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Discussion Starter #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?
 

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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.
 

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Discussion Starter #23
thanks I will try adjusting that to see if it helps. My feeling is I am dealing with a lean condition now at full throttle, that’s why adding choke fixes it. I will try what you said and see if it helps.

thanks again
 

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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.

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Discussion Starter #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.
 

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Discussion Starter #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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If your engine only had 45psi compression, it definitely wouldn't run.
Did you hold the throttle wide open for the test...or remove the slide altogether.
 

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Discussion Starter #29
Throttle held wide open during test and choke was not on either. Motor was not ice cold it was just cool enough to touch. I was worried about that too, how could it run this low.

Today I ran the motor for 5-7 min and tested it again the same way and got the same 45psi. Tried a wet test as well and it only went up to 47 psi. This tells me the rings are good.

As you I couldn’t believe it would run this low so I though perhaps the gauge is bad. Setting my compressor to 80psi and connected the gauge to it and it read 80psi. Rules that out.

I do not have a leak down tester to see if the valves are leaking. Need to see if one of the auto parts stores has one in their tool loner program.

I am not seeing smoke from the pipe, well there was after the wet test, but normally I don’t. Plug is not wet or oily. I’m very confused by the reading I am getting.
 

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Discussion Starter #30
No luck at the auto parts store, the ones they have do not have the 10mm adapter. May need to just get one from harbor freight, cheap ones on amazon get very hit and miss reviews.
 

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45 lbs would feel like no resistance on the kickstarter I would think. Mine was around 90 and had to be push started. Valves were the big problem but did the whole top end since the head was off.
 

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Discussion Starter #32
Based on the carbon build up in the exhaust area that is my bet, the valves. There isn’t a lot of resistance on the kick starter for sure. That being said, I really have nothing to reference to Since this is the first Z50 I have ever owned and ridden.

I tried spraying some B12 in the carb while it was running but I double it will do anything. I found Minigunz in CA and cttrailbikes in TX are the closest that specialize in these types of bikes and motors. They offer rebuilds “Restorations”, per their websites, and seem to range in price from $750 &1100. I don’t need a restoration, not making a show bike just want a solid runner. Think I will reach out to see if they have a rebuild package also. May try and still find a local person familiar with these bikes and motors that an go through the top end.
 

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Discussion Starter #33
Bike is running better than it every has, but the motor is still not as healthy as it should be. After bore scoping the intake and combustion chamber its clear the valves are leaking oil into the combustion chamber and the combustion chamber walls show age. After playing with the carb a bunch, it has the #60 jet and the needle one notch down from center and it seems to run the best this way.

Plan is to next month ship the motor off to Minigunz for a full rebuild. While the motor is out it seems like a good time to do a few other things. I picked up a used swingarm, since the threads for the shock mount is damaged on one side and the back of the other shock mount is half ground off on the other. I think I will have that swingarm and the frame stripped and powder coated. Since most of the bike is apart at that point seems like a good time to do this.

My wife keeps saying, "didn't you just want a bike to putt around on at the track"? Developing a sickness, HAHA
 

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Discussion Starter #34
Little update. Been riding the bike around the neighborhood and to pick up the mail. Really enjoying it now that it is running better.

few more improvement. I replaced the bent front brake lever and installed a new cable. Also picked up a proper kill switch, CHP got them in stock finally. I also replaced to wire cover with the grey type so it matches my headlight switch.

picked up a few parts for the future after it gets fully stripped down. Got a new front fork from TB, since mine has now headlight ears, it was in their discount section due to the color being off. Also picked up All Balls steering set and swing arm bushings.

Just an update to keep my build alive.
 

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Nice I just picked up a 72 as well very hard to find but wanted it as that was also the year I was born. Mine looked good but didn't run and still can't get it to run...has spark but won't fire. I have zero knowledge of these bikes so I am learning. Problem is you never know what was done to them before you get them.... I know this one was apart so is it back together correctly ....who knows. well good luck
 

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Discussion Starter #36
Congratulations on the 72. I’m still in the same boat as you but it’s getting better as I have had time to dig deeper into the bike. i was shocked at some of the things I found and how some of the previous owners incorrect repairs result in other problems or damage.

the great thing is there are some of the most helpful people on this forum with endless knowledge. Good luck with yours and post a picture.
 

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yes there is, I will once I get it back somewhat together its all pieces . Just working to get it to fire up has me stumped.
 

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Discussion Starter #38
I had that issue with mine, as you probable saw in my thread.

what I have learned is if your getting spark then check the points to ensure they are opening at the right time, basically that’s your timing. If that’s right make sure your getting fuel, wet plug is a good sign of fuel. Basic motor stuff which is great, keeps it simple.
 

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Discussion Starter #40
I had to freshen up on that as well since I had not played around with point since the late 80s on my 1970 350 Pontiac Lemans. i was able to adjust those in the dark back then.

i found several approaches using ohm meter, lights and feeler gauge. For me to get it at least running the feeler gauges worked just fine.
 
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