Poor power from ZX50

[benhogan73]

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

[zombie]

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

[benhogan73]

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

[zombie]

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.

[benhogan73]

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

[Shaka]

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.

[zombie]

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)

[benhogan73]

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.

[benhogan73]

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

[zombie]

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

[Shaka]

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!

[benhogan73]

Thanks.  I will pull the pump and replace the o-ring for my next step.  I have the manual.

Tim

[benhogan73]

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

[Shaka]

Maybe try and pull off the reed block, clean it, and reinstall.  Might have the same luck as with the oil pump. 

[zombie]

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.