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Discussion Starter #1
Hi all,

I've been rebuilding from basket cases, 2 z50's (72 Z50A and 78Z50K3) and just had the motors completely rebuilt. On the problem motor, it got new clutch, new 72cc piston and jug etc., and everything inside (crank, bearings, etc) was fine with no obvious issues. The guy that does my work is an old NASA engineer and serious gear-head and mechanical genius. He's like Rainman for anything mechanical. Anyway, I have no question regarding his work quality/knowledge.

I get the bike back, put 800ml of Honda oil in it and when I go to kick it over, it kicks fine once or twice then binds rather hard but does go through the stroke and returns to an easy/normal kick. This repeats over and over. If i pull the plug, it is simple and I can hand crank it though the stroke.

I'm worried something is binding or bent or something along those lines. Could this just be the new high-compression feel from a bigger head and new piston? I did put bit of starting fluid in the carb and it kicked over and ran fine until it ran out of 'fuel' so that leads me to believe the internals are not binding as I feel with the kick start lever. However, I'm afraid to run it like this or kick it further in fear of damaging the newly rebuilt motor.

Thoughts? Any ideas what could cause this weird binding feeling? It doesn't grind or make noise, just a VERY harsh and hard push through whatever part of the stroke this is that grabs before it frees up and turns over fine.

Thanks y'all!
 

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Since you do not feel it with the plug out it sounds like you are feeling the compression pushing back. If there is no other grinding or odd noises I would say that’s what it is.
 

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When you push the kick lever, the kicker spins the transmission, which is connected to the crankshaft via the clutch. You now have good/high compression, which needs a lot of force to overcome. If you kick harder than what your clutch can handle, the clutch just slips without spinning over the crankshaft. It's a common problem/well known characteristic of our engines. This is very likely what you're feeling. Your engine is fine. Just kick it a little slower to give your clutch a fighting chance. It may get better as your clutch breaks in a little. If not, you may need to adjust the clutch. The clutch needs occasional adjustment...it's a pretty simple procedure.

For now, keep in mind, you're only kicking over 49CC's. Just give it a slow, steady but forceful, shove with your foot :)
 

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Discussion Starter #5
Thanks guys. I also did have a new clutch put it while it was apart so I think Kirrbby hit the nail on the head. I heat cycled it (idle and 1/4 range up to temp, shut off to cool, repeat) a couple times, then took it for a spin down the end of the street and back. She runs great, really is torgue'y at the moment from the clutch being new and all, and makes no odd sounds, noises, vibrations or anything else.

Scared the crap out of me...it had that feeling (like money falling out of my wallet!!) but I guess it's just what these things do. It was really strange riding a bike with gears and no clutch!

All set, thanks for the help!
 

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Even though you don't have a hand clutch, the shifter can be used just like a hand clutch in the respect that when held in the full up or down position, it does exactly what a hand lever does. Congrats on your build!
 

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Discussion Starter #7
Figured I’d post a pic of where I am now. About to disassemble for paint, waiting on a couple items; big bike pegs, air filter, new seat. Otherwise, she’s done. Came as a complete (mostly, lots of unusable parts) basket case. Motor fully rebuilt (restomod, obviously) with 72cc kit. My first ground up build of anything.
273294
 

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Discussion Starter #11
Well done!! (y)
tmas
Thank you. Gonna be a lot of fingernail chewing on the next one. Going full custom with a 78 Z50R basket case. Got a set of KLX110 forks, TBParts triple, XR80 swingarm so going with 12-14" wheels. Want that old school bobber feel, maybe even chopper-like. Don't really know where it will take me. :)
 

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Thank you. Gonna be a lot of fingernail chewing on the next one. Going full custom with a 78 Z50R basket case. Got a set of KLX110 forks, TBParts triple, XR80 swingarm so going with 12-14" wheels. Want that old school bobber feel, maybe even chopper-like. Don't really know where it will take me. :)
Below is a member's different take on a mid 80's Z50R, I'd have to go into the archives to find his build thread.

273295
 

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Spadedace she likes like a ripper! Those are some really nice rear shocks as well, do They have an adjustable collar for height?
 

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Discussion Starter #18
Spadedace she likes like a ripper! Those are some really nice rear shocks as well, do They have an adjustable collar for height?
Thanks, yes, set screw allows you to adjust the preload. Not too bad for what they are. I upgraded the forks to the Fast50's beefier bushings (can't recall what they're called...thick black plastic inserts), new heavier springs and then put this big boys out back. While this is technically my wifes bike, I'm a hard enduro goon so who knows what we'll really get up on with this. Figured worth it for the better ride and not fearing bottoming out. Cheers.
 

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Discussion Starter #19
Yep, that's it, tmas, thank you for locating it....
Thanks for the link to that build...I read everything on all pages, following along his progress. Killer build. I booked marked that one for safe keeping. ;-)

Anyway...I'm super stoked to get this off to paint and get busy with #2. Thanks for sharing that link again.
 

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Discussion Starter #20
Thanks, yes, set screw allows you to adjust the preload. Not too bad for what they are. I upgraded the forks to the Fast50's beefier bushings (can't recall what they're called...thick black plastic inserts), new heavier springs and then put this big boys out back. While this is technically my wifes bike, I'm a hard enduro goon so who knows what we'll really get up on with this. Figured worth it for the better ride and not fearing bottoming out. Cheers.
Thinking now that I misread your question. No, not height adjustable, only pre-load/damping adjustable.
 
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