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Discussion Starter #1
Hey all, I have a 72 Yamaha CS5 that I am currently have troubles with. A bit of info, the odometer is at 1700 miles not sure if its true. I took the carbs off cleaned and replaced them, it has pod K&N filters new plugs wires and NGK resister caps. New left cylinder head gasket. I can't seem to get it adjusted just right.. The engine will fire and run but very poorly and needs a lot of throttle to stay running, it will not idle.. Pulled the plugs fired when set on the head. . I think my air fuel is off it backfired last time I tried to start it... What do you guys think?
 

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Did you check/set the timing? Replace the points?

Put the stock AIRBOX back on and see if it makes a difference.
 

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Discussion Starter #3
I put the filters on 150 miles prior to the idle problem. I have not checked the timing but I'm not sure why it would be off I haven't messed with that. I feel like the problem is from something I have done. (Carbs) i will check the points tonight. I just put new brushes in, I have also been battling charging issues.. After cleaning the commutator and putting in new brushes it went from 11.5 at the battery to 12.5 @3k RPM I know it should be higher but now it won't even run.
 

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Usually I would say "yeah if you touched it you probably fucked it up"......

....but your timing system is a regular service and maintenance item and if you have been ignoring it then that is the same as fucking with it.

get a manual and a timing light. It takes no time at all to check the timing and at the very least you can rule it out. Make sure the points felts are oiled, and the vacuum advance mechanism is functioning.

Have you done anything else? Did you pull the baffles to make it louder? Because you know it won't run right without those baffles.
 

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Discussion Starter #5
I thought about pulling the baffles but a friend of mine has the same bike and made a custom exhaust that cause all kinds of headaches so I left the pipes alone. Other than the filters it's fully stock. I have a craftsman timing light for cars I'm assuming it will work the same on the bike. I will look into the timing tonight and get back to you. Thanks for the feedback!
 

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Yeah your Yamaha is a two stroke. The baffles are part of the expansion chamber exhaust, pulling them would mean the bike would never run right.

Rule out the timing completely, then you can go back and focus on the carbs. Have you checked the floats for leaks?
 

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Discussion Starter #7
I have not checked the floats, I think I need new ones though when I was cleaning them they rattles like bells.
 

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Get a cup of gasoline and drop them in. Wait an hour. If they sunk they are crap. The rattling noise you heard was probably solder slag inside the float and doesn't mean anything. You can also hold them under the surface of the gas and look for bubbles.

Do you own a manual for this bike? I get the feeling you aren't used to working on bikes....you are using the wrong senses to evaluate things. You can't hear a leak - you need a visual inspection. Some things you can hear but something immersed in gasoline isn't one of them.

what are your spark plugs telling you? Do you know how to read plugs? Since it is a two stroke is it a surface gap plug or an electrode? Is it properly gapped? Are you running premix or oil injection?
 

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You should perform a leak down test... you might have a crank seal leaking. Also check your service manual regarding the timing procedure: I believe you have to use a dial indicator to set the timing X below physical TCD as with most 2T's
 

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Discussion Starter #10
I own a manual and I am not as familiar with vintage 2 strokes as I am with modern cars. I don't own a dial indicator but I will get one. I pulled the plugs, they were a little wet I'm thinking from not being able to start, the gaps are correct and they were evenly blackened
 

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You should perform a leak down test... you might have a crank seal leaking. Also check your service manual regarding the timing procedure: I believe you have to use a dial indicator to set the timing X below physical TCD as with most 2T's
Have you ever done a leak down on a two-stroke?
You have to remove carbs and exhaust system, block up the holes and pressurise case to around 7psi.
The big holes in cylinders mean you can't/don't do a leak-down same as on a four stroke motor
You can do a compression test but it usually won't tell you much
CS5 has a starter-dynamo and not an alternator, there are multiple things that can go wrong, very few people know what they are doing with them
Setting timing accurately is real important if you don't want to hole pistons.
You need a special dial indicator with plug adapter, the normal DTI will contact frame tubes, the correct one is only about 30mm diameter (I'll take pictures of them side by side if you want)
If the mileage is correct, the crank seals may be dry rotted
You would be far better off making it as stock as possible then sell it to a collector, the 250 or 350 will be a much better bike if you want to build a 'cafe' :rolleyes:
 
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Discussion Starter #14
I used my dial indicator and this video here
but TDC on my left cylinder lands in a very different spot than his.. Also when I hooked up my audible alarm it goes off the whole time I have to rotate the motor half way around for it to go off.. when I tried to adjust my points assembly it still goes off.. I need a pointer..
 

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TDC is TDC, doesn't matter where the DTI needle is as long as you have TDC
Check heel on points then check you set points gap at maximum opening position, there isn't a mark for that
Make sure none of the wires are rubbing on moving parts
BTW, That is a pretty good video to show how to do timing
 

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Discussion Starter #16
I used a feeler gauge my points are at spec.. I cleaned them with a strip of paper.. I have 2 questions..

One, which wires go where on the dynamo cover... He shows that he removed the wires going to the coils but on my left cylinder.. Think it's second in from the left has 3 wires under that screw..

Two, is 2* advanced safe? Should I run higher octane?
 

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Originally there was a tape with coloured blocks showing what went where.
I have it written down but will have to check later
You can probably use RD200 diagram as it has the same DC generator/starter
 
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