650 only running on 2 cylinders

[ski_guy]

With cleaned carbs and optimum fuel delivery, I went out to the lake to finish my break-in. This darn thing is still running on only 2 cylinders. The mag cylinder plug is waaay to wet, so I leaned it out to try and alleviate...no luck. Heres the wierd thing, if I go out at about 50% throttle and hold it there for about 5 seconds the third cylinder will begin to fire and the thing takes off like I just hit the NOS button. After a few seconds running at 50% on plane it dies. Taking the plugs into consideration, the two rear ones look great...dry and tanish. I know its getting fuel because its wet. Spark also looks fine when tested. The only other thing I can think of is a bad coil. Is this a possiblilty? Could it act up like this at higher/lower compressions? I have the procedure to check resistance and will probably do that soon. Is it ok to swap coils to try and troubleshoot? Any other ideas of what the problem may be? Im about at the end of my wits with this ski...
Thanks for all the advice

[dsolie]

Re: 650 only running on 2 cylinders

It could very well be a coil going out.. Seems like it's shorting and eventually makes a connection. Not good either way. You can swap coils, they are identical except for the length of the wire. Use the size closest to the one you are worried about. Another thing to try is to snip all the cables back 1/4 to 1/2 inch and reseat the boot. These cables get bad, and snipping them back rejuvinates them quite well.

Coils are about $30 each for that ski. I would reccomend swapping all three though, that way all is consistant.

I have a whole 93 SL650 that I am parting out, let em know if you need anything.

dans@scattercreek.com

[ski_guy]

Re: 650 only running on 2 cylinders

Replaced coil with a new one and no luck...same thing. Im starting to think carbs again? Could it have something to do with pop-off? What else in the carbs would wield these symptoms. The only problem is with the mag cylinder, the other 2 are firing fine. I've put way too much into this thing to not have it running right yet. Any other ideas?

[dsolie]

Re: 650 only running on 2 cylinders

Rebuild the carbs and make sure your internal filter is clean. Check the high and low speed jets. You might have something clogge din the Low jet, which is not delivering fuel until the higher RPM (high jet activating). Also, check all of your fuel lines and make sure there is no leak or clogging. At the same time, you might want to look an aftermarket 3 outlet fuel pump for it... Those stock fuel pumps are cr*p.. Replace all of your gaskets etc. Also, while you are at it, check compression and pull the head of the one cyl.. just to make sure everything looks right.

[ski_guy]

Re: 650 only running on 2 cylinders

I had a feeling thats what you were going to say... Ive never dealt much carbs but Id rather not pay to have it done. The only concern I have is setting pop off pressure. I would probably get a rebuild kit from SBT and try to git-r-dun. I just want to make sure that this is the problem before I attempt a rebuild. How do you check pop off?

[dsolie]

Re: 650 only running on 2 cylinders

I will get roasted for saying this by others on this board.... I do not check pop off! Or at least had to yet. I know there is a great pop-off article in the Tech forum here, check it out. I have always made sure that the spring assembly was set just about flush with the carb body. You will know what I am talking about once you get it opened up. Dealing with carbs really isn't that hard, in general. Some can be a pain the the arse, but most of the time, it's cakewalk. Get the rebuild kits and replace all the diaphrams, fuel filters, etc. Make sure that the needle and seat are operating correctly on all the carbs, esp. the one that is giving you problems. They should have a smooth action and the spring should return the needle easily. If not, check your needle and seats, if all are well there, replace your spring with the same colored one in your rebuild kit (it comes with a few diff colors). Make sure you pull the high and low jets out and clean them as well (you will need an "eyeglass" screwdriver for the low speed). Make sure that all the passages are clear. I use a can of compressed air and blow through all the passages.
Also, on the atmospheric side of the carb (with the needle and seat) make sure that the little pin hole on the cover of the carb is not blocked. That will make your diaphram malfunction, which directly relates to how your spring assembly works.

You said in your first post, "With Clean Carbs". Did you just rebuild the carbs? Or what? I would also double check the fuel rail on the carb system.. These things get gummed up with degrading OEM lines.

[ski_guy]

Re: 650 only running on 2 cylinders

Thanks! I had the carbs cleaned by a local dealer, one I thought was going to do me right. They said they were pretty bad and cleaned them up for me. Nothing was rebuilt. Im gonna hopefully get into them in the next few days here and winterize the ski, snow is gonna fly real soon here.

[dsolie]

Re: 650 only running on 2 cylinders

Ski guy,

Yhea, Cleaning and Rebuilding are two different things. Get them rebuilt and make sure everything is good to go. If you have a highspeed connection download the SBT "How to" on Carbs... Great little video. Snow's about to fly here too... That's why I bought winter gear!

[Polaris_Nut#1]

Re: 650 only running on 2 cylinders

I had a simillar problem. One carb would not clean up no matter how I adjusted it, after removing the diaphram. I found that the one carb giving me trouble was missing a small, small screw that held the pin that held the jet. It just would not seat properly. I cannot figure for the life of me why the screw was not in there, and it didn't fall out of the carb when the cover and diaphram were removed. There was no where for it to go. I figure it had to be missing since the day I bought it. Too much wave jumping and a tiny bit of wear must have cause it to stop seating. Put a screw in and fixed the problem. I'm just curious has anyone else ever found something like that?

Check and make sure none of you reeds are broken, cracked, or missing a corner peice while the carbs are off. I put new reeds in my 1995 SL750 in 1996 just to get better performance and the stock ones had corners peices missing after just one season. I put aftermarket reeds with reed spacers and it made a huge difference.

[ski_guy]

Re: 650 only running on 2 cylinders

Okay, got the carbs all pulled apart, they are the Mikuni Super BN's. Nothing looks horribly bad but then again I dont know what bad looks like. Some of the adjustment needles have very thin rings around them towards the tip, but feel flush with the rest of the needle. The needles and seats all look fine, no bent or mushroomed tips and the taper is fine. Springs look ok, and the pivot pin arm looks like its the same height on all 3 carbs. Nothing really stands out on the mag carb that would make it run like this...that I can see. The check valve body on the mag carb had a ring on the underside where the gasket was, the other ones didnt have this. Could this have an affect on anything? A lot of the screws looked a bit rusty and were extremely hard to remove, so at some point before I owned it water was in the carbs.

Im gonna get them cleaned up with carb cleaner and air, but what else should I be looking for? Im not really sure how much to replace outside the SBT rebuild kit; jets, needles, springs, arms. Any advice or pics would be appreciated.

[dsolie]

Re: 650 only running on 2 cylinders

Another possibility is your fuel pump.. Do a search on this site, it has been covered NUMEROUS times. Polaris is notoriously known for it's poor fuel pump design on these early skis. That can cause a lack of fuel to the farthest (MAG) cyl. There is a 3 outlet pump you can get for about $60. Also, SBT has an additional item for this situation. Member "Drydock" just had a topic on this under the polaris forum.

[dierdorf]

Re: 650 only running on 2 cylinders

Take a look at this: A great " How To", re-build carbs with super pixs

http://www.sbtontheweb.com/pdfs/mikunibn.pdf

[ski_guy]

Re: 650 only running on 2 cylinders

I have the "extra" square pump kit installed from SBT. My problem was too much fuel, the plugs were wet all the time, partly because there was no combustion. Im having the same problem with the extra pump that I did with just the stock, thats why I think its a carburetoration issue. Again, im not sure how to tell what is bad so Im gonna just replace what I can and hope it works. I'll be sure to pick up a pop-ff guage to check that as well. Does the SBT Super BN kit include the pivot pin arm and fuel filters?

[dsolie]

Re: 650 only running on 2 cylinders

You will have to verify that wth SBT. I beleive mine came with the filter, but no pivot arm...

Fuel Filter
Diaphram
internal gaskets
internal orings
fuel pump gaskets (for SBN fuel pump rebuild)
3 springs
orings for h/l adj screws

I think thats what came in my polaris rebild kits from sbt... it's been a while though.

[Polaris_Nut#1]

Re: 650 only running on 2 cylinders

Did you check your reeds yet?