doggercdn

Got a weird problem that has me pulling hair out
Have a 93 SL650 that doesn't run on #1 (mag) cylinder.
Mechanical : Compression is 150 on #1, 150 on #2, 145 on #3. Did case pressure test today and held 10psi for over 10 min. Checked crank index and runout. 120deg across the board, and .0014 runout.
Fuel : Carbs all check out fine, and squirting fuel in #1 carb bore doesn't make cylinder fire. Fuel flow and pressure to each carb identical. Reeds check out fine for condition and visual seal, but are original reeds.
Ignition : Spark will jump 30kv gap on all three cyl (1/2"). New BR9EIX spark plugs, and have been swapped cylinder to cylinder as well as wires.
All my knowledge says this engine should run great.

Little history : Engine was rebuilt approx 10 tanks fuel ago, and triple outlet fuel pump added at that time. Last summer son burnt #3 cylinder (PTO) running lean when he run tank dry at full throttle. Changed cylinder, piston, and rings, and ran great for three tanks after that. Pulled it out of the water, running fine. Two weeks later put it back in water, runs on center and pto cylinder only.
Engine gives a tiny little extra kick if pull plug wire then reattach, but only for a split second.

Any ideas? I feel I am having major brain fart here

pwcpro

Is Your engine reaching full rpm or 5000 only. Also does your fuel valve have a reserve pos.?

doggercdn

Has a reserve position, and only reaches much reduced rpm in water

pwcpro

What does it Rev to out of water? Some Polaris modelshave limp mode which will stumble ignition
Also there is a fuel line routing update that t fuel in from center instead of having to go through 3 then2. To get to one. New boysen power reeds will wake that thing up if you get it fueling

doggercdn

Did fuel line rerouting when engine rebuilt. Revs out past where I'm comfortable revving it out of water.
It doesn't ignition stumble or miss. #1 just doesn't contribute anything to engine. Dead just like blown piston or dead plug. Looked in cylinder with borescope camera and everything is perfect and matches #2 and #3

pwcpro

wow, sounds like you have a gremlin in your ski. good luck.

killer454

spark/fuel air/compression

start at spark now