jondeere

I am wondering what could be wrong with my mower (john deere js63, about 2 years old). One day it was running, after about an hour of running rpm noticeably dropped for about 1 minute, then it died and cannot start it again. When attempting to start, it pulls normally and black oil drops leak out of exhaust. Cleaned carb with compressed air &carb cleaner first, then checked spark, works, timing is right - magnet on flywheel touches the coil (righ in the middle) about 5-10 deg before TDC, and also cleaned head and valves because suspected leak thru valves as I used by mistake 2-cycle gas with lead substitute. Also does not work when starting fluid is sprayed into the cylinder although there is a spark. Compression reads some 4.5 bars at the normal pull. Also, found out there overfilled oil, about 1/2" above max. Could this cause some damage to piston rings, which would prevent it to start, even for a fraction of a second?

K-B

First drain the oil, and inspect it for these two things 1) is it watery (not thick enough) 2) do you notice any gasoline smell in it? If you notice any of these it probably has a problem with the carburetor. If not, replace the spark plug, refill to the correct level with oil and try again.

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jondeere

replaced oil for a heavier one (castrol 20W50) but symptoms are still the same. again it was not like sitting in the garage over winter and now trying to start it, it was running and suddenly stopped so carb is quite unlikely. Spark is OK too, although I am using regular car spark plug as the original old one just cracked in half and I don't have original replacement (champion sells totally different sprak plug for this mover, and with this spark plug the engine does not run too)

Replacing piston rings is what I am going to do (at least the lowest one).

Have one more question - are piston rings pretty much the same for bs engines or are really model specific? JOhn deere sells such parts only thru dealers, and the closest one is 6000 miles west, so I will have to use whatever I will find on ebay

Midnight Tech

JD, you should be able to get a ring set and gaskets from anyone who sells B&S parts. You'll just need the model and type numbers from the side of the engine.

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K-B

I kinda doubt it's the rings, from what you describe. What I meant regarding the carb was this, if the float or needle valve mechanism is damaged, bent or stuck, it will allow gas to seep into the crankcase, raising the oil level, and one of the places it'll come out of is the muffler.

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jondeere

well I cleaned the carb first, disassembled the float and needle valve, there is some red rubber gasket and looked clean, then reinserted it then blew through the fuel inlet and it seemed to hold the pressure when float is up and release it when the float is down. and ealier cleaned it with compressed air and carb cleaner.

In addition oil spits from the muffler even when there is no carb (i.e.put a thin textile between intake and carb leaving some space for air) - tried like 2-3 pulls with just starting fluid sprayed into the intake but the engine did not start even for a fraction of a second.

And also is there another way fuel can seep to the crankcase except thru broken piston rings?

RIGHTE0US

Pull the plug, give it a very quick squirt of ether/starting fluid, replace plug, and give a few pulls. Get back to me after that

jondeere

rightsheous - ain't working, was the first trick I tried. Then tested spark

jondeere

I double checked what k-b said about the oil, and in fact it is watery. I put a heavier fresh oil (20w50 castrol) and I was able to start it after disconnecting hose which was going from under the filter to the crankcase. When connecting again, no start. Now the oil is quite watery and smells a little gas-like. And the air filter is slightly wet from fuel. What could be wrong with the carb except damaged needle? What is the hose going from the air filter assembly for?

K-B

It's not necessary to put heavier oil in it. Use SAE30.
You asked about how oil can get into the crankcase if the piston rings aren't broken. It goes through the valves, if they aren't completely sealed (and chances are they aren't, unless the engine happens to be exactly at top dead center), and in the valve chamber there's a weep hole into the crankcase (to allow oil from the crankcase to lubricate the valves). The gas seeps right into the crankcase, raising the oil level.
There's a couple things that can cause this. Damaged or worn needle/seat, damaged float, or a bent tang on the float. What you can do is remove the float from the carburetor, hold it up to your ear and shake it. If you can hear sloshing inside, the float has a leak in it and is the cause of the problem. If that's not the problem, set the float height (if you post the model & type numbers, I can tell you what to set it at). And maybe replace the needle & seat.

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jondeere

Thanks everyone, I have fixed it. Can't believe how simple it was

K-B

Hey, you didn't say what the problem was!

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strate8

Whoa ! Wait a minute ! I don't care what you say ! It should've started if it's got spark,compression and fuel ! I mean it should've exploded the gas ! Right ? Make sure you have a good spark ! Even if it's out of time due to a sheared flywheel key,it should let ya know it'll at least POP. If you're using another plug,it may show spark,but,may not when under compression. Get the Right plug and go from there !

strate8

C'mon John Dear ! Don't keep us hangin,now ! The answer is in your hands ! Give it up !

jondeere

Right? No. It needs 4th thing and that't the air. So simple. I would never think that air filter can become so air-tight even after cleaning it with high pressure wap and sitting freely on the intake. Just too many things happened at the same time when air filter became totally clogged from almost-clogged (too much oil in crank, hit a bump heavily, used incorrect spark plug which however was giving spark but who knows if a good one... the original one cracked on the top). It seemed to be sucking oil through the vent tube. When I disconnected it in fact I bypassed the air filter. One good news is that I did not start to dig into the crankcase.

K-B

Oh yes, I should have thought of that. Oil on a paper filter will permanently ruin it.

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