# L120 Surging / Not Cranking Already Replaced Nearly EVERYTHING!



## L120_Atlanta (Aug 23, 2012)

I posted once about this before, but it never got solved, and this has gotten more complex (or at more least confusing) since my earlier post.

John Deere L120 Intek 20HP with right at 100 hours on it.

Was running fine earlier this summer then would not start at time for the next cut. (Battery fully charged, engine tuning over typically.)

Fiddled with under-seat switch and it cranked. Assumed I had found problem, but engine immediately began surging. Didn't matter if idle speed or running fast. PTO on or off. Once warm, I could take choke off, no particular change similar surging-- engine races up then idles down cycling every few seconds and I can see whatever is under the carb messing with the throttle-- revving it up and down in a very repetitive cycle. A couple of times it stalled out when I left it running for 5 or 10 minutes.

If it stalled, mower would restart but nothing seemed to smooth it out. I ran out of time to mess with this so I came back to it later, but a few days later? It wouldn't start at all. (Battery fully charged.) 

I let it sit and tried days later still-- it cranked but it still surged. I got some carb cleaner. When I clean the carb, the surging stops for a moment when there is carb cleaner going through the carb, then back to surging.

I loosened gas cap in case the vent was clogged. It is not clogged. Even removing the cap makes no change, but I can confirm air through the vent openings in cap with compressed air as well.

I decided maybe there was bad gas in mower so I drained the tank COMPLETELY. Using a (pneumatic only) vacuum setup, I evacuated all the fuel from the tank and all debris I could locate-- there was a bit of trash from years of typical use. 

After blowing out the fuel line from the filter to the tank, which was seemingly completely clear before I cleared it, then re-vacuuming the tank (again, not with an electric motor, just compressed air) and then pumping a lot of compressed air into the tank to completely dry it out, I replaced fuel filter, plus the line to the fuel pump from the filter. Next I added spanking fresh fuel just brought from the gas station and cranked it. No change. It surges as before. This with a brand new air filter and pre-filter. Also, it runs the same way as before with the filter housing open. This is not an air restriction to the carb. issue.

So I move towards the engine and change the fuel pump with a new OEM unit from a John Deere dealer. No change, but as before, a touch of carb cleaner makes it run like new for a few moments. In fact sometimes it won't crank at all, but with a touch of carb cleaner, it fires right up. (I don't know what's in carb cleaner, but it acts a lot like starting fluid.)

The service manager at a John Deere shop 15 miles up the road told me it must be trash in the carb somewhere. That made sense, and I've had enough of this-- I need a running mower, so I bought a new carb, figuring I can clean out the old one later for a spare.

I put on the new carb, and now it won't crank at all. Linkage all looks correct. I can see choke operate and throttle position moving as well. It acts like it has no fuel at all, but if I crack the line at the carb, I see fuel and enough runs out that there appears to be a bit of pressure in there. If I put the line into a clear container and turn the engine over, I can seem fuel pumping out of the line. The pump is pumping.

I didn't replace the surge line (or whatever it is called) on the back of the fuel pump. (Whatever drives the pump with a vacuum, I presume?) I didn't think to buy one, but it looks to be intact. Certainly there are no major issues with it and it works well enough that the pump absolutely pumps fuel.

If I drizzle in a little gas manually, still no start, but if I add a touch of carb cleaner? Instant start and smooth running for a moment, until carb cleaner burns out and then it stalls.

If I manually work what I assume is the throttle on the carb itself, also no change.

I stopped and thought about the solenoid wire. Plug seems to have a polarity (wedge shape on one end), but socket in carb does not. I reverse the plug pins (rotate 180 degrees) there is still no change. 

Carb cleaner fires it right up EVERY TIME (plug either dirction) but it stalls. Nothing else makes it crank. I'm keeping the battery fully charged as I work on this, so that is still not a factor.

I'm sort of out of ideas...

I've completely replaced the whole fuel system except the freshly cleaned tank and the confirmed non-clogged fuel line which is behind a new filter, so any bits from that line should be caught well before the carb., (and I see none at all) clear up to the intake manifold except the one small vac line at fuel pump, which looks fine. 

I will say that the new filter appears much less full than the old one, but I can confirm fuel is passing through it. I suspect the old one was partially clogged. There was a little water in the tank before I cleaned it out-- I saw a few drops in the gas I removed-- some may well have been clogging up the old filter too and making more gas visible behind the filter element.

I used new gaskets on both sides of the carb. (OEM, which came with carb.) There were no apparent conventional gaskets at intake to heads, but I see something that looks like a giant O-ring built into (or set into?) the plastic manifold, so I don't have the impression anything has been left out. 

Besides, even if the seal was not perfect, with the new carb, the engine has not "hit" a single time when cranking on gas alone. A slight leak might make it run rough, but I cannot see a potential small opening there keeping the mower from running completely. All appropriate surfaces were also wiped down properly at gasket surfaces and on the heads, etc.

What could I be missing here? Is there some new carb setup procedure or should it work right out of the box? This is driving me really insane... 

Please help!


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## bigl22 (Sep 16, 2003)

you seem to have a vacuum leak that has happened when it heats up, and that big squirt from the spray can is overwhelming the leak, , the PLASTIC manifold may be loosened , or warped or that o ring broken, try lubing that o ring with a thick grease[ even vasilene will work to test it , and grease or use gasket in a tube on the actual manifold mating surfaces- have you looked into weekend end freedom machines website? when my 260 with 1 cylinder Kawasaki was doing this sort of thing i replaced all those things and it finally [ after new carb , fuel pump lines etc,] turned out to be a slowly failing ignition coil,


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## 2jdeeres (Apr 14, 2010)

It sounds like you have already narrowed it down a great deal, I would suggest looking closer at the carb., I had a smaller "Brigs" engine that had similar symptoms, I tore down the carb and rebuilt it took care of all the problems.


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## jhngardner367 (Apr 5, 2011)

A leaking/loose/damaged manifold could cause these symptoms. It could also have a leaking head gasket/valves. 
You might also check the crankcase breather ,to make sure it's working properly. It supplies the vacuum needed to run the pump. If it sticks/leaks it won't pump enough fuel.


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## mowerguru (Oct 24, 2012)

Your plastic intake is cracked. Common on certain spec codes on those Briggs engines. Spray your carb cleaner around seams of intake and you should here engine change.


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