Hot start issue

Hi all

I’ve got a starting issue with my 1980 KZ1300A2 resto project. I’ve got the engine running after a full rebuild (still needs fettling) but I have come across an issue when the engine is hot. On cold start the starter turns over like a good’un but when the engine is at full temp, the starter only just turns but just enough to kick the engine into life. It’s almost like the battery is flat but when I metered it it was fine. I’m wondering if it could be an issue with one of the battery leads or starter motor as I did not replace them?

When the engine cools down again it’s fine. Could so it looks to me to be a heat issue but has anyone had this issue?

Any ideas?

Thanks in advance and apologies if this is on a thread somewhere else.

Howard

Hi i had this kind if a problem before, where cold engine start was not a problem but when hot the starter could barely turn the engine over. Have you rebuild the starter it self already? Also I have seen on my bike the ground cable being rotten inside, and contact area to the engine is very small. Also there is the starter relay which could be bad, if you measure voltage across that, the problem could be there.

However you should first measure the voltage drop across the poles of the battery with good multi meter (be careful because if sampling rate of the instrument in slow it will not show you proper results as it averages the value only, that's very important). You kawa's battery must be able to output at least 230-240 ampere of current, and it is written somewhere on it and if its less than that could be the issue. 200 amp is not enough and it was the issue i had.

Now to the pictures



Rep manual where you see the Y50N number



Thats the weak battery from Varta despeit the Y50N number being the same as in the manual it can only output 200A



And now the 240 Amp Yusa battery.


All in all start with simple stuff first in my opinion its the battery but measure again like i said.

Daro

I had exactly the same problem with my 79 A1 - starter motor would crank the engine adequately when cold but would barely turn the engine over when hot. I replaced the battery to a high power Westco Platinum which helped a little but did not solve the problem. I overhauled the starter motor, including trying to measure the winding resistance but this is very difficult without the right very low resistance measuring equipment. (I tried making my own simplistic Wheatstone bridge but without much success). The overhaul again did not make any significant improvement. I then borrowed a current clamp and discovered that the starter motor was drawing about twice as much current as it was supposed to - indicating a short in the windings somewhere. I was fortunate in being able to "borrow" a starter motor from a Z1 (uses same starter motor) which solved the hot start problem immediately. My theory as to why this only affected hot start and not cold start was either 1) the short only occurred when the starter motor was hot or 2) the higher resistance in the windings when hot reduced the current flow through the motor and with a limited number of winding "turns" producing a reduced magnet field which led to poor starter torque. My understanding is that the Z1300 starter motor is marginal for an engine of this size - confirmed by the same motor being used on the Z1.
Second hand Z1300/Z1 starter motors are like hens teeth so I ended up having to buy a very expensive re-conditioned unit from the US. However, no more hot start problems.

No guarantee that this also your diagnosis but it sounds mighty similar to me..

Another timely thread for me as I have a similar issue.
The lead acid battery of 1980 with its 20 amp capacity was only just good enough when the bike was new and everything working properly - give them a few years -carb problems start to show up and is it any wonder so many of these bikes were pushed into a corner and forgotten.
Many owners , like myself, purchased the Odyssey 680 with it's 170 cca. A huge step forward from the original. We were all quite happy for a while, having overcome one of the bikes weaknesses.
But once I installed the big bore kit ,a somewhat similar problem showed up as mentioned by you other 3 guys. Hot engine, stop to fill up with gasoline , attempted a restart and the engine appeared to be "locked". No clicking of starter solenoid, battery at 13.5 volts, but push the starter button and nothing. I have re-wired the whole bike, installed a larger starter solenoid, swapped out several starter motors but nothing has changed.
Several early model Goldwing owners have told me of similar problems -essentially the motor stopping just in the wrong position when stopping for fuel for instance, And then the electrical system not having enough oomph to turn the engine over. I don't know whether that is correct or not, but in my case, I would pull the clutch in, make sure the gearbox was in neutral, and after several more pushes of the starter button the engine would start - but the peculiar thing with that is , the engine wouldn't even turn half a revolution before it would fire.
Solutions : Most people would be using a modern battery with huge power output over the original. I have a 270 cca lithion -ion battery on my MV Agusta but that didn't help the Kawasaki .
Peculiar to me again, put the gearbox into 2nd or 3rd gear and rock the engine past the "locking point" - haven't had to do this yet.
As Neville mentioned - the starter motor , like the oem batteries is not really upto the job.
Several years ago , new starter motors became available - they were around $100. Then nearly 300 and now...……


canadianautopart.com/new-mitsuba-starter...yvgGfEAQYASABEgLLl_D

This is a vey good price. Amazon has them for nearly $300

Replace the battery ground wire. Only old piece of wire on the entire bike.

I had an identical problem and it turned out to be the rectifier was on the way out, changed it and no issues since

The starter motor on the Z1300 is a Mitsuba SM 220 0.8kw. It is used on a number of Japanese bikes. You may have to turn the outer casing round to get the live terminal in the right place but otherwise they are all the same. The Honda cb 750 twin cam 1979-1982 for instance uses the same starter motor. Lots of them available on the bay of fleas.