1969 Triumph Daytona

[murdo]

One of my local club members has been having his 500cc Triumph Daytona repaired by an older gentleman who has sadly passed away. It is a very nice bike with only 9,000 miles on the clock. The bike has developed a slight miss on the right cylinder and he has asked me to have a look at what maybe wrong. It has a single carb, electronic ignition with good spark to both plugs and swapping coils makes no difference. I am thinking that it may be valve trouble and was wondering what I should set the clearances to before I do a compression test. Any advise would be very helpful as I have never worked on a Triumph twin before.

[rogerwilko]

Try another pair of plugs.

[wink]

Exactly what I thought. But I would have swapped them over to see if the left cylinder is misfiring.

[murdo]

Done that. Swapped plugs, then new plugs, still the same which is why I think it may be valve.

[rogerwilko]

A valve wouldn't cause a misfire. You can check clearances if you like but check the points gap for both cylinders if it has twin points.

[R]

A valve can cause a misfire, if it has no clearance.
Just check that both valve pairs have the same clearances.

Says it has leccy ignition.
Tried swapping plug leads. ?

A broken valve spring can cause a misfire, if all other avenues check out good.
You wouldn't expect that with low miles, but you never know until you look.
So can a cracked valve seat...

[murdo]

If anybody can tell me the clearances for the valves, I will do a compression test and leak down test to confirm that all is well mechanically. If all that ok, then I will have to look at maybe changing the ignition system.

[L.A.B.]

http://www.classicbike.biz/Triumph/Repair/350-500/63-74-350-500cc-Repair.pdf

[murdo]

Thank you. 

[rogerwilko]

There's misfires and misfires, is it only running on one cylinder or is it intermittent? Intermittent will be electrical .

[murdo]

Thank you Gents for the help.
I had a bit of time today so checked the valve clearances, all good, the compressions are 150 psi in both cylinders, new plugs, checked coils and leads/caps, all good. So I started it up (first kick too) and it would miss on the right cylinder up to 3,000 rpm when it would pick up and run good. I thought it may be an air leak so I pushed the tickler down while idleing as instantly it picked up on the right cylinder. Removing the intake manifold revealed two parts of the gasket missing. Think I found the problem. I cut two new gaskets, a wipe of sealer and put back together. Running lovely now. Time for a road test before tea.