KymcoForum.com
Scooters - 50cc => zx50 => Topic started by: benhogan73 on September 22, 2009, 09:08:12 PM
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I recently rebuilt the engine on my ZX50 and put on a new muffler as the old one was clogged. The engine starts right up and idles, but it has no power. I sometimes see a puff of smoke below the carburetor from what appears to be a backfire. Also, there have been a few minutes when it ran as expected. I don't think it's a carburetor issue. I suspect an old or weak reed valve. The bike was left outside, unattended, for a couple of years. I bought it as a project and got WAY more experience than I expected.
I just reviewed the parts list and I think the puff of smoke is coming from the oil pump area. I will look to see if I can replace a gasket to seal the crankcase.
Thanks for any help you can give.
Tim
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If it indeed backfireing the mixture is too lean. also check that you have the correct spark plug. If your's is too hot it will cause a predetonation. There are lots of replacement reeds for the zx, but I would check the carb first. Could just need another shot at cleaning. I use CHEM DIP. 1 gallon will last forever. Just leave the metal carb parts to soak for 24-48 hrs, and they will come out like new
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I will get the Chem Dip as that is the cheapest option at this point. As for too lean, do you have source for a jet for the stock carb? I tried to buy one, it is much smaller (outer diameter) than what is installed now.
Thanks.
Tim
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For a stock zx/50 the main jet should be 82-85. You need the exact make of the carb as they all take different jet diameters. You can also use a .085 pin drill to open the jet.
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I put the carb in Chem Dip for 24 hours. Now it won't run. It starts up, but quickly dies. It's as if the fuel isn't filling the bowl quickly enough. The engine runs very fast, like it does just before you run out of gas. Then it dies. Maybe the needle in the carb bowl is sticking shut. I'll work on that tomorrow.
Other ideas are welcome.
Thanks.
Tim
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Check the petcock, the screen may be plugged up and not allowing fuel to flow quickly enough. The fuel filter also. Also check that the carb slide is dropping all the way down. Mine acted similarly when the throttle cable was too tight and not allowing the slide to drop all the way down.
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Sounds like a lean condition still. Try checking as shaka suggested, and check for air leaks ie. reed gasket, cyl base gasket, carb mount, case seals... I saw a post on utube where the fella used a rubber bulb (like a blood preasure thingy) removed and plugged the exhaust port, removed the carb, and preasureized the entire engine to 6lbs. Great idea for finding bad seals. Ps... I hope you took the carb completely apart before dipping as the dip will DESTROY all the rubber parts. Pss. silicone based gasket sealers will not work around fuel. (just an after thought)
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Thanks. I have a vacuum pump that I can check the seals with. And I may need a new carb float valve as I did not take that out prior to the dip. I have a couple of new jets on the way as well.
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I ran a test today. The scooter carb was not generating enough vacuum to open the valve under the gas tank and no gas was going to the bowl. In addition, the way the engine was dying, it was clear no gas was being drawn from the bowl. I sprayed a little starter fluid into the carb and started the engine. I placed my hand over the carb air intake to see if I could detect a vacuum. I felt a strong vacuum and I found that fuel was now going to the carb. The engine kept running until I took my hand off the carb.
Can anyone interpret the results? Do I need a new carb or should I look for a crankcase leak? Do I need to pull the carb and apply a vacuum to the crankcase to test the seal?
One additional note. I am able to wiggle the oil pump slightly and I have noted a puff of smoke from that region when the engine backfires. Is that a normal condition? Seems like it might be as the pump is not bolted to the crankcase, but held in place by a bracket. I suspect the backfire through the pump seal is not that unusual.
Thanks.
Tim
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Wow that's alot. You are spot on w/ the trouble shoot. The inj. pump should be rock solid on the engine. There is a problem there that is causing the vacum leak. pull the injector out and, look at it close to see what the prob is. With your hand over the carb you are forcing the fuel to pull into the engine, and the air is being supplied through your trouble spot. I forgot where I found the manual for the scoot, but if you want I can email it to you. I'm not too savy w/ the comp. but I found if I convert it to a rar it should send
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There is an o-ring around the oil pump that seals it. The bracket just keeps it from popping out. You may just need to replace the o-ring. I found one the right size at the auto parts store for mine, and it was only like 60 cents!
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Thanks. I will pull the pump and replace the o-ring for my next step. I have the manual.
Tim
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I pulled the pump and tried a new O-ring. It created an oil leak. I put the old one back on and snugged it all up. Now the pump is rock solid in the crankcase. The symptoms have changed again.
Now, it runs a bit and dies, but not exactly like before. Also, there is fuel around the reed valve. And I observe smoke in that area while the engine is running, however briefly. It seems there is another leak. Note that smoke does not come out of the carburetor, so it appears the reed valve is working. Should I just replace everything associated with the reed valve? Is there another test I can run to confirm there is a problem in this area?
Thanks.
Tim
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Maybe try and pull off the reed block, clean it, and reinstall. Might have the same luck as with the oil pump. ;D
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Absolutely, It sounds like this scoot. has been sitting for QUITE awhile. For ALL my gasket surfaces I use OMC Perfect Seal. You can get it at a marine supply house. If that cannot be easily found the fall back would be Indian Shellac. Perfect seal never hardens as the shellac does, but both are better than all of the silicone base materials around fuel. Sounds like you got it now.
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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
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Hope to see you turn into a "tuner" so all can get some experience from you! But please keep posting!
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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
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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.
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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!
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I guess Zombie beat me to posting! ;) Compression is what I suspect as well!
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Early bird!
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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
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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.
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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
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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.
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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!
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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
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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
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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.
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Follow shaka's advice to clean the screen, and DO NOT use Chem Dip for this. It will destroy the diaphragm. Once you clean it just test it for flow. Glad to here you found your main trouble. I assume by upside down you mean 180 degrees turned? I also use an inline fuel filter from Ace Hardware. $1.25 each, and I relpace it about once a month. W/ your scoot sitting there is most certianly junk (rust) in there. I have used Hydrocloric acid to clean rusted tanks w/ good results. You can get a gallon for about 5 bucks at any good hardware store. It is usually sold as brick wash. If you deceide to try it be carefull. 1 minute will burn the rust 2 will burn the tank!
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Thanks for the advice. Nothing wrong with the petcock that I could tell. Just needed some gas in the tank. I now see a full tube of fuel when vacuum is applied. That is the good news.
The bad news is that the motor will no longer run at all. Even starter fluid has no effect. I have pulled and cleaned the plug. I will try again when I get back to the garage. Maybe it was just flooded.
Tim
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For the couple of bucks they cost, I would pick up 2-3 new spark plugs. Cleaning the tip doesn't work too well. By the time you get it running well you will most likely go thru 1-2 of them, and you should ALWAYS have a spare.
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Final post. I gave up on the scooter and sold it for $100 to a mechanic. With a new grandbaby and other things going on, I just don't have time to work on it. He got it running. The latest issue was a glob of gasket cement interfering with the operation of the reed valve. He cleaned that off and it started right up. No carb problem at all. Top speed with the 70 cc cylinder was over 50 mph. He sold it for $600 after painting everything. Good for him and thanks to all for your suggestions and ideas. I learned LOTS about scooters and feel very confident I could rebuild an engine if the need ever arises.
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Aw! Ben... You could have offered it here. Well Thanks for the thanks.
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Lucky machanic.