Triumph Repair: Spit not starting.., spark test, starter fluid

Question
QUESTION: Hi Howard,
My Spit will not start. I have checked compression (135 psi on all cyllinders dry), checked timing (thumb/spark test on #1 good), have gas in the float chamber. Fuel pump good. I am at a loss as to what is wrong. New 6 volt coil, new wires,cap, plugs,rotor and Pertronics breakerless module. I am at a loss at what could be wrong. CD 150 carb is clean, air valve works. Any ideas? I'm running out of things to try.

ANSWER: Hi Steve,

Sounds like you read one of my test procedures but you missed one. After the compression test and spark test you were suppose to spray starting fluid into the intake and if it starts for just a second or two and quits unless you keep spraying then you still have a fuel related problem.

If you don't get an run with starting fluid then your ignition test was not complete. Go back and do the thumb over each plug hole while watching the spark of each plug.

I learned to never look for items that failed but always look for "End Result". Compression is the 135 PSI you got, With ignition it is the spark at EACH and EVERY plug at roughly the correct time. Even the weakest spark and poorest compression will ignite starting fluid so if you don't get a run on starting fluid you missed one of the first tests.

Howard

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

QUESTION: Howard,
I did the "thumb" test on all 4 cylinders and they were OK. I sprayed starting fluid in the carb and it still would not fire. Thinking maybe the choke was not working I held my hand over the air intake, all that did was cause the carb to flood......

ANSWER: Steve, physics tells you that it is just about impossible to have spark in a starter fluid and not get some kind of explosion.

Starter fluid ignites if you sneeze at it, so you either don't have any compression (nor vacuum for the intake) or you have no spark.

The choke has nothing to do with it when using starting fluid.

Look at the plugs. Are they wet after trying to start it? Pull the air cleaner off and spin the engine over with your hand over the carb to see if it is pulling a good vacuum. How much difference in the compression of each cylinder?

Howard

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

QUESTION: Compression is 135 p.s.i. across all cylinders. Checked the plugs, seems 3 & 4 are wetter than 1 & 2. Put my hand over carb and it floods the carb so there is vacuum enough to draw gas out of the float bowl. The plugs spark when I check them out of the cyllinder but wondering if for some reason they are shorting out when I install them?

Answer
Several items. Wetter? meaning 1 & 2 are wet too? A wet plug will not fire because the current runs across the liquid fuel and thus no spark. When the plug is out and wet it will fire but a spark has a very difficult time jumping a gap while under pressure (compression). So you need to clean or replace the plugs and don't use the choke but do use starter fluid (all auto parts stores sell it)

Second, You should test your compression gauge as over the years I have run thousands of compression tests and it is very rare to see four cylinders have the same compression.

When you had the plugs out and on their plug wire and seen the spark was it blue in color? and thick as a pencil lead? (not in bright sun light)
If it was orange or yellow and thin like a hair it is a weak spark and probably don't fire at all under compression.

Remember that you can not ignite gasoline as a liquid, it will only ignite gasoline vapor so a wet plug can not fire as it is a good conductor of electricity especially under pressure. That is why it is so important to use starting fluid as a test. Starting fluid vaporizes almost instantly.

If you can't get a few seconds of run on starting fluid YOU HAVE NO IGNITION OR NO COMPRESSION!!

Let me know,

Howard