Two questions

I just finished a 1600 mile trip on my '82 KZ750 E3. The bike ran spectacularly for the better part of the trip. However riding through Eastern Washington in the hot weather didn't sit very well with the bike, and I pulled off a couple of times to let her cool down. I think that the previous owner painted the engine black with some of that duplicolor high-heat paint, which I know uses ceramic. Can the ceramic insulate an air-cooled engine enough to cause overheating? It got hot enough a few times that it wouldn't idle.

My next question is related to this. About 1300 miles into said trip, the bike didn't want to start when hot. The starter motor would crank her over just fine and she would usually fire up, but if for some reason I shut it off or it died, I could crank it until the battery died without so much as a sputter. Push starting worked fine. At the same time, my idle started becoming rough, and she would missfire and die sometimes if I let off the throttle. I'm suspicious that the hot running mentioned above may have compromised my plugs. They're pretty coated in white scale. Is it likely that my problem is as simple as that, or should I look to valve lashings, etc?

Thanks much,
Casey

How do your plugs look?

Its not the paint my friend. Paint actually contributes to the amount of available cooling surface, and sheds the heat slightly faster. I've tested this theory, as I was worried before my own rebuild.

Is the bike stock? Sounds like your jetting is too lean, maybe for the altitude you were at?

I've had the same issue, and just needed to get more fuel in there. Don't forget, fuel is a lubricant, and assists in maintaining proper combustion/engine temperatures.

You can sometimes help this situation by adding more mixture at idle. (Turning the pilot mixture screws appropriately, for your carbs.)

Someone else with more exp. will likely chime in soon...

Cheers.

it does kinda sound like you need your valve clearances adjusted to me. typical hard to start hot and odd idle hot are two clues

My plugs are pretty white, with a little build-up, which confirmed my idea that I'm running hot. I picked up some new ones just in case that solves the problem because it sounds like its just misfiring occasionally at idle. I may be jetted lean as well, it's true. The last owner put pod filters on, and I don't know whether he re-jetted to accomodate, but if I go up a size or two from stock, then maybe I'll run cooler?

I was wondering about the valves, so I'll check those. However, the problem only developed within the last 400-500 miles. Before the last leg of my trip I never had trouble with starting, cold or hot. Is it conceivable that the valve clearances could go outta whack that fast? I've never gotten it as hot as this last trip, so I suppose it may have never manifested itself for that reason as well.

Thanks so much for the input thus far. Forums like this are lifesavers.

Casey

charwood89 wrote:

I may be jetted lean as well, it's true. The last owner put pod filters on, and I don't know whether he re-jetted to accomodate, but if I go up a size or two from stock, then maybe I'll run cooler?

Running richer definitely runs cooler.

Hope you are running synth oil considering how hot you were getting it.

bountyhunter wrote:

Running richer definitely runs cooler.

Hope you are running synth oil considering how hot you were getting it.[/quote]

I'm not actually... :dry: I run short oil change intervals with a high-shear diesel oil like rotella or delvac. I've been told that they hold up well in air cooled bikes, but should I really switch to a synthetic?

Also, because I can't seem to find my shop manual handy, does anybody know off hand what the recommended spark plug gap is?

Thanks,
Casey

KZ stock plugs :

I use NGK B7ES - the engine likes these much better for in town / freeway use at ~70 F

When I go on a long distance trips I often use B8ES. But, if you are running a lot of miles in one day at highway speeds and are in an area where the ambient teperature is high + 80 F , you should try B9ES and run 20 W 50 weight oil. The engine will thank you for it.

My 0.02 cents.

KR

I like KOOL RYDER's advise. Iv'e had problems with synthetic getting past my valve seals, and switching to Castrol 20w50 took care of that. Could have been the synth I used...

I still use the B8ES plugs though.

I just got a colortune plug, and re-jetted, and now my bike runs alot smoother/cooler in 90+ temps all day long.

I had symptoms much like yours before this.

...and yeah, super hot temps can mean a temp no gap condition suddenly on valves that are already very tight. Had that problem last year, and it does make the bike VERY hard to re-start.

Cheers.

PS. recommended gap for mine is between .28 - .32
Try the .32, if it stammers at high rpm, then close the gap some, as it might be straining your ignition system.

charwood89 wrote:

bountyhunter wrote:

Running richer definitely runs cooler.

Hope you are running synth oil considering how hot you were getting it.

I'm not actually... :dry: I run short oil change intervals with a high-shear diesel oil like rotella or delvac. I've been told that they hold up well in air cooled bikes, but should I really switch to a synthetic?

Syns hold up better under extreme temps. The stuff you are using is really good, I just think syns work better at the extreme end of the temp range.

I also vote that B6ES is a good plug for city ONLY riding, but too hot for highway use and WAY too hot for highway riding in warm weather. B8 is probably a better choice for the latter service.

charwood89 wrote:

Also, because I can't seem to find my shop manual handy, does anybody know off hand what the recommended spark plug gap is?

Thanks,
Casey

7 - 8 mm which is .028 - .032".

Sounds like your running lean. Check the jets and see if they are the stock size. If so with the pods you might need to go up a size or two. I tried 20 50 in my bike and it didn't like it at all. It ran hotter than hell. I'm thinking that the oil was to thick to run freely. It was all good when I went back to 10-40. Also check your valves and timing. Were you down in the tri-cities? It gets hot down there. I went through there last weekend and it was 110.