any 2 stroke experts?


Old 06-09-05, 09:32 AM
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Join Date: Apr 2005
Posts: 242
any 2 stroke experts?

I have a 1986 BW80 yamaha my buddy sold me about 5 years ago. he had rebuilt the engine with 50 over piston. it ran good with only a mild flutter at or just before full throtle. It wasn't a problem because it was not very noticable. Over the years it got worse, around half throtle or so it strarts fluttering, if you let off the gas a little it will level out and start back pulling again. i took of the air cleaner to look at the intake of air flow while it was fluttering. when fluttering it is blowing compression and fuel out the air intake of the carb, once you play with the throtle it will clear up sucking the air fuel back the correct way into the engine. bike mechanics have told me everything from carb, vent valve to rings. I recently put new rings but that didn't make any difference, actually made it worse. I am thinking its the reid valve, I inspected it and there was no trash under it but was told that they do get weak over time. Is this the next thing I need to change? Or does anyone else have an idea.
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Old 06-13-05, 07:06 AM
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had many 2 strokes

well id say it is your reed valves i use to replace mine once a season atleast
it could also be a stuck float or could need a rebuild kit start by taking apart the carb and cleaning it well and see if everything appears to function correctly then go for reed valves
Old 06-14-05, 12:42 PM
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frank c

Do The Valves
Old 06-21-05, 10:37 PM
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Location: Victoria, Texas, USA
Posts: 138
yea, do the valves, if reed valve replacment or carb cleaning doesn't work. they could be not seating well and you could have some back_____. i forgot what it was called but it shot back up through the carb. it threw up good luck!

Edit: i'm an idiot, we're talkin bout 2 strokes here. just kidding yall. but do the reed valves. they could be bad
Old 06-29-05, 04:49 PM
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Bw 80

I had one of these and found that the muffler had become clogged and it did not run very good,you should look at that and also check the jets in the carb,
make sure they are the correct ones. I have seen people swap things around
not knowing what they are doing and put the wrong jets in.
Old 07-01-05, 09:26 PM
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Join Date: Dec 2003
Location: Victoria, Texas, USA
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they found a 26' python in africa. just livin under some guy's house. how do you miss that??? how do you miss that your muffler is full of shtuff. engine sounds different. plus, how does so much stuff as to mess up your running engine get in your muffler?
Old 07-04-05, 03:41 PM
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Location: South Fork of The Edisto River, SC
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how does the plug look is it black and wet or is it a nice light bown color, if its black then you ar rich(to much fuel) if its brown the the jetting is correct. it is possible the reeds are weak, but it will still run, it is possible that the expansion chamber may have something in it , if it has sat for a while.
i built a yam. blaster 200 4 wheeler 2 years ago that when i bought it the motor was in 3 pieces in a cardboard box. it had been tore down for 2 years be fore the guy decided to sell it. i reassembled the engine rebuilt the carb, added the exhaust and silencer, like i did every time i had buit a motor, it cranked on the 5th kick, idled good, run well but was lacking power, i happened to notice that not much exhaust smoke was coming out the silencer, but it was pouring out the exhaust flange on the cylinder. i pulled the expansion chamber off and hooked the water hose to the outlet end and flushed out the largest RAT NEST i'd ever seen. so for obstructions anything is possible!
Old 07-04-05, 04:31 PM
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I have worked on smaller two-cycle engines a lot (mopeds and dirk bikes)... I would say that there are two things you need to do very first thing,

1) Replace the reed valve, if you have gone several seasons on the reed it needs to be replaced.

2) Do a plug chop on the engine.
Run the throttle as high as it will go (with the f'd up throttle) for at least a half mile or mile and then kill the engine, pull over and take the plug out. The color of the plug will tell you what is wrong - too dark or very burned smell (easily noticable right away) means way too much oil if you pre-mix or a malfunctioning oil-injector. Too light (almost all white) means wrong fuel mix (too lean) etc, etc, you get the idea.

Post back here with a picture of your plug-chop and we can tell you much more. Are you pre-mix or oil injection?

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