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Charles, Marine Mechanic
Category: Boat
Satisfied Customers: 3713
Experience:  US Navy (Ret) Certified Mercury Marine Tech with over a decade of repair experience.
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85 js 550, new battery, new plugs, new premix, im getting spark,

Customer Question

85 js 550, new battery, new plugs, new premix, im getting spark, and turns over great, but wont start, all i get is a backfire out the exhaust, any answers?
Submitted: 1 year ago.
Category: Boat
Expert:  Charles replied 1 year ago.
Hello, my name is***** will assist you.Was the ski sitting for some time before now?
Customer: replied 1 year ago.
yeah sat for god knows how long, tags have been out since 2011, but hey guy i bought it from was a avid jet ski owner, and put westcoast exhaust, and a after market fuel tank
Customer: replied 1 year ago.
i took off the carb last night and inspected it, looked good to me, i just dont see any squirting of fuel down the carb if i press on the throttle, im new to two strokes, but own 3 dirtbikes, a hotrod, and a hotrod boat.
Expert:  Charles replied 1 year ago.
with the ski sitting for so long, you are going to need to remove the carbs and do a total cleaning on them. The fuel and oil that was left inside them has evaporated and varnished. This is plugging the jets. If you need a link for parts, I can get you one.
Customer: replied 1 year ago.
there is only one carb correct? aswell as i just checked for spark and i cant seem to see any spark now...i have two other 550 motors that i bought with the ski, i should have available parts
Expert:  Charles replied 1 year ago.
Yes, just the one carb. Here is the link to the pats breakdown on the engine.
Customer: replied 1 year ago.
awesome that helps, im taking apart my carb now, i have an after market carb on it now, that one isnt working, but i aswell have a stock carb, for a spare. im going to rebuild the stock to see if i can get it running, any ideas on testing spark? i take one plug wire off set it next to the block and i cant really see any spark, my cables seem to fine to getting extrwemely hot or anything, but enough to let me know im getting power, just maybe not spark, im very unsure.
Customer: replied 1 year ago.
is the jet on the carb the needle jet screw?
Expert:  Charles replied 1 year ago.
For the spark, you will need an adjustable spark test tool. You can get one at most any auto parts store.On the carb, yes the jets are the needles on this model. Make sure to count the number of turns out that they are by turning them all the way in first, then remove them totally out.
Customer: replied 1 year ago.
ok i took it all apart all the way down to the float and seat, looks pretty clean no varnish, ima going to soak it and carb cleaner and give it a shot, im hoping this works
Customer: replied 1 year ago.
how much compression should each cylinder have?
Customer: replied 1 year ago.
i just did compression check, one cylinder has 30lbs, and the other has 120lbs, seems to be one cylinder is dead
Expert:  Charles replied 1 year ago.
Yes, one is dead. It should be over 100 each. Look thru the spark plug holes and see if you can see any scoring.

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