Valve clearances?

[bagmaker]

You may well have already tried putting a strobe on it to check ignition timing plus advance/retard working OK with motor hot and cold? May reveal something wierd?

Seems key that it is so temperature/airflow related (If riding on a cool day open roads its OK, if riding in traffic with no air flow its a nightmare). Does hot motor always correlate with poor/annoying performance?

How hot does it get on the gauge when it messes you about?

Seems really unlikely as a cause but I would be checking the cooling system is all good; sounds like you have tried everything else electrical and changing carbs has done nothing. Run with no stat perhaps and see if that changes anything.

Good luck with it; I will keep thinking of other ridiculous possibilities!

I haven't put a strobe on it, no, another on the list, thanks. I have checked a little and it seems always the left pot to the point where the header on that side will go cool to touch.
The temperature is key, yes, its also frustrating because I pretty much cannot get it to happen during the cooler months of the year without going into heavy traffic.
Come summer and it happens before 5kms come up on the clock. It has actually been a nightmare (traffic, hot day) AND GONE AWAY after getting to the open road for a while.
Hot motor yes, but only a third up the gauge as normal.

If I keep over 4000rpm she runs fine..................

Plod dis-agrees

Do you mean thermostat? Or electrical stator?

Thanks for your input MDW

[misterdimwiddy]

Still sounds a daft suggestion to me but I meant run with the thermostat removed from its housing located above the cam cover.

There is no logic here other than thinking this may reduce the coolant temperature sufficiently to cure the problem (in the way that a lower ambient temperature appears to do the same thing). It doesn't help explain the problem however.

I cannot see that the operating temperature of the two cylinders would differ significantly with changing ambient temperature.

Still makes you think sparks or fuel but you have eliminated almost every component in these areas.

I assume it does not use/lose any coolant?

Does the expansion tank fill right up when it is playing up suggesting it is bleeding hot?

I think overall you are saying that air flow on the open road removes the issue which develops either in traffic or in hot weather (or both).

Does the rad fan come on a)when it is hot on the gauge and b) when it goes bad? Does it even get that hot on the gauge when it messes about? Mine reaches about 100C before the fan (now removed) comes on.

This is so off the wall as a suggestion but out of sheer desperation I would check the water pump is working and that you are actually getting fluid flow. The cooling system should of course control the motor temperature within defined limits even in the worst traffic on the hottest day. Ambient air flow (open road) appears to remove the symptoms and all that can provide is cooling! Why just one pot goes dead I do not know. The water pump rotor is easy enough to get to for inspection from the side cover. Not sure how you actually demonstrate that you have flow.

Could run the motor when cold and remove the rad cap; usually shows at least some movement/flow when you rev the motor.

If coolant flow was poor or non existent, the gauge sensor would not necessarily pick up the true motor temperature. The fan sensor could also fail to operate and motor temperature would continue to rise unchecked.

I am almost pleased this is a forum and I do not have to face everyone having made such bizarre suggestions! Forensic engineering is part of my job and I do enjoy it but I feel these mine are the ramblings of an idiot. This is quite a puzzle however and I am intrigued.

If this does give some answers I will claim my prize!

[bagmaker]

Ok, so many questions!

Coolant temperature doesn't seem to change the issue much, to say, when its cold it doesnt happen, when its warm it happens, generally the coolant temp only gets on the high side of warm (on the gauge) BECAUSE i am thrashing the shit out of the motor and clutch to keep running. Its more like an electrical (?) item -or valves but I have eliminated them from the mix- that warms up and fails but can be cooled down with airflow and it will come good.
The coolant temperature doesn't differ between pots, just the header temperature. When happening if you hold the throttle in the problem area in neutral, one header pipe will cool down enough to touch. If left to idle it heats up again.

no coolant loss issues, the coolant expansion tank stays pretty much half full.
The only time the fan comes on is in traffic, hot day. I have convinced myself this is mainly because at the time I am slipping the clutch and trying to keep RPM above 4000 to stop the thing stalling and bitching.
To be perfectly frank, your honour, I have got a bit on my mind at the time. Even in first gear a 5000rpm start in heavy traffic on a hot day is disturbing for the road-users around me

EDIT- its important and most interesting to note the definate band that the miss occurs in. Idle is un-affected, high RPM is un-affected -its like a switch flicks over at around 3800 rpm. I cannot think of a coolant or mechanical issue that would do this

Thanks for the forensics sir, I am regularly in cahoots with large mobs of like minded fellows and we have been struggling with this for a while.
We will not be beaten

[cobbadiggabuddyblooo]

The pick ups for the inductive ignition. Is it a harmonic problem around the pick ups once things heat up tollerences close or harmonic vibration causing movement around those stated revs where the problem comes into play.

[bagmaker]

The pick ups for the inductive ignition. Is it a harmonic problem around the pick ups once things heat up tollerences close or harmonic vibration causing movement around those stated revs where the problem comes into play.

Replaced the pickup, and the stator, same issue remains.
There could be substance to what you say if there is play in the main bearings causing the crank/rotor to move.
I can't feel any play, it all sounds tight enough when running -hey some gravity here, its not a quiet engine at best- with no significant knocks or clunks.
But OK, loose flywheel issue could account for it. JohnKTM suggested the woodruff key along the same lines.

On my list

[Mincehead]

It`s an odd one, did you or CAN you run a TRX without the rev counter connected? Mine never had any TRX instruments on it so I`m not familier with them at all.

[bagmaker]

nope, same symptoms with tacho dis-connected

[misterdimwiddy]

It`s an odd one, did you or CAN you run a TRX without the rev counter connected? Mine never had any TRX instruments on it so I`m not familier with them at all.

I have run for a while with no tacho at all and had no problems other than not being able to hold it at 5500rpm for noise testing.

I did however mess up once and swap 2 of the 3 tacho wires when refitting standard clocks and it ran very roughly until this was corrected. Seem to remember it would fire but would not even start and run............certainly not rideable.

[wiemer]

Just replaced the stator and ignition pickup, thats it, nothing more to replace but bits of wire.
I have tried a different CDI
I have tried different coils
I have replaced HT leads
I have replaced the plugs

My son has a Honda NTV, with a similar but not the same story.
On many days, after 10-20 kms. one cylinder would stop firing.

Because that spark-signal was also the signal for the fuel pump, one kilometer later both cylinders stopped. [the signal for the other spark from the transistor ign unit was for the tach!]
Waiting for 10 seconds on the emergency ramp....starting and going for the whole day as if nothing had happened.


Checked| carbs: OK.
Changed the fuel pump...no result.
Coils were ruled out, because the pump got no signal and stopped.
Measuring the pickup coils while running gave a diff of 30% in voltage...but we did not take them out.
The ignition unit print looked a bit messy. Just like the pickups, some reason to doubt.

Changed the ign unit: presto: problem gone. EUR 60,- from Munich.

But..you HAVE already changed the item......

Wiemer.

[bagmaker]

ya changed with a friends CDI and got same result so re-installed original.

[cobbadiggabuddyblooo]

Are they a resistor type spark plug your using? Maybe your getting unwanted RF from there corrupting the ignition..

[bagmaker]

Are they a resistor type spark plug your using? Maybe your getting unwanted RF from there corrupting the ignition..

I am not sure on the actual plug, didnt know there was non-resister type. What do I ask for?

I have changed out the resistors in the plug CAPS, put solid brass bits in there, old style, didnt help

[cobbadiggabuddyblooo]

The plug code will have an R within it like.. DPR 8EA-9 and the resistor is built within the plug.

[bagmaker]

The plug code will have an R within it like.. DPR 8EA-9 and the resistor is built within the plug.

OK but what do you think I should try if not an "R" coded plug? (thanks)

[bagmaker]

Now she sports a whole different wiring loom

Same result. I am bleeding to death here