Poor power from ZX50

[benhogan73]

Zombie and Shaka,

Thanks for the replies.

Yes, it has been sitting for a very long time.  Outside.

I have ordered new gaskets for the reed valve and I will use a sealer as suggested.  Should all happen next week, so expect an update then.

This scoot has been quite an experience for me.  So much that seemed complex a few weeks ago is now crystal clear.  As I build my scooter hobby, no doubt what I learned in these weeks will pay off big.

Let's hope it runs next week!!!

Tim

[zombie]

Hope to see you turn into a "tuner" so all can get some experience from you! But please keep posting!

[benhogan73]

My latest efforts have failed.  I put new gaskets on the reed valve, applied sealer and I no longer see any smoke from inappropriate places.  I must now conclude that the engine is properly sealed.  Yet, it won't run except briefly after spraying starter fluid into the carb.   The carburetor does not generate enough vacuum to open the valve on the gas tank.  I now suspect a faulty carburetor body. 

I can get a stock carb for about $90.  Before I go to that expense, I would like opinions from the forum about anything else I might check.

I am gone next week and I need to buy a shop light since the time is changing back to real time.  So, it will be a while before I can do anything.  I will wait a few days before ordering the carb in the hopes someone has an epiphany.

Thanks for all your help.

Tim

[zombie]

First off, borrow a compression gauge to see if the top end is in good shape. You should see at least 100psi for it to run. Second is to remove the carb, and exhaust to do a vacuum check to verify ALL the seals are working. If EITHER is off a new carb. will not help! The Piston/rings are what I suspect. You had the reeds out, so I believe you would have seen a problem there. the stator side seal is more likely to go bad w/ the scoot sitting, (rust on the crank shaft). Check the compression first! Whenever I do a top end job I pre-lube all the parts w/ synth. 2 stroke oil, and it will take QUITE abit of cranking to start, so I use a cordless drill w/ a 1/4" extension on the socket (17mm I believe) This will spin it fast enough to get a fighting chance. It is easy enough to pull the cyl. , and cheaper than a new carb. Best of luck, Let us know.

[Shaka]

Here are a few things to check if you haven't already:  

-The fuel petcock, disconnect the vacuum line and the fuel line and suck on the vacuum.  Fuel should come out the other line.  
-The engine compression
-The o-rings between the carb & manifold
-The needle valve & float in the carb

These are about the only things I can think of as possible causes for vacuum not being sufficient enough to pull fuel.  I don't really think the carb would be the culprit because the vacuum line comes off of the manifold before the carb.  Unless, the carb is just letting air leak right in  with enough flow that there is not sufficient pull at the manifold.

I have a used stock carb I could sell if you do end up needing one, just let me know.  Good luck!

[Shaka]

I guess Zombie beat me to posting!  Compression is what I suspect as well!

[zombie]

Early bird!

[benhogan73]

Thanks for the ideas.

1.  The piston, rings and cylinder are new.  It runs fine when it has fuel available.  I don't really suspect compression, but it's easy enough to check.

2.  I will check the vacuum on the crankcase next.  Pull the muffler and seal the exhaust port.  Pull the carb off and snake a tube through the reed valve.  If that holds vacuum, then all is good.  If it fails, pull the reed valve and check again.  That makes sense.  If the crankcase is leaking, nothing else will much matter.

3.  Vacuum applied manually to the petcock valve does in fact release gas to the carb.

Tim

[zombie]

As benhogan suggested plug the exhaust port, AND the intake manifold you will apply vacuum directy through the plug you placed in the exhaust. Dont forget to plug the vacuum line to the fuel petcock. At 6" of vacuum all the mechanical seals should hold. Any more than that, they will naturally open so 6 is the magic #. It should hold there for 20 minutes. I keep overlooking the petcock. I also lost track of your first post stating the rebuild (piston/ rings). The petcock only takes 3-4 inches vacuum to open. If it is drawing more than that, this would be the problem.Have you tried to gravity feed the fuel? a simple container on the seat w/ no petcock may tell you something. Also have you tried to suck on the vacuum line? there may be a simple bad hose.

[benhogan73]

All,

Thanks for the ideas.  I have pulled the carb and reed valve and sealed the intake.  I then used a boat plug to seal the exhaust port.  I applied vacuum to the crankcase with no luck.  I got nothing to register on the gauge.   I now believe the crankcase has a severe leak.    What is a next step?

I thought about applying liquid detergent to the engine and pressurizing the crankcase, looking for bubbles.  Where should I apply the detergent?  Anyone have a better way to find a leak?

Thanks.

Tim

[Shaka]

That's not good news!  I believe the sealing points are the crank shaft seal on either side, oil pump, spark plug, cylinder head & base, around the center of the crankcase, and the intake manifold.  You could probably just mix up some real sudsy water in a spay bottle and spray those areas.

[zombie]

Welcome back Bro! Try the same set up only this time w/ pressure.   A small compressor will do (12v tire pump). Like you thought use dish soap to wet EVERYTHING. Bubbles will show what is bad! The most likely suspect is the seal under the stator, if the scoot was on the kick stand. Pulling the mag. flywheel is easy w/ a cheepo three way puller. The crankshaft seals will "blow" before 6 psi because they are positioned for vacuum so don't worry too much about them first. You may have a cracked case, or bad install on the cly. Since you can't get vacuum, keep your options open to look around. Pressure will tell!

[benhogan73]

As luck would have it, I have a 12v pump and I can certainly keep constant pressure on the crankcase.  I will have another opportunity to work on this next Monday.  I sure hope it's not a cracked case.  That would really stink.   The other stuff sounds simple enough to fix.

Tim

[benhogan73]

OK.  I put bubble soap around every seal I could find and most of them leaked.  I took the cylinder off and found I had put the gasket on upside down.  Pretty dumb.  I reran the pressure test after bolting it all together and there were no apparent leaks.  I then used some starter fluid and fired it up.  It ran briefly and died.  With repeated testing, I found that I now have a very strong vacuum at the carburetor.  If I cover up the intake, the engine stops, so I think the crankcase is sealed nicely.

I am not sure that the vacuum cutoff valve under the gas tank is working properly.  I am not sure fuel is feeding the carb like it should.  Would it be OK to remove it and put it into chemdip for a couple of hours?  Any other ideas?

Tim

[Shaka]

Have you tried cleaning the fuel petcock?  It has a screen on the inlet side that may be clogged.  You might try removing it and just cleaning it out.  I have used carb/choke cleaner to clean them before, not sure about chemdip though.