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'95 Ocean Runner 225 backfiring...why? (link to video included)

piercer808

New member
Bottom-right carb keeps backfiring. I recently rebuild all carbs, and set the floats to level with the edge of the bowls (when holding the bowl upside down). For this particular carb, I adjusted the float even lower to ensure that it wasn't flooding out. Even tested the float valve by removing the bowl while leaving the fuel line connected, and pumping the prime bulb -- no fuel overflowed over the edge of the bowl. Even applied gasket sealer to the bowl gasket to make sure that no fuel was leaking around the gasket and into the rest of the carb.

Any ideas or suggestions? Thanks!


 
Typically the carburetor is blamed for this.-------------I would start with a compression test on this motor.------------Perhaps mark the flywheel for -TDC ---for each cylinder and check the firing.----Have you checked the reeds for that cylinder ?-------Have you looked into faults with cranshaft seal rings ?
 
Typically the carburetor is blamed for this.-------------I would start with a compression test on this motor.------------Perhaps mark the flywheel for -TDC ---for each cylinder and check the firing.----Have you checked the reeds for that cylinder ?-------Have you looked into faults with cranshaft seal rings ?

Thanks for the quick reply!

Prior to rebuilding the carbs, I did check the compression and all cylinders were within 10% of each other (but I can't remember offhand if this particular cylinder was lower or higher than the rest). Haven't checked the reeds nor crankshaft seal rings, though.

I do notice that when this carb backfires, a small burst of fuel spits out of the little hole at the bottom of the carb venturi (I assume this is where the fuel/air mixture gets fed into the engine). In fact, you might be able to see from the video that a little bit of fuel pours out of the carb after every backfire. I'm not quite sure yet whether this little fountain of fuel occurs before or after the actual backfire...kinda too afraid to get too close to the carb to observe that closely. ;)
 
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Have you tried switching a different carburetor there to see if it is carburetor problem ??

Nope, but....derrrrr! I should probably do that. :) I guess I didn't swap because I read somewhere that the carbs should go back in the same place they came from. However, basic troubleshooting technique dictates swapping the defective unit with a known good one to see if the problem is replicated. So I'll most likely do that tomorrow.

Also, upon reading other forums, I may have what is known as a "lean spit." Air may be getting into the air-fuel mix somewhere past the carb, perhaps between the carb and throttle body. I'll check that, as well as make sure the reed is properly adjusted and fully closed at idle.
 
You might check this....
All butterflies must be absolutely closed at idle. None of this "that is close enough" stuff.....absolutely closed.

So....there is a stainless steel link between the bottom carbs, both sides, that can allow #5 and #6 to be slightly open, especially if you have had the throttle bodies off, and since you said you just cleaned the carbs...well the throttle bodies should have been off too......sooo.....

Check that the butterflies are fully closed. It will idle like crap and lean sneeze if not.

And if you didn't clean the throttle bodies, especially behind the side plate, then that may be your problem too. Tiny, tiny holes that gum up.
 
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