First off, please don't suggest I clean carbs or change carb settings until you read what has been tried.
Here goes:
Two years ago we bought the sled (used of course, odo read 5000km but could be 15k?) and it's had the same problem ever since - it's boggy, slow to build revs off idle and doesn't build good power until the mid range. Above that it runs fine. My first thought was old gas or plugged pilot jets.
At the best of times it'll build revs reluctantly until the midrange kicks in and it takes off. If I didn't have other 380s to put it beside, I might believe it was running ok. But compared to the 96 and 97 machines we've got, it runs like crap in the bottom end and something is obviously not right.
We've blown the top end on it twice, both times the PTO cylinder overheated and looked to be running lean. That side has always read leaner on the spark plug and I've adjusted the needle clip to try to compensate. The second time the top end let go (disintegrated piston), we went up a size on the pistons, re-sleeved the PTO side and fresh bore on both, and we rebuilt the bottom end too, with all new bearings and seals, since I hadn't ruled out leaky crank seals beyond doing a leak down test (which passed and proved to hold pressure but not necessarily vacuum, and didn't prove that the centre crank seal was ok).
I'm not so concerned about the top end blowing - that's something I can compensate for with carb settings, unless the underlying cause of the bog is causing that too. My goal is to get it to run right at low RPM.
Here are the other things we've done. The basic bog problem has never, ever disappeared through trying all this:
Intake/Fuel/Motor
-Made sure the airbox and intake are clean and clear. New airbox.
-Cleaned the carbs, replaced pilot jets, needles and seats. Sync idle, set needle clips and air screws to factory settings
-Put complete carbs from a '97 formula S 380 on it (that sled lifts the skis off idle) and it ran exactly the same.
-Put complete carbs, including slides and needles from a '96 Touring E 380 on it, and it ran exactly the same.
-Cut out the restrictors on the boots between the carb and motor.
-New top and bottom end, all new bearings, gaskets and seals. Leakdown test passed perfectly prior to rebuild. I put the whole motor underwater and not a single bubble after 5 minutes at 5-6 PSI. Compression still seems a bit low - 105 to 110 PSI both sides
-Replaced fuel pump and fuel filter
-Pressure tested fuel system at 4-6 PSI when running. Pressure tested carbs - needles and seats held at 15 PSI.
-Blew compressed air through expansion chamber and muffler (separately). All clear.
Electrical
-New stator
-Swapped CDI from good running sled (a 2005 GSX 550 I believe)
-New wires, caps and plugs
-Checked every wire on the sled for shorts and bad grounds, though I will admit wiring isn't my strong point and I may not have done a perfect job of this.
-Unplugged everything that wasn't required for the sled to run, including all handlebar mounted items, lights, etc
-Added ground wires from motor to frame and main ground circuit to frame
-Had the sled to a skilled small engine shop. They did the bottom end rebuild, CDI swap and checked spark current - test ok. They cut out the carb boot restrictors and thought they solved the problem. But it didn't change a thing.
Drive
-Tried multiple settings, different belts and primary clutches, new clutch spring, wondering if the drivetrain was taking too much power off the motor too early. In the end, even with belt and primary clutch removed, it's still boggy and slow to build RPMs off idle.
I'm probably missing a bunch of things too.
I think we've ruled out drive. I want to say we've ruled out intake/carburetion with the new components and known good carbs. I know it seems like a carb issue at first thought but we've had 3 sets of carbs on the thing and it runs the same every time. The other sleds that the carbs are from run just fine and I don't think they changed the 380 motor so much from mid 90s to mid 2000s that it would be so picky.
Electrical doesn't seem like the problem if the spark current is good and components are new/swapped. Unless their test was faulty - is it possible for a spark to be weaker at low RPM? Can a CDI cause this issue?
One thing that's fishy is that the timing mark on the flywheel does not line up with the mark on the case at TDC. It's probably 30-40 degrees out. It's a ducati flywheel which is the stock make, and it's keyed in place so there's no adjusting timing. Is it possible that either the flywheel or crankshaft are not stock, and its timing is off? Would wrong timing cause it to run poorly at low RPM, but run fine at idle AND at mid/top end?
Are there any other components that could be non-stock on the machine that could cause the bog issue? Wrong exhaust pipe or something silly like that?
I've sent this list to my local Ski-Doo dealer. They get great reviews online and have a mechanic who's been there for 30 years. They won't touch the thing for fear they'll try the same things I have and not solve the problem. Can't say as I blame them, but I'm trying to get them to take it anyway just in case their experience leads them somewhere that I've missed. My only other option is to buy another one and start swapping parts. But I'm not too keen on spending another 40+hours wrenching on it if I can get some expert advice and be more targeted with my effort. Everyone tells me to sell it, but I've never ridden a sled that handles so light and predictably. It's the perfect sled for my wife. Plus, the more I fail to solve the problem, the more curious I get about what's really causing it. I won't give up til this thing runs right!!
Huge thanks to anyone who read through this far! And many more if anyone has any ideas that doesn't involve carb cleaner and sticking wires through old pilot jets :nerd:
2005 GSX 380 Off-Idle / Low end Bog
