Triumph Repair: TR6 Backfiring In Carb, throttle shaft, lean mixture

Question
QUESTION: Greetings,

'75 TR6 started acting up last spring.  Noted abrupt high speed misfiring in spring with engine warm and outside air temp cool to cold.  Engine generally hesitates on accel when cold. As well, lots of "burble" or popping on decel.  The plugs on cylinders 2 & 3 have been showing brilliant white, 1 a little whitish and 4 through 6 proper tan.  Comps 135# plus on all cylinders except #4 which is 90#.  Wet compression brings it up to 120# indicating a ring issue.  Ignition is pertronix electronic with idle set neutral at 2 Deg BTDC @ 850-900 RPM as I am running unleaded 91 octane fuel.  Vacuum advance is working as I get 1250-1300 RPM with the vacuum line off the carb. Exhaust system is Monza Pacesetter free flow.  Carb cleaner leak test on manifold joints and throttle shaft spindles is unremarkable. 1/4 inch air valve lift tests results in stall.  I just rebuilt the carbs and have only the air bypass valve spring left to set (currently fully closed).  Both temp compensators are free to move/clean and crack open at nominally 100 deg. I have good fuel level at the filter (which was changed) and a new fuel pump in summer '09.   Needles have been set to full rich (full up) but I am still getting reverse flow through the carbs (particularly the front carb). Carbon cannister is still installed but the anit-run on valve is not installed.  EGR valve looks to be the original.  Haven't tested it (nor am I sure how one does that).   It seems to be worse as the engine warms up and as I move the throttle off idle.  I know I'm getting good fuel flow as the reverse flow through the carb gives me a nice wet blast on the wheel well. Everything points to a fast burning (ie lean) mixture.... but I'm at a loss.  Any things you can point me towards?

Thanks

ANSWER: HI Nelson,
The lifting of a piston in the carb and the engine dies is an indication of a lean condition. The needles adjusted all the way up and still lean is a real problem. Your one dead cylinder is a real problem too and the engine will never run right as long as that cylinder is dead. (100 PSI and below don't even run)
Other than all that, I believe you have an EGR leakage problem. Remove the EGR valve and hold it open by hand and either blast it with a Spark plug cleaner or a sand blaster to try to clean the carbon out of the valve and check that it does not have manifold vacuum applied to it. It should only receive ported vacuum and that is suppose to be through a flame trap.
Howard

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QUESTION: Howard,

Disregard my previous e-mail on the blow down tests.  The results were confusing to me so I redid the test but backed off all the rocker arms as I found the engine would turn just enough under the line pressure so that valves were just cracking open when I thought they were shut.

I redid the test with the rockers fully off the valves and found the following:

1) 1 2 and 3 cylinders were consistent.  a slight hissing but believed to be a leak in the bayonet fitting to the air compressor.  No flow or sounds from the other spark plugs, exhaust or intake.  Got a good "whoosh" from the cylinder when I disconnected the pressured line.
2) #4 cylinder had loud hissing.  Tracing the sound I found it coming from the carb.  So flow was getting past the #4 cylinder intake valve
3) #5 slight hissing.  Some very weak intra-cylinder flow noted from the #4 spark plug hole
4) #6 cylinder same as cylinders 1 ,2 and 3

So based on these results, I've decided to pull the head.  Tonight I got everything off the head itself and have tagged and bagged the parts.  Found lots of things from the DPO that will be rectified on reassembly (most notable was the intake manifold lower clamps being only finger tight!  That might explain the lean problem.

Anyway, any tricks on how to separate the head from the block?  I'm thinking some compressed air but I haven't done this before and I don't want to launch my head through the roof of the garage.

Answer
Hi Nelson,
It sounds like you have it pinned down as to the cause of all the problems. On pulling a head that is stuck you must not give in to the urge to drive something between the head and block.

Over the years in dealerships and shops I have seen many different methods used and putting compressed air in either #1 or #6 combustion chamber works some times. I found that you need to work at the ends and only one end at a time. I always try to find a lug or even a manifold stud and put something down below even it it reaches all the way to the lower part of the block and then pry up on a manifold stud at either end of the head. Other times I bolt something to the head at one end and use an engine hoist to apply lifting pressure and just walk away with a load on it and most of the time I can come back to it a hour or two later and find that it has broken loose.
Jaguars are the worst and one mechanic in our shop was fighting a E-type head and he had a chain bolted to the front of the head and has a engine hoist lifting so hard that he had the front wheels off the ground and he just left it hanging over night. Yes it had broke loose by morning.
Don't do what I seen one mechanic try and that was to take a grease gun and put a lot of grease in a combustion chamber and put the plug in and he hit the starter. It broke the head loose but also bent a rod and destroyed the piston.
Howard