89 sp 580 backfires through carb

[fordworker]

My 89 sp has been running fine all summer. this week it suddenly started to backfire through carb when accelerating. <br /><br />Replaced plugs, rear was very black<br />new plug became black in a few seconds of running. <br /><br />checked fuel system, good pressure, clean, no water or debris in filter, and refilled very fast when cranking. <br /><br />disassembled, cleaned and inspected carb. no problems visible. <br /><br />compression check 150 and 145 psi. <br /><br />removed air box and spark arrestor no difference. <br /><br />removed flywheel cover, no loose wires or bad connections. <br /><br />checked main engine ground and electrical box connections. <br /><br />need more ideas on what to look for. thanks

 

[Jeff Walkowiak]

Re: 89 sp 580 backfires through carb

pull the exhaust system and look for obstructions or broken baffels in muffler check inside hoses for tears look for sand in the muffler.I had a bad rotary valve gear and it would do that just before the gear stripped and the engine quit running, on the other side of the coin a lean cough is also possible and that could be your problem You may have a fuel problem even though you didn't find it, replace the diaphragms in the carbs, when you took them apart was there any fuel on the outside of the diaphragms when you removed the cover. if so they need to be replaced, buy yamaha diaphragms they are the same and a lot less money than sea doo part numbers.

 

[fordworker]

Re: 89 sp 580 backfires through carb

took apart the muffler, screen is clear, no rattling or visible obstructions or sand. had dealer check coil and they said it was fine. claimed they never see coil or cdi problems on the older seadoos. they suggested possible crank seal leak or twisted flywheel key. I am trying to take off the flywheel with a universal puller and it is very hard to get off. <br /><br />what do you think, am I going in the wrong direction? should I go back to the fuel system?

 

[Jeff Walkowiak]

Re: 89 sp 580 backfires through carb

may be one carb is flooding out, does it smell of gas with the ski sitting off overnight with the fuel switch left in the on position? If the flywheel slipped the key it would probably not run but a timing light can tell you if the timing is off, I use the pto and make marks with chalk at t d c for each piston, then look at where it is firing and rev it to see if it advances, lot easier than removing the flywheel

 

[fordworker]

Re: 89 sp 580 backfires through carb

Update on status, had coil and timing checked said was ok. rear cylinder is fouling plug in about 20 seconds of running time (single carb model) lots of blue smoke, rich fuel smell, and no top end power. plug turns black and oily. backfiring seems to have stopped. rebuilt carb with new diaghrams and checked all jets clear. <br /><br />any more advice?<br />rotary valve seal? or maybe oil pump sending too much oil to one side? (is that even possible?)<br /><br />dealer wants to tear down engine and start looking around

 

[Jeff Walkowiak]

Re: 89 sp 580 backfires through carb

you may have a bad plug wire, to the rear cyl, or a bad seal at the rotary valve compartment on the crank

 

[fordworker]

Re: 89 sp 580 backfires through carb

plug wires are not replaceable are they? and would that have shown up on the dealers test station?<br /><br />Will I have to pull the engine to get to the rotary cover, or just remove the intake and work down the side?<br /><br />I am still wondering about the high energy coil on the stator plate, also.

 

[Jeff Walkowiak]

Re: 89 sp 580 backfires through carb

the engine has a center section with oil in it for the rotary valve shaft gears, often a crank seal will leak oil in to the crank area of the cylinders and the engine will smoke bad and foul plugs, you have to tear down the engine and put in a new crank because the seals can't be replaced without disassembling the crank shaft ,, it is a pressed crank ,, this sounds like your problem, I do have what I call a temp fix that works sometimes depending on how bad the seal is. there are 2 large oil hoses going to your engine rotary valve compartment, one on top of your oil tank one on the bottom, first drain the oil from the tank, then close loop a piece of vinyl tubing to the two fittings to bypass that part of the system, take the oil out of the rotary valve compartment, simply place the hose from the carb side in to a container and blow in to the other line forcing the oil out of the compartment. go to an auto parts store and buy a quart of synthetic motor oil and a can of oil seal conditioner, also buy a small auto flush kit that fits in a radiator hose, the type that allows you to hook up a garden hose for flushing out car cooling systems, be sure to get one that has small enough ends to be placed in the oil lines on the ski. loop the two big oil lines over the engine and hook them to the lines that you removed from the tank, un screw the cap on the flush fitting and add a few ounces of seal conditioner and the synthetic motor oil, when it appears that the lines are full, replace the cap on the fitting, you now have a thicker oil and seal conditioner inside the rotary valve compartment, and isolated from your 2 stroke oil that is used in the combustion chambers, be sure to refill your regular oil tank with 2 stroke oil and now you should have reduced the oil leaking it to the combustion section of your engine, if the seals are really bad this probably wont do you any good, but it works most of the time, always check the oil level in the rotary hoses and add oil when it looks like it is needed. the flush fitting allows you to add oil pretty easily. if you have eliminated the oil pump and use pre mix you can just drain all the oil from the existing oil tank and just put in synthetic motor oil and seal conditioner as the tank is only providing oil to the rotary valve area and is not being used for the engine combustion chambers.

 

[fordworker]

Re: 89 sp 580 backfires through carb

Hey Jeff! I want to thank you for all of the time you put into helping people on this forum. I started to tear down the engine to find the problem, and the first thing I did was to pull the flywheel, just to double check the stator position. I found a crank seal leak behind the stator. lots of dried and burned on oil residue behing fw and on stator. wiped off as best i could with rag and electronic spray cleaner. did ohm check and got good readings on all tests.<br />I am going to replace the seal, and reassemble and see what happens!<br /><br />Appreciate all of your help.

 

[Jeff Walkowiak]

Re: 89 sp 580 backfires through carb

no problem be sure to put grease on the inner lip of the seal before you install it, also replace the key on the drive shaft if possible, once the seal is in put a small amount of silicon sealer around the outer edge of the seal when you tighten the cover over the seal it will make for a good air tight seal and should last a long time, however the bad news is when you re assemble the engine it is still going to foul the plugs and smoke, the seals that cause that problem are in the center of the engine.