Dear Learned Colleagues.
I have a conundrum. My trusty warhorse has developed a fault and I am at a loss as to what is causing it.
At tickover and low/medium revs she runs like a dream - BUT, at high revs (Please note I do not thrash the poor old thing so high here is a relative term) she misbehaves in terms of uneven running.
It feels like fuel starvation but I have checked the fuel system from tank to inlet port, stripped down the carb and all is clean.
I have also double checked the timing and all is well.
Going on the wise words of 'always suspect the last thing you fiddled with' gives two possible lines of enquiry:
1. I have recently fitted a temporary dynamo off a later bike which gives a higher output while I fix the original one (it's nice to have brighter lights and a charging battery!) QUESTION: With the higher output at high revs will this cause a 'charging' of the potential difference which may effect the strength of the plug spark? maybe in conjunction with a bad earth connection?
2. the rear pipe blew it's baffles around 3 - 4 months ago and I have been running on effectively a straight through pipe since then (not a lot louder so I left it). QUESTION: Would this be a possible symptom of problems developing due to lack of back-pressure, ie, exhaust valve burnout? (no detectable change in compression when starting though)
I await your advice oh wise ones!
Kimble

email (option): Kimble.west@xeiad.com

Assuming you have a mag and not electronic ignition, then the output of the dynamo will not affect the spark from the mag.

If you have worked on the carb, then check the flange is nice and flat and a good fit to the barrel and that no air is being sucked in where they meet.

email (option): sacombsashtrees@hotmail.com

Could it be a partially blocked fuel pipe or tap not allowing enough fuel through? try undoing the pipe from the float bowl turn on each tap in turn and run some into a receptacle to see if the fuel flows OK.

Rob

email (option): robmiller11(a)yahoo.co.uk

Do you mean it's misfiring at high revs?....

Check that it's not arcing to earth through the pickup/HT/plug cap at high revs..(and fit a non supressed plug cap if you don't already have one)

Check for signs of tracking marks on these components..Better still substitute them with some others if you have them and then test out on the road...Ian

email (option): ian@wright52.plus.com

Check if the choke is fully lifted.
You can feel that in your carb when the engine is off.
That may also cause uneven running

I'm no expert but believe in the adage that its probably the last thing you touched...

I would re-check all the connections on the mag - maybe smear a little dialectric grease in there or replace the plug lead? Connections oxidize over time and there are usually 2 states - working and dead. You may be somewhere in between?

Also, maybe the advance?

email (option): cas.vanderwoude@gmail.com

The "outlaw mower cycle" spat the muffler off a couple of years ago and since then I have been running an aftermarket Shorty HD muffler which at one time most likely had some fiberglass in there.
I had to go up 2 sizes on the main jet to compensate for it.
So yes, no muffler will make a difference
As will being out of time having just replaced the dynamo.

Find a bit of a hill to ride up,
A long one if possible.
In third gear roll the throttle on slowly if you get to 3/4 and then you loose power without the engine missing then the main is too small.

Go back up the same hill again and again at 3/4 throttle, slowly retard the engine, if it picks up & runs better your timing is out .
A little trick we used to use was to open out the points a bit say to .015".
This advances the spark and if it makes the engine run better then you have to retime the engine.
Same for closing the points down, this retards the spark, however you can do that with the lever on the handle bars.

And if you are wondering why I changed the jets & not the muffler, two reasons.
1) to annoy the tractor riders who leave their Beesas in the garage
2) because I am getting Barry Bligh ( overlander) to make me a longer headder to fit into a fishtail I picked up a while back.

email (option): bsansw1@tpg.com.au

Thanks people,
I have double checked everything.The main jet being too small due to missing baffles is worth pursuing (thanks Trevor) and Ian's sage advice on arcing was taken on board and enacted, all other points have been double/triple checked, However...
It seems to be getting better slowly (I know, weird right?) - I did put a small amount of old fuel in the tank from a J can that somebody gave me the other day and I'm just wondering if there may be a wee bit of H2O in the tank which is gradually clearing?
Anyway, why on earth are you all reading this in this weather, in the words of Mr mercury...
'Get on your bikes and ride'...
thanks again guys
K

email (option): Kimble.west@xeiad.com