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Help with a 2 stroke yz 60

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Help with a 2 stroke yz 60

Unread postAuthor: jor2daje » Sun Jun 06, 2010 11:34 pm

Hey guys I just got a yamaha yz 60 of craiglist for 100 bucks. Its going to be my summer project to fix up and make it look nice(r). Anyway, when I got it, it barely started and died as soon as you touched the throttle. I figured the throttle was dirty so I took it completely apart and soaked everything in carb cleaner. Unfortunetly now the engine barely starts and still dies when you try to rev it. The old owner said that he thinks the carb may need a new needle. I think there may be a leak in the intake but I have no idea. This is my first two stroke, Ive played with quite a few 4 strokes though.

So if you guys could tell me, what are good settings for the air and fuel mixture knobs to begin with? What do you think the problem the prevents it from revving? What do you guys know about this bike?

Thanks guys, I tried this at the gokart forum but things are a little slow there.

Image

also does anyone what this clear tube is for? I dont see it attaching anywhere but there is already a drain tube on the bottom of the carb.

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Unread postAuthor: Crna Legija » Mon Jun 07, 2010 1:14 am

get a new spark plug for it, mix up new gas(usually about 30:1) and i bet it will run just fine. The clear tube is over flow it shouldn't connect to any thing.

make sure that theres trany oil.
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Unread postAuthor: Technician1002 » Mon Jun 07, 2010 1:25 am

It is common for 2 stroke engines to have a couple problems. Both are covered above. Due to the oil mix, if the engine is run a lot with short runs, the plug gets fouled with soot (carbon is conductive) which shorts out the spark. Higher pressure requires a higher voltage to spark. Opening the throttle raises the pressure and this tends to stop the spark if it can take the carbon path instead of jumping the gap.

The other fuel issue is again related to the mix. When the gas evaporates, it leaves the oil. Now the mix has too much oil, and by the same reason, has too little gas. It is simply too lean. Engines with separate oil injection tend to have less trouble with this.

If the jets in the carb are crusted with dried gas varnish, the carb will need work to recover it. Don't forget to check the air cleaner. If it is plugged, opening the throttle will draw too much gas and get too little air.

A quick check to see if the engine is not getting enough gas (plugged jets) remove the air cleaner and slowly rev the engine until it starts to bog down and die. Use a propane torch that is not lit but with the gas on and feed some propane into the air inlet. If the revs pick up, it was running lean. If it doesn't change much, it is probably ignition related.

Don't run it long with propane. It is getting too little oil.
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Unread postAuthor: jor2daje » Mon Jun 07, 2010 1:30 am

Ok thanks very much guys Ill try both of these tomorrow. However Im having a bit of trouble even getting it started after I messed with the mix screws so what are good baseline settings?
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Unread postAuthor: Technician1002 » Mon Jun 07, 2010 1:35 am

Baseline is a tough one. In the future (doesn't help now) close the valve and count the turns such as 1.5, 1.25, or 3 full turns. Then use the same baseline if it is too far out to start. Check Google to see if you can find an owners's manual online.

Remember if it isn't burning right, it could be fowling the plug and returning to the baseline won't return it back to how it was. The plug will need replaced or cleaned before continuing.
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Unread postAuthor: jor2daje » Mon Jun 07, 2010 1:42 am

Ok thanks Tech, looking online i cant find the manual but I did find I only had about half the proper fuel ratio, so Ill change that tomorrow. I took the plug out it seemed fine, just had a little unburned gas or oil. I cleaned it off but will have to wait till tomorrow to how it works.
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Unread postAuthor: Crna Legija » Mon Jun 07, 2010 2:19 am

to clean plugs brush it with a wire brush or steel wool till its silver when wash it in petrol and burn the exess off
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Unread postAuthor: jrrdw » Mon Jun 07, 2010 5:53 pm

1st take the mixture screw out and look at the tapered part and see if there is a groove in it, if there is you need a new one.


Set the mixture screw to 2.5 turns out from a lightly seated position. Set the fast idle screw by looking through the air intake at the slide, let it all the way down then turn the screw in until you see a sliver of space under the slide. These are the settings for any 2 stroke engine.

You may have to turn the mixture screw in a quarter turn to a half turn to get it started but no more until it starts. It's far better to start it at a rich mixture then to lean and damage the piston and cylinder.

If after it starts slowly turn the idle screw out to get a low idle with out stalling. Then slowly turn the fuel mixture in until the engine starts revving a little (smooths out), then keep slowly turning it in until you hear the exhaust start to "pop", note that position.

Then start turning the fuel mixture back out counting the turns until the engine stumbles, then turn the screw to the middle of those 2 positions. Then readjust the fast idle screw until you can grab the throttle and open it up full throttle with out it stalling out.


Air leaks: Use a can of starter fluid with a straw and the engine running and give a little squirt around the carb mounting boot and count to 3. If the engine revs a little and returns to idle you have a air leak that will affect the way it runs. Repeat the test around the cylinder base and cylinder head. DO NOT allow any starter fluid get into the air cleaner, you will get a false reading.

Unbolt/remove springs from exhaust pipe where it joins the cylinder and look at the port to make sure it's not clogged. If it is use the kick starter to rotate the engine until the piston has the port blocked and spray some cleaner and use a popcycle stick and rag to clean it out.

Use gasoline in the exhaust pipe swish it back and forth and drain very well and air dry, then reinstall exhaust pipe.

Good luck...
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Unread postAuthor: jor2daje » Mon Jun 07, 2010 8:23 pm

Thanks guys I got it running :D , the problem was there was some crud keeping the reed valves open so I cleaned those up and after a little persuasion she started. Only issue now is the excessive amounts of smoke (could be normal ;) ) and the kill switch didnt seem to work. But thanks again for the help guys, cant wait to take her out for a ride.
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Unread postAuthor: Technician1002 » Mon Jun 07, 2010 9:26 pm

Excessive smoke could simply be excessive oil from the original gas/oil mix having dried. When it didn't run properly, this oil remains in the engine to be burned later. This is normal for an engine in that condition and should clear up some with use.

If there is excessive carbon on the cylinder, plug, piston, etc, that can soon become incandescent and work like a glow plug. After the oil is burnt out and the carbon burned down, the kill switch may work better. Oil has a lower ignition temperature than gas. With cylinder build up inside this raises the compression ratio, so the engine is more likely to diesel while there is excess oil in it. Be gentle on the throttle while it is behaving this way to keep peak compression pressure down to prevent putting a hole in the piston. Don't ride it hard.
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Unread postAuthor: jor2daje » Mon Jun 07, 2010 11:19 pm

thanks, I do think extra unburned oil is part of the problem, also I think my fuel mix might still be a little rich.

I figured out that I just made a bit of a stupid mistake on the kill switch :oops: it there was a loose connection from it into the cdi. It looked like it was connected but no metal was contacting. But thanks for the tip, because that could also be possible/likely to happen.
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Unread postAuthor: Technician1002 » Mon Jun 07, 2010 11:29 pm

A sign of pre-ignition is often excessive backfiring. If it starts to backfire a lot, keep this cause in mind.
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Unread postAuthor: jor2daje » Fri Jun 18, 2010 9:13 pm

K guys ive spent a while getting it going pretty good. I also found out about the clear tube coming of the side of the carb. I believe this is a powerjet carb, used in yamahas from 76' onward, they have a separate tube that goes into the intake. It uses the same principal as a sand blaster, when air passes this tube going into the exhaust it creates low pressure inside the tube, which adjust things inside the carb which ensures you have the right mixture at full throttle.
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Unread postAuthor: Wayfast73 » Mon Jun 28, 2010 2:28 am

Hows the compression feel on it? Not sure what the compression should be but dirtbikes are higher than the normal 125psi. My kx 250 is suppose to be in the 215psi range. For a old air cooled bike like that I'd run it rich on both fuel and a little richer on the oil they run hotter. If the smoke comming out is blue its the oil, if its white/gray its tranny fluid which would usually be caused by the crank seal on the clutch side.
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Unread postAuthor: Wayfast73 » Mon Jun 28, 2010 2:30 am

And get the right air box for that, 2 strokes will never run right with out the back pressure from atliest a filter. If you use a pod filter bump the jetting up one size.
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