1982 Gpz1100 won't start when warm

i have an 83 that had the same problem you need too junk the fi and put carbs on there and the spark is on its own it will always spark the fi wont work right the air sensor will tell the bike its over heated and wont start

i have an 83 that had the same problem you need too junk the fi and put carbs on there and the spark is on its own it will always spark the fi wont work right the air sensor will tell the bike its over heated and wont start

The EFI has always worked very well. This problem started after the top-end rebuild. I'm going to insure that the timing advance is working and lubricated properly (I've never done that and my research says that this could be the culprit) and if necessary, recheck the valve clearance. I also removed the headlight fuse & tried to start it, but that didn't work either. But it ALWAYS starts cold and with a push-start whwn it's warm. It is definitely heat related. I may also try 'icing the coils' (Bag 'o' ice to cool them off) to see if that's the problem, but I'd be surprised if that's it as the spark is fine when warm.

Are you running stock ignition or a Dyna S type unit?

In the past, I have had ignition's fail when hot. Not the coil but the Ignition itself. When the unit get's hot, it shuts down (mainly happened with old Dyna S units). Let it cool down and it would fire right off. I replaced the ignition and problem solved.

If you are running a self contained electronic ignition, this might be the problem. The internal circuitry gets a lot of heat and, over time, can break down. Notorious problem on HD nose cone igtion pickups.

I considered that and I do have a spare. I'm everything ignition-wise is stock except for the coil-mod. But if you're talking about the control unit in the tail, that doesn't get hot so I 'ruled it out', but it would be easy to try my spare one. I already replaced the IC igniter with my spare, but that made no difference.

Post edited by: howard95132, at: 2007/10/04 15:13

Interesting development, although not to be confused with I’ve resolved this problem as I haven’t tested it yet. But in my research, I’ve found that supposedly if you don’t do ‘proper maintenance’ on the timing advancer, which involves removing it, taking it apart, lubricating it, and reinstalling it, it can stick and cause pinging, overheating and hard warm starting. Since this is quite easy to do, and the fact that I’ve never done it in 25 years and this bike has essentially all but sat for the last 7 years as I purchased a ‘more modern’ bike Back in 2000, I decided to invest a little time and do this. It was certainly ‘bone dry’. Of course afterwards it started right up as it always does when cold, but has anyone experienced pinging and hard warm starting due to the timing advancer being ‘dry’ and therefore sticking? I’d somehow be surprised if this is it, and I won’t know for about a week or so, but I am curious if anyone has seen this. I was going to recheck my valve clearances, but I think I’ll give this a chance to work before I do..

Post edited by: howard95132, at: 2007/10/04 22:41

Well, keep your fingers crossed. Once again I have high hopes of eradicating my warm starting gremlin. All of the changes thus far have certainly improved the way the bike performs, and currently, I’ve been able to warm start 6 out of the last 8 times. But it’s still a pain having to ask someone to push-start me when it won’t start. So since I’ve all but exhausted everything I could think of, I had to revisit the valves. Sure enough, after just 700 miles of the rebuild and valve job, the #1 intake and #4 exhaust valves were a bit on the tight side, i.e. < 0.05mm and the #2 exhaust valve was on the loose side, i.e. > 0.15mm. 3 of 8 valves out, which is almost half. Also, I was unable to re-torque the inner-most head bolts after I put the valve cover on because my socket wouldn’t fit through the valve cover holes, so since it’s off again I re-checked and sure enough, the head was under-torqued. Also, some of the cam cap bolts loosened up a little as well. Unfortunately, I won’t be able to be certain until later in the week as the bike shop is closed on Monday and it’s supposed to rain on Wednesday, but I’m cautiously optimistic that this warm-start gremlin may be on his way out of town..

Post edited by: howard95132, at: 2007/10/08 02:14

So far, so good. Got the bike put together last night. It fired right up twice in a row. I then rode it to work 13 miles today and restarted it after I arrived. No problems so far. It certainly runs smoother with the valve clearances in spec and the head is torqued down properly. I put the stock B8ES plugs back in and while my ‘pinging’ is certainly reduced, I think I may still have to go back to the colder B9ES plugs to completely eliminate it. I also noticed that if I ‘punch it’ at HW speeds, it seems to rev up a bit (RPM’s) faster than before. I did recondition my clutch plates and install stiffer springs when I did the rebuild so I’d be surprised if the clutch was slipping. Could this be because I lubricated the timing advancer and it’s now advancing properly? Anyway, I'll know in a day or three if my warm starting gremlin has been eradicated, but I sure think it has, as I’m running out of ideas if it hasn’t. The engine sure is ‘purring nicely’, though..

On a mechanical advance, the arms sling out from centrifical (not sure how to spell it...) force because the crank spins faster. This force rotates the advance mechanism to advance the timing curve... I believe that would be to fire the plugs a little earlier than at idle. If the advance mechanism didn't work, I would think that performance would be degraded at higher rpms and that starting wouldn't be affected as there is no advance dialed in by the mechanical advance unit. The only exception would be that the advance was stuck in its advanced position and that would hurt starting as the spark would be too early for low rpms... I am not a big theory guy but that is how it seems it would work. It is good that you cleaned the thing because rust tends to set up under the thing... or at least on many of the bikes I have worked on... I suggest you get a timing light and check the function of the advance... with an inductive timing light, you clip the lead onto the #4 plug and shoot the light at the advance with the bike idling. There are marks on your advance for 1/4 I think... At idle, the F mark and the mark on the case should align and if you rev the engine, you should see the advance rotate clockwise (if memory serves) but you can see it advance...

To be honest, I am thinking you may not have fixed the problem. I think that the guy who told you to look at your FI set up may have been on the right track. If I owned the bike and it was a daily rider, I might consider a new ignition, like a Dyna S to eliminate any possibility of the IC Igniter being the culprit but a Factory Service Manual has some checks for those things. I have not had good luck with old factory ignitions and have pretty much given up on them and just install a Dyna S. After that, the FI would be the next thing I looked at.

Thanks. I'll see after lunch today as if I go for a short ride, stop & then restart, that's when the problem occurs. I have two IC igniters and there is no difference with either one. As for EFI, I have had no issues with mine in 23 years and this problem started after the rebuild. We'll see how it goes as I'm off to lunch now....

Post edited by: howard95132, at: 2007/10/11 18:17

I’m all but ready to call this fixed. Four warm starts; no problems. It now starts ‘right up’ as it always did. While I appreciate everyone’s comments, I personally feel that suspecting the EFI is incorrect. I’ve had this bike 23 years (got it new in '84) and there pretty much isn’t a place on it I haven’t torn apart at one point or another. It’s my understanding that in 1981 when they first put EFI on the Kz1100 motor, there were some problems, but that was fixed in 1982. This bike has never had a warm start problem until now and ‘now’ is after a big-bore kit and a valve job. Now that the head is torqued properly and all eight valves are in the middle of the spec., it appears to be ‘Happy as a little girl’. I’ll be certain when I’ve had a week or so with no starting problems, but it sure feels fixed to me.

Post edited by: howard95132, at: 2007/10/11 18:16