The stuttering happens primarily in 5th as thats the gear I tend to wind out the most to attain and maintain freeway speeds. The way the bike bucks and slows down does feel like either fuel or spark is being cut. Its a very violent stutter, and the bike will continue to do it unless you backoff on the throttle. I know some problems with fuel/ignition can be rode through....this will not stop unless you do. I don't want to start throwing money at this bike, so I'm going to replace the small inline fuel filter with a piece of straight hose. If it persists I'm going to get a CDI without a rev limiter, as they're only about $25-30. If it still happens I will step up to a new high performance coil and wire.

The plug gap being set at .025 or .027 doesnt make a difference and is what I believe spec is. The plugs don't foul, and don't have any remnants of a lean condition. I think the jetting is very close to perfect.

I think you are on the right track with the cdi/coil.

Allen

I recommend a new NGK plug wire before anything else. An NGK wire will likely be about 1000 ohms less than the Chinese part. After you peel back the boot at the coil, the stock wire simply unscrews from the stud inside the coil.

I have a new NGK plug in it. D7EA.

Anyone know what size NGK wire to buy?

I'm not sure about your machine, but ours took the stud type of plug boot. Just unscrew your existing wire and boot assembly, and take it to a local motorcycle shop. They'll likely have the NGK wire available for between $10 and $20. It even comes with a new NGK decal; that must be good for another 10% horsepower. :D

Well, that sputtering at wot sounds more to me like a fuel starvation issue, especially given the bigger jets and opened exhaust. What is your plug telling you? You want to pull the plug, clean it, then go somewhere where you can rapidly spool up to top speed, hold it while it sputters the sputter a bit then chop power, kill the motor, clutch in, pretty much all at the same time. Get to a stop and pull the plug. It will tell you what kind of mixture you've got where you're having the stutter. If its showing lean, you want to check for fuel restrictions. Drain the tank and check the little filters/mesh on top of the petcock. Crap can accumulate here and you never know it till WOT. Also, make sure the fuel line from petcock to engine isn't kinked somewhere. If you have an inline filter here's the deal. These things can slowly fill up and provide enough immediate fuel so that for a quick WOT the engine won't starve, but when you sustain WOT, it won't be filling as fast as its draining and once you get to that point, the starvation in the line will become apparent and you get sputtering so if you're going to use one, use a BIG one. Remember, there's only three things involved in an internal combustion engine. AIR, FUEL, and SPARK. Make sure you're getting plenty of each in the right amounts.
Last thing, make sure your float is operating correctly inside the carb. If it doesn't have the designed amount of free movement, It WON'T open up enough to supply enough fuel to your main jet to sustain WOT.
good luck. :)

Just to go against the flow of opinion here I note that too large a main jet can have this effect - you are not really on the main until the last 20% of throttle and if too big this is when a rich mixture can cut in - you try to rev out and it will stutter and cut out but come back on song as you drop the throttle.

I had similar symtpoms with the 125 jet that came with my pod filter - simply way too big a jet! (I asked for a 112 but hey..........)

I'd give a 110 a try just to see.

Frog

Agree. I didn't know this until a few days ago but, there's such a thing as a weak mixture stumble and a rich mixture stumble. I don't quite know how you tell the difference as the symptoms are similar.

Add me to the list also. The jump from a 102 to 115 likely was to much. Going up to a 120 did not help. Most people end up going up a size or 2 with those mods not 10 sizes. Maybe the 110 could be put in and given a try?

Just as a quick survey, who has experienced jetting problems and at what altitudes? I would think that they would be set up from factory at near sea level settings, however, that would usually translate to overrich, as opposed to too lean. OTOH, maybe factory is setting up super lean for the EPA specs and most need to be richened up. I'll be running between 1 and 2k elevation initially then down at sea level etc. so I'll be looking to invest in a range of jets but will have to wait to get the bike to know what carb to get the jets for...sigh...

jeez I wish the damned thing would just get here LOL.

seer

I keep seeing reports that the Japanese bikes are set up very lean from the factory to meet EPA standards. However, my Zongshen Sierra 200GY-2 came supplied with a nice, big main jet in the carburetor. Also, the pilot mixture screw is easily accessible, and it was turned wide open at the factory. In fact, I had to lean out the pilot mixture a little bit! :) I live and ride at elevations of 4,400 feet above sea level, and higher. I frequently ride above 8,000 feet of elevation, and I have not had any carburetor problems. :)

Spud :P

I am about 1100 feet. My jetting is almost spot on now, but it was very lean from the factory.


Trying a 110 may be just the ticket.

Elevation makes a big difference.

Allen

An excellent point, Allen. ;) I frequently forget that many members of these forums are lowlanders! ;) :lol:

Spud :)