kz750 chugging and stalling

A couple of weeks ago I thought my bike had been running a little lean so I decided to turn the adjustment screws all the way in to count where they were. After turning them out to where they were my bike started chugging and stalling any time it gets going over 5 mph.

This is the first time I have ever worked on a bike (or any engine for that matter) so if I say something that doesn't make any sense, don't be surprised.

Also, I got a vacuum gauge to check if the carbs were synced but I have no idea where to connect it. Does anyone know where the connection for that is on the kz750s?

juangonzo wrote:

...so I decided to turn the adjustment screws all the way in to count where they were. After turning them out to where they were my bike started chugging and stalling any time it gets going over 5 mph.

So what were they set at? They should be *around* 1.5 turns out, but mine are more like a little less than 2 turns out...

Also, I got a vacuum gauge to check if the carbs were synced but I have no idea where to connect it. Does anyone know where the connection for that is on the kz750s?

You see that little black hose that is connected *between* the two carb manifolds? You pull off that hose, and use the two brass nipples that are there. Oh, and make sure that hose is okay when you put it back.

Also, this is weird... you're the second guy on this forum to buy a 750 twin that lives nearby me... what's going on? Was there a sale running on 750 twins?

As a rule I always check ignition first especially if you have points ignition ,, Make sure your Spark is good before making any carb changes ,, Point condition , point gap , Ignition timing is more important than you might think ..

Shoe48 wrote:

As a rule I always check ignition first especially ...

Good advice.

My top three rules to new 750 twin owners:

1.) Investigate/dismantle/inspect your starter clutch to make sure it's not an engine lock-up waiting to happen
2.) Do the Coil-power mod
3.) Replace the coil. Just do it. Get a Dyna from z1Enterprises.com for $70, or something else, but just do it
4.)........ and so on...

Biquetoast wrote:

1.) Investigate/dismantle/inspect your starter clutch to make sure it's not an engine lock-up waiting to happen

What should I look for while doing that?

My screws were set to 2.5 turns out. I turned them in to 1.5 and the bike is idling a lot better but still chugging to the point where 5 mph is my top speed.

Before messing with my bike my spark plugs were bright white. Now, they are really sooty. I think the cold weather has killed my battery, I have been using the kick starter for the past month or so because my battery doesn't have the power to even run the headlight.

I am looking at the coil mod and it looks pretty easy, I'll definitely do this over the winter. However, my wife is starting a grad school program and money is pretty tight so I don't see myself replacing the coil.

I suggest you find a way to purchase a factory service manual and tune the bike; this usually involves, valve adjustment, cam chain tension, ignition timing. Also, since the bike is old, check the carb holders for integrity and air leaks. ONCE YOU HAVE THAT STUFF DONE tune the carburetors. Attempting to resolve performance or economy issues by carburetor adjustment without going through the necessary steps is more or less a waste of time.

I have the service manual. Until I started messing with the adjustment screws the bike was running pretty good. The only times it ran rough were cold mornings. I was hoping to get the bike back to the state it was in so I could get a final ride or two in.

The bike was tuned up and checked over professionally about 2,000 miles ago and has 15,000 miles on it total. I will look into doing the full tune. Thanks for the help so far.

I always start by fixing what I know is broken first, before moving on to items that may be ok. I suggest if you believe the battery to be bad you should start by replacing it with a fully charged battery. It's possible that your electrical system simply isn't up to the task of charging a bad battery while supplying ample spark at the plugs. If that doesn't help, or if the bike runs ok but the battery discharges, I would then check the charging rate to be sure the electrical system is operating properly. Turning those screws 1.5 or 2.5 turns out shouldn't prevent the bike from going more than 5 mph. Ed