[TR] Rough Starting and Idling

[Brian.L.Jones at gsk.com]

Bob wrote: <snip>. While it was idling rough, I pulled the wires off 
cylinders 3 and 4 with no change. I pulled the plugs and found 3 and 4 
clean while 1 and 2 were extremely rich....rear carb??? I checked the 
float bowls, needle valves and pistons on the H6's....all seemed OK. 
Installed fresh plugs...no change. Cleaned the points and contacts in the 
distributor cap...no change.

Bob,

Given that you need three things to get 'fire': spark, fuel/air mix and 
compression, I'd work my way through these to establish your issue, though 
on first glance at your description, I'd say something is not right with 
your rear carburettor.

Remove #3 and then #4 spark plugs and establish if you can see a spark 
when the threaded part of the plug is grounded to the engine block, and 
the engine is turning over. If NO, chase faults back through the HT lead 
to the distributor cap/rotor.

Check your compression in all cylinders and compare. If you have more than 
10% variance, and a low reading in #3 and #4, you can start investigating 
the cause. There is plenty on this in the archives and web, and you'll be 
able to establish the source of the compression failure (rings, inlet or 
outlet valve). My poor starting and rough idling was due to poor 
compression in #1, caused by an oversize (i.d.) exhaust-valve guide having 
been installed heaven knows how long ago. It purrs like a pussy cat now.

Fuel/air delivery: maybe the simplest way to establish that it is the rear 
carburettor at fault could be to swap front and rear carbs and see if the 
problem moves to #1 and #2 cylinders. Another lister recently established 
a carburettor as his issue's cause in this way (it looked like any one of 
a number of possible ignition failures). If it is the carb...it looks like 
you'll need to tear down that item. Do you have a fuel filter? Could it be 
partially blocked?

Good luck, and let us know how you get on.

Brian
TR4 14455 1963
Valley Forge, PA