Join Date: Apr 2019
Location: NW Oregon
Thanked 2 Times in 2 Posts
ATV: 2007 400 Automatic 4X4
2007 400 Auto 4X4 bogging, overfueling
I acquired this bike from my Dad about 1 1/2 years ago. It is all factory as far as I can tell and has 4,000 miles. It had been sitting for a couple years when I got it so I drained the fuel, disassembled and cleaned the carb, replaced the fuel lines, replaced the spark plug, replaced the battery and changed the oil (Maxim motorsport oil). After this it starts and idles perfectly but has a significant bog on acceleration and backfires through the exhaust. I got sidetracked on other projects and just got back to it last month.
Since then I've recleaned the carb, removed and flushed the gas tank, checked the air filter, adjusted the valves and ran a compression test (175 psi). With the air intake duct removed from the carb I can see the slide is moving freely and there is a heavy mist of fuel coming from the needle off idle. If I hold my hand in front of (not covering) the air inlet it gets fuel on it. There is air pulsing out of the carb inlet and also the crankcase vent hose. With my temp gun the exhaust pipe near the head reads about 850 degrees revved up in the shop. The bog is worse under load and the new plug is already getting black.
I've been a diesel truck and equipment mechanic for 20 years but this single cylinder unit is new territory for me. Are the air intake pulses normal for a single cylinder? I've searched this forum and Googled a lot looking for a fix.
The auto choke moves freely, is spring loaded out and measures 5 ohms across the coil. The needle on it is perfect and I can't see issues with the seat although its tough to see into the carb.
I removed the spark arrestor to see if maybe the exhaust was restricted and had no change.
I thought maybe timing so I tried to follow the procedure in the manual to check timing with a timing light through the inspection hole but it was splashing too much oil to see the marks. I read about the flywheel magnet issues so I thought maybe the magnets had come loose and damaged/bent the ignition pick up so I removed the magneto cover and found that it has the updated flywheel (looks like it could be an RM Stator FW) and no damage to the stator or pick up.
The carb has all the factory jets and the only thing I haven't verified is that the needle is factory. I'm near sea level, maybe 200 feet.
I'm stuck on troubleshooting until I get the mag cover gasket and reassemble that but I'm nearing my wits end. I was studying up on the CVK carb last night and have a better understanding of the Pilot screw and that it effects A/F ratio over the entire range not just idle. Am I over thinking this? Is it simply a pilot screw adjustment? I'm at 1 3/4 turns out per the manual base setting.
Sorry this got so long but any input would be greatly appreciated.
2007 Arctic Cat 400 4X4 Automatic