Please Help ! I Think I'm Losing My Mind

[avtech]

I folks, I'm a new member to this forum, and I've reached my witts-end.

Here's the story:

A friend of mine purchased a 2000 Supersport 550 with about 1750 miles on it. He bought it from the original owner. When he bought it, it wouldn't idle. The previous owner had already put new plugs in it, but it still wouldn't idle. He said that it hadn't been ridden in two years, and probably needed a good carb cleaning. My buddy brought it over to my shop for a good look-through, and service.

The carbs were dirty (pilot jets were plugged-solid). And other than the fact that the intake-side of the pistons were badly scored, the sled just got some badly-needed attension with regards to normal service items. Once all the work was done, it did idle, but was a real bear to get the idle to stabilize. I took it for a test-drive, and I could barely get 6000 RPM out of it. At first, I thought it was just really loaded-up, so I let him take it home and put some miles on it....It never cleared-up. It just won't make power. The odd time, it will jump up on the pipe and sing for a fraction of a second, then burble again. I rechecked the carbs again...still chrystal clean. All the jets are per the parts manual, except for the needle, which was changed up to the new one, as per Polaris' technical bulletin (e-clip 3rd position). Still won't run right. Just burns lots, and I mean lots of fuel.....(about a tank and bit for 70 miles). It's definitely engine, and RPM related. I runs fine up to about 3000 RPM, then starts to burble.

Here's some things I tried:

Raised e-clip one notch - no appreciable difference.
Carbs were miticulously synched, as was the oil pump.
compression 120 psi - both cylinders.
New plugs - BR9ES 0.028"
checked airbox - no obstruction
Ran without airbox - same
Ran without pipe- same, just louder!
Checked under the flywheel / fan - everything intact, tight and clean.
Checked all resistance values for stator, trigger, and ignition coil as per OEM service manual - good
Disconnected kill circuitry at CDI box - same.
Checked all electrical connections - good.
Checked fuel pump pulse line - dry.
Drained cranckcase - small amount of fuel came out. - still ran the same.
Replaced ignition coil with good know unit from another 2K 550 fan. - same.
Timing checked - 1/2 line out - within limits. Watched the timing marks while engine was operated through its full range of RPM, and seems to retard itself accordingly, and smoothly.

After a couple of days of playing-around with this thing, I talked my buddy into changine the pistons out. Cylinders were OK, just honed, and all polaris parts put back in ( with new updated pistons). - Still burbles and won't come up on the pipe. With the tack raised, at full throttle, the most you can get is 5500 RPM.

I even got a couple of my buddies to come over last night, which are also good sled mechs, and we were all exasperated after a full night of playing with this thing. All I got was a "Good Luck!" when the left at 3:00 am this morning. We all came to the conclusion that it wasn't fuel related. It just didn't sound (or run) right. The only thing we couldn't try is a new CDI box. We didn't have a spare, and weren't about to spend 360.00 on a "hunch".

Could someone please give me some more ideas, or maybe some past-history on these early 550's. I could easily give it back to my buddy, but It's driving me nuts, that I can't get this one right!

Avtech

[63November]

Are the air tubes between the carbs and the air box intact (and the airbox closed up well)?

Do you know that every port and passageway, not just the jets, in those (both carbs) are clean and open?

Do these problems with engine rpm happen regardless of load to the engine? (Are there possible clutching issues - especially wear or neglect related?)

You might play with dropping the jet needles to the #2 or even #1 clip position to see what, if anything, that does.

I have the 2001 SS and have had to "tune" it to get it to run properly. One of my early discoveries included the fact that there are two small tubes, one running between a carb and the airbox. Disconnecting one of those makes the engine run rich I think - it burbles anyway. Re-reading your post, I saw that you were getting the same performance with or without the air box. I think your carbs need a vacuum "draw" from the airbox. If so, those tubes are critical as is having the ports they connected to open.

Another issue I have had with my "straight from crate" machine has been that pulling a load in deep snow or even working at low speeds has left the engine acting guttless sometimes to the point where power is lost or other times able to respond if one successfully "worked" the throttle enough to clear things out. One simple position change on the jet needle has seemed to solve that in running for most of the past year.

[Plamb]

Fuel filter plugged?

[avtech]

The carbs were cleaned in commercial cleaner, and all passages verified to be clear. With VM carbs, you can shine a light in an adjascent passage, and verify this visually. The carbs are basically "bone-stock". That's usually my starting point to diagnose driveability problems. I am of the belief that things should at least run "OK" out of the box, then go from there. As for the carb vent tubes, they are essentially like new, and connected to the airbox. I only did one engine run without the airbox.

As for the drivetrain, the clutches were removed, disassembled & inspected at the initial service. Only the secondary buttons were replaced. The springs, weights & helix were OEM issue. Chain, belt & track tension are as per the Polaris factory service manual. No tight bearings, etc.

The fuel filter in this sled is in the tank. I never checked it, as there never seemed to be a lack of fuel. No backfiring, No sags or dead spots etc. This thing burns fuel like it's going out of style !!!! But nonetheless, I'll check it for lack of anything else to try.

I'll try dropping the needle again, maybe to the second, and maybe the first groove. I've got nothing to loose.

I don't have a whole lot of experience with this model of engine. I rebuilt one last year, but that's about it. It runs at a fairly low RPM (6800). I guess maybe I'm expecting it to "sing" like a liquid, or an older 440 / 488 fan. The local Polaris dealer, when asked about this sled chuckled and said "yup, they run like crap, and burn fuel like nothing you've ever seen before." He claimed that it was one of Polaris' Oops machines. 2000 and 2005 models only.

I'll let you know how it turns out.

Avtech

[avtech]

Engine was definitely overfuelling. Raised eclip position to #1, and definitely breathed some new life in her. I still had to be rather gentle, as there is hardly no running miles on the new pistons. I dropped the e-clips down to #2 (2001 stock position), and it still burbled a bit, but definitely came up on the pipe (6500 RPM on a fairly short run). I'm a bit reluctant to leave it on the first postion for fear of it being too lean at certain throtle settings. I'll let the owner drive it for a while, and report back to me.

I must say that I've never had to drop needles to that extent to make a factory-stock sled run good enough to be at least driveable!

Avtech

[63November]

Well, the 550 is not exactly the most endearing powerplant though it does have some good points. It sure wasn't a "finished" engine from and engineering standpoint when it was first issued though it does look good in terms of basic construction improvements over the older 440/488 block motors. They are terribly cold blooded to start when the temps dip and nearly need to be clutch-turned by hand to loosen them. I have not had issues with excessive fuel use though I have heard of it. I do know that some models had issues with leaness in certain rpm and use ranges. Their power is nice compared to the older 488s when they are set-up right. I guess I am still somewhat ambivalent about them overall. On the one hand I am unhappy that Polaris released them to let us do their product testing at our expense and risk to life and limb in some cases. On the other hand, I respect the fact that they have persevered and stuck by the motor working continually to try to get it right and constantly improving it. Maybe they will eventually make make it become a 550 worthy of the highly reputed fans on the older, smaller cases.

[Polaris Doc]

Engine was definitely overfuelling. Raised eclip position to #1, and definitely breathed some new life in her. I still had to be rather gentle, as there is hardly no running miles on the new pistons. I dropped the e-clips down to #2 (2001 stock position), and it still burbled a bit, but definitely came up on the pipe (6500 RPM on a fairly short run). I'm a bit reluctant to leave it on the first postion for fear of it being too lean at certain throtle settings. I'll let the owner drive it for a while, and report back to me.

I must say that I've never had to drop needles to that extent to make a factory-stock sled run good enough to be at least driveable!

Avtech[/b]

well sir, i must commend you of your knowledge and willingness to tackel such a project! not many guys are willing to dive this deep into something. sounds like your local dealer is an ### and doesn't know a whole lot. i used to help my customers all the time no matter what! i've had some of these sleds in the shop and they are not speed demons, but from what i experienced, they weren't half bad either!
anyways, here's a few things to consider. check the carbs for all the correct parts as i've seen some sleds have mixed up jets from the owner trying to service their two sleds at once. do a leak check of the needles and seats. verify that the chokes aren't too tight. pull the primary and see if the seal looks good and wasn't ripped up by a blown belt. if it will idle well enough, take some carb cleaner and spray around on the crankcase sealing area, seals, carb boots, etc to check for air leaks. since you've rebuilt the engine, i'm gonna rule out some things. have you verified the timing marks on the flywheel with a dial indicator? also, verify that the crank is indexed by using a degreel wheel and a dial indicator down the plug holes.
you say that everything electrically has checked out for resistances. here's a good one for ya: way back when i had a similar problem and the resistances checked out on the stator as well. turned out that one of the wires had only one strand left on the stator due to the flywheel rubbing thru the rest of it. it would run but had no top end. the spark voltage was insufficient at higher rpms to jump the gap on the plug. just something to check.
how about the cylinder reeds, how do they look? check the fuel tank vent line for pinching. take the belt off and see what it does; could be a drivetrain problem. there's no reason you should have to run the needles that low. you will have problems down the road if you do. that is a ton of fuel to be using as well! how high is the float arm in the carb? should be level. check the needle jets too to make sure they are positioned correctly in the carb. the open part should face the engine, not the airbox. that will also keep it from coming up on rpm.
how about an obstruction in the exhaust? try running it without the pipe once.
there are no checks you can perform on your own for the cdi box. however, i've had a few go bad and it will cause running problems. if you have anyone to swap a box with, try that. or sweet talk the dealer into letting you try that or a new one. there's always ebay or scrap yards. i've got one i use if you need the info.
other than that man, i'm not sure. you've covered many things, more than most. i'll keep brain storming though and ask the guys i work with. please keep us up to date and let us know what it was. if you have any questions, please ask. -Polaris Doc

[avtech]

Thanks, Polaris Doc.

Part of the issue with this sled is that there's a bit of mystery surrounding the Original owner's claim to the history of this machine. He claims that he is the original owner, and that it has never been touched as far as mechanical issues go. Oddly enough the carburetor fuel bowls had a large "L" and "R" carved into them. The carbs were badly out of synch, the oil pump was adjusted way to the "less oil" side for starters. Even the primary clutch basically fell-off when I took the retaining bolt off ( on account of the copius amounst of anti-seize compound on the crank taper). Six and a half inches of toe-in had to be adjusted out of the skis (nothing was bent or stripped). Just lots of weird stuff. Since the engine didn't run right, I couldn't do a before and after run to confirm that it was running right. For all I know, this thing might of been running like this since new. Who knows? I've never really ridden a sled with a 550 fan in it. I've only ridden liquid cooled and older 440 and 488 fan machines. I've ridden a 95 440 SS, and it'll kick this one's butt.

Regardless, the carbs have completely been gone-through. All the jets and internal components have been verified against the Owner's manual supp and the Pure Polaris parts website. All are as per what should be there, except the needle, which is a 6BGY16 (-3) in this case, as per the tech bulletin. Needle and seats were tested, float hight OK (arms parallel with the base flange). As far as the needle jet goes, I'm not sure that you can put it in backwards, due to a locating pin in the NJ bore. These are correctly mounted. Slide synchronization was done via drill bit 1/4 inch in this case. Slides and choke plungers have the required amount of freeplay. Mounting flanges and o-rings were inspected and deemed serviceable.

The pistons were badly scored on the intake side, indicative of the likelyhood of snow injestion. Exhaust side was good. There did seem to be a fair amount of black staining on the sides of the piston around the pin bores due to gas-path leakage through the rings (none seemed to be stuck in their grooves either). Indexing was fine (locating pins still intact). Pistons were found to be installed with the correct orientation, etc. Before I tore it down, it still had 120 psi compression (cold, WOT, ig off). It dropped off to about 115 when done hot. Both jugs were equal. New pistons were installed, I believe that the original part numbers changed-up at least two times. I'm not sure of the p/n at the moment, ('cause it's back at the shop). Cylinders were good, so we honed them up nice, and since there was no appreciable wear, we went back to std pistons and rings. And oviously new head, exh and base gaskets. the reeds were found to be in "new condition". No issues there. The crank was inspected, and considered to be in exceptional condtion. Pins and upper bearings were cleaned-up and re-used. After the new pistons, it still ran like a bag of U know wat. Even tried without the pipe - still wouldn't come up to RPM (even on the stand)!!

As it stands now, the carbs are bone-stock, but the 6BGY16 needles are now at "-2". This whole setup with the new style pistons / rings and the new needle @ -2 is precisely the stock setup for a 2001-2004 550 fan, so I'm not too paranoid to let the owner ride it this way. It runs way better now with the needle @ -2 with the new pistons. A quick run at -2 prior to changing the pistons out did not yield arm-straightening result. But I guess due to the lack of port sealing of the pistons, some ring leakage and a slightly over-rich condition (It was also slightly below freezing when most of the miles were put on), it just made it "sick". It does have some snap now. At least it comes up on the pipe at 6500+ RPM. I'm just not happy on how smooth the delivery of power is throughout the throttle range is. I'll let him put some miles on it, and see what happens. The temps are dropping as we speak.

Thanks again Polaris Doc for your interest and expertise on this topic.

Avtech

[SnoFast]

Did I miss something, or has there been no reporting on what the plugs look like, before and after the needle drop, and what about those reeds ( 550's have reeds, right?)

[63November]

I wouldn't be much concerned with getting the engine lean by adjusting the clips on the jet needles. Getting rid of "gurgle" is hardly like tuning on the edge.

This does raise a most obvious detail which has, maybe, been overlooked: the main jets. Are they correct for the temp range you are running? ( I know in this part of the world reputable dealers will, when setting up a machine for a customer, typically jet it as cold as it gets in the area they are shipping it to. That means the machine will burn a lot of gas and run ragged in the majority of use it sees but is less likely to "burn down" when the temps fall - the most likely time to toast the engine.) If your mains are off - and it sounds like they could be if the needle adjustment helps, perhaps you could drop them one size and see what you get. You'll probably need to re-adjust the clip settings on the needles and also watch those plugs. I would also look at the jetting temp chart to see what the recommendations are.

One of the problems with these 550s was that the originals were set up quite well in terms of timing, jetting, and clutching for decent response, speed, and fuel economy. What happened in practice, though, was that engines were toasted. I don't recall that the lower-48 was seeing it so much, but some dealers in Alaska stopped carrying the 550 fans because there was so much of an issue with them. (Most people pull sleds some or most of the time - they're work machines IOW.) In the early models, it wasn't so much "if" the engine would fail, it was "when." I did hear of them going 10,000 miles, but they went, many with far less miles.