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Z50A crankshaft questions

3K views 21 replies 5 participants last post by  dpranno 
#1 ·
Need some help from the experts please...I am restoring/resurrecting my first Z50A. The crank to flywheel fastening seems to be wrong, at least from the standard drawings/videos I have seen. The flywheel is secured with a bolt into a female threaded hole in the crankshaft (see pics)...but all the drawings I have seen show a nut on a male threaded crank.

Am I missing a part here or is this some kind of weird home repair? Thanks.

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#8 ·
Kirrbby...need some more expert help with getting this first time project running.

So flywheel and spark are all good, and compression is reading about 100 psi on a lower quality tester off a cold engine that hasn't been started in many years. Carb has been cleaned (Keihin type that was a mess with a stuck float) and I tried to kick it with the help of starting fluid and........... nothing. Any suggestions?

Another possible issue is the throttle...there seems to be way too much play in the cable as most of the twist just takes up slack, and only the last little twist engages the jet needle. Any tips on this too? Thanks in advance.
 
#9 ·
A new sparkplug is ALWAYS a good idea. The points should be clean and set at .014-.016 inches. I usually put a little gas right into the sparkplug hole. Then, instead of kicking it, put it into 2nd or 3rd gear and start pushing it down the street, or around in circles on the driveway. That should get the motor spinning, sparking, and sucking air/fuel if it's going to.
 
#10 ·
Great tips, thanks. Forgot to mention spark plug is new and I ran some fine grit sand paper between the points to clean them up...did not adjust them yet though. Spark looks pretty good when I test it on the engine block.

I will buy some feeler gauges, make the adjustments and try the push start / gas trick next.

Am ideas on the throttle cable issue? It just doesn't feel like it is doing much, and it definitely does not snap back. Thanks...
 
#11 ·
The stock throttle does not return Very well...Snap back.
But it sounds like yours has a problem somewhere. Wrong cable? Wrong cap? Something broke or missing? Would need some more info, and or some pics, etc to help you figure that one out. There is usually a adjuster at the tip top of the carb cap, under the rubber tube cover. Maybe yours is missing, or needs adjusting to take some slack out of the cable..?
 
#14 ·
Oh ya. That's a good bike.

The cap spring and slide look correct. But the carb is not correct for your 69-70 K1. Looks like it's from a newer Z50, but it still should work. I'm thinking the cable is wrong, unless there is something wrong with the in-bar twist throttle setup.
 
#16 ·
Looking again at your pics, the cable looks right. It's holding the slide, with the spring somewhat compressed, looks correct. With the cap off the carb, twist the throttle. If it draws the slide all the way up to hit the cap, it's working properly. If it doesn't, somethings wrong in the handlebar.
 
#17 ·
OH...just thought of something. When you put the slide into the carb, you have to index it properly. The long skinny slit in the slide, HAS to line up with a little nub inside of the carb. Put the slit exactly toward the right side of the bike. Spin it slightly until you feel it line up on the nub. THEN it should drop all the way down into the carb. It should bottom out in the carb so you can not look thru the carb at all anymore. If it's at all dirty in there the slide might not go all the way in either. Might be a good idea to remove the carb so you can see, and check it all out.
 
#19 ·
So I finally got the chain on and had my son push me up and down the street in 2nd gear with no luck...other than a few mini-backfires or pops with lots of smell. I even put a little bit of gas right in the cylinder head with no luck. I have not checked the points with feeler gauges yet (that will be tonight's job), but before I do that I wanted your opinion on the compression first. My cheapo gauge is showing just under 100psi...do you think that is enough to get her going or am I looking at a real compression problem rather than a fuel issue? Here is the latest fully assembled / not running pic....


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#20 ·
So I wanted your opinion on the compression first. My cheapo gauge is showing just under 100psi...do you think that is enough to get her going or am I looking at a real compression problem rather than a fuel issue? Here is the latest fully assembled / not running pic..
Normal operating PSI is in the 160 to 180 range for peak performance. Check the link and make sure your doing the test correctly.
tmas


Dan's Motorcycle Compression Testing
 
#22 ·
Just saw this post now, I am a little behind.

...and this is definitely another issue. The slide is getting hung up half way down the carb on the nub. Looking at the nub in the carb, it does not appear to be a perfect fit for the nice, straight slot that runs all the way down the slide. Any ideas? I'm think about filing down the sides of the slot in the slide just a bit.
 
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