Bike Stalling Out Easily - 1980 KZ750 LTD

Hey all,

I was directed to this site from the owner of the 1980 KZ 750 LTD that I just purchased. I'm new and read through some policies but I apologies for breaking any rules or missing a thread that speaks to my question already. If you know of one feel free to share a link and I'll defer to that.

So my bike, on and off, has trouble in first gear. Some days it's ok, buy others it just completely stalls out even after 40 minutes of riding. I have to keep revving the engine to keep it idle. I also will have to rev it to just get it started. And almost always it is impossible to roll into first. I usually have to gun it, so i'm thinking that has something to do with the clutch. Any insights I would appreciate. This is also my first bike, so I may not be in the know how with any technical lingo, so please ELI5.

I have been looking for a good mechanic to work on my bike, but the two I've called have turned me down because it's too old and they don't want to take the risk of fixing one thing and breaking another. I live by Paramus NJ, so if anyone knows of any mechanics in that area who work on older bikes, I'd appreciate the reference.

Thank you a ton in advance.

If it won't idle without touching the throttle, the pilot circuits may be clogged & the carburetors need to be cleaned. You could remove the carbs from the bike, remove the float bowls, then do a cursory cleaning without disassembling the carbs much.
PS: owning a vintage motorcycles means you kinda have to learn to do a lot of this yourself.

Manual. 750turbo.com --- Index .
1980-84 KZ750-4. 1983-85 ZX750. pdf manual. good scans.

Wiring diagrams. mbsween. bike-night. KZ750L3 . Scroll down & click "The Bible" link.
Note: some of the wiring diagrams are mislabeled in the links: the 1981 Ltd is an H2, the 82 is an H3, & the 83 is an H4.[/quote]

Hey! thanks for getting back so fast.

That's where my head was at too. I started watching a few YouTube videos on carb cleaning, trying to get myself familiar with it. I ordered some Sea Foam and hoping that will clear some gunk out as well.

Get yourself a copy of the factory service manual and start doing maintenance. Cleaning the carbs is a good place to start but there are many other tasks as well.

Realize that your carbs are full of 35 year old rubber O-rings so the proper fix involves updating those. This complicates the cleaning matter but is the right thing to do if you want your bike to run reliably.

Another bit of critical maintenance is valve adjustment. Failing to adjust the valves as required will cause engine damage so consider this your warning.

There are dozens of different maintenance tasks so you may want to learn to do some work yourself. Paying someone every time the bike needs some work will put you in the poor house.

Thanks, warning acknowledged.

Battery & charging system. The bike needs a good, fully charged battery to run right, so make certain the battery is good. new or fairly new doesn't necessarily mean it's good --- test it. the bike will run poorly with a weak battery.
also, there are simple charging system checks outlined in the manual.

I got a Scorpion AGM from batterystuff.com last August. it seems like a good battery.
also, I use a Ctek US 0.8 smart charger & VC97 digital multimeter. after charging, the battery should be 12.6+ VDC.

A simple load test (engine off): charge the battery. it should be at least 12.6 VDC, but a good battery will be higher. turn on the headlight high beam by turning the ignition switch to ON but don't start the bike (assuming the headlight comes on when the key is ON). the voltage will drop. a good battery will drop to around 12.2 VDC. If it drops to less than 12 volts, the battery may need replacing. If it drops below 11 volts, the battery is probably shot.

Easy and cheap thing to do, while at idle from start up, is spray water on the exhaust pipes and make sure all 4 sizzle. I'm guessing, from your description, that not all 4 cylinders are running at or just above idle. Lots of new bike owners do not recognize how a motorcycle sounds running on all 4. Also just revving it from idle will seem sluggish to an experienced rider but not to a new guy.

Your carbs are most likely in need of a good cleaning especially the idle jets/circuits. But my water trick will tell that not all 4 or firing or they are. If the bike sat idle for a year prior to your buying it, almost assuredly the carbs are clogged and need cleaning.

Ignition system. The problem could be as simple as poor spark plug wire connections as they become oxidized over time. either clean up the connections or get new spark plug wires & caps. I would check the spark plugs as well. Or it could be the ignition coils. sometimes they test fine cold, but when they get hot from riding the bike, they short out internally. if cracked, replace them. a simple test is to ride the bike at highway speed, then stop & feel the coils -- press hard with your fingers. they should be warm, not hot. don't get burned by the valve cover --- practice feeling them when the engine is cold. My bike started running poorly at high speed, then would quit. one time it was the coils which were getting very hot. some time before that it was the battery as the electrolyte had gotten low. doh.

Replacing the spark plug wires n stuff is part of the routine maintenance/tuneup. as is lubricating the timing advancer.

And valve adjustment.Sometimes overlooked or ignored. :whistle:
Steve

On the whole 'learning to be your own mechanic' end of things, I would encourage picking up a compression tester. Relatively inexpensive, but occasionally (annually works depending on how much you ride) testing each cylinder and writing down the values in your service manual will help you spot trouble coming. Also, make sure the bike is warmed up, all plugs out, battery fully charged and that you hold the throttle wide open when testing compression.
There are various rubber parts that can impact your fuel system. Depending on how well (and recently) the bike was maintained (and your willingness to drop a little cash on parts 'just to be sure'), it may not be a bad idea to pick up a petcock rebuild kit, carb boots, carb diaphragms (these maybe only if you spot tears in your current ones, or they've obviously swelled up due to ethanol exposure) and as Nessism suggested o-rings. You can pick up a carb rebuild kit to go through the carbs (FYI some people discourage replacing the needle valve with ones out of a kit if you don't have fuel level problems), I have a metric o-ring assortment from Harbor Freight, it is relatively inexpensive and can replace most of the o-rings on the bike.
Martin_csr suggested replacing plug wires. I do agree with that, In the short run, to see if it helps, you can cut about 1/4 inch off of each end of your existing wires and then reconnect (this is not a substitute for replacing the wires, but something you can do in an afternoon in the shop without running to the store and it can help improve spark if your wires are wearing out).

Hey Ya'll!

So i got the bike fixed and it was spark plugs.

WE HAVE A WINNER! It was spark plugs.