See full version: What would cause a 2 stroke outboard to backfire
Furthermore, what causes a boat motor to backfire? Most backfire conditions are a result of a lean fuel condition. A clogged or dirty carburetor is a very common reason for backfiring. Water in the carburetor bowl will also cause a lean fuel condition. Improper ignition timing can allow the engine to backfire.
On a two stroke the reeds generally block it ends up sounding more like an "umph" than a bang. A backfire out the exhaust is generally the result of the engine failing to ignite the air/fuel mixture for several revolutions. The air/fuel mixture passes through, filling the exhaust system with a burnable mixture. [links]
In this regard, what does it mean when a 2 stroke backfires? more
If it is backfiring and spitting back through the carb it may be what is known as a lean sneeze. This is due to a slightly lean mixture due to dirty jets, incorrect mixture adjustment or low fuel level on the float chamber, in turn due to flow restriction or faulty pump.
I had fuel stabilizer in the gas when I used last used it. (last year) I will buy a spark tester and start with that. If it's ok, I will run over to the lake and test on the water before I do much more. Maybe tx1961whaler's point of this being normal on muffs is all that's going on. (With my luck, it's something more. ) more
Looks like I need to get a spark tester. The coils "appear" to be in good shape. (no cracks..and they look pretty new.) I do have one spark plug boot that has a small tear in the rubber near the end of the boot but isn't near the connection. I taped it with black tape so I don't think that has anything to do with it.
I'm not much of a mechanic but thought if the spark checks out ok (after I buy a spark checker) then I will try running some engine tuner through the carbs before I start taking things apart. Thanks for the input. here
Last year, I had a problem with it dying once in a while as I was idling at the dock. I didn't get a chance to use it much last year so I didn't deal with it. Anyway, I think it is probably related to the above as I do recall it doing that last year as well.
Sparkieboat,
The engine is a '83 115hp evinrude, off the top of my head I cant remember the model.
I would hope this is not a problem! The crankcases surfaces were spotless and I used a good anerobic gasket maker and the case slid straight down on the taper pins as I installed it. No movement at all between them at assemble and all the bolts got torqued down per spec.
Since I haven't run the rpms up yet I'm not sure if I will have a weak or boggy situation. I guess I'll find out when I get it broke in and can feel comfortable getting it up on plane and enjoying it. I am running premix at 25:1 and will probably do that for a couple of tanks of gas until I feel comfortable with the rebuild. [links]
UPDATE
Well, I removed the carbs this morning and tore them down, cleaned them all pretty again and reinstalled them on my newly rebuilt power head. Started it up and my idle was very high, adjusted the idle to 800rpm with the motor on the muffs and it purrs like a kitten.
Readjusted the idle to around 1100rpm and took it to the lake. Started it in the water and my idle is steady at 800rpm and it shifts and runs wonderful.
Not sure what I did different but it did make a difference.
wyngo,
I replaced all the recirc lines when I reinstalled the intake manifold. Those should not be an issue but I will check them when I pull the carbs.
Thanks,
Larry [links]
Have always used, for many years, Gunk Carb and Parts cleaner and soaked the stripped carbs. No danger of damaging plastic parts with this product and it breaks down the grunge or shelac if you prefer. more
The engine should still idle ok at a low rpm if the idle passages are open. Not unusual for tachs to be off somewhat-unless it is a digital tach. The analog ones can be off a little at various points throughout the whole rpm spectrum, including at idle rpm's. You could try to advance the idle a hundred rpm or so to see what happens, keeping in mind a low idle is optimal for shifting the clutch dog into/out of gear. more
When tuning a bike for the first time, it may be difficult to figure out if your bike is running too rich or too lean. Both conditions can be very harmful to your bike and cause serious damage as well as create an unsafe riding condition. The following list will help you determine whether your Bike is running rich or lean.
1 - It is difficult to apply the throttle quickly or the engine picks up speed when the throttle is rolled off.
2 - The engine knocks or Pings or overheats.
3 - The engine surges or hunts for a stable RPM while cruising at part throttle.
4 - Engine acceleration is flat or slow to pick up.
5 - When the pilot circuit is too lean, there will be popping or spitting in the carburetor as the throttle is opened. Sometimes there will be popping or after fire in the exhaust on deceleration after the throttle has been closed.
6 - Engine performance improves in warmer weather, or runs poorly in cold weather.
7- Engine performance worsens when intake is removed.
8 - Baked white and flaky spark plugs. here
1 - Engine acceleration is flat, uneven, not crisp.
2 - The throttle needs to be opened continuously to maintain consistent acceleration.
3 - The engine performs poorly when the weather gets warmer, or the engine works better in cold conditions.
4 - Black smoke coming out of the exhaust.
5 - Poor fuel economy.
6 - Engine performance improves when the intake is removed.
7 - When the pilot circuit is rich, the engine will idle roughly, or not return to idle without blipping the throttle, the exhaust can smell of excessive fuel and burn the eyes.
8 - Black sooty or fouled spark plugs, black and sooty exhaust tail pipes.