Bike Gets Hot Then Dies?

Hello,

I have a 1976 KZ400. It has 2 in 1 exhaust into a shorty muffler (with baffle.) The pipe are wrapped, the engine is painted. After about 10 minutes of use the bike will start running a little rough and sputtering off an on. After about 20-30 minutes of use the problem gets severe and eventually the bike dies. It starts first kick no problem, the spark plugs look normal. I have replace the ignition coil hoping it was a bad coil, but the problem still occurs.

I set the timing, but it was not very accurate because the timing marks kept "jumping around" both at idle and at over ~3k rpm (by jumping around I mean the light was erratic, indicating erratic firing?) However, this "erratic firing" was only indicated by the timing light, it doesn't sound anywhere near like it looked.

I can't think of any other things to mention with the motor. Has VM30s with pod filters. It's my first air cooled bike but it seems to get wayyyyyy hot - hence that's what I think is causing it. It has the standard plugs in it, B8ES? I thought about trying colder running plugs such as ex. B10ES?

It used to run fine but all of the sudden developed this issue without changing anything. Well, actually the only thing that has changed was I set the valve clearances to spec (they were slightly loose) and in the process I snapped one of the valve clearance check bolts in two so I replaced it with a generic steed drain bolt from the auto store. I can't think of anything else that changed from the time it worked to when it didn't. I would not expect the motor to be that picky though - works with loose valve clearances but not tighter both of which in spec?

Are you sure you have set the valve clearances to spec, (they were slightly loose), is not a numeric value !?!?

I snapped one of the valve clearance check bolts in two so I replaced it with a generic steed drain bolt from the auto store.

Do you talk about the aluminum caps ???

Sounds like weak spark advance springs.
Steve

Scirocco wrote: Are you sure you have set the valve clearances to spec, (they were slightly loose), is not a numeric value !?!?

I snapped one of the valve clearance check bolts in two so I replaced it with a generic steed drain bolt from the auto store.

Do you talk about the aluminum caps ???

They were originally at the bigger limit of the spec. I adjusted them to the lower end of the spec. (EX: Were at 0.22mm and I set them to 0.17mm)

Correct - I snapped one of those aluminum caps.

SWest wrote: Sounds like weak spark advance springs.
Steve

I hope it is that simple, and makes sense. I will read more into this and may buy new ones.

Some pics of the spark plugs could be very helpful

I set the timing, but it was not very accurate because the timing marks kept "jumping around" both at idle and at over ~3k rpm (by jumping around I mean the light was erratic, indicating erratic firing?) However, this "erratic firing" was only indicated by the timing light, it doesn't sound anywhere near like it looked.

I would try to set the ignition timing (points) with the static method.

If not already done, would re-check valve clearances when the engine is stone cold (as in after sitting over-night),

Good Fortune!

I rechecked the valves - they were as I set them, at .004. I changed them all to .006 which is the upper limit.

Also I took another look at the points system. I opened the points gap to the max, 0.016?, which allowed me to set the static timing properly. I rode it twice about 10 minutes each and it ran much better - but I'm afraid they were too short of rides to allow the previous issue to arise. I will try to get some more time on this and see how it does.

Plug pics?
Steve

You mentioned you replaced coils, what did you replace them with ? Could it be those coils get hot and shut you down?

No eBay APP ID and/or Cert ID defined in Kunena configurationNot sure what coils it had, Emgo or something, but that's what i thought the problem was. So I replaced the old coils thinking they were the issue. I replaced them with these:

That is a pic of a late 400/440 head.
You need one for an early 400.
Those bolts are just the rocker fulcrum.:whistle:

Scirocco wrote: Are you sure you have set the valve clearances to spec, (they were slightly loose), is not a numeric value !?!?

I snapped one of the valve clearance check bolts in two so I replaced it with a generic steed drain bolt from the auto store.

Do you talk about the aluminum caps ???