300/440/550 Js440 runs better than ever.... sometimes?

[Nottjbarlow]

So ive had this js440 for a while now and its always had this thing where 1 out of 3 rides, after about 2 hrs of riding she likes to act funny at low rpm. Runs great but after rippin it for a while (1min or so of full thottle) she wants to bog out if you let it go down around idle rpm range? I did a carb rebuild and left the pop off spring from before(the sbt one made it run SUPER rich), and it ran great for like 5 days on the water. Its running better than ever now minus the bog issue.

Oh and if you hold the throttle just right when its bogging out you can get her rippin again fairly easily. When it bogs it feels similar to how it runs when you get a little water in her.

 

[amitchell]

You are rich on the high end. When you go from full throttle to idle their is an excess of fuel, and that is causing the bog. What do your plug chops and piston wash look like? Do you run the BN or the SBN?

 

[Nottjbarlow]

I believe its a BN, I know whatever one it is, I've been told many times it's the crappy one of the bunch.

The plugs are nice and dark brown, but they do foul out fairly fast, 4 tanks of fuel and their toast.

Also I'm running that poopy 2smoke out board oil from Advance Auto in it, but I just got hooked up with a AMS oil distributor.

 

[amitchell]

When I had my JS550's the best upgrade I did was get sbn44's to replace the bn44's. Night and day difference for tuning and starting.

The plugs are likely fouled because the tuning is off.

 

[Nottjbarlow]

Just pulled this plug from the front cylinder this morning before work, has about one take of gas on it.

Looks slightly on the lean side, but then again I haven't had a chance to do a specific RPM plug reading.

 

[Nottjbarlow]

Also i'm running 40:1 btw