Gpz900 stutter at 6k and lack of high end power

Where are we on this thing ?

You don't need bail money do ya?

Haven't had to much experience with whistling tanks myself so I be using logic instead of experience and that's a last resort.

pcbisnice wrote: this stumbling at high RPM's really made me think there was a lean condition and it was lacking fuel. However my spark plugs tell a completely different story as they are saturated and very dark to almost black. My bad tank whistles when I come to Stop also. Maybe not venting enough? I guess it has to be with the spark plugs looking as they do.

I apologize if I missed something relevant to this thread, but perhaps the bike is running fat at the lower revs, then the carbs start to run low on fuel when the revs are amped up? Your tank should not be whistling dixie. Take the cap apart and make sure it's all clean.

OR, possibly broken or weak valve springs? OR ignition intermittent?

I have had personal experience with a Mallory dual point distributor (a hot ticket item back then) that was in my 68 GTO. (Also had the holley double pumper and Edelbrock high rise manifold)) I owned this while taking college auto mechanics. It would start breaking up over 3K rpms. sputtering and popping and running like crap. I actually think this was the reason I was sold the car in the first place, because the PO couldn't figure out why it wouldn't couldn't rev. I checked EVERYTHING, carbs, valve springs, etc.. Well, the school had a Sun distributor machine sitting in the corner covered with dust. One day, out of curiosity, I pulled the distributor out and stuck it in the machine and spun it up. there was a sort of strobe that lit on a degree wheel when the sparks fired. (I also cleaned up the machine) You could clearly see the sparks popping and breaking up all over the place the higher I reved it up. I stuck a STOCK points distributor in that ground pounding 400, and it instantly straightened up and flew right. This was a really FAST old 68 goat, that a few with a old vette's or hot rod nova quickly found out. It pulled like a freight train after that. Much like my bike. Sorry to get so long winded, just thinking about some things that will stop an engine from reving.



This is also why I am somewhat skeptical as to what actually works, and what is a big ole waste of money. IMHO, most "upgrades" are actually just the opposite.

I tend to discount no possibility when troubleshooting and instead concoct in my mind a flow chart whilst keeping in mind I might not be looking at "a" problem but rather a few problems that add up to a poor running machine. Once you have determined that the basics are within spec, then go down the list; you've got good spark and the timing is right, the advance is advancing. plug gap is right, yada yada. Then go through the fuel system. Gas cock filters are clear, fuel flows freely, float levels to spec and clear of debri.

Relegate the process to procedure not guesswork.

Just today my bike was spitting and popping, I almost turned around but I was halfway to where I needed to be so I tanked up and the problem has gone away. Water? Dirt that got sucked through the system? May never know but it still bears looking into.

Of course you have to suspect a clogged vent if your tank is whistling whether it's caused by a vacuum or a pressure buildup. Address that and then take it off the list.

If the bike used to run fine but all of a sudden that has changed that's important info especially if nothing has changed. Even something as simple a clogged air filter might get overlooked by looking for a bigger problem and could explain this situation to a T.

sorry for the long delay I have basically given up on this bike. I did a plug chop and it showed a slightly rich condition but no matter the Jets that I put in it is still has the same problem. I'm convinced now that it is not a carb issue and maybe something in the electrical system is messed up. If I do any more testing before I get rid of it I might try to swap out a set of coils from my friends gpz750. But at this time I am tired of wrenching and I just want to ride.