Question about Yamaha WR 250 F Motorcycles
Posted by Anonymous on
Sounds like the crankshaft has come out of phase. If the crank is out of true, damage to rod and crank bearings can occur.
Posted on Jun 05, 2017
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Posted on Jan 02, 2017
I bought a cbr 600 fy new back in 2000. After about 3 years I've always had the same problem in summer when sitting in traffic, ie. anything that put the temperature up to about half way causing the fan to cut in. I thought it was a carb problem. also thought it could be the spark plug caps(coils built in breaking down only when warm).
Anyway, mine had become so bad recently that it had become almost unrideable as it kept cutting out and spluttering, only at tickover and low revs. Anything over 3000rpm it was fine. I thought it might be an electrical problem so put a meter across the battery. It was only showing 11.5v when running at tickover. Rev it up to 2000rpm it was showing about 12.5v. It should at this rpm show more. If you have the same problem you can rule out the alternator by taking the plug of the rectifier/regulator( under the seat cowling, you can access it by removing the seat) and putting the the leads of the meter across the yellow wires. test all 3 wires. ie if you were to number them 1, 2, 3 then test form 1 to 2, 2 to 3 then 1 to 3. You should get somewhere in the region of 20v at tickover and 50v at 5000rpm. If this figure varies by a large amount between each wire ( alternator winding) then the alternator is the likely problem. But i reckon it will be your regulator/rectifier. They are not cheap at £141 from honda. You can get them from ebay but the guy at honda (mechanic)reckons they are inferior and he has had to repair bikes with boiled batteries and burnt wiring looms. This maybe nonsense but I took the safe route. Whatever one you do decide to get(if it is the rectifier/regulator at fault) then make sure it is the cast ally heat sink type not the original one which has the gubbins incased in rubber.I reckon its a design fault with the originals hence the updated replacement which disippates the heat better.
Going back to diagnosing the problem. I found mine by running the bike stationary until the fan cut in, make sure your lights are on then operate the front or rear brake light. by doing this you are loading the electrical curcuit. When I did this my bike cut out straight away or very nearly did so. Yours might not if your battery is very good. If you notice it running worse then I would bet that you have the same problem.
Hope this helps.
Posted on May 23, 2009
Replace the spark plug caps and try again. On Honda's the cap is often part of the wire (a dealer part) NGK makes some inexpensive plug caps about $5 each. They should OHM out to 5000 anything above or below and you need to replace them. This should fix the problem.
Posted on May 27, 2010
It sounds to me that your carbs might be a little gunked up - you mentioned the gas may have been old, so it's possible that the smaller (idle) jets are slightly plugged up. Fresh fuel might do the trick and/or you could try using a fuel system cleaner and water remover. This problem might 'solve itself' with a little time.
As far as the backfire - this might be either from the carb issue or it could be related to that rattle you mentioned - you could have a loose connection at or near the head - this can **** air and cause a backfire.
I hope this helped!
Posted on Jun 10, 2010
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