What's the color of the spark plugs look like with it removed? If they are black, then your a/f ratio is rich. Another symptom of a rich mixture is being able to start the bike cold without the choke.

 

Are you running a standard set-up on your 93 L1 or has your emissions gear been removed?

 

Plugs look OK, ie NOT black or sooty. I'm in a warm-very warm climate down here so "cold" starting never gets much below 15-20 deg even in Winter.

 

I'm "down on the deck" with the original needles, with no washers and all standard jetsfitted. The only non standard part is the exhaust; Motad headers and Micron open race can.

 

If, by emissions systems, you are referring to the secondary air system, proper removal of rhe vacuum setup and blocking off the ports has absolutely zero effect on fueling or ignition. You must be leaving something undone for the engine to run so differently with or without the SAS.

All the secondary air system does, by way of a vacuum pot in the intake line and some reed valves in the head cover is to inject a fresh charge of air into the exhaust and dilute the hydrocarbons with oxygen and nitrogen, making the exhaust sample "cleaner". I've removed them from several Kawasaki 4-cylinder machines with no ill effects and better access to the top of the engine for maintenance.

 

Wrap your fuel lines with some form of heat insulation to keep the radiant engine heat from boiling the fuel in the fuel lines. Engine radiant heat temps are the highest for the first 5 minutes after engine shutdown. I believe your issue is vapor lock due to the spike in temperature around the engine for the first few minutes after shutting it off.

 

Thanks to all for the input here. Having since found a few more discussions on this subject on other period Ninjas I'm going down the road of 1/ checking fuel tank vent function, including breather pipe. 2/ thinking seriously on that idea of wrapping the fuel lines from the pump to carbs in some heat-shield material & 3/ Researching this Secondary air system more fully, to get my head around the part at least that vents the carb overflows. This is the part that I tried to eliminate without success. I think that I fully understand the other circuit that directs engine vapours from the cylinder head via reed-valves to the air-box, and I believe this circuit is completely separate from the fuel vapour circuit?
Back to the engine (not carbs) vapours circuit; If I was to remove this one, inserting blanking plates (that I have to hand) I'm wondering if something should be done about the engine breather from the top of the gearbox area (that goes to the airbox via an inversion shut-off valve), at the same time?

 

Thanks to all for the input here. Having since found a few more discussions on this subject on other period Ninjas I'm going down the road of 1/ checking fuel tank vent function, including breather pipe. 2/ thinking seriously on that idea of wrapping the fuel lines from the pump to carbs in some heat-shield material & 3/ Researching this Secondary air system more fully, to get my head around the part at least that vents the carb overflows. This is the part that I tried to eliminate without success. I think that I fully understand the other circuit that directs engine vapours from the cylinder head via reed-valves to the air-box, and I believe this circuit is completely separate from the fuel vapour circuit?
Back to the engine (not carbs) vapours circuit; If I was to remove this one, inserting blanking plates (that I have to hand) I'm wondering if something should be done about the engine breather from the top of the gearbox area (that goes to the airbox via an inversion shut-off valve), at the same time?

The crankcase breather (on top of the transmission) is vented to atmosphere on my L model.

@2fat2fly made a good suggestion to wrap the fuel line in heat shielding material.

Checking the fuel vent on the tank is also a good check. Sometimes the fuel door/cap ceases to vent when pressure builds and the vent sometimes gets clogged.

 

I've checked my fuel cap and tank overflow systems and they are both "clean". I've a spare fuel pump to hand that I tested to see if flow is possible when no current is applied. The pump does not allow flow in these conditions. So my hot starting, if caused by flooding due to heat build-up will probably need me to design a heat-shield to try and protect the fuel lines between pump and carbs. Watch this space!

 

Aluminium tape on the line is probably enough to do it. Heard of others using it and it working

 

HOT STARTING ISSUES; Time for an update.
After going through each and every carb check and swapping air-filters as I had an old K & N to hand. I next wrapped the fuel line in heat reflective tape (suggestion from 2fat2fly), but the Hot starting problem just persisted.
I was then however surprisingly helped-out by a competent local mechanic (These guys can be cagey about giving out trade secrets down here) and he in his wisdom said " Maybe your problem is NOT Carburetion related, have you checked the Pulser Unit, the problem could be electrical"? So I changed out the pulser unit for a used spare one that was to hand. As the problem only affected Hot starting, and not running, I thought it doubtful. But after fitting it I found that the problem has DISAPEARED!
I ran the bike a few times and took it out on a couple of runs and it behaved itself on every hot start that I tried; but I have now had to park the bike up for a couple of weeks whilst I await the arrival of a new cush-drive rubber, that has just started to show itself on every accelerating away from a cruise situation (upon jacking up the rear end it was found to be absolutely knackered, with about a 10 deg. sloppiness / slack on the rear wheel rotation).
So when the Cush drive arrives I'll change it plus also get the "standard" (Euro-Filter) air-filter put back in as my mechanic mate also tells me that these K&N filters are NOT a good idea on carburetted bikes down here.
So no surprises; once again my little diva seems to be very demanding, she's definitely still high maintenance (time/labour wise at least), and she insists on lots of attention, but I do still love her!

 

HOT STARTING ISSUES; Time for an update.
After going through each and every carb check and swapping air-filters as I had an old K & N to hand. I next wrapped the fuel line in heat reflective tape (suggestion from 2fat2fly), but the Hot starting problem just persisted.
I was then however surprisingly helped-out by a competent local mechanic (These guys can be cagey about giving out trade secrets down here) and he in his wisdom said " Maybe your problem is NOT Carburetion related, have you checked the Pulser Unit, the problem could be electrical"? So I changed out the pulser unit for a used spare one that was to hand. As the problem only affected Hot starting, and not running, I thought it doubtful. But after fitting it I found that the problem has DISAPEARED!
I ran the bike a few times and took it out on a couple of runs and it behaved itself on every hot start that I tried; but I have now had to park the bike up for a couple of weeks whilst I await the arrival of a new cush-drive rubber, that has just started to show itself on every accelerating away from a cruise situation (upon jacking up the rear end it was found to be absolutely knackered, with about a 10 deg. sloppiness / slack on the rear wheel rotation).
So when the Cush drive arrives I'll change it plus also get the "standard" (Euro-Filter) air-filter put back in as my mechanic mate also tells me that these K&N filters are NOT a good idea on carburetted bikes down here.
So no surprises; once again my little diva seems to be very demanding, she's definitely still high maintenance (time/labour wise at least), and she insists on lots of attention, but I do still love her!

When you say "pulsar unit", Are you referring to the ignition rotor or the ignition rotor pickup?

 

Sorry I'm literally translating here, directly from Portuguese. The item that I changed out was the Pick-up coil that stays static, mounted on the engine cases and situated level with and in front of the crankshaft.

 

Your translation is really good. I think this is the first time I asked for clarification. No need to apologize. I'm glad that you found the solution to your hot start problem and posted it. That's what counts.