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Triumph TR6 - Rough running

About a month ago I stored a perfectly well running TR6 in my garage.
Until today I did not have an opportunity to drive the car.
The 74 TR6 has two HS6 SU carburetors and runs with a Pertronics ignition.

When I fired it up it ran very rough, like it misfired on one of the plugs.
There was even a tendency to back-fire on the carbs.
I cleaned the spark plugs (runs a little rich), checked the ignition timing to be ok.
With the powered stroboscope I can not spot any misfire on the plugs.
The compression test gives the same readings as a year ago on all cylinders.
All cylinders are very close to 10 lbs, the deviation is the same as last year.

I topped the dampers on the SU with oil. Choke and throttle linkage seem to be working correctly

Any idea’s how to progress to diagnose further?

Erik
Erik Creyghton


If you are confident that the plugs are firing at full voltage and at the right time (timing, points, etc..)then I would wonder about the fuel. You say it was stored for some time. Did you use fuel stabilizer when you stored it? Old gas can cause what you are experiencing. So can a fuel filter. Maybe that is filled up with scale from the tank. These would be something fairly simple before going after valves or carbs or any other things that can cause the same problem.

One question though.. when you say 10lbs of compression are you talking about the difference in pressure between cylinders? If you are talking actual cylinder pressure then that is extremely low. From my memory it should be somewhere around 100 psi or so.

The backfire through the carbs could be a valve hanging up.. but then you should have seen that in the compression test. Try the simple stuff first.

Henry
HP Henry Patterson

Henry you are right the compression is expressed in BAR's or PSI’s
I measured around 10 BAR’s which is the equivalent of 145 PSI’s.

This is however not the only error I made.
I humbly admit that I swapped the leads on number 5 & 6 plugs when I cleaned away some oil spill when I garaged my six a month ago. I discovered this today when I took the valve cover off to check for broken springs on the intake valves.

Problem solved whilst my ego is shattered

Erik
Erik Creyghton

Erik
We all have done it.

File it under "Man...that was stupid of me"
And then laugh.

Could have been worse:)
Rick
Rick Crawford


Erik... I can top that one.

Once when I was taking my sink drain apart in my house
I got the "S" trap off and was holding it in my hand and saw that it was full of water (of course). I decided the best place to dump the water was in the sink (yes, the sink I just took apart). Of course the water went through the open drain and on to the floor.

I had a good laugh. I didn't tell my wife about that one.

HP Henry Patterson

Glad to know that I am in good company
I will have that laugh now :-)
Erik Creyghton

Or flipping the light switch when the power as gone out in an ice storm, then looking at it like "What the hell?" DUH. I've done it.
Tom

Hi Erik... Congrats on going world wide with your admission. Collectively we could have a book out by Christmas.

I can embarrass myself very well but the list is too long so let me share this neighbour's quickie. He was showing me his grisled hands one day (we both do a lot of woodworking) and explained that the reason his right index finger looks so disfigured was that he checked the blade of his band saw while it was running - to see if was running, and sharp. It was.
K. T. Shaddock

Don't feel too badly about messing up two spark plug leads. Years ago a buddy had his TR250 dropped off at my shop. His local mechanic had worked on it and gotten the firing order REVERSED. It was only firing on 2 cylinders! To say the performance was lackluster was an understatement. It would do about 20 mph flat out. Took me a bit to find it since I didn't know (at the time) what the rotation on the cap was.....
Tom Sotomayor

This thread was discussed between 21/10/2006 and 26/10/2006

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