GSX starting issue

After taking my SV off the road I have an old bike that I am trying to keep running... It has a problem I'm hoping you guys can help me with...

The bike is a '93 GSX600F

When it is cold if it starts straight off it is fine but if it fails to catch, it then enters a period of not be able to start at all.

The engine turns over and an occasional cough, but no firing up.
On inspection the plugs are not fouled or wet. The carbs have been cleaned the coils have been checked. There is good compression, good spark, the plugs are new. The fuel has been changed there is good flow. When running it runs well and is firing on all four. The battery has full charge. Jumping on a car battery has no effect. The only solution is to leave the bike for an extended period of time over night or part/half day. i.e. it did not start on Thursday night after being recovered and left in the garage overnight started first time Friday morning It has a cyclone C11 alarm installed not by us which seems to work perfectly. We have just tried disconnecting the automatic start but that has mde no difference.

Any ideas please...

cold start sensor ??

don't believe there is one... certainly don't have a clue where it is and can't find one in the manuals...

[yorkie_chris]

You tried new plugs, those motors can be fussy?

There is no fancy sensor... they are just bandit engine with 1mm larger carbs..

It has new plugs (done about 250 miles)

I know it's not them )

Oh and Yorkie_Chris I'm just in Brighouse... some beer in it for you if you wanna come solve the problem first hand! ;o)

My Cub 90 and my old 125 spent plenty of time sat sitting, and would take a bit of time to start properly. Often leaving for 5 mins or so would "fix them" if they started and died. Don't forget if left sat around oil all drains south, fuel can get stale, also if the engine doesn't "catch" the fuel drawn into the cylinder condenses, which IIRC can cause trouble starting. Try turning the engine over a few times with the carbs drained and the fuel tap turned off. Then turn the tap to PRIME for 10-20 secs or so, and try starting again. Make sure the tap goes back to ON after.

New plugs are a good plan, they always work better than year old ones, even if properly gapped.

My plan: Get some fuel system cleaner, a tank full of new petrol, change the oil (and filter if you can be arsed), clean the air filter. New plugs, or at least clean and gap old ones, and a day to spare. Once started, ride the bike; first gently, progressing to a good workout using all the revs. Continue until the petrol is (nearly!) gone, re-fill, dosing with fuel system cleaner (work out correct dose for your tank size, use a Calpol spoon to measure). Use a good bit of this petrol, ride at least 20 miles daily for a week, keep using fuel system cleaner for a few tankfuls. After this, use the bike regularly. My guess is your problem is caused by the bike not being run enough, the exact cause - ??? You have gone through the usual checks, it might be a combination of small issues. Regular running will get rid of your poor starting, I bet.

This post is not BASAT approved. I have used these techniques, whether they ACTUALLY work, or I just think they do, I cannot prove.