81 KZ305 hard starting

The colder it gets, the harder it is to start. In warm weather a cold start only takes a couple turns of the engine. Now that the days are colder (mid 40s hear in Virginia), it takes alot of cranking. To the point I fear wearing out the starter or draining the battery. 
So far I have opened the mixture screws another turn and retarded the timing a couple degrees below spec., but it still takes alot of cranking. The bike starts and runs fine when the engine is warm.
Is there something I can do to the choke or choke plates to increase choking? Or am I barking up the wrong tree?

Try connecting a voltmeter red lead to battery positive black lead to coil positive feed, now crank when cold. You are looking for a reading no higher than 0.5v ( you are measuring the difference between the battery voltage and what gets to the coil)

This may be a dumb question, but have you verified that the chokes are actually choking?

A worn and/or bent linkage may prevent the butterflies from closing properly.

I agree with Nerdy. Is the choke/enrichment circuit functioning properly? I don't know what carb is on the 305 but the Mikuni's are susceptible to poor starting due to the fuel bowl not allowing fuel into the well for the enrichment circuit. 

They are Keihin carburetors. I don't know model or size. There is no enricher. Threre is a lever that closes the choke plates.
To eliminate voltage drop, I ran a jumper wire from battery + to coil +. Also jumpered from a car battery. It still would not start with a reasonable amount of cranking.
I will look into choke opperation some more. Maybe not compleatly closing or the hinged door on the plates are not working correct.

Ebay pic of a kz305 choke plate.

A couple of suggestions.

if the bike has not run in a while make sure the float bowl(s) are well primed and have the required level of gas in them.

spray some starter fluid  - Quick Start - Easy Start in the air box. If it fires but wont run then probably a fuel issue. Dont over do it with the starter fluid.

I'm getting somewhere. Two cold mornings in a row now, the bike started easily by blocking the air box intake with a piece of cardboard.
The choke plates are fully closing, but I'm wondering if the springs on the hinged flaps on the choke plates have gotten weak and are opening to easily. Partzilla does not break the carbs down far enough to just get the hinge springs. What is the purpose of those flaps and what may it hurt if I seal them shut?

wrote:

I'm getting somewhere. Two cold mornings in a row now, the bike started easily by blocking the air box intake with a piece of cardboard.
The choke plates are fully closing, but I'm wondering if the springs on the hinged flaps on the choke plates have gotten weak and are opening to easily. Partzilla does not break the carbs down far enough to just get the hinge springs. What is the purpose of those flaps and what may it hurt if I seal them shut?

Sealing them shut will probably cause it to stall out, with the flaps closed some air still needs to get in to feed the motor. If they where sealed you would likely need to start backing off the choke too soon to allow the motor to run

How many turns open are the pilot screws?

Right now the pilot screws are open 11/2 turns, but have tried every where between 1/2 and 4.
One thing I neglected to metion, I shimmed the needles up .010" to solve a dead spot on accelerating off idle, 3 years ago when I first got the bike. I haven't been in the carbs since.
The bike has been hard to start when cold ever since I had it, but this year it seems worse. 

wrote:

I'm getting somewhere. Two cold mornings in a row now, the bike started easily by blocking the air box intake with a piece of cardboard.
The choke plates are fully closing, but I'm wondering if the springs on the hinged flaps on the choke plates have gotten weak and are opening to easily. Partzilla does not break the carbs down far enough to just get the hinge springs. What is the purpose of those flaps and what may it hurt if I seal them shut?
 

If a new spring isn't available, I wonder if adding a small amount of weight to the flap would help. The additional mass would keep it shut a bit more - using gravity rather than spring power - while still letting some air in (which is necessary, as Wookie58 indicated). You might be able to tape a washer to the flap to start; it shouldn't take much weight to change the operation.

wrote:

Right now the pilot screws are open 11/2 turns, but have tried every where between 1/2 and 4.
One thing I neglected to metion, I shimmed the needles up .010" to solve a dead spot on accelerating off idle, 3 years ago when I first got the bike. I haven't been in the carbs since.
The bike has been hard to start when cold ever since I had it, but this year it seems worse. 

I'd open the pilots to 2.5 turns open.  1.5 is kinda lean.