Advice needed on 1971 CT70H dying randomly

Hi everyone. Some years since I've been on this forum! My '71 CT70H is slightly modded (88cc with a PZ19 carb) with an engine built by a member here some years ago. It randomly quits when I'm out on the trail. This issue has happened unpredictably off and on over the years. Took it for a 25 mile ride and ran pretty good the other day, with the exception of the clogged idle jet I always get after leaving gas in it over the winter. Easy fix, just clean the idle jet. So I took it apart and the spacer between carb and intake disintegrated. Ok, no problem. Ordered a replacement from DRATV, put it in tonight, (with the cleaned up pilot jet) and took it for a test run. About 5 miles from my house, it bogged and quit. It would start again, but wouldn't run under load. Had to walk it home. Dang, I thought I had this issue fixed! I've replaced the coil (first thing you'd think of, gas cap, and even removed the gas cap to make sure the vent wasn't clogged. I don't get it. No difference between ON and RES positions on petcock. Checked fuel screen in carb, and it's clean. What haven't I thought of?
 
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OLD CT

Well-Known Member
To check the timing you would check the points gap. .016 is where I set them. If they are the points from ten years ago, I would replace them along with the condenser. Order from dratv specific to the type of flywheel you have. Mitsu or Hitachi 4 speed type. The rubbing block on the points wears down so put a very thin coat of dielectric grease on the points cam and only a light dab of solder for the condenser. Check the valve lash cold at tdc, like lukelaw mentioned.
 
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Well, I suddenly remembered who built this engine for me! Hard to believe it's been 10 years. I probably haven't put 200 miles on it in that time. But yeah, points are something I have never looked at. The problem is really odd because it runs just fine until it doesn't. I've been working it like it's getting fuel-starved, but I'm willing to look at anything. The issue has plagued me for a long time though!
 

OLD CT

Well-Known Member
You cant even buy a proper PZ19 with the left side choke and dual inlet anymore, I am hoping it's still good. :) Let me know how it goes with the lash adjustment and points and condenser. The two things that I can think of that would shut the bike down after running awhile, is a tight lash and bad condenser. 10 years goes by quick!
 
You cant even buy a proper PZ19 with the left side choke and dual inlet anymore, I am hoping it's still good. :) Let me know how it goes with the lash adjustment and points and condenser. The two things that I can think of that would shut the bike down after running awhile, is a tight lash and bad condenser. 10 years goes by quick!
Yeah, I'll definitely order the points and condenser. I don't know which type it is, so I'll have to take the cover off again. Valve lash is also easy, and I admit, I've never done it since you built the motor!

What about this carb that dratv carries? That looks a lot like the PZ19L you recommended way back when...
 
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OLD CT

Well-Known Member
That carb is pictured is a right side choke, single fuel inlet. It could work, but you will burn yourself turning off the gas and need a remote petcock for reserve. There are left side choke pz19's but I do not see any with dual fuel inlets for years now.
 
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That carb is pictured is a right side choke, single fuel inlet. It could work, but you will burn yourself turning off the gas and need a remote petcock for reserve. There are left side choke pz19's but I do not see any with dual fuel inlets for years now.
Ha, maybe I never had the right one, but I remember the conversation! My choke IS on the right side, and yes, it's difficult to reach. I often reach across the carb from the left and operate it that way. I assumed you could re-use the dual-barb.
 

Blaine

Member
To save myself the hassle of cleaning the carb every season, i turn off the petcock and let it run until the carb is empty, on all of my bikes and power equipment.
 

dipstik78

New Member
When it dies, close the petcock immediately, open the float bowl drain screw and see how much, if any fuel comes out. Sounds like it's draining the bowl after something is plugging the tank fittings, fuel lines, petcock, float valve.
 
When it dies, close the petcock immediately, open the float bowl drain screw and see how much, if any fuel comes out. Sounds like it's draining the bowl after something is plugging the tank fittings, fuel lines, petcock, float valve.
This is what I've been thinking all along. Now this time, I changed a spark plug and it's running just fine! BUT....I haven't taken it on a long trip yet.
 
Wow, I put a new plug in it, and it's running great. The old one was looking pretty rough! SHAME on me for not checking the obvious. Now to be fair, it has always run just fine until it's been running for a long time, or until I've held the throttle open on a long stretch, so I've always assumed it was getting fuel-starved. But that doesn't look like a fuel-starved plug! Anyway, it had a CR7HS in it, and all I had available was a CR7HSA, so I stuck that one in there. I can't seem to find any real information about the difference between those two. Anyway, I haven't taken it on a long run, so I'm not entirely sure if I've really fixed anything yet. Also haven't looked at points and condenser like you suggested, but that's on my list.
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OLD CT

Well-Known Member
Adjust the pilot or air screw also after the needle setting. That might be on the rich side now, as well. Test and see how it goes.
 
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