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72 for a 72

9K views 94 replies 16 participants last post by  cspcrx 
#1 ·
A bit over a week ago I picket up this 1972 Z50 that just so happens to be my birth year. I have been watching for one for a while to use as a pit bike. I have a 1986 CRX that I race and I figured what better way to get around then on a classic Honda.
Untitled by Victor M, on Flickr
MayPIR_zpsb556d3be by Victor M, on Flickr

I realized before buying it a few things were off like the paint color, which the seller had matched to his 32 Ford, removed headlight and tail light, wrong chain guard and painted wheels. It was not running the best so I cleaned the carb and that really helped a lot but it was while digging in I found the other issues like a unique way to keep water out of the wheels. This explains why the front wheel wobbled.
Untitled by Victor M, on Flickr
Untitled by Victor M, on Flickr

As I dug further I found other things like the wrong throttle, all the electrical is gone only one wire going to the coil and using the headlight switch as a kill switch. Lots of little things that have been fixed incorrectly over the years to keep it running. I also found this little bike is a very early production of the first year to have rear suspension. It's vin is 1000355, so the 355 bike made. I was concerned that the motor was not original as the serial number is Z50AE-359420. I then saw a post from a member in April of 2016 asking about his 72 that has vin 1000344 and motor Z50AE-359418. I was shocked to see his bike was made eleven before mine and his motor was two before mine.

I am so happy to see there are places like CHP, DRATV and lots on EBAY for these bikes. Also a great source of information like this web forum. I went all the way back to 2014 threads in my quest for knowledge. Been buying lots of parts to get it functioning correctly and safely. After that is done I will work on making it look nicer. Eventually I will put all the wiring back and I will have to source new forks as the ears were chopped off of mine.

One thing I can't seem to find in reproduction for the K3-78 is the muffler stinger. Mine does not have one, the screwed a thing piece of chrome pipe to the end to extend it past the shock. I see the the earlier bikes have reproductions of this part but not the K3 and up. Does anyone know of someone who sells these?

Thanks and sorry for the long introduction, I could share more, EXCITED if you can't tell, but I would bore you I am sure. i am sure I will post progress and questions as I go on the rehab journey.
 
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#2 ·
Awesome CRX, welcome to Planetminis!

Those are some RAGGED out wheels dude. Also check out PhatMX, TboltUSA, TBParts. The Z50 restoration community raves about PhatMX but I've personally never used it. The owner seems like a super down to earth guy. He just hand made a bunch of awesome bike stands which I think is rad.
 
#3 ·
Keith owns PhatMX which is located in Canada. Mike (the owner) and Dalton are both at TB Parts, they are located in Southeast PA. Vince owns TBolt USA and is also located in Southeast PA. As stated above, all three are great companies to do business with, and have been strong supporters of the sport/hobby for many years.
 
#4 ·
Thanks guys. I have those on my list. Day I got it I built a list of sites that I found parts on, think I have about a dozen and those you mentioned are in my list.

When I get to stage of making her look pretty I am for sure hitting up some of those you mentioned as they seem to have paint sets. I have no idea what color it was originally but I like the candy gold they came in and that screams 70s to me.
 
#6 ·
Thanks,

One thing I have run into is the gasket between the carb and intake manifold. There was one there when I took the carb off but it was damage. I made my own for now. I can only find the two gaskets that how down by the isolator buy it appears they are larger. I don’t even see any listed in parts diagrams. I know the later models had an o-ring system. Any help is greatly appreciate.
 
#8 · (Edited)
Thanks I have been using those a lot to figure out what is missing or not correct on this bike. If you look the gasket seems to be in the photo, by bolt #15 but there is not # for it. There is #8 down by the isolator but those are larger. Also the carb illustration doesn’t show one either.

Mine had one there and it seems you would need one there. At the illustration above seems to depict one but I see no part number or reference for it.

has anyone from the US ordered from them? They seem to have lots of stuff.
 
#9 ·
I have personally not ordered from them but that's because we have too many great options here in the US. When in doubt, I always try Dr. ATV as well. The Dr legend in the vintage community. If he doesn't have it and the other aforementioned sites don't, then I would consider CMSNL. I heard shipping takes a while and can be pricey but they have plenty of parts.
 
#11 ·
That’s what I noticed in some of the pictures as well but mine has no groove. The intake pipe and carb both have flat surfaces. I just picked up some gasket material and made my own. I appreciate the help.

I also just ordered materials to build my own stinger pipe. Going to be a bit larger than the stock tail pipe section but should replicate it enough to work. Muffler opening is so small finding materials was not as easy as regular exhaust materials but I found some. 15/16ID pipe to slide in then some some 1 1/8 OD to slide over than to get it to about the same OD as the section coming out of the muffler. Then some 1 1/4 to slide over that section and complete the tip to past the shock. Looks like it will need a slight bend based on the pictures I have seen. I will post up when I build that.
 
#13 ·
Thanks very nice of you.

found a new issue. Went to pull the flywheel, have the special puller tool, and found the first series of threads are stripped out so it won’t thread on. Then I noticed someone drilled and tapped two holes in the flywheel For a puller I am guessing.

If this was a car flywheel I would be very worried that the balance is now messed up. Should I be? seems like this is not a part you can just buy either.

appreciate the help.
 
#16 ·
After much fighting and the use of a steering wheel puller I got the flywheel off. Discover a few things are missing, as I anticipated based on the fact the wiring harness has been stripped from the bike. Points actually look very new.

Untitled by Victor M, on Flickr

The only thing I see of concern is the lower screw hole for the coil that is missing looks like it experienced some damage. Looking inside I see threads. I also see a mark on the inside of the flywheel which has me asking if the screw fell out and the coil or screw impacted the flywheel at some point. Perhaps why it was removed. Since I am just trying to get it running well at this point I will leave it like this until I replace the harness and lights, that are all missing.

I also found that cover on the left side of the bike was cut. Those of you with more knowledge probably picked up on that in the original picture. I discovered this taking it off and finding rough edges. So I asked myself why. Well the chain adjusters are maxed out to the rear and the chain has soooo much slack. It appears they changed the chain and sprocket at some point and decided making the chain the correct length was more work that cutting the cover. AMAZING! When I see stuff like this, on anything I just don't get it.

Waiting on a stack of parts right now to fix some of what I have found.
 
#17 ·
Seems like one step forward one step back right now with this thing.

Got the, new to me, flywheel. One thing that stood out was just how badly beaten the one was on my bike. It didn't even have a full key, as you can just see in the picture below.
Untitled by Victor M, on Flickr

Replacement has some surface rust so spent some time with EvapoRust removing that on the magneto surface and the surface the points ride on. Put the new flywheel on bike fired right up and idled fine. Took it for a ride and about 40 feet from the house it just slowly died like it ran out of fuel, which I did not put much in. Pushed her back added more and it wont start. Found I had no spark! Check the points and found that now the .3mm feeler has to be forced in between the points, actually lifts them. I realized from the picture above they were already maxed out so the small difference in flywheels has now caused a no spark issue. So my assessment of the points looking new was way off! Still learning!

New points are ordered and should have them next week. Also installed the correct throttle assembly, that was a fun learning experience to get things to line up. I do need to adjust the carb needle. I put a K&N filter on the bike and while I had it running I noticed it would not rev fully. With some choke it would so I will lower the needle to see if that fixes the lean condition. Installed new front wheels, tube and tire as well so feel like the front death trap has been repaired correctly.

Lots of other small things like replacing nuts and bolts with proper hardware and what not. Fun little project.
 
#19 ·
i noticed that too. They removed all of the wiring from the bike. they also wired the headlight switch as the kill switch. once I get it running better I will get a new harness and stator kit since it’s missing. i will also need to get the tail light assembly along with a new front fork and headlight assembly. They also cut the headlight ears off. This poor bike was abused over the years.
 
#20 ·
in the process of working on the bike I found another issue. The threads on the right side rear lower shock mount is completely stripped. I noticed it was moving as I was tightening the rear axle.

I do not see a replacement for this. It appears to be welded to the frame. other than trying to rethread it, which will result in a smaller nut being used. Is there a know repair?

thanks
 
#21 · (Edited)
So now that she starts and runs I think I need to take the carb apart. It starts and idles just fine. I followed the adjustment process I found on here. Thing is it will not take full throttle, it just goes flat. While I’m riding though I can use the choke to fine tune it and get a nice sound out of the motor and good throttle response with no full throttle flat spot. Needle is in the middle, with the needle clip all the way down it is too much fuel and struggles to start and idle.

to me it based on what I have read this sounds like the main jet is plugged. I purchased a rebuild kit that came with all new parts so I’ll just swap in those parts. Does it sound like I am on the right track here?
 
#22 ·
I would try tuning the carb a little first. There is a relationship between the pilot and main jet when starting the bike where the fuel is supposed to come mostly from the pilot jet and partially from the main. The balance between these two can be off, where you are getting too much/too little from one or the other jet. What you want to do is find "lean best idle." This means tuning the air screw to get the leanest setting at which your bike will idle smoothly. On these carbs, leaner setting comes from turning the air screw counter-clockwise. As you do this, the engine should start revving up (if it does not rev, but instead dies, you need to turn up the idle screw slightly.) When it revs, turn down the idle screw till you get back to the slowest smooth idle you can. You then repeat doing this till the idle screw is as low as you can get it, and the air screw is as lean as possible while still giving a smooth idle. Once you set the idle, go on to the needle setting to tune the middle portion of the RPM range. If it runs well all the way to the top and then falls flat at the highest range, your main jet is too big. If it were too small, it would cut out and falter at WOT.
 
#24 ·
With these carbs, the most common problems I've had is with part #33.
It's a flat rubber disc that sits in the bottom of the bowl. When it goes bad/hard, the engine will run super rich.
Otherwise, they work well on a stock 50cc with only a cleaning, and one click toward rich on the needle clip...which I think is the middle notch.

Text Line Diagram Black-and-white Monochrome
 
#26 · (Edited)
Okay, I have started my fair share of new threads with all of the questions I have had on this bike. So first, thank you to all you guys who are so very willing to help a new guy out.

Little update on the bike, pictures always tell a bit of the story so here is a picture of day one and as of today. Not as dramatic of a transformation as some on here. There were so many things repaired incorrectly over the years that actually caused damaged to other parts along with them so I have had to replace more things than I wanted to.
Untitled by Victor M, on Flickr
Untitled by Victor M, on Flickr

Here is some of the work that has been done starting at the front and working back.
  • New front wheel halves, tube, tire and sanded all of the rust out of the front brake and got that adjusted and working.
  • Replaced the incorrect throttle assembly with the correct type and a new cable to go along with it.
  • Fuel tank was cleaned, replaced the non existent fuel screen and repaired the alignment ears so the tank sits level.
  • Carb has stripped cleaned then run through the ultra sonic cleaner for a while. I am still fighting to get this running right. Also replace the foam filter that was literally falling apart with a K&N. Can't seem to find the correct filter for this bike so went this route.
  • Engine was another small can of worms. All the electrical was stripped and it just had the one stator for spark. The flywheel was damaged so sourced a used one of those. Got a new stator kit, coil and wiring harness. While I had the stator plate out I discovered the cam chain tensioner was locked in a down position so it actually was not touching the chain at all. Also replaced the missing exhaust gasket and made a new muffler tip. I ordered a new side cover as mine was cut by the prior owner because the chain was too long and the up and down motion caused it to hit I am guessing.
  • Everything on the rear wheel was replaced as it was all damaged due to prior hack jobs. Sprocket actually moved up and down it was so out of whack. Got new chain and sprockets to go along with that.
  • Many other small items but this is the big list
Thanks again to you guys who have helped me and I am not done yet. I was just trying to get this thing to be safe and functionally. I feel it is safe now just fighting the function part. It fires up first or second kick about every time. Just need to play with the carb and get it running right. This weekend I am going to check the valve adjustment, gauge finally showed up to do that with. I know this can impact how well the motor runs.

Future plan is to drain the oil and dig into the right side of the motor. The bike seems to have shifting problems mostly going into neutral. Also seems that as it gets warmer it likes to go into neutral less and less easily. I need to check that the start and arm are not bent and while I am in there I am going to rebuild the clutch. Want to do this after I at least get it running better.
 
#27 ·
We’ll valves were way open, which I figured by all the noise they made. Set them to factory specs and the motor is so much quieter.

Through me another curve ball though. I decided to check the compression and am only getting 45psi. Clymer says it should be 170psi. Soooooo sounds like the motor needs to be freshened up.

Anyone here know a shop in Phoenix AZ that is familiar with these motors and reputable? Also if valves and piston rings need to be done what would one expect it to reasonably cost?
 
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