Trouble starting my KZ750 when cold

Hi, it takes me about 5-10 minutes of playing with the starter and throttle to get my bike started if I haven't ridden earlier that day. That is in 50-70 degree weather with the choke on. I figure its a fuel delivery issue. What can I make it do to start up a little easier? The bike is a 1980 KZ750 LTD with Keihin CV34 carbs. Thanks

Don't touch the throttle when starting the bike. Doing that is counterproductive to the enrichment process. Does your bike have the stock air box & filter? Ed

Don't touch the throttle when starting the bike. Doing that is counterproductive to the enrichment process. Does your bike have the stock air box & filter? Ed

I know that's true on the KZ1000's and others that use that style carb. But The Keihin CV carbs use a true choke, not the enrichener circuit, so opening the throttle shouldn't counteract the choke. Normally with a true choke you want choke at full, and throttle open when starting. Don't see why it would be any different here.

It does have the stock airbox, but it has a k&n aftermarket air filter.

The idle is right around 1000-1500 RPMs, so I don't want to adjust that. If it is having that much trouble starting it's probably running lean right?

Lean with the choke on is pretty hard to do with those carbs. One possibility is that your choke circuit is clogged up. Does a shot (quick shot, not soaked in like you would a car) of starting fluid into the air box make any difference?

Have you checked the tops of your carbs for leaks in the membranes on the throat slider?

Check the plugs for burn color. Tan is good, white is lean, black is rich, oily is oil.

There are lots of things that all need to be right for your bike to start when cold. If everything works once the bike is warmed up and you're happy with the performance and response of the bike, chances are that the specific enrichment/choke circuit is where your problem is.

On the other hand, I've heard horror stories about bad rectifiers, resistor plugs with resistor caps, bad ECUs, and a dozen other 'non carb' issues causing similar problems. Make sure your battery is in good shape, that you're getting good spark, and everything else that needs to be working before you get boresighted on the carbs. Taking 10 minutes to check the rest of this stuff might end up saving you hours working on something that's already working.

This, by the way, is the voice of experience nattering away. I wasted three weeks trying to adjust a set of carbs on a bike with a leaky vacuum membrane in the fuel petcock.

The charging system is good, and I just replaced the plugs. I got zapped pretty good checking the spark, so it's getting good spark. The bike runs great once its started, its just tricky to start with the starter. When I bump start it, it fires up no problems. Could it be the starter? It sounds strong, and works great when the bike is warmed up.

You're not supposed to get shocked if you're holding the spark plug boot. You may need plug wires.

Mine was hard to staret when cold too. It would run like cr*p for the first mile or so and would die unless I kept juicing the throttle. The problem went away when I adjusted the valves. Just an idea...
Good luck,
Jim

If your bike starts fine cold on a bump start or kick start, then your battery/charging system/starter isn't up to snuff. I would believe that the starter is causing enough of a drop in voltage to the coils that the spark is not strong enough to ignite.
How old are your coils/wires?
Have you checked the voltage to your coils?

What kind of oil is it using?

I'm actually about to do an oil change. I was gonna use 10W-40. Also, the charging system seems fine, I've checked the voltages going across the battery when the engine is being revved and its around 14V. The starter also works immediately whenever the bike has been warmed up.