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Discussion Starter #1
Any advice is welcomed!

Here is the skinny:

Bought this bike(A '76 I believe) and its beat up twin for $100. The motors were swapped by PO. Said he could get good spark, but no start, so I took on the challenge.

I cleaned out the gas tank tea, degunked the carb(Wasn't even getting fuel to the float bowl), and set it back to what I believe stock settings. Still no start. So I completely stripped both carbs, submerged them in Yamaha carb cleaner overnight and blew out every hole with spray carb cleaner. No start with either one.

So here is where I stand: Good spark, good compression(Can really feel the difference spark plug in versus out), and I think I am getting good fuel now. So what am I missing?

When I kick it with the choke on, sometimes it will fire a flame burst out the carb intake, but that seems to be the closest I can get to "firing". I took out the plug today and looked at it after trying to start for awhile, and it was pretty wet.

Possible problems: Air might be leaking past carb to engine connection, but not sure how to test or fix. Bad/old fuel in crank case(is that even possible?). Poor carb settings(But I would think at some point it would turn over from being too rich since i have adjusted it up and down).

This engine is so simple that it's frusterating that I can't get it started.
 

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I have no idea how a rotary engine works but are you sure the timing is correct? Seems odd it would be backfiring out the intake.. ?
 

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Discussion Starter #3
No timing on a rotary valve. The valve can only go in one way unless you modify it or damage(not likely) it. It's basically a metal disk that has the purose of sealing the crankcase during the downward stroke of the piston.

As for my progress, I adjusted the float level as it was way off and noticed that the gas in the float bowl keeps mixing with what I believe to be spit out 2-stroke oil. I'm not sure if this is a problem as I don't have much experience with 2-stroke motors. I wouldn't think it would be a problem since a lot of engines require them to be pre-mixed anyway.

I'm about to the point of trying some starter fluid to see if I can't at least get it to run a little bit.
 

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I bought a 125 single cylinder Kawasaki with a rotary valve once upon a time and some one had pulled the clutch cover off and let a o ring off and it was sucking the transmission oil in the motor and burning it.I think it was a 76 model.
 

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Seeing as the oiling system is an unknown in this unit, I'd continue with premixing fuel anyway.

There are two types of timing, ignition and valve. You may be out on ignition timing.

Ether is nearly solvent, using it as a fuel source in a two stroke would be a mistake (fuel is used to lubricate crank or rotor in your case).

Please define 'good' spark. What is the condition of your plug?
 

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Discussion Starter #7
It's not a twin, it's a single. Here is a picture:



I will check O-rings around the tranny. The floats aren't sticking or filling with fuel.

LFU: The plug looks good and gets a fat blue spark. What is a good way to check the condition of the oiling system and how much is it going to matter to starting if the auto-lube isn't working?

I definately do need to check ignition timing. For some reason I just didn't think it would be off enough to cause no-start, but at this point, it would probably be the easiest next step to check.

Thanks!
 

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Hi I agree with the 'Brother' answer. I have run two stroke racers for years and have found on a few occasions the the oil seal goes on the transmission side and will suck the transmission oil into the engine. This will also happen if someone has filled the transmission case too full of oil so that the crank seal is below the level of the oil in which case it will act like a pump and the crankcase vacuum will suck it in, go up the transfer ports and quickly oil up the plug. Once a plug is oiled up it is usually not much good after that as it has probably tracked up inside the insulater. You will find oil in the exhaust system but if you 'smell' or 'feel' it you can normally tell the difference between two stroke oil and transmission oil
You say the rotary valve can only go in one way but with most engines they can normally be turned over and still fit but now is out of timing. Take off the carb and look down the intake. now slowly rotate the engine (ign off) and see when the valve opens and closes. It should open just before BDC and close just before TDC. Plus or minus a few degrees.
Also you say you get a good spark but check the ignition timing is correct. To not fire, it would have to be a long way out but if it has just slipped then it should still fire but start coughing.
The only other thing is poor compression which will not support ignition but you did say this felt OK. Hope this may help?
 

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Any advice is welcomed!

Here is the skinny:

Bought this bike(A '76 I believe) and its beat up twin for $100. The motors were swapped by PO. Said he could get good spark, but no start, so I took on the challenge.

I cleaned out the gas tank tea, degunked the carb(Wasn't even getting fuel to the float bowl), and set it back to what I believe stock settings. Still no start. So I completely stripped both carbs, submerged them in Yamaha carb cleaner overnight and blew out every hole with spray carb cleaner. No start with either one.

So here is where I stand: Good spark, good compression(Can really feel the difference spark plug in versus out), and I think I am getting good fuel now. So what am I missing?

When I kick it with the choke on, sometimes it will fire a flame burst out the carb intake, but that seems to be the closest I can get to "firing". I took out the plug today and looked at it after trying to start for awhile, and it was pretty wet.

Possible problems: Air might be leaking past carb to engine connection, but not sure how to test or fix. Bad/old fuel in crank case(is that even possible?). Poor carb settings(But I would think at some point it would turn over from being too rich since i have adjusted it up and down).

This engine is so simple that it's frusterating that I can't get it started.
heres your problem; the condensor on the points. have u checked it? mine started spittin and sputtering and eventually did the same as yours currently is. ur right it is very simple engine but u cant overlook the simple stuff. replace points condensor and she'll fire right up
 

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WOW i have the exact same problem but i have a 1976 kx125 bought it for 100 bucks has great spark and compression but it still will not fire, and yeas the carb is as clean as a whistle. it will "belch" and back fire even when push started. it has cdi ignition i thought the timing might be off so i loosed the the stator back and moved it all the way to the left kick it over loosed it back up and move it. sweeping all the way though the total advance and retard settings of the ignition timing. i thought the rotary valve might be bad so i removed it and checked for oil entering the crack case but found none. the disc was in spec .016. the o-ring for the rotary disc was on and wasn't sucking oil. like you i am dumb founded i have no possible idea what might be causing this, i even talked to my buddy who has over 25 years in dirt bikes and motorcycles. and even he dosen't know whats going on i hope we find out whats wrong any thing i find to help my bike i will definitely post to help out.
 

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What "exactly" is the compression reading?
Also, if the crankcase is not tight, it will not run.
On a bike this old, I am guessing it is one of the two.
 

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I've thought of this too, my buddy was thinking it might be the spark because the spark might be good on the out side of the casing, but under compression it might not be as good. and i was looking for a main crank case oil seal but found none, do i just use yamabond on the crankcase? I'm going to start working on it tomorrow I'll keep you posted with information and pictures.
 

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Always use a proper spark tester for checking for spark. They are cheap and one of the best tools you will have. Nine times out of ten, the old lay the plug on the case trick works, but that tenth time... zap! You put your CDI at risk and I am sure that you do not need to add that to your list of problems.
You may be losing spark under compression ( I doubt it) but how much compression are we talking about? Without knowing this, you are just chasing your tail. Never tear into a motor until you have at least an idea what you are looking for.

Post back
 

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very true, my buddy has a compression tester i am 98% sure it is in the great compression range. but i will test and update you, but just say the crankcase is leaking oil into the cylinder. would i use yamaha bond to reseal the case after i took it apart?
 
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