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Discussion Starter #1
Any ideas what could be wrong with my 79 Honda Z50. Fresh oil change w/Honda GN4 20w50 oil

Starts right up, idles great, but after a minute or so of a high load, it seems to quit or lockup. 30-45second of a cool down it fires right back up and runs fine for a few minutes and then does the exact same thing. I’m leaning towards clutch plates are sticking, clogged oil screen, or bad pump? Thanks for any help


 

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Sounds like fuel starvation. Take the bowl off and put a container underneath. With the float hanging, there should be enough flow to fill the carb bowl in less than 30 seconds. If not, pull the hose from the carb and test the flow from the hose. It should be a steady stream without any dripping. If flow is still not good, pull the hose loose to test the petcock directly. Once again it should be a steady flow. If the petcock is clogged, sometimes a drill bit can be used to clear the passages, twisting it by hand, and blowing it out with compressed air.
 

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Discussion Starter #3
Thanks for the response. I’m not sure fuel starvation would cause the rear wheel to lock up though? Could be wrong though
 

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Fuel starvation(or false air or just a lean mixture) causes the fuel mixture to lean down wich causes the engine to overheat which causes a lockup.
Oil starvation, screw of the lower valve cover, after a few kicks oil should come out.

It is a overheating problem, clutch plates have nothing to do with this.
 

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Discussion Starter #5
Here’s what the plug looks like after it does it, I think the mixture looks OK. Leaning towards oil pump
271230
 

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I have seen two ways oil pumps fail: a bad sprocket or a broken shaft on the oil drive caused by rust seizing the pump. The sprocket can be inspected by taking your stator plate off, the oil drive shaft can only be seen by removing the pump, or splitting the cases. The teeth on the oil drive sprocket can get worn down to the point the pump won't work, and the teeth on the end of the oil drive shaft can shear off. If it is oil starvation, the valves sticking in the head could be why it dies. The locking up of the rear tire is not totally surprising if you are loosing power, especially in first or second gear, but is the engine locking up to the point it cannot be kicked?
I would still check the fuel delivery at the carb. A more simple way to check is to shut off the petcock immediately after the engine dies, and then see if there is a significant amount of fuel in the carb bowl through the drain tube. If there is a shot glass full, fuel is not the issue.
 

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Discussion Starter #8
I think I’ve narrowed out any fuel issue. I transferred the complete carburetor/air filter/gas cap/tank/fuel line to my 81 Z50 and it shows no signs of overheating or fuel starvation.
 

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Didn’t see you mention switching over the petcock also.

Having just read thru this thread for the first time, I have to say that it sounds like you have already decided the problem is the oil pump or clutch plates despite what others are telling you so I would recommend you pop off that clutch cover so you can remove the clutch and oil pump to see if your hunch is correct.
 

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I'm not sure if you have the right oil weight in your engine. I watched the short video you made and it sounds like your clutch is slipping as you try to kick it over. If your oil is to heavy then it could also lock up your engine and cause damage to it. I wold drain all your oil and try a 10W-40. If you have a newer clone engine on it then it takes a US 10W-40 oil, not the 20W-40 it calls for. The US oil class is different then other countries. How ever they are the same 10w-40=20w-40. I would try changing the oil too. A 20w-50 is way to heavy for that little engine and the port holes for your oil pump.
 

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That sure sounds like soft-seizing to me. Did you recently do any work to the engine? I'm going to guess you are either not getting oil pumped around or you have too much/too little oil in it.

Here's a little test for you. Remove the spark plug and remove the right side engine cover (3 bolts) and the cam cover will also come off. Wipe off any oil that comes out. Now, start kicking the engine over and see if new oil is coming out from the lower right stud that's now exposed by taking that cover off. You should get quite a bit coming out from this exercise. If not, the oil is not making it to the top end. Lastly, when was the last time you cleaned out your clutch pack and such?
 

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That sure sounds like soft-seizing to me. Did you recently do any work to the engine? I'm going to guess you are either not getting oil pumped around or you have too much/too little oil in it.

Here's a little test for you. Remove the spark plug and remove the right side engine cover (3 bolts) and the cam cover will also come off. Wipe off any oil that comes out. Now, start kicking the engine over and see if new oil is coming out from the lower right stud that's now exposed by taking that cover off. You should get quite a bit coming out from this exercise. If not, the oil is not making it to the top end. Lastly, when was the last time you cleaned out your clutch pack and such?
He stated that he used a 20W-50 oil instead of a 10W-40 and I think that's whats going wrong for him. It's just to heavy for the oil pump to move.
 

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The 20:50 runs fine in these bikes. Many of us run it in the warmer months, and on bikes that always get warmed up good before a ride.
 

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The 20:50 runs fine in these bikes. Many of us run it in the warmer months, and on bikes that always get warmed up good before a ride..

I can understand that but what about this time of year? Oil gets heavier in the colder months and even after a warm up it would start getting thicker as the engine cooled.
 

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I've run straight 30 in them when I was a kid because that's all that we had...and it wasn't MC oil either. Never an issue. I run Rotella 15/40 in every wetclutch bike I own, all year without any issues. I don't suspect it's the oil weight, I suspect if it's soft seizing it's a mechanical failure. You need to test the oil pump and pull and clean out your oil sling.
 

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I've run straight 30 in them when I was a kid because that's all that we had...and it wasn't MC oil either. Never an issue. I run Rotella 15/40 in every wetclutch bike I own, all year without any issues. I don't suspect it's the oil weight, I suspect if it's soft seizing it's a mechanical failure. You need to test the oil pump and pull and clean out your oil sling.
It could be a jetting issue to. It all depends on if there was work done to the engine and what it was. I have had that problem myself.
 

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Discussion Starter #17
Sorry for the delay in response. I’ve ordered new clutch plates and oil pump and will work on that soon. All oil is currently drained. Will likely try a lighter weight oil but from what I’ve read 20w50 isn’t necessarily a bad oil to use? Whats the easiest way to tell if this is a original motor or a clone?
 

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Post a pic. Look for a plate by the shifter shaft on the engine that has a bunch of numbers and letters.
tmas
Post a pic. Look for a plate by the shifter shaft on the engine that has a bunch of numbers and letters.
tmas

Does the engine vibrate while it's running? the last time I rode one that old it ran smooth. I have a Honda Cone and it shakes like a small Harley. :)
 
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