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Triumph Repair/1972 TR6 stalling out

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Question
Howard, my TR6(1972) is hard to start. When it starts it runs  OK for 30 seconds and stalls. When it starts after that, it has a rough idle and sometimes backfires through the carbs. and will eventually stall. I have replaced the points and condenser, coil. Checked the timing and valve clearance.checked for any vacumm leaks. Replaced float needle valves and adjusted float heights. Adjusted fuel mixture on carbs. Viewed that needles are moving in and out with adjustment. checked spark plugs(all new and gapped) #3 and #6 to see if getting fuel-they are damp. Checked compression-within specs.New gas filter and checked fuel pump-within specs. Pulled distributor-no signs of play or wear in drive dog. Any ideas, need help. Thanks, Gabe

Answer
Hi Gabe,

When working in the dealerships we could not and would not try to guess what is wrong with any engine when it didn't run correctly. It required a systematic test procedure to have a 100% fix rate and no stone can be left unturned in the procedure.

The tests are for systems not items and the tests must be done in order. There are only 3 systems that make all piston engines run. Compression, Fire and Fuel and they must be tested in that order.

Compression -- Compression must be from about 135 to 170 PSI (throttle open) and not be much difference between any cylinders. If you don't have this, it is no use proceeding until that is corrected.

Fire --- (Ignition) This can easily be tested with a can of starting fluid which tests for Fuel too. Spray starting fluid into the intake on both carburetors and have someone start the engine and set the RPM up to a fast idle. Be ready to spray again when it tries to faulter as you stated it does. If you can keep it running with the starting fluid, then it is a fuel system failure. (unless you have a stopped up exhaust system)

If you can't keep it running with starting fluid then you have a Ignition system failure. (providing the exhaust system is not stopped up) At this time you need to correct the Ignition system before testing the Fuel system as it too can be failed.

To test for a stopped up exhaust system you will need to loosen the exhaust pipe from the header. You don't need to remove it, just get a gap between the header and the pipe. When the nuts are rusted badly some mechanics will drill a small hole in the pipe close to the header and sized so he can drive a short piece of brake line into the pipe. This gives him a port to connect a hose to a low pressure gauge like a fuel pressure gauge. Then start the engine and note the pressure. It is quick and a sure thing on the readings. If it is 1 PSI to 1.5 PSI it is ok but a stopped up exhaust system will quickly climb to 5 to 7 PSI. After the test is run they pull the short piecs of brake line out and put in a heavy sheet metal screw to seal the hole.

Only after the Ignition system has been declaired ok can you look at fuel. The first test here is to put a "T" fitting on the fuel line just before the carburetors. On the "T" put a fuel pressure gauge and start the car again and watch the fuel pressure as it runs. The fuel pressure MUST stay above 1.5 PSI all the way to when the engine dies. If the pressure drops before the engine dies then you have a fuel delivery problem. (Just testing the pump's capability to pump 1.5 to 3 PSI is not a suficient test.) The test MUST be run "Real Time". (in normal operation)

If everything above had passed the tests and NOTHING skipped for any reason then the carburetors need to be removed and opened up to first check float operation and level.

An engine dies because it lost one or more of the 3 systems. While it is true that it is unlikely compression as compression will not usually come and go and return again. But that is a stone we could not leave unturned so we Always tested compression (throttle open).

We had to learn NOT to suspect any part and only test and only in the correct order. If you follow the above test sequence, it is impossible to fail to find the problem.

Let me know,

Howard  

Triumph Repair

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Howard M. Fitzcharles III

Expertise

Triumph TR-4 up & Spitfire, and Engine theory

Experience

Dealership line mechanic on MG, Triumph, Jaguar for 15 years, Instructor in commercial mechanics school 2 yr. Product information manager for piston and valve manufacture, Instructor & hotline answer man for import car parts importer 15 yrs.

Organizations
Associate member SAE EAA member

Publications
Import Car magazine

Education/Credentials
ASE Master Auto with L-1 certification up to 2000

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