300/440/550 550 pops and backfires through carb

score602

score602

Location
Amity Harbor, Long Island
hey guys, recently pick up a 90 550 piston port, all original except for a mariner waterbox, prop, ocean pro ride plate and nozzle.

got it running ran like crap,checked compression, compresh was good, rebuilt the carb, threw it back together, acually ran worse.
riped the motor apart to find bad crank seals, and a going bad crank bearing.

replaced everything, new seals,gaskets,pistons and rings.

still runs terrible, death revs, backfires and no power.

talked to a guy said to throw a 38 on it.

just got done with a jre intake spacer and a brand new sbn. bypassed the fuel switch, new pulse line. STILL RUNS LIKE CRAP

getting fed up, this is the only ski out of 4 i cant get running =((
 
screaming440

screaming440

The Old Skool Professor
Location
KC/Lake of The Ozarks
check this stuff:

spark plug gap! do this first please!
loose water box baffle i think some of the mariners had these.
fuel system sealing.

bypass the stop button.
check ohms on the plug wires. 4.5 to 6.7k ohms
also try pulling the plug wire caps and cut them back an inch or so
check ohms on the stator's coils.
inspect the stator wiring
 
score602

score602

Location
Amity Harbor, Long Island
when i tore the engine down pistons and cyl were in great shape, still had cross hatches on the cyl walls, since i had it apart i threw new pistons and rings in just because.

never checked compression before i tore it down.

gunna take a look at current compression and wires. from there ill check the stator
 
cookn

cookn

Kamikaze
Location
where you live
Whats the carb jetting? did you mean a sbn 44 or was it the 38. im 90% sure the 1990 intakes were 44mm. The sbn is a good mod as long as the jetting is right. My sbn spurts a little fuel out the top but if your jets are too big like in most sbns then you will never get it to run correct. what did the carb come off that you put on?
 
score602

score602

Location
Amity Harbor, Long Island
cookn said:
Whats the carb jetting? did you mean a sbn 44 or was it the 38. im 90% sure the 1990 intakes were 44mm. The sbn is a good mod as long as the jetting is right. My sbn spurts a little fuel out the top but if your jets are too big like in most sbns then you will never get it to run correct. what did the carb come off that you put on?
Click to expand...

the ski had the original 44bn, it now has a 38mil intake and sbn carb part number bn38-34-8113.
not sure current jetting, definatly is wrong. motor has stock head stock exhaust, what kind of jetting have you used with success?
 
yamarider

yamarider

Location
new zealand
On a two stroke there are always four areas to check. Spark, Compression, Timing and Fuel. It sounds like you have spark and compression covered but do check your plug leads and gaps.

If you have recently pulled the motor apart and rebuilt it you most probably would have made sure that you put the stator back in the correct position. To eliminate a possible stator fault Check the timing with a timing light and check ohm readings to rule out a bad stator coil. Also make sure the stator wires are in good condition and not corroded etc.

Correct jetting in your new carb will play a huge role as to how the engine runs. At a guess i would say that any SBN that you can buy new will come with jets that are too big. If your jets are too big it will make alot of fuel splash back out of the carb and will smoke alot foul plugs or not run at all.

I would start with a 1.5 needle/seat, a .90 main jet and a .60 pilot jet. Buy a couple of extra jets a bit bigger and smaller they are pretty cheap but i think that should be pretty close.

Use the mixture screws to get that nice light brown colour.
 
Last edited:
score602

score602

Location
Amity Harbor, Long Island
yamarider said:
On a two stroke there are always four areas to check. Spark, Compression, Timing and Fuel. It sounds like you have spark and compression covered but do check your plug leads and gaps.

If you have recently pulled the motor apart and rebuilt it you most probably would have made sure that you put the stator back in the correct position. To eliminate a possible stator fault Check the timing with a timing light and check ohm readings to rule out a bad stator coil. Also make sure the stator wires are in good condition and not corroded etc.

Correct jetting in your new carb will play a huge role as to how the engine runs. At a guess i would say that any SBN that you can buy new will come with jets that are too big. If your jets are too big it will make alot of fuel splash back out of the carb and will smoke alot foul plugs or not run at all.

I would start with a 1.5 needle/seat, a .90 main jet and a .60 pilot jet. Buy a couple of extra jets a bit bigger and smaller they are pretty cheap but i think that should be pretty close.

Use the mixture screws to get that nice light brown colour.
Click to expand...

ok will get some jets and post back my results, thanks for the info guys
 
rwilliamtaylor

rwilliamtaylor

Ride, Wrench, Repeat
Location
San diego
i bet your woodruff key is broken. if it backfires through the carb and runs rough it's probably timing. What can happen is the key breaks, the flywheel spins and then locks on the broken key only way off because the broken halfs of the keys hit each other. I speak from experiece here after a couple of broken keys.
 
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