95 SL 650 STD backfiring through one carb

[tony98zj]

Hello everyone, I'm new to the forum. I just bought a 95 Polaris sl 650 std that I'm having some issues with and I'm in need of some ideas. So far I've replaced all of the fuel lines, put on a new triple outlet pump, and rebuilt the carbs with mikuni carbs kits including needles and seats. The ski will start and idle fine but it backfires through the magneto carb when you give it some throttle. I did not check the reeds when I had it apart, could it have bad reeds? I've swapped plug wires in every configuration and still have the backfiring on the magneto cylinder. Its not a making a pop but I can see fire in the carb under acceleration and it seems to be struggling.

[tony98zj]

double post edited out

[K447]

Check the reeds.

Is it an actual backfire with flame and noise or just compression gases blowing back up the cab throat?

[tony98zj]

it is an actual flame that I can see in the carb. there isn't any loud noise but the engine is not revving like it should

[K447]

it is an actual flame that I can see in the carb. there isn't any loud noise but the engine is not revving like it should

Check cylinder compression.

There should never be flames inside the crankcase regardless of reed condition. Fire is supposed to only happen in the combustion chamber above the piston.

[BlueFishCrisis]

I've swapped plug wires in every configuration and still have the backfiring on the magneto cylinder.

Swapping plug wires will not affect anything with respect to timing as all plugs fire at the same time.....

[tony98zj]

Compression is a low, about 105 in all three cylinders, but it only backfires from the magneto cylinder. I was swapping plug wires to see if the backfire changed to another cylinder, and it didn't. Once it gets to about half throttle it seems to have no power with the occasional spitting of fire in the base of the carb. It actually wont rev past that point like its bogging down. Could it be a fuel issue?

[tony98zj]

So now its not backfiring but it has no top end power and it is spitting some fuel air mix out of the carbs. also I'm premixing 40:1 so should I adjust my hi and low speed screws differently? I set them to factory specs to start with and that's not working!

[tony98zj]

I just took the carbs and manifold off to check the reeds. I found that every single reed petal is staying open about an 1/8 of an inch and two of them have small chips on the corner. Is it possible that the reeds are my problem?

[K447]

Compression is a low, about 105 in all three cylinders, but it only backfires from the magneto cylinder. I was swapping plug wires to see if the backfire changed to another cylinder, and it didn't. Once it gets to about half throttle it seems to have no power with the occasional spitting of fire in the base of the carb. It actually wont rev past that point like its bogging down. Could it be a fuel issue?

Something is not right (obviously).

Has the flywheel ever been removed from this engine? I am wondering if the flywheel has sheared the woodruff key and the ignition timing is moving around as the flywheel twists on the crank shaft.

Even with bad reeds there should not be fire in the crankcase. Crankcase flames suggest the ignition timing is wrong or the crankshaft is out of phase.