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Triumph Repair/Triumph tr3 will not start


QUESTION: I Purchased a tr3 that had been sitting for 10 years.  I have been working on getting it stared.  Below is a summary.  

1. Compression is 150lbs +/- 10 percent on all 4 cylinders.
2. Verified I have spark at the spark plugs when next to the engine block.  I am not sure if the spark is blue though it appears to be.
3. Sprayed starter fluid resulting in a single back fire when turning the engine over for approx 15 seconds.
4.  Rebuilt the carbs.  Front carb jet or slide is sticking slightly.

Please let me know what to do next.  Should I and how would I determine if the spark is strong enough to at least get the engine to turn over via starter fluid.  I will also check to see if the 2 plugs tied to the front carb are wet.  I did check the 3 and 4 cylinder spark plugs and they were not wet.

Thanks in advance for your help.


ANSWER: Hi Steve,

The sequence to test an engine that will not start is Compression, fire and fuel in that order and since you ran a compression test you can proceed to ignition. You need to confirm several things. First is a spark and it must be blue in color (not in sun light) and it must be thick as a pencil lead. Next you must check ignition timing. Third you must check firing order and that every plug wire is firing not just one. If you don't have this, it is a waste of time to check fuel.
If you do have the ignition correct, then you can test fuel by what you did and that is spray starting fluid in the intake. However, if it does not fire off for a couple of seconds then you didn't do the ignition tests correctly because starting fluid will fire off with even a poor ignition.

There is a simple but effective method to test the ignition system and we often did this as a preliminary test. Remove all the plugs and if any are wet or heavily carbon coated either clean them or replace them and put each plug on it's plug wire and lay all the plugs on a metal part of the engine. With the ignition turned on put you thumb over #1 plug hole and watch the #1 plug as you spin the starter. The compression will blow your thumb off of the plug hole with a "Pop" and at the same time you will see the #1 plug spark with a "Click".

If you see the spark "Click" and it seems as though the "Pop" caused the "Click" it means that the timing is close enough to start but does not mean it is timed correctly. Next put you thumb over #2 plug hole and repeat the process and continue on to #3 and #4 the same way and that will confirm the firing order.

Don't waste time by skipping anything. An engine must fire off on starting fluid or you can not bother looking at fuel yet.

AFTER you get it to run on starting fluid you can work on that carb that has a sticking piston which will never run correctly until that is corrected. Most likely the jet in that carb is not aligned in the center and must be centered. The only other common cause is a dent in the top pot or a bent needle.

Let me know,


---------- FOLLOW-UP ----------

QUESTION: I really appreciate the very helpful suggestions including the removal of the spark plug and putting a thumb over the hole to verify that the spark and compression match up.  I will try this out.  The plugs are new.  Through this process of trying to get the car started, I started to clean the gas and black residue on the spark plugs and will continue to do this.

I am jumping ahead a bit, but wondering how I would know if the spark is strong enough or if it is too weak.  I do not have a reference to compare it against what I am seeing on the TR3.  If this is an issue, would it be due to a problem  with the coil?   I have another coil that I was thinking of swapping out and try.   I first go through the checking of the spark plug and compression at each cylinder.

I agree that the issue with the carb is that the jet is not aligned and I will address this.  The needle is new as I rebuild the carb last week.   I am thinking it is more of an alignment issue.

I will follow up on your recommendation regarding each cylinder spark and compression alignment (verify timing) and will let you know.  I really appreciate your suggestions.  They are very helpful.  I am certainly learning quite of bit about a cars timing and how it works.



You can make a rough estimate of the power of a spark on any of the old British cars even without a scope. On a scope it will show up as between 25,000 volts and 35,000 volts but to make a rough guess at it's value, just take a good look at the spark either in the garage or in the shade (not is bright sun light).

With the plugs clean you should see a thick spark about as thick as a pencil lead and the color should be blue. If you have a thin spark like a hair and colored yellow or orange it is a weak spark and may not fire off.

When you try to start an engine using starting fluid and it does not fire off for at least a second or two, and you have good compression and good vacuum, you can be certain that you have no ignition.

let me know,


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Howard M. Fitzcharles III


Triumph TR-4 up & Spitfire, and Engine theory


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.

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