300/440/550 90 550 sx backfire issue...need help..

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standupjetskirider

Location
upstate ny
hi i have a 1990 550sx that is a piston port motor ..it keeps backfiring through the carb and even a flame shoots down the pulser line...i figured it was timing related and pulled the flywheel off and the keyway was good but i noticed oil in the cover so i replaced the crank seals and thought it shorted out the pulser coil...so i bought a new exciter and pulser coil and installed them put everything back together and still backfiring....so now confused i took the electrical box out of a working 87 js550 and installed and still no change..i also cleaned the carbs for hell of it and still cant fugure it out..it even had low compression at 100psi so for the hell of it i even threw in a top end rebuild and to kinda see what kind ov shapeit was in...ive been through this whole motor its driving me crazy...any insight would be greatly appericated.....thanks..
 
onedumbtrucker

onedumbtrucker

Now with 20% more pulp.
Location
London, ON
I would check orientation of your stator. Being off even a few degrees in rotation could lead to back firing. Also make sure you have the wires on the right plugs. If it is firing when piston is at the bottom of stroke instead of top will cause the same issue.
 
E

EightySeven550

Always just this close
Location
Tampa (Carrollwood)
stupid question but have you put new spark plugs in and gapped them correctly? made a HUGE difference on my 550pp. I dont remember the proper gap sorry, maybe someone else can chime in with that.
 
augustaf

augustaf

Location
central florida
standupjetskirider said:
could it be a twisted crank??? one i havent thought of....does any one know how i could check that??
Click to expand...
You'd need a degree wheel and a dial indicator to see if pistons are in phase at their tdc. But I don't think that is causing your backfire - you'd have to be quite a few degrees off. If you have checked all else, I would suspect the cdi /igniter. That is a very expensive part new. Would be nice if you could borrow one for testing.
 
S

standupjetskirider

Location
upstate ny
im stiil lost on this ski...a new year and i still cant get this thing running... so stumped just bought a carb rebuild kit just for the hell of it and still no diference...it olnt back fires when revved up?? and back fires thru carb?? whats up with this rev box thing im thinking of overrideing it.. i heard you could do it with a .003 jet...i dont know what else to do?? it will back fire and even a flame will shoot down the pulser line..
 
augustaf

augustaf

Location
central florida
It would seem that the spark is occurring at the wrong time. You might consider marking TDC on the rear coupler (dial indicator in sparkplug hole) and checking with a timing light
 
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standupjetskirider

Location
upstate ny
im going to re wire the whole stator back because it is a 20 plus year old machine see where that gets me then try to figure out how to use a timing light on it.. i dont know how to control the revs like it says to time it but we will see...
 
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standupjetskirider

Location
upstate ny
it worked!!!! i havent taken it to the water yet but it dident backfire :) i think the two pulser wires were touching them selfs...so stoked to see the 550 alive again..at least i wont run into this problem again hope this helps someone else out there..
 
dbattersby20

dbattersby20

Location
New Jersey
nice.
Just an fyi to some of the guys above. The spark plug wires both spark twice every rotation so it doesn't matter which plug you put where. So ive been told...
 
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