I noticed from my s-type with 3.8 that the no 1 spark plug is much cleaner than the others, suggesting that it either runs much leaner or hotter than the others. I use ngk plugs. Would it help if i use one plug that is cooler than the rest or do all have to be of the same heat range?
When I had one clean plug it was caused by a head gasket leak, allowing water into the cylinder, steam-cleaning it. Open your radiator cap, fill it to the top, and look for bubbles when the engine is running.
Mike Eck
New Jersey, USA
'51 XK120 OTS, '62 3.8 MK2 MOD, '72 SIII E-Type 2+2
Or it has a vacuum leak. Check whether the cylinder is neat and shiny on top, if so, water. If not the manifold gasket might be gone, how‘s the idle? (Or could it be compression related?)
Wouldn’t hurt to check the valve clearances. Pretty easy to check. Pretty hard to change.
Pat H
It has a slight miss coming from that side of the exhaust so i will follow up on all advice given. The engine has done 4500 miles since complete overhaul.
I have been using her as a daily driver the past 3 months, by june i can take her off the road and look at all the remaining issues i can not check now.
I like that! Until then you can run our suggestions but if nothing is obviously wrong I might want to check compression if I were you - nobody wants a burned valve! Although those engines generally don’t break easily.
How about something simple like a bad plug wire or a crack in the distributor cap causing tracking to the next wire? Have you done a cylinder load test, pulling off wires one at a time and see which one doesn’t cause a drop in rpm?
All new and replaced again for incase. Will do load test today. Thanks
Riaan.
As Davidxj6 suggests this is a vacuum leak.
The vacuum take off is at the rear of the manifold and a leak in the
system primarily affects number 1 (rear) cyl, causing a lean mixture.
If you are lucky number 1 exhaust valve is OK.
Other symptoms of a vacuum leak are poor / no operation of the
bulkhead air flap and heater water valve
Peter B.