1982 Gpz1100 won't start when warm

I have a problem where my 1982 Gpz1100 won’t start when the engine is warm. I just rebuilt the top-end with a big bore kit and a valve job. The bike runs great, doesn’t smoke or eat oil anymore and the stator is new and the charging system and starter motor work fine. It always starts when cold and if it won’t start when warm, it always starts with a ‘push start’. I’ve replaced the temperature sensor with one from a parts bike and checked the cold resistance (about 2K) and checked the voltage output of the control module. I did the famous ‘coil mod’, checked the resistance of the coils (3 ohms) and replaced the plug wires. I’ve also replaced the main fuse holder and will be installing a new fuse block this weekend. The one thing I’m a little concerned about is that when I set the valves after the valve job, I didn’t loosen the cam chain before I installed the cams. But it still always starts either when cold or with a push start! This is very perplexing and I know this bike inside & out! Anyone have an idea I haven’t tried yet?

how big of a big bore kit did you go and how much compression? , my 1170 shit the starter clutch out already at 1500miles and turns over slow when warm.

put your bikes and performance mods in your siggy so we can help you out more easier.

if its too big and your starter cant turn it over you could try a honda cb1000 starter, 80's i think, you just have to clearance the sprocket cover for the positive post.

Post edited by: themachine, at: 2007/09/28 14:15

Post edited by: themachine, at: 2007/09/28 14:18

I went with MTC 74mm pistons to 1136cc's. I expected better compression as it's in the 120's, but the bike cranks over just fine and the spark is good. It just won't start when it's warm. I didn't have this problem before I rebuilt the engine. I also just put a new connector on the temperature sensor thinking that might help.

does the starter not crank it when warm, or is it just wont run when warm.

have you tried adjusting the valves.

No, it just won't start when warm. It 'tries' to start just fine. It acts like there is no spark, but the spark is fine. The valves were set 600 miles ago, but when I installed the cams after the valve job I didn't loosen the cam chain tensioner. If the valves were tight, my information is that that could be causing this, but they were 'spot on' when I set them.

Well, I think I may have resolved this problem although I’m not completely sure what the root cause was as I made several changes. The famous ‘coil mod’ certainly helped as afterwards, the bike ran noticeably smoother and I inspected the spark (plug) and it looked stronger. I also replaced the female connector on the temperature sensor as the connection looked a bit ragged. Another modification I did was to replace the fuse-block completely with an aftermarket block where I soldered the wires from the white power connector (from the original fuse-block) directly to the new fuse-block lugs as opposed to using slip-on (spade) connectors. I had previously replaced the main 30 amp fuse with an in-line fuse holder as that connection went south many years ago, but this new fuse-block now replaces the in-line fuse holder as well. I also replaced my stator with an updated (better output) version than the stock version as the stock stator was shorted, and I replaced my plug wires. So far, I’ve been able to start the bike on two separate occasions after it was ridden first for about 20 minutes. Hopefully with these electrical modifications, my warm starting problem is resolved. I suspect that the coil mod, the temperature sensor connector and the new fuse-block combined, essentially replaced my old electrical connections which with any luck, resolved my warm starting problem.

Your compression will come up as the rings seat. One thing that has me curious... 3 ohm coils on an 82? Hmmm... do you have inline ballast resistors? On an older bike; say a 79/80, this ballast resistor was mounted to either the battery box or between the front fork down tubes near the horn. The resistor looks like a 4 inch long white bar of insulating material and has some wires and stuff on it. Power goes through it and it raises resistance... generally the coils on the bikes with these ballast resistors is either 1.5 Ohms or 2.5 Ohms. If you have aftermarket 3 Ohm coils and the resistors are in place, the overall resistance (ballast resistor plus coil) will be very high and your spark won't be as good as it should be even with full power. PS: I know the guy who wrote that famous coil repowering tip bhwhahaa

Thought I had this licked… But Nooooooo! I needed a push start after lunch today. The coils are stock and I replaced mine with a pair of stock coils from my parts shed (I had a ‘parts bike’ I took a bunch of parts off of. Comes in real handy!) And I measured the resistance of the coils at the coils. They are 3 ohms as the manual states they should be. No ballast resistor that I’m aware of and none in the coil mod configuration. So I’m down to three options I can think of. Even though I checked & rechecked my valve clearances after the rebuild & valve job (all between 0.05-0.15mm), I didn’t loosen the cam chain when I put the cams on. Also, ‘could be’ that the valves ‘seated’ after the 1st 500 miles (700 on it since the rebuild now) and I now have a tight valve or two. That’s the first thing I think I need to recheck. Second, when I installed the injectors, they were a ‘real bitch’ to put on. I attributed this to both the injectors (boots) amd myself being older then when I last did that. Maybe I now have an air leak of sorts that gets exasperated at temperature. Thirdly, maybe, just maybe the coils are ‘acting up’ at temperature and Dyna coils will resolve this. But I doubt this as this occurs on two sets of stock (although both sets are 25 years old) coils. Any other ideas before I just jump off the bike prior to crashing it into wall??

howard95132 wrote:

Any other ideas before I just jump off the bike prior to crashing it into wall??

:ohmy:
PLEASE DON'T!!!:blink:
OK, I'm assuming you're just :lol:
Have you checked the coil resistance hot?
On the other hand...
Since it starts w/a push hot, but doesn't start hot when the starter is drawing power, I would start with electrical. Either your starter draws too much power when hot (thus not providing enough juice to FI, since you say you do have spark when hot) or you have an ignition problem. Have you had your battery tested?
Or....
Maybe space aliens have moved into your tail piece, and they're munching on the EFI box!:pinch:

I’ve been treating this as an electrical problem all along which is why I’ve since replaced or upgraded most of it! I checked both coils when cold and only one when warm (the right side) and they all read 3 ohms. Since this is my second set of coils (parts shed) I’ve kind of ruled out coils, with the exception of realizing that they are 25 years old. But I never had this problem before the rebore/valve job. The starter turns over just fine and the spark is fine too when warm. The battery is maintence-free purchaced last year and I have it connected to a solar trickle charger, so it’s always charged up. And yes, the motorcycle Gods have been messing with me big time on this. I’ve been trying to resolve this for 3 months now! Fortunately, I have two other bikes. But I’d like this to be my daily commuter bike, so it would be nice if I didn’t have to flag someone down for a push-start every tome I go out for lunch!

Post edited by: howard95132, at: 2007/10/01 18:41

There’s one more thing that comes to mind, and if this is it, I’m not going to be very happy. This is not a race bike. It’s a commuter bike. When I rebuilt the top-end, besides needing an oversized exhaust valve guide installed when I had the valve job done, I noticed that several ( of the cam bearings looked a bit worn. Since I had an ‘extra head’ that had it’s own worse issues, I salvaged some of the cam bearings from that head and replaced the worn-looking ones with some of the ‘good looking’ ones from that head. If this were a race bike, I would have replaced all of them with new ones. I can’t believe that this is the problem. The bike runs freekin’ great. It only sometimes won’t start after a short ride. If I keep going, it keeps going. If I start it cold, it always starts. I did get some ‘pinging’ when I excellerated at freeway speeds, but by droping my plugs from 8’s to 9’s (one step colder) and with the afore mentioned electrical modifications, the pinging arrears to be reduced, but isn't gone. Otherwise, the engine sounds & runs great.

Post edited by: howard95132, at: 2007/10/01 19:50

Post edited by: howard95132, at: 2007/10/02 01:58

One more, then. Assuming that there's not an issue with spark, but that it's electrical...
and that for some reason when you use the starter on a hot bike, SOMETHING isn't getting enough juice...
and if it's not the ignition, it sure could be the FI...
try pulling all the FI connectors, and using some di-electric grease on all of 'em. It can't hurt, and it might be your gremlin.