Hi all, first post here. I don't know how many have a Z50, but I was hoping you could help. I have an old 1983 model, I couldn't get it started, so replaced the points and condenser. Well, success, kinda. Now it starts and runs, but very poorly. For some reason, the choke acts as the throttle. When I choke it, it revs up really high. When it's unchoked, it accelerates poorly, or "bogs," and can't keep a steady idle. I took the carb all apart, cleaned it out real good, and put everything back. Still no help. I've played around with the air screw, but it really doesn't make a difference where it's set. Whenever I rev up the throttle, the RPM decreases very slowely, and won't return the the original idle. Nothing about this makes sense. What else can I check?

 

I have a '74 Z50 (check my photo page). I got it when I was 5 and rode the crap out of it. I would love to know how many miles are on it. It sat idle for about 15 years. Last winter I got it out and put on a new carb, air filter, chain, spark plug and points. The dang thing fired right up and purrs like a kitten. My 8 year old ran it all summer.

I don't have any advice for you on what to try next, but I can tell you that a dealer in Cincinnati is very well stocked in old parts for those things. If you need a new carb try calling Beechmont Motorsports.

 

Three things come to mind...the pilot jet is almost totally plugged, or theres a big air leak, or the slide is sticking in the bore of the carb.
I know you said that you cleaned out the carb...but did you remove the pilot jet, and look thru the center hole...just like looking down a straw. You should be able to see light coming thru, and its posible the deposits are very hardened. If thats the case, buy a new one, they are like 5 bucks from dennis kirk.
Seems to me , theres a rubber o ring on the intake flange where the carb bolts up...is it pinched or missing?
Does the slide move easily..or does it feel sticky in the bore?

I had a 69 model, bought it brand new for 250 bucks..sure wish i still had it. But i replaced it with a 1971 ct70h, check out my pictures, its got 400 original miles, and is showroom new.

Welcome to the forums

 

I did make sure that all those tubes and orifices were unpluged; I ran safety wire and compressed air and parts cleaner through everything. Thinking that the slide was sticking, I pulled it out then put a couple drops of oil on the slide. I guess theres no really good way to tell if the carb is shot. Would you recommend just replacing it? BTW, this thing also has been sitting for about 15 years.

 

The carb is still most likely good, just plugged. The mixture screw and the pilot jet need to be cleaned better. Those deposits are like dried glue, and the hole in the pilot jet is about .008" in diameter. Your not gonna be able to get a safety wire thru it. Try one strand of 20 gauge or 18 gauge stranded wire. If you cant get the wire to push all the way thru, get a new jet. your local dealer should have one on the shelf.
Whats probably happened, is the pilot jet is plugged, and the idle screw has been raised so it can idle. This raising of the idle, is actually raiseing the slide higher in the bore, which at a point bypasses the idle circuit, and the motor is now running on the slide cutout. Thats why the mixture screw has no effect.
once the pilot jet is new, or cleaned out, the motor can idle at a normal rpm, and the mixture screw will work again.
Its a very common problem, especially on smaller motors, because the pilot jets hole is so tiny, it doesnt take much of a piece of crud to totally block it.
If you take off the gas cap, and look inside the tank...do you see rust? Might be a good time to add an inline fuel filter too.
let us know how it goes, but theres no need to spend a lot of money, you can get it running for very little money.

 

When you say pilot jet, you mean the removable main jet in the center of the carb, right? The one the needle at the end of the throttle valve modulates through? You were right, I took it out again and it was completely plugged. So I used some wire and compressed air to get it completely cleaned out, put it back together, and bolted everything back up. Well, unfortunately it still won't run right. Seemed to run a little better, but the air screw still has no effect. I can actually remove it from the carb with the bike running, and it runs the same as if it were turned all the way in. What else is in that carb that could be blocked?

 

My mistake , that little carb doesnt have a pilot jet, it has a slow air jet. If you look thru the carb opening, the same way the air flows, youll see a small opening, in the intake venturi. take the mixture screw out, and blow air thru that air jet, you might need carb cleaner to help remove the gunk, this is where the air for the idle circuit starts at.

does the motor run ok at higher throttle settings..like 1/4 throttle and 1/2 throttle?

If that mixture screw wont have any effect on rpm, or idle quality, the air jet is still plugged, or the slide is being held open too far for the idle circuit to operate. How fast does it sound at idle....1400 rpm is where it should be.

 

It seems to run okay at higher power settings. THe idle varys based on where the choke is at. The choke really affects the idle, so much that I can actually use the choke as a throttle. Fully choked, it SCREAMS, I mean it sounds like its going full throttle. Once it warms up, I can slowely open the choke, then mess with the idle screw a little bit, and it gets a somewhat normal sounding idle...for a bit. I'll rev it, and sometimes it comes back down, other times it hangs at some mid throttle setting, then slowely comes down. It's bizzare. I checked the throttle linkage, cleaned and lubricated the cable, everything seems to move okay. I'll try blowing air through that tube for the air screw again.

 

Sure sounds like an air leak somewhere.
The motor cant rev, unless it has air. Putting the choke on, should be restricting air, but what the choke is doing is enriching enough for it to run, and the motor is getting its air somewhere else. Either the slide isnt returning to the bottom, or theres an intake leak.
Was there a o ring groove and o ring in the intake tube?
I tried finding an old parts finder, with a diagram of the carb in it, so you could look at it and see if all the parts are back in the correct spots.
Theres supposed to be a gasket at the top of the slide, where the large nut attaches the cable assembly to the body of the carb...it may be leaking air there, if the gasket isnt sealing very good.
Keep at it, youll get it figured out.