95 sp 587 backfire

[Ryan356]

About to give up on this thing but figured I would see if anyone in this forum had any ideas with trying to figure out this issue with new 587 short block just installed in the SP from sbt.

Basically, got everything installed and it idles well, but backfires when you try to give it gas both out of exhaust (bit of flame noticed at one point) and pops out of the carb too. I had checked the exhaust for restriction (none). SBT Tech recommended new valve and valve cover. Installed both and timed per spec; no change. New cover actually still slightly out of spec...but anyways...

I turned to focusing on the electrical system as I had put a timing light on it and it seemed to flicker and go dark sporadically at the higher RPMs so figured it was losing spark. Went down the electrical road, checked voltage (13v) at idle seemed ok, unplugged rectifier anyways didn't change anything. Clipped plugs back, no change. Battery was weak so replaced that; no change. Got a complete ebox off ebay (used) installed that no change. I had also cleaned the flywheel as there were some metal shavings in there from the starter. Thought that may have been shorting the stator/flywheel as there was a couple very slight scratched on the stator. Also replaced stator after that; no change. So only thing left on electrical system is flywheel not sure how it could be that. I also ran it with the start stop button unplugged...no change. Same thing with the buzzer line which I have never heard make any noise btw.

Puzzled at this point and looked other directions. Searched and saw that backfire could be caused by lean condition so ran off of fuel bottle. That didnt change anything. Seemed for maybe a moment that it was helping but dont really think so... Changed plugs at the same time, still backfiring... So rechecked the carb to make sure that its pumping correctly and the replacement jet was the right size. Had rebuilt originally and adjusted everything to spec. Pop off was a bit low but hadn't worried about that at the time. Had noticed the high speed screw was out a few turns on rebuild. Its at 0 now.

Next I re-pulled the carb and RV cover. I even found exact TDC to be sure (not screwdriver method). All lined up right on for both valve open and close per the manual. Timing light showed it firing right spot on per manual (in between flickering).

I then took carb off and tore it down again. This time I rigged up a pressure testing apparatus so tested things there. Pop off was low (15 psi or so). Changed out spring to one that got me to like 25 psi so think that is better. Also pressure test on pulse line seemed fine. However, when I did the testing of the fuel in/out lines I discovered a pretty good leak between the diaphragm assembly and the carb housing. I was wondering if that contributed to the possible lean condition at high rpms. Basically the more vacuum at high RPMs would cause it to pull air through this leak... Ended up fixing that leak but it still does the same thing.

I'm running out of ideas at this point. Still think it's odd that the timing light flickers at high rpms but what are the chances that the new ebox is also bad? Any other ideas to look at? Only other thing I thought of was is that I am running without the prop and shaft...would too little resistance here cause an issue? Thoughts appreciated. Thanks.

Ryan

 

[mikidymac]

Are you sure the stator marks match the case mark?

Did you time the rotary valve using a degree wheel per the manual instructions?

What carb kit did you use to rebuild the carb.

 

[Ryan356]

Thanks for the reply.
I am fairly confident that the stator marks lined up. It is hard to tell where they are but did make out some fairly faint Mark's near the Allen head screw on the starboard side and lined them up the best I could. There is only like a half inch of play all together to rotate and appears it will only go on one way...?

I did time the rotary valve with a degree wheel about 5 different times now. The factory Mark's are pretty much spot on from what I could tell. The valve and cover are new.

Carb kit was first one i found on Amazon so likely no name from china.

Thx again

Ryan

 

[mikidymac]

Thanks for the reply.
I am fairly confident that the stator marks lined up. It is hard to tell where they are but did make out some fairly faint Mark's near the Allen head screw on the starboard side and lined them up the best I could. There is only like a half inch of play all together to rotate and appears it will only go on one way...? Sounds like it's probably ok.

I did time the rotary valve with a degree wheel about 5 different times now. The factory Mark's are pretty much spot on from what I could tell. The valve and cover are new. The factory marks that are scribed int he cases are not correct in my experience. You need to use the degree wheel to align with the bottom of the MAG intake port then mark a mark per the manual, then use the top of the MAG intake port and make another mark, then place your rotary valve to match these marks. Also did you berify you got the correct degree rotary valve?

Carb kit was first one i found on Amazon so likely no name from china. The junk carb kits cause flooding and all kinds of issues. If it is flooding I have seen them backfire out the exhaust. I would get an actual Mikuni Kit with new needle and seat and try that first.

Thx again

Ryan

 

[Sportster-2001-951C-Stock]

Backfiring is unburned fuel burning in the exhaust system which can happen if one cylinder fails to fire the charge. The charge may be too rich to fire or if the engine isn't breathing properly then unburnt fuel can load up in the exhaust and burn there.

If your timing light is blinking in and out, sure sounds like the ignition is malfunctioning. Test your light on a known good engine and does the problem engine seem to miss at this point, confirming lack of ignition? What is the RPM, is it hitting the rev limiter?

If plugs are misfiring due to being wet with fuel, an inductive timing light will probably not flash.

 

[Ryan356]

Thanks for the comment.

I have two different timing lights and they do the same thing where once you rev it up it starts flickering out and backfires. I am not sure exactly what rpm it starts backfiring at but I would guess 3 to 4k as there is no tach on this ski. I am not sure how the rev limiter comes into play but it's not just cutting out. This thing backfires very loud. I was nearly certain it was an electrical issue and scooped that ebox up. I also went thru and tested all the resistance values on both eboxes and all were within specs of the manual. I also tried unplugging the rectifier as recommended in some instances and that did nothing. Same with the stator wires.

A related issue that I had when I first was getting the thing up and running was I had to crank it a decent amount to get it going initially. The starter ground up a little in the mag housing creating metal chips in there. There were a couple chips that were big enough to get caught between the flywheel and the stator and it scratched the stator slightly so that why I got the extra stator. Is there a possibility that the flywheel could have been damaged as well? I removed it and went through and picked out the metal flakes and there were one or two larger chips lodged in the pickup spaces that I picked out. Also I have checked the flywheel key and its fine.

As far as the carb kit goes I have went thru and performed all the pressure tests the manual recommends. The only one that seems kinda off if where you test the check valve on the intake and return line. It is possible to go both ways with air in those if you blow hard enough just wasn't sure that was a deal breaker.

Thanks for the tips this far. Still not exactly sure what to do yet buy additional suggestions would surely be appreciated.

 

[Ryan356]

Regarding your question on the valve timing, I watched multiple YouTube videos and also followed the manual plus I have the degree wheel and also found true tdc by using a piston stop. I am 99 percent certain it is correct. I also confirmed I had the correct valve which is new and matches the one which was in there previously. I had gotten the new valve and cover as it was all scratched and the tolerance was over what the manual said. This was due to the original root issue of previous bad engine. The oil injection pump was not delivering oil correctly as it appeared to have been installed wrong. I had wondered if there was a way to check for vaccum leak around the cover...but never figured out a way to do that easily.

Again, thx for the help and look forward to hearing back from you.

 

[Sportster-2001-951C-Stock]

Yeah, I'm not yet convinced this is an electrical problem.

Another test of your timing light you can try is temporarily short the plug on purpose to simulate a fuel fouled plug and confirm your timing light cannot detect the ignition signal. I'm pretty sure if the plug is shorted (wet-fouled) your light will stop flashing (the voltage signal will be too weak to trigger the timing light). What I mean is, even if the ignition system is operating normally but your plug isn't firing due to it's fouled, don't expect your timing light will detect the signal b/c it likely won't. I think you already absorbed that from above, so I'm just repeating. That's fine.

I also wonder (This might be a long shot but I'll throw it out there anyway) if the ports in the cylinders are in the wrong position or if the piston skirts aren't the correct ones. This will throw off port timing and make the engine breath incorrectly. Were the pistons installed facing the incorrect direction?

Quick way to locate a marginally fouled plug (performing a drop test with an important IMO twist)

While I'm at it, I want to share an old trick. To locate a fouled plug while the engine is running, pull off the plug wires one by one and make the spark jump the gap from the wire to the plug (1/8 inch or so). Remember, a fouled plug is a shorted plug. Plug contamination is a week conductor that bleeds off spark energy so the voltage cannot build high enough to jump the plug gap.

Doing this, many times a fouled plug will begin firing as you hold the wire closely, not touching but making a gap for spark to jump from the wire to the plug b/c the voltage will build (ie: voltage cannot be bled off by the shorted plug) to a point when it jumps the tempory gap to the plug there's enough energy to create a spark in the cylinder with the marginally shorted plug. If the cylinder comes alive, then you know that plug is/was fouled. The ignition voltage on a fouled plug is shorted, so it's being bled down by the wet-shorted plug thus it cannot build high enough to jump the plug gap. As soon as you pull the wire away slightly, the voltage returns to normal 20,000V level, jumps the temporary test gap to the plug and there's normal amount of energy the partially shorted plug begins firing. Don't be fooled if the engine runs fine now, it will foul again pretty quickly so replace the plug and/or correct the reason it's being fouled.

Of course if you pull the wire off and RPM's drop, your drop testing of that cylinder is complete.

 

[Sportster-2001-951C-Stock]

Is there a possibility that the flywheel could have been damaged as well?

The only one that seems kinda off if where you test the check valve on the intake and return line. It is possible to go both ways with air in those if you blow hard enough just wasn't sure that was a deal breaker.

I have doubts the flywheel was damaged, I could be wrong. The ignition pickup wasn't damaged, correct? The stator is just for the charging circuit on the Seadoos I know of, if these are damaged they might not charge correctly but you already investigated that possibility.

Maybe I'm not following you on the check valves, do you mean the 2 circular disk check valves in the fuel pump?

If yes, an air hose sounds like a lot of pressure that could damage them, 5psi or 80psi? They're in series so if one leaks and the other seals air can't pass in reverse yet the pump won't work correctly so I test the fuel pump by respirating the pulse port to make sure it pumps fuel, I just do this using mouth pressure to simulate the pulse.

 

[Sebastian Bluecrew]

My 2 cents here.. The Rotary valve you have in there, is it a 132 degree valve? That is what is needed.

 

[Ryan356]

I havent had a chance to digest all the comments as I'm at work but the last one caught my attention. The valve I ordered and which was in the original was 147. What makes you think it needs to be 132? Also it's a 95 sp.

 

[Sebastian Bluecrew]

OHH. So you have a 1995.. My bad..That shows a 147 degree RV , timed at 130 degrees opening and 65 closing... A 1997 uses a 132 degree, so I had these numbers mixed up.. When you timed it using your timing wheel, the RV you have matched right up to 130 open and 65 closing? Do you have the single carb that it came with or did you upgrade to dual carbs? My current 720 build in the 1997 SP was stock with a single carb and 132 degree RV, but when I swapped out to the dual 787 carbs for my factory pipe, I had to change the RV from a 132 to a 159 to keep it from backfiring out the intake and exhaust like yours is...

 

[Sebastian Bluecrew]

I had to read the entire thread again to see I am asking questions you already answered, sorry.. My guess is an ignition issue/timing issue. Something is not right (DUH), But I have had this same issue with a bad coil in the ebox, bad start/stop switch, bad lanyard switch, wrong RV, air leak, bad MPEM and even brand new plug that was new out of the box and was bad, causing it to spark when it wanted to..

 

[Ryan356]

SEE MY RESPONSES IN CAPS I PROMISE IM NOT YELLING JUST DONT KNOW HOW TO MAKE BOLD ON PHONE...

Yeah, I'm not yet convinced this is an electrical problem.

Another test of your timing light you can try is temporarily short the plug on purpose to simulate a fuel fouled plug and confirm your timing light cannot detect the ignition signal. I'm pretty sure if the plug is shorted (wet-fouled) your light will stop flashing (the voltage signal will be too weak to trigger the timing light). What I mean is, even if the ignition system is operating normally but your plug isn't firing due to it's fouled, don't expect your timing light will detect the signal b/c it likely won't. I think you already absorbed that from above, so I'm just repeating. That's fine.

I also wonder (This might be a long shot but I'll throw it out there anyway) if the ports in the cylinders are in the wrong position or if the piston skirts aren't the correct ones. This will throw off port timing and make the engine breath incorrectly. Were the pistons installed facing the incorrect direction?

IS THERE AN EASY WAY TO DETERMINE THIS? I HAVE THIS ON MY LIST TO CHECK BUT DIDNT WANT TO TAKE THE HEAD OFF. EITHER THAT OR HAVE TO ORDER A SMALL CAMERA...?

Quick way to locate a marginally fouled plug (performing a drop test with an important IMO twist)

I HAVE GONE THRU ABOUT 10 PLUGS NOW. ORIGINALLY CAME WITH BR8ES TRIED 7S AND 9S SAME THING.

While I'm at it, I want to share an old trick. To locate a fouled plug while the engine is running, pull off the plug wires one by one and make the spark jump the gap from the wire to the plug (1/8 inch or so). Remember, a fouled plug is a shorted plug. Plug contamination is a week conductor that bleeds off spark energy so the voltage cannot build high enough to jump the plug gap.

Doing this, many times a fouled plug will begin firing as you hold the wire closely, not touching but making a gap for spark to jump from the wire to the plug b/c the voltage will build (ie: voltage cannot be bled off by the shorted plug) to a point when it jumps the tempory gap to the plug there's enough energy to create a spark in the cylinder with the marginally shorted plug. If the cylinder comes alive, then you know that plug is/was fouled. The ignition voltage on a fouled plug is shorted, so it's being bled down by the wet-shorted plug thus it cannot build high enough to jump the plug gap. As soon as you pull the wire away slightly, the voltage returns to normal 20,000V level, jumps the temporary test gap to the plug and there's normal amount of energy the partially shorted plug begins firing. Don't be fooled if the engine runs fine now, it will foul again pretty quickly so replace the plug and/or correct the reason it's being fouled.

CAN THIS TEST HELP DETERMINE IF THE COIL MAY BE FAULTY?

Of course if you pull the wire off and RPM's drop, your drop testing of that cylinder is complete.

 

[Ryan356]

I have doubts the flywheel was damaged, I could be wrong. The ignition pickup wasn't damaged, correct?

DIDN'T SEEM TO BE DAMAGED JUST HAD TO PICK METAL SLIVER/CHUNK OUT.

The stator is just for the charging circuit on the Seadoos I know of, if these are damaged they might not charge correctly but you already investigated that possibility.

Maybe I'm not following you on the check valves, do you mean the 2 circular disk check valves in the fuel pump?

YES. I.E. IF I BLOW ON THE RETURN LINE PORT HARD ENOUGH IT WILL PASS THE AIR.

If yes, an air hose sounds like a lot of pressure that could damage them, 5psi or 80psi?

JUST MY HOT AIR.

They're in series so if one leaks and the other seals air can't pass in reverse yet the pump won't work correctly so I test the fuel pump by respirating the pulse port to make sure it pumps fuel, I just do this using mouth pressure to simulate the pulse.

 

[Ryan356]

OHH. So you have a 1995.. My bad..That shows a 147 degree RV , timed at 130 degrees opening and 65 closing... A 1997 uses a 132 degree, so I had these numbers mixed up.. When you timed it using your timing wheel, the RV you have matched right up to 130 open and 65 closing?

YES.

Do you have the single carb that it came with or did you upgrade to dual carbs?

SINGLE CARB BUT THIS ALSO HAD ME SCRATCHING MY HEAD. WHEN I WENT THRU AND REBUILT IT THE SCREW SETTINGS WERE OUT OF WHACK... IE HIGH SPEED SCREW HAD A TURN I BELIEVE.

My current 720 build in the 1997 SP was stock with a single carb and 132 degree RV, but when I swapped out to the dual 787 carbs for my factory pipe, I had to change the RV from a 132 to a 159 to keep it from backfiring out the intake and exhaust like yours is...

I HAVE SUSPECTED SOMETHING FROM THE START WITH THE VALVE TIMING BUT EVERYTHING HAS CHECKED OUT SO FAR. I HAVE HAD PLUGGED WIRES SWITCHED ON V8S AND IT KINDA SOUNDS LIKE THAT BUT WORSE.

 

[Ryan356]

I had to read the entire thread again to see I am asking questions you already answered, sorry.. My guess is an ignition issue/timing issue. Something is not right (DUH), But I have had this same issue with a bad coil in the ebox, bad start/stop switch, bad lanyard switch, wrong RV, air leak, bad MPEM and even brand new plug that was new out of the box and was bad, causing it to spark when it wanted to..

I WAS NEARLY CERTAIN IT WAS A FAULTY COIL. MAYBE I JUST GOT RIPPED OFF ON EBAY...

AT THIS POINT IM THINKING IT MAY BE GETTING SO MUCH GAS AT HIGH RPMS THAT ITS CAUSING THE MISFIRE, POSSIBLY PISTONS BACKWARDS (NEED TO SOMEHOW CHECK THIS) OR SOMETHING IS STILL FUNKY WITH THE IGNITION. IS THERE A WAY TO TEST THE SPARK SIGNAL WITHOUT EXPENSIVE EQUIPMENT? MAYBE THAT TRICK FROM SPORTSTER?

 

[Ryan356]

Here is a pic of the old stator for reference. Had a big enough piece of metal to make a scratch.

 

[Sportster-2001-951C-Stock]

Well yeah there COULD be way too much fuel (backfiring = fuel burning in exhaust) but that should burn your eyes (raw fuel irritation) and rich 4-stroking should be happening (your timing light might be confirming this). Giving it choke makes it even richer, as well.

Rich 4-Stroking Youtube:

Not saying I know what's going on, just trying to flush out anything overlooked. 587 is a great motor, but you see not all years were configured same. For instance, were cylinders swapped out and are the cylinder ports tuned to work with the the RV (132 vs 147 degree)? I don't know if Rotax moved the ports too but I'm wondering.

 

[Ryan356]

I'm leaning towards not four stroking. This thing backfires violently... I am also wondering if there was something changed in this engine core from sbt where it may require a different valve setup or something...?

Also is there a certain position that the flywheel should be in at tdc? I wondered if it was possible to spin the center part of the flywheel if it got overtightened...I suppose that's a possibility as well. Still puzzled.

 

[Sportster-2001-951C-Stock]

What does that stator have to do with ignition? I'm not making a connection.

 

[Sportster-2001-951C-Stock]

I am also wondering if there was something changed in this engine core from sbt where it may require a different valve setup or something...

This is what I'm thinking as well, just I have no way to prove it. Cylinder casting number?

And I'm still wondering if you have a big air leak. I realize this doesn't help much.

 

[Ryan356]

I was wondering if the metal shavings I pulled out of the flywheel housing may have done some damage and caused a short in there. Maybe I'm misinformed but doesnt the pickup on the flywheel send a signal to the coil to spark? So potentially there could be a arc or short where the metal shavings are?

 

[Ryan356]

This is what I'm thinking as well, just I have no way to prove it. Cylinder casting number?

Where is that located?

 

[Ryan356]

Where is that located?