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Discussion Starter · #1 ·
Hey guys,

I've got a 1970 Z50 K2 that I've been working on.

It was running last summer, and even started up 1-2 months ago after being stored for the winter. I rode it around for 20-30 minutes and then parked it.
Now I can't get it started.

Based on other posts, I've done the following:
Carb cleaned - gas flows out the bottom when I open the drain screw
Checked Cam Timing - ensured proper alignment of "O" to markings on case when flywheel is at "T"
Verified Ignition timing - point gap and open/close timing
Adjusted Valve Tappet Spacing to OE specs - .002" or .05mm

I'm pretty sure compression is good, but I have a tester showing up later today to verify via gauge.

Any ideas what I should be checking next? Could it be piston/piston rings?
Again, nothing changed from riding it 1-2 months ago to it not starting. Items were done in the order I typed them out above.
If any additional info is needed, just let me know.

Thanks!
 

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A bike that ran fine and then poorly after storage is almost always carb/fuel related. I know you said you cleaned the carb, but if the jets (particularly the pilot jet) were not properly cleaned, that may be your problem. A guitar string ( .009 or .010 gauge) can be used to make sure the pilot jet main passage and cross holes are clear. The air passages should also be blown out with some compressed air. Other than that, make sure your gas is fresh, that there is no rust or other junk coming from your tank, and use a filter if there is.
 

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Discussion Starter · #3 ·
Davmo - last week when I cleaned my carb, I did use a small wire after spraying everything out, pilot jet included, to make sure things were clean.

My spark plug is also definitely getting gas, as it's wet from gas. So I still plan to do a soak of my carb, but I think there's a bigger issue.

Pressure gauge I got showed zero movement, despite the fact that I feel pressure if I'm holding my finger over the spark plug hole. Actually got a 2nd gauge, and still nothing.

I also noticed the exhaust pipe area on my head being like the picture. Is it supposed to look like that with threads exposed? If not, would that be my issue? If yes.....am I looking at replacing piston/rings?

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I'm guessing that a PO used a piece (or two halves) of threaded pipe instead of the two "collars" that go between the pipe end and the flange that holds the pipe in place.

Parts #2 shown HERE
 

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Discussion Starter · #5 ·
I'm guessing that a PO used a piece (or two halves) of threaded pipe instead of the two "collars" that go between the pipe end and the flange that holds the pipe in place.

Parts #2 shown HERE
Thanks for that. Would that matter at all for my non-starting issues?

It clearly looks like it's been like that for awhile, so it would've been that way when I road it last summer and then just a month ago. Wasn't sure if it had "broke further" and caused an issue.
 

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Make sure you hold the throttle wide open while doing a compression check.

Did you check to see if your plug is sparking??

What gap did you set the points to?
Did you clean the points...make sure they aren't corroded? Sand or file off the white scale kinda crap?
 

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Discussion Starter · #7 ·
Make sure you hold the throttle wide open while doing a compression check.

Did you check to see if your plug is sparking??

What gap did you set the points to?
Did you clean the points...make sure they aren't corroded? Sand or file off the white scale kinda crap?
For the compression check, I tried closed and wide open throttle and in-between.
Since I still wasn't getting anything, I opened and closed the choke different times, but still nothing.
Will admit it's a compression tester from Amazon that was only 20$, so maybe not the most accurate, but I still expected to see some movement on the gauge.

Set the points to .3-.4mm per the manual. And I made sure they were totally clean.

And my plug is sparking. Seemed to get 1 or 2 pops from the exhaust when I tried kick starting it a few times.
 

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Davmo - last week when I cleaned my carb, I did use a small wire after spraying everything out, pilot jet included, to make sure things were clean.

My spark plug is also definitely getting gas, as it's wet from gas. So I still plan to do a soak of my carb, but I think there's a bigger issue.

Pressure gauge I got showed zero movement, despite the fact that I feel pressure if I'm holding my finger over the spark plug hole. Actually got a 2nd gauge, and still nothing.

I also noticed the exhaust pipe area on my head being like the picture. Is it supposed to look like that with threads exposed? If not, would that be my issue? If yes.....am I looking at replacing piston/rings?

View attachment 278605
Low compression engines can sometimes be started with a push. Since you haven't had it running recently, a squirt of oil in the spark hole would help make sure the ring are sealing as well as possible. I agree with Dirtbkr188 about the threaded parts sticking out on the exhaust. Looks like someone has put that together in a questionable way that warrants checking (if the flange is tight against the head like it appears, it may not be sealing properly.
 

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Discussion Starter · #9 ·
Low compression engines can sometimes be started with a push. Since you haven't had it running recently, a squirt of oil in the spark hole would help make sure the ring are sealing as well as possible. I agree with Dirtbkr188 about the threaded parts sticking out on the exhaust. Looks like someone has put that together in a questionable way that warrants checking (if the flange is tight against the head like it appears, it may not be sealing properly.
So I squirted some oil into the spark plug hole, and still no start. Even hooked the gauge up and still nothing on it, again despite feeling pressure if I hold my finger over the hole.

Also will say I tried roll/push starting it with no luck down my driveway.

I'll dig into the exhaust and see what was done to it. It did just run about a month ago. And last year, it was running just how the exhaust currently is.

Anything else I can check/verify? Or is my next step to order some parts?

I was trying to keep it stock and restore it, but I'm not totally against doing like the 88cc upgrade, if it's going to be easier than finding a new/used stock head.
 

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I always recommend...
Put a couple tablespoons of fresh fuel right into the spark plug hole, then replace the plug. Then turn the key on, petcock on, choke open and closed and back...then put it into 2nd or 3rd gear and start pushing it. Walking beside...down the street and back...or around in circles in the driveway or street works for me. You need to get the engine spinning, sparking, and sucking air and fuel. It's easy because it's only 50cc.

This is my last chance to start a bike before I start wrenching on it.

If your motor will blow air past your finger when you're holding tight on the plug hole and kicking it...you have SOME compression. No matter what your gauge is telling you.
ZERO compression on the gague = something isn't right, in my book.
A valve stuck open...hole in the piston...no spark plug installed... Something isn't right. Maybe the gauge itself.

A engine will run with NO exhaust installed.
 

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a couple things i noticed from the picture:
1 you have a whacky looking spark plug boot that looks like its made of metal. throw that away and get a rubber spark plug boot
2 the head gasket looks like its leaking A LOT. are the four nuts holding the head snug?
3 if the exterior of the head is that dirty/oily I would assume the engine has been neglected and never had the valves adjusted. pull the valve tappet covers and check your clearances. most likely you have a valve that's too tight
 

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Discussion Starter · #12 ·
a couple things i noticed from the picture:
1 you have a whacky looking spark plug boot that looks like its made of metal. throw that away and get a rubber spark plug boot
2 the head gasket looks like its leaking A LOT. are the four nuts holding the head snug?
3 if the exterior of the head is that dirty/oily I would assume the engine has been neglected and never had the valves adjusted. pull the valve tappet covers and check your clearances. most likely you have a valve that's too tight
Spark plug boot is plastic. Came with a tune up kit from CHP I think. Replaced the old rubber one because it was torn up.

Nuts holding the head are snug, but I get what you're saying. Looks tight on one side but not the other.
I'll see about loosening the nuts and the side bolt tonight to see if I can get that lined up a bit better.
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I 'll double check the valve clearances again. When I checked them before, there was actually a ton of play, so I got it gapped with my feeler gauge to 0.05mm. I'll double check them though once I try to get the head better aligned.

Thanks for the feedback.

I'll get that stuff done and try to start her and let you guys know.
 

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Discussion Starter · #13 ·
Alright guys, so I went through all of the items. I also gave my CARB a pinesol bath.

Got it all back together, still an issue. But as I walked it around in gear, I noticed air coming from somewhere.

Air is pushing back out of the Carb intake. I assume this means issue with intake valve and it being stuck open. Would it be anything else?

Everything was moving as it seemed it should and seems to be timed correctly.

What would be my plan of attack for the intake valve if that's what everyone thinks it is? Sorry, I'm a pretty mechanical guy, just am not usually working on engines.

Thanks!
 

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Discussion Starter · #15 ·
Sounds like a tight valve. pull the tappet covers and check the gap with a feeler gauge. should be .003" intake and .004" exhaust
So I set the gaps to .003 and .004.

Still blowing out the carb. I'm guessing my next step is pull the head again to see what's going on.

Any other thoughts? I plan to pull it tomorrow night after work, so if there's anything else I can try before then, just let me know.

Thanks!
 

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So I set the gaps to .003 and .004.

Still blowing out the carb. I'm guessing my next step is pull the head again to see what's going on.

Any other thoughts? I plan to pull it tomorrow night after work, so if there's anything else I can try before then, just let me know.

Thanks!
When all the normal stuff doesn't seem to be working, check for the oddball stuff. I had one not that long ago that the muffler was so full of oil, it would barely let any air through. Sometimes a bug or animal can get in a pipe and clog it. A buddy of mine went through everything trying to get a bike going, pretty much rebuilding the engine, only to finally figure out it was a dirt dauber in the end of the exhaust pipe. Maybe a long shot, but doesn't hurt to check while you are taking it apart.
 

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Discussion Starter · #17 · (Edited)
I got the head off, and it seems my intake valve is stuck open. I even got it to open up further by moving the camshaft, doing my best to see if anything was stuck (didn't see anything) and letting it re-set and it still stays open. Pictures are "normal state for my head. Does this mean a bent valve and valve replacement is needed?

Not sure if that's an obvious answer. Only ever helped on one valve job and it was a long long time ago.
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Discussion Starter · #19 ·
Get a new head. If you want a cheap upgrade, the E22 heads have larger valves
Rusty - is that because of how bad it looks? Or just for simplicity. I guess is there a reason to not just rebuild with the stock head.

My thoughts with this bike were to get the stock engine back up and running, and then once I did that, I'd probably do a big bore kit on it like the pic/link.

If it would make that much more sense just to do the big bore kit, maybe I'll just go ahead and do that.


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Thanks.
 

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I recommended a new head because they're cheap, they come with a new cam that has roller bearings, new rockers, rocker shafts, valves guides etc...

You certainly could try to put a new valve in the original head but, the cam "bearing" surfaces and valve guides are probably shot.
 
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