I first married my wife 10+ years ago we rode it with her family on occasions but it hasn't been ridden in 5+ years and has been sitting under his back porch. It has seen a decent amount of wear over the years. Anyways, since it has just been sitting (and he knows I love all things outdoors including 4-wheeling and also fixing things) he told me if I wanted to fix it up and get it running then it was mine. So I brought it back home to Colorado and have been working on it. So far I have done quite a bit (forgive some of my crude methods as I learn as I go and do what I can). I fixed up the body (gave a new paint job, conditioned the leather and sanded/primed some of the rusted body), new spark plug, new battery, emptied the old oil and replaced, brand new air filter, drained small amount of gasoline that was in it (checked gas tank and clean/clear of debris), pulled the carb (soaked it in 90% isopropyl alcohol as this was recommended somewhere else) and cleaned out all the junk that was in it (not too bad but yet a moderate amount of debris/buildup). I verified the best I could that all the jet holes were blown out but did this just manually by blowing through them myself but I could tell they all were patent as air passed through freely by creating a seal with my lips around the holes (wish I had a an air compressor)! I reassembled it and had a bit of a clutch issue as the clutch slide in the top of the carb wasn't sliding correctly but I figured out and now the clutch is working fine. So after that long drawn out story here is the problem...

I believe the electrical system is all running well. I get power to the lights and the neutral indicator light. When pushing the start switch (with the engine set to 'run' on the left handle and the fuel intake to the carb set to 'on') it keeps trying to 'turn over' or start but it never does even with choking it and trying to give it some gas from the throttle. Thinking that maybe it was just 'cold' and needed a push start that is what I tried. I actually hooked it up to the back of my truck and had my wife pull me on it. I was pleasantly surprised that I was able to get the motor running when I shifted it into 1st gear. However, when my wife stopped I wasn't able to keep the motor running (w/ or w/o the throttle). So I had her pull me again but this time I thought that maybe I could 'warm it up' if she pulled me further after the motor started to keep it running. So she pulled me around the block a few times. During that time the motor kept on running and I shifted up to 2nd, 3rd and 4th while she pulled me and it kept up just fine. However, while she pulled me I tried pushing on the throttle and I was able to hear SOME engine reving but was never able to gain any speed beyond that of the speed that my wife was towing me at which must have been between 5-15 mph. After the few laps around the block she stopped towing me and once again I wasn't able to keep the engine going even by throttling it. Thinking that maybe now being a warm engine it might start on its own I tried starting it again withe the electronic push button and that kept firing but wasn't able to fully start the quad. So I am trying to figure out what is going on. My best guess is that it has something to do with the fuel intake/injection but am not sure where or how to fix. Any thoughts at all are helpful!!!!!!!

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Start  by making sure  it  has spark. A compression  check would also be a good idea to  make  sure  valves are  not  sticking  open.  If  it  seems to  have  good compression  and spark,    it's time to  pull  the  carb off again  and recheck  everything. Make  sure the  gas is actually  flowing  from the tank  to the  carb.   You  can  use  some  "Canned  air"  like  they  use  to  blow  dust of of computer  towers  to  blow through the  passages  in the  carb.  After  cleaning the  jets ,   start  by setting the  screws for  the needle  valves about  1  1/2  turns out  from  closed and    adjust out or  in from  there  about  1/8 to 1/4  turn if the  motor  tries to  run, or starts  and runs  rough.

Intermittent or no spark could be a problem  with the  stator, pickup coil,  CDI  box or ignition coil.


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I merged this topic with your other one in the General forum section and added 1990 Yamaha YFM250B in to the title. :)

I agree with davefrombc to check for spark first. You need spark, fuel, and air so start with those first.

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Sounds like you're limited on tools/experience. Does it turn over by itself with the electrical system - when you push the start button does the engine go "rnnn rnnn rnnn rnnn" or do you just hear a "vrrrrrmmmmmmmmmmm" of the starter motor spinning? Does it do anything different with the pull start? Are you certain you have good spark at the plug? (remove the plug, reconnect the sparkplug wire and leave the threaded base of the plug touching the cylinder head, pull/crank it over - you should see a bluish spark).

If you have a spark I'm betting that your carb clean is incomplete (pilot jets are virtually impossible to clean without proper tools) I've found that a wire bristle from a wire brush is just about the right size to poke through the orifice of the pilot.

Try opening the airbox, removing the filter and spraying carb cleaner or starting fluid directly into the carb while the engine is cranking. If it starts it's definitely the carb.

Has the unit been welded on (broken frame repair) or jumped off a booster box? That can kill the stator/pickup assembly.

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