Mis-firing Mirage

Hi John and all,
Excuse me for interupting with a small comment on all the good stuff that's been said.

Just today I stuck my head into a spaceframe being built by a friend, and when he started up, it had small pops and bangs, and small misfires. It could run better on higher revs exactly as you described John.
All is new, he have lot's of experience, but still this happened.

Looking at things it became obvious that the small rubber tubes running between carbs, was left off. You know, the ones you take off for syncronizing carbs. Just forgot them.


So my advice, apart from 3 new sparkplugs, would be to look vary carefully at shose small rubber tubes, the T-piece, and looking for cracks etc.
The do get a lot of heat, so they get old and leaking prematurely.

Just my dime,
Jacques.
 
Well - I finally found it!!!
I had rechecked (stripped, cleaned, refurbished) carbs several times, electrics and valve clearances and timing sveral times, swapped carbs between right (offending cyclinder) and centre, all to no avail.
I then checked the vacuum - very low on offending cylinder. Checked the inlet tract rubbers etc.
Then checked compression - very low on offecnding cylinder.
So nothing else for it - but to remove recently refurbished head again and there it was - a slightly, slightly bent exhaust valve. It must have picked up on the guide in my first few miles of running after the rebuild. Not enough to damage the engine or guide, but enough to stop the valve seating properly.
I'm jarred off that I've missed out on a lot of summer riding on the Mirage this year, but extremely pleased to have found the problem.
I'll keep my carbtune and compression gauge closer to hand in future!!
Thanks for all your help.
John
 
John,
A question on your newly refurbed head.

Have stainless valves been fitted into cast iron guides.?
If so, there lays your problem, unless they have excessive clearance they will nip up and seize.

Red
 
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