Planet Minis

Eric Kammerer

Hi all! Newbie here, with a real simple question.

We recently bought a 79 Z50R for my son to learn to ride on. It was not running at the time of purchase; the throttle cable had broken, and the previous owner just left it sit for a number of years.

When we brought it home, I drained the fuel and disassembled the carb. Left all the carb parts soak in carb cleaner (GM Top Engine Cleaner) overnight, then blew out as much gunk as I could.

I got the bike running, but it seemed to run lean. It would run much better with the choke 2/3 closed, and would not stay running with the choke open. I adjusted the pilot needle to the next to lowest groove, and adjusted the idle and initial screws as described in the Clymer manual. It was better, but still not great. The idle seemed to drift quite a bit.

Then, I took the bike completely apart to clean and paint it. I reassembled it and added an OE gasket to the intake tube (between intake and heat block) and a new air filter element. Otherwise, the carb was as I had it when it ran OK but not prefect.

Yesterday I started it and tried to get it dialed in. It runs better, much less lean. I have the needle in the middle (as delivered from the factory), and it will now run with the choke open when warm. I am guessing I had a pretty good vacuum leak without the gasket between the intake and heat block.

However, the idle still seems to drift, and it has developed a new symptom. Complete and total shutdown, ocurring gradually no matter the throttle position. It starts to die, and twisting the throttle doesn't help. It only happens when the engine is at operating temp, and it doesn't seem to havppen at the same time. I have had it happen immediately when the engine gets warmed up, and I have had it happen after riding it for 5 minutes.

So, after all that I get to my questions:

1. Could I be having float related issues? I took the float and valve out and cleaned them, but it's the plastic float and tangs, and isn't adjustable. I do not have fuel pouring out the float drain, so if antything I think I may still have some kind of blockage that's starving it.

2. Is there a generic replacement carb for stock bore engines that is less than the $100 or so I'm seeing? I see used carbs on ebay, but I'm not sure they'd be any better than what I have.

3. Could the gradual shutoff be ignition related? The system on the bike seems so simple, but could I have the coil heating up and failing or something going on with the points?

Thanks in advance for any help! I haven't had a dirt bike for 20 years, so I guess technology-wise, this 79 is right about where I left off to play with muscle cars. I'm getting a little frustrated; I can turn a 69 Camaro from a rolling hulk to a running driving big blcok car, but this little 50 has me a bit baffled...

Kurlon

Does the bike fire right back up if you let it sit for a second, or does it take longer to cool and come back? What happens if you pop the gas cap immediately after the bike dies?

Eric Kammerer

It won't start right away, but it doesn't need to cool down either. I haven't tried popping the gas cap, but now that you mention that I did notice that the tank was wet around the cap when I quit in disgust last night. I didn't give it much thought.

Are you thinking I maybe getting a vacuum in the tank, or a pressure build up?

Kurlon

Yeah, I'm thinking it's not venting well, so you end up running the bowl dry. If it sits, it slowly fills the bowl, and you can run again for a bit.

Pierce

I had the same problem with my ct70. Drilled a small hole in the top of the gas cap and it ran like a champ.

Eric Kammerer

Well, that gives me a place to start.

I drained the fuel tank, but I didn't remove the petcock, so I'll take that out and inspect/clean, and also see if the Clymer shows me how the venting system works.

Actually, as a silly but possibly related question: is the 79 model supposed to have a vented gas cap? The cap on this bike is solid (no center vent tube), so if it has a vent it must be internal to the cap. If internal to the cap, it could certainly be non-functional at this point. I've never had a Honda 50, and I took for granted that the cap was OE. I know the later Z50 models have a vent tube in the cap.

Eric Kammerer

I love this forum!

I soaked the gas cap in carb cleaner and blew out the vent passage, and voila! No more shutdown issues (the sound you hear is me knocking wood).

Thanks for the help!
E

Pierce

Nice, nothing better than a free easy fix!

d0n

there's some smart fockers here! Nice job guys!

arlindsay1992

I had the same problem. It was the gas cap. But that was on my 1980. I sold that. Now I have a 1984 Z50R and it's got the vented gas cap.