Toro 16-38HXL Very Loud, Backfires, & Gas in Oil

ntl1991(6)June 21, 2013


My Toro 16-38XHL lawn tractor has been giving me quite a bit of trouble. I recently re-engined the tractor with a good used 16HP Briggs and Stratton, same Toro labeled model.

The tractor ran perfect when I first installed the engine. I then replaced all the belts, along with the fuel filter, air filter, spark plug, oil and filter. The tractor sat for about 2 weeks and I started it back up. Smoke was blowing everywhere and the engine ran rough and backfired. I stopped it and checked everything. I had massive amounts of gas in the oil.

I pulled the carb. The cut off solenoid is working perfect, and there was no varnish or gum in the carb when I took it apart. The needle seals completely, I couldn't blow into the fuel nipple with the float up, so I can't imagine how gas is leaking in. The float seams fine, not filled with gas or anything. I cleaned the carb anyway while I had it apart.

I changed the oil and filter again, cleaned the plug, and started her back up. She's real loud but I can't find any muffler leaks. Doesn't sound like it's running right. A relative had it since new before me, but the engine blew on them. The tractor itself is in great shape along with the hydrostatic transmission. Their old engine was always backfiring on them when turning the engine off. Could the backfiring have damaged the muffler enough to make it very noisy?

The exhaust from the engine isn't smooth like my other tractor with an Briggs IC. It's long, harsh puffs of exhaust from the muffler, not a smooth even puffing... Once I get past mid-throttle, the tractor is too loud to run. It's also backfiring and stumbling when I adjust the throttle up or down.

Here are a couple videos of the engine running:

At Idle:


Any help would be appreciated! :)


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Ahhh, yet another person who thinks the fuel solenoid is supposed to stop all flow of gas.
The fuel solenoid is only for preventing the afterfire BANG! that happens when the engine is shut down. It has no other purpose, and in itself can't prevent an engine from being drowned by gasoline leaking past the needle valve......because the solenoid valve blocks ONLY the carb MAIN JET.........the carb pilot jet remains open and even a very small (relatively speaking) leak past the needle will drown the engine, given enough time during storage. Overnight is more than enough time for a leak, so small you can't detect it with normal means, to empty the gas tank.
There are 2 ways to protect against this type of drowning.
1, you can somehow remove all the gasoline from the tank before parking the tractor.
Or 2, you can install a manually operated, inline fuel shutoff valve in the gas hose between the tank and the fuel filter, learn to always shut off the valve except when you are actually operating the engine, and this will guard against future episodes like this, but only if you use the shutoff valve consistently.
Argue the points if you will (anyone) but I speak the truth.
Now, for the rough running and such.
This tractor has an electric starter......correct?
Any chance you have at some time (related to the engine swap) had the flywheel off this engine? Do you know if the flywheel might have been removed from this engine BEFORE you acquired it?
The questions above are because: Fuel overflowing into the cylinder from the carburetor can (and often does) create a "hydrostatic lock" condition (meaning the cylinder is filled with liquid) which stops the piston from moving when cranked.
Having the cylinder hydro locked will result in shearing of the flywheel key, especially likely if the flywheel retention nut/bolt was not re-torqued to Briggs specs when installing the flywheel.
For accurate torque specs we need to know the Briggs Model and Type numbers of the engine (taken directly from the engine).
The flywheel key can be checked for shearing by removing the flywheel retainer nut/bolt and observing whether the keyways in the crankshaft and flywheel are EXACTLY aligned with one another.
If there is ANY misalignment of the 2 keyways, the key is sheared, or is in the process of shearing.
Back to the carb and fuel leakage. Leakage past the needle valve is not always due to worn parts, sometimes it can be caused by a miniscule piece of trash getting trapped between the needle and its seat. Often the offending piece of trash is dislodged and gone by the time somebody gets around to looking for a cause.
Sometimes the wear or misfit of needle to seat is sooooooo slight that normal tests (like blowing with mouth) will not show any discrepancy. But what you can't detect is that even a leak so slight in volume at first glance as to be deemed non existent...................can still result in a lot of fuel leakage given sufficient time.
My philosophy and opinion is that every OPE engine should have an inline fuel shutoff valve (it was industry standard at one time) and the valve should be turned off whenever the engine is not running.
Fuel leakage so slight that you can't detect it WILL NOT cause mixture problems DURING ENGINE OPERATION.
The rate at which a running engine consumes fuel far exceeds the rate at which a small leak past the needle valve would add to the mix.

This post was edited by mownie on Sat, Jun 22, 13 at 11:33

    Bookmark   June 21, 2013 at 11:55AM
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Well said, Mownie.. and well explained.

    Bookmark   June 21, 2013 at 3:46PM
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Thanks Mownie, thorough post.
I purchased a couple of inline shutoffs last time I did a parts order online. They were originally for my snow blowers, but I think I'll be putting one to use for this Toro. That's definitely a sure way of stopping the fuel flow.

As for the function of the solenoid valve, I appreciate your explanation. I'll have to see how the seat of the needle looks, or perhaps just rebuild the carburetor to be safe. The small engine ship that I purchased the engine from claimed the carb. was dipped before they shipped it.

The sheared flywheel key makes since, that would throw the timing off enough to cause the backfiring, odd exhaust behavior and stumbling on acceleration/deceleration. I'll have to get the exact Model Number on the valve cover for torque specs on the flywheel bolt.

I've had my trusty 38" Wizard for almost 20 years now. I figured I'd revive the nice, newer Toro and save it from the scrap yard. Hopefully all this trouble will pay off in the end...

Thanks again,

    Bookmark   June 21, 2013 at 6:46PM
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Also, just another thing came to memory about the flywheel key.

After putting the engine in, I had trouble with the battery not being able to turn the engine over sometimes. The engine would turn maybe twice and then stop. I figured it was just a bad battery, but when I put the battery in my Wizard, it started its 12HP Briggs IC just fine... I just though the 16HP needed a more powerful, healthier battery, so I bought a new one.

But it did it a couple more times, which puzzled me. The engine could've been hydrostatically locked then. It was well before I discovered the whole gas-in-oil problem.

Makes sense. I'll definitely have a look at the flywheel key.


    Bookmark   June 21, 2013 at 6:56PM
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IS the engine an OHV type?
IF SO, adjust the valves using the proper procedure.
Valve lash affects the compression release.

    Bookmark   June 21, 2013 at 9:28PM
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Took the flywheel bolt off, and you're correct, the key was sheared off, and the two pieces of it were about 25 degrees off on the shaft.

I'm ordering a new key now. I'm going to get a carb rebuild kit as well as the oil is again filled with gasoline. I guess my vice grips weren't enough to stop the gas from flowing into the engine. Tank is completely dry again. I installed a proper fuel shutoff valve in the fuel line so this hopefully will be my last time draining the oil and replacing the filter.

What torque specs will I need to tighten that flywheel retaining bolt down to?

The engine numbers are:

286H77 (Model) 0121E1 (Type) 030211ZD (Code)

Thanks for all the help,

    Bookmark   June 26, 2013 at 8:25PM
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Ideally use the black (796355) key and tighten to 110 ft pounds.
The original spec was the aluminum key and 100 ft pounds.

    Bookmark   June 27, 2013 at 12:06AM
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Thanks tomplum! Will be working on it on Tuesday. I'll post back with my results.

    Bookmark   June 28, 2013 at 8:26PM
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That IS an OHV engine, so the valve adjustment (properly done) is important.

    Bookmark   June 28, 2013 at 10:54PM
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Valves were (supposedly) adjusted before the engine was shipped out to me. I can always pop the valve cover and get the feeler gauge in there to double check.


    Bookmark   June 29, 2013 at 5:22PM
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Replaced the flywheel key. Torqued the flywheel bolt to 100 foot pounds, replaced the spark plug, drained the gas-contaminated oil, installed 2" pipe nipple in oil drain, filled with new Mobil 1 5W30 Synthetic, replaced gas-contaminated oil filter.

I have a brand new Nikki carb on the way, but in the meantime I'll be using the shutoff valve before turning the engine off to burn all the gas in the fuel line and bowl, guaranteeing no contamination of the oil.

Reinstalled the Toro grass catcher, now I just have to re-level the deck. When mowing on slopes, you can hear the blades slow down and speed up. I've already replaced the mower deck belt and traction drive belt.

I also have to adjust the brake, and see if there's an adjustment for reverse. Perhaps I can adjust the pedal linkage to the transaxle. The mower doesn't have enough power to reverse uphill without the engine being on full throttle, and even then, it's mediocre.

Thanks for all the help and support!


    Bookmark   July 2, 2013 at 10:31PM
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