Motorway misfire - FIXED...?

[dickie14]

Well, we made it home! The misfire became quite intermittent - would drive for a few minutes with it happening at almost any speed, then it seemed to clear and had many periods of over an hour where we just cruised along happily at 60-65. Full throttle was even occasionally available without the popcorn soundtrack, though the engine seemed consistently down on power. Then, almost out of nowhere the symptoms would return, usually precipitated by lifting off the throttle.

However, it has developed a lumpy idle and sometimes stalls in Drive against the brake (it's an auto) when hot. Also sounds much more tapetty than when we left 3000km ago - seems to be coming from cylinder #2 coincidentally... And it turns out the other spark plug served by that carb is just as sooty (potentilly pointing to float valve as Covkid suggests?), and swapping the plugs doesn't move the problem.

So, the intermittent nature makes me think crap in the carb may well be involved, the idle issues point to an air leak (as could the popping I guess), and the tappeting may indicate the hydraulic lifter could be in need of adjustment?

My plan of action is now (one step at a time):

1. Oil change
2. Search for air leaks again. And then again.
3. Strip and clean the relevant carb, rebuild with new gaskets etc to address any crap in jets and air leaks.
4. Use a colourtune to get the mixture right, re-balance carbs
5. Adjust hydraulic lifter (never done this before - how likely am I to make everything worse?) - should I do all of them?
6. New dizzy cap, rotor arm, HT leads

Is that a sensible approach? In a sensible order?

Cheers,
Dickie

[dickie14]

It looks like it was the tappets...

Most needed slight adjustment and the two on cylinder 3 were way out. Now the engine's back to running as strong as before! No pops, bangs or anything else anymore. Haven't touched the carbs yet.

However: my first concern is whether the lifters were pumped before I adjusted them - I tried to run the engine for a good long time prior to adjustment, how can I be sure they were primed? Shamefully, it's the first time I've ever been under the rocker covers...

My second concern is that the exhaust valve on #3 was particularly far out - the inlet on that cylinder was bad too, but I had to wind the adjustment screw almost to the limit of its travel on the exhaust. Does that indicate a knackered lifter? Or just that it wasn't primed?

Also found a small hole on the exhaust where the LH heat exchanger meets the silencer/back box. Will try to get that looked at.

Cheers,
(a much happier) Dickie

[123-jn]

This sounds like either the screw on number three exhaust is very worn down (shorter than the others) or your exhaust valve seat is making it's way out of your head?

[dickie14]

Sorry, my mistake - it was #2 that was really bad, not 3.

Valve seat coming out of the head? How does that work? Sounds bad...