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Briggs black smoke and back fire

Posted by ceesneezy (My Page) on
Wed, May 26, 10 at 23:37

Hi, I need some input here! I have a 7 year old 13.5hp Briggs & Stratton vertical shaft I/C Intek OHV lawnmower engine that I have been tuning up over the past four weeks. There is one problem that is still bugging me. When I start the lawn mower, it gives a puff of black smoke then clears up. It also emits black smoke when I start the PTO blades. It runs ok at full throttle (not real smooth, but not too bad). At low idle, it sputters and backfires out the carb. It will occasionally stall at low idle.

Here is what I have changed or fixed in the past 4 weeks:

1. Changed the oil with HD-30. The oil level was below the good range, with some oil on stick, at start of season. Also the oil was pretty black and thin. The oil hadn't been changed in 2 seasons (lesson learned), but is now in the good range with new oil.

2. New air filter and also cleaned pre-filter with soap and water, then dried, and lightly oiled.

3. New spark plug (gap 0.030 in). Old plug was somewhat black but not oily

4. Drained old gas, blew out plastic gas tank with compressed air, changed fuel filter and added fresh gas.

5. Removed carburetor. Removed mix screw/spring, idle screw/spring, fuel solenoid, bowl, float, needle, main jet, and the brass nozzle that goes up the center. I soaked all the small metal parts in carb cleaner (except needle). I shook the float to make sure it wasn't leaking. I wiped down the needle with a tiny bit of carb cleaner ( I did not soak it because it has a rubber tip, which looked ok). I sprayed carb cleaner into all holes of carb, then I used compressed air to blow off carb and in holes, and also all the small parts. The mix screw I adjusted out 1 1/2 turns. The idle screw I adjusted out 5 turns. After putting the needle and float back on, I turned the carb upside down to make sure the float was about level. I also blew into the fuel inlet to make sure no air would pass. If I lifted the float then air would escape. I also hooked up the fuel solenoid to 12V to make sure the plunger pulled in when powered up (it worked fine).

6. Since it was running rich and the float/needle seemed ok, I decided to check the flywheel key to see if it had sheared causing it to be out of timing. I pulled the cover/screen then removed the flywheel nut. The key was perfectly in tact and lined up beautifully with the notch on the crankshaft. Damn I was really hoping this was the problem after all this time!

7. Adjusted valve clearance (this fixed my hard starting problem). Thanks Walt Conner!

At this point, I focused on the magneto. I removed it. I sanded the two contact points with 600 grit sandpaper until there was only very little rust left. I also checked the flywheel magnet with a screwdriver and lightly sanded it. Can rust here make a difference? Also when I pulled the spark plug boot off tonight, the metal piece that is crimped onto the wire stayed on the spark plug! I pushed the wire back in. It still ran the same (black smoke, back fire, hesitates on slow idle)

Well, I just wanted to mention a few things before I go. These may or may not have lead to the problem I'm having now:

- Oil was changed very infrequently (every few years)
- Left the mower outside (uncovered) for approximately half a season (lesson learned)
- Always use water to spray grass off deck and engine, after engine is cooled. Also spray water to clean flywheel screen
- Always mow grass on sides of sandmound (steep incline). Whenever I would mow with carb side down, it would smoke (blue), then when I would get on level land, it would stop smoking
- one year I had a problem with a belt (now fixed). I would have to start the the mower with the PTO blades on
- didn't adjust the valve clearance until this year, which caused hard starting and two fried solenoids.

The Briggs engine is:
Model 280H07
Type 0117 E1
Code 030220ZA

Any help or input would be appreciated! Maybe I overlooked something or did not do something correct.

Thanks,
Chris


Follow-Up Postings:

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RE: Briggs black smoke and back fire

  • Posted by baymee LehighValleyPA (My Page) on
    Thu, May 27, 10 at 6:18

Slight rust on the flywheel won't affect anything. You have a 7 year old motor with an adjustable carb main jet ??

Even though you cleaned your carb, I still think there's something inside. A couple tanks of Sea Foam and you might not have that problem anymore.

The main jet starts out at 1 1/2 turns, but your idle air screw should be about the same.

Try this. Put the idle air screw at 1 1/2 turns. If it won't idle, there's dirt somewhere. If you can get it to run at high speed, back out the main jet until the engine just starts to lose RPM. Then turn it back in until the same. Adjust somewhere in the middle and favoring the rich side.

If you can get it to idle, go from slow to high speed suddenly. If it stumbles, increase or decrease the idle air screw until there is a smooth transition from idle to high speed with a sudden throttle, like gunning your car engine.


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RE:: Briggs black smoke and back fire

  • Posted by baymee LehighValleyPA (My Page) on
    Thu, May 27, 10 at 6:21

It wouldn't hurt to do a compression test or leakdown test on your motor to see if the internals are OK.


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RE: Briggs black smoke and back fire

As you already know, it's running rich. I think you have to replace that coil/plug wire or at least put a new terminal on it. You're losing spark there. I agree to try a solvent in the fuel and oil. At first, use some auto fuel injector cleaner in the gas, no more than an ounce on a full tank. Add two ounces of Marvel Mystery Oil to the oil in case you have a sticky valve or rings. Later switch to Sta-Bil Marine Formula in the gas - put it in the gas can every time you fill it.


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RE: Briggs black smoke and back fire

baymee, thanks for your reply. The carb does not have an adjustable main jet. It is just a brass piece that screws in snug with a hole in it. I did find a piece of dirt in the main jet and cleared it out. I was hoping that fixed the problem but it didn't. I will try the seafoam. I always wanted to try that stuff anyway. Heard good things. I will try adjusting the idle air screw. I am a rookie at this adjustment but I have seen people do it. You basically have to find the sweet spot between lean and rich (slightly favoring rich side). Turning it in CW is leaner? Correct? Also I have a compression tester. I will check out the compression. This engine has OHV with compression release for easier starting. Won't this make a difference in the compression reading? I've heard of a leak down test. Do I need special equipment for this?


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RE:: Briggs black smoke and back fire

Saxman1, thanks for your reply. I will definitely fix the spark plug terminal. Also, I checked out the websites for Sta-bil, Seafoam, and Marvel Mystery Oil. They all appear to be stabilizers. Seafoam claims to do it all: clean, lubricate, control moisture, and stabilize. Website says it can be added to intake and crankcase. Any particular reason you prefer using marvel mystery oil vs seaform in the oil? Also, what are the benefits of marine stabil vs regular stabil?


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RE: Briggs black smoke and back fire

Ok, I fixed the spark plug terminal and put seafoam in the oil, gas, and into the carb. The smoking got better initially, but now it's back. It does idle better though.


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RE: Briggs black smoke and back fire

Marine Sta-bil is more concentrated than the red, and is designed to prevent corrosion in fuel systems related to alcohol-mixed fuels. It also has more cleaners than the red. I like MMO because it actually is oil with solvents added. Seafoam doesn't strike me as an oil, but even kerosene can be considered a 'lubricant' under certain conditions. Definitely nothing wrong with Seafoam - just a preference of mine. I did not find reference to MMO being a fuel stabilizer and would not recommend it be used as such. I use it along with a stabilizer.


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RE: Briggs black smoke and back fire

UPDATE:

The smoke appears to be GRAY in color (not black as I originally thought), and it uses a few ounces of oil in an hour and a half of mowing. The spark plug has carbon AND oil residue on it. I'm thinking head gasket at this point.

So far I have checked:
- compression 120 - 130psi (3 - 5 cranks) Is this good?
- valve guides seem ok; the valves do not bottom out when turning engine; each valve moves about 3/8 - 7/16"
- rocker studs tight
- pulled out both push rods; they are both straight
- readjusted both valve clearances for .005in
- when cranking over engine (valve cover off & spark plug out), oil spews out from around the the lower pushrod area
- checked the reed in the oil breather; it is clean and not cracked or chipped; seems to be working properly


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RE:: Briggs black smoke and back fire

UPDATE:

The smoke appears to be GRAY in color (not black as I originally thought), and it uses a few ounces of oil in an hour and a half of mowing. The spark plug has carbon AND oil residue on it. Walt said it sounds like a head gasket.

So far I have checked:
- compression 120 - 130psi (3 - 5 cranks) Is this good?
- valve guides seem ok; the valves do not bottom out when turning engine; each valve moves about 3/8 - 7/16"
- rocker studs tight
- pulled out both push rods; they are both straight
- readjusted both valve clearances for .005in
- when cranking over engine (valve cover off & spark plug out), oil spews out from around the the lower pushrod area
- checked the reed in the oil breather; it is clean and not cracked or chipped; seems to be working properly


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RE: Briggs black smoke and back fire

  • Posted by baymee LehighValleyPA (My Page) on
    Tue, Jun 8, 10 at 11:21

A leakdown test would be helpful. Google it. Compression is good, so maybe a bad breather???


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