Thats why the call singles cylinder motors thumpers, they thump the counter balancers help but will not get rid of it completely . As for the rattle does the 550 XP still use those rattly Bendix drives the 500s have?

 

Haven't been on in a while but heres your answer on the 550 shake, rattle and hum. The charging system requires a higher idle than other machines. It is a design, idle is about 1600 RPMs. That is why when you mash on it the shake goes away. Don't care for it but its normal.

 

Also as the cc's go up the vibe gets worse becuse you have more mass. If they were to design it so it eliminated the vibes completely, the counter balance would be so heavy that it would negate the horse power of the engine. The other way to dampen vibration is powertrain isolation. That said, theres only so much room on a wheeler in terms of physical size, weigth, and profit margin.

 

Wonder how the big singles like the 700 Grizzly and 750 King quad thump at idle,they have paint cans for pistons.LOL

 

I don't mind shaking at idle but it needs to have a good cam lope to go with it
A couple of things off the top of my head than might explain why the 550 idles rougher than say a 500 is,and one hasn't been widely talked about,on the XPs the tranny is hard mounted to the engine to prevent clutch mis-alingment. This likely will transmit more of the idle vibration through the machine than a seperately mounted tranny like the older sportsmans had.
Also,and this one has been talked about alot, the the engine is turned on a different Axis,with the crank running fore and aft..this means the engine will tend to vibrate side to side within the machine, which will be harder to dampen(easier for the vibe to rock the machine side to side than it is fore and aft). From what I gather reading between the lines,Polaris Engineers worked closely with Fuji to get the vibration down on the engine it self. Given the engine and mouting configuration you can only isolate so much force without making the mounts too soft/loose.
These issues are not as big of a problem on a twin,it is inherently smoother,and on the 850 they run 2 counter balance shafts..like someone elluded to earlier..it has the power and room within the block to be able to do that.
JMO

Why would the fuel pump cycle on after the engine was shut down? I highly doubt it being residual oil pressure...

 

Mega,

I certainly understand what you and Ruggo are saying... your 550's don't vibrate that bad, and I'm sure they are fine ATV's. The two 550's I've heard start up vibrated and rattled pretty bad. That tells me that some are probably worse than others... for whatever reason.

Anyhow, I didn't have to ride them, as I didn't like how they sounded, and wouldn't spend my money on them. Other folks are certainly entitled to spend their money the way they like... at least they know what to expect and can come to their own conclusions.

 

the fuel pump only comes on when u turn the key on, and that is to pressurize the fuel line then it shuts off.

 

This is true until the engine is started. The the fuel pump kicks back on because of the drop in pressure. The pump continues to run while the engine does and shortly after the key is turned off until the pressure switch shuts it down. The noise you hear on the 550 after shutoff is the fuel pressure relief. It occurs 5 or so second ater the key is shut off. It does this so the efi fuel pump will kick in to give you a fresh shot of pressure when you go to start it the next time. This feature also lets you use the system as a primer in cold weather starting, by cycling the key in steps descibed in the addition to the owners manual.