basic troubleshooting

I don't want to sound presuptous. I don't know everything, yet, I've noticed that a recurring problem occures, engine not starting. If the engine has a fully charged battery, and turns at proper speed, there are two reasons that a gas engine will not start. One reason is no fuel is getting to the cylinder, and the other is no spark. I usually factor out the spark first by removing the plug wire from a spark plug and inserting a spark tester with the ground clamped to the block. If a healthy spark jumps the gap of the spark tester, we can act on the engine having good spark. The fuel can be checked several ways, such as spraying ether into the air intake and listening to whether it fires enough to burn off the ether. We can also remove a spark plug and smell for gas etc. Once we know which system is at fault, we can start factoring down the most likely causes. I hope that might help, and I hope it doesn't sound presuptuous.

Presumtion is not a problem. (your diagnostic statement is not presumptious though)
There is precious little common knowledge anymore. In 1950 there were still substantial numbers of rural raised people making a living using their many farm earned tallents and insights.
Today people think that because they have access to information, that they are knowledgable. What a mistake.
Your sentences speak volumes, but there is a need to contain the 500 pages of what to do when there is all three but no running. (like the timing is off, or the manifold has shop rags still in it). My reading has included 1950s books on how cars/tractors and trains operate. These were written describing pre WW2 technologies. Keep on thinking and reading. Jim

I realize that there are still a few(I don't know about 500 pages), yet, most of the problems will be factored out with verifing those two systems. If a person has checked those two systems, most problems are covered. Yes timing, especially ignition timing, would evade that spark test, as a spark would be produced, allbeit not when it should be. Other telltale indicators include what maitenance was recently done immediately before problem started. If I had a nickle for everytime I started troubleshooting a problem that was caused by someone improperly preforming a maintenance on the equipment, I would be filthy rich.

I recently retired as a Coast Guard mechanic MK1. Two of my last three units were with the Sector/Group Engineering office. This included assisting the troubleshooting of equipment from a distance. When the unit being assisted can verify those two systems, trouble shooting from miles away, often in a different state, is far more productive. Imagine the difference between;

1The engine won't start!!!!

2 The engine won't start. It has spark, but isn't getting fuel.

Just because there is fire going to the spark plug dosen't mean that there is spark at the end of the plug . Yes , I agree that if there is spark going through the wire to plug ,then chances are that the plug is firing ,but that is not always the case . Plug could be dead or fouled out with carbon or oil and not firing. You actually need to pull plugs out and check for fire there by grounding the plug out . On multiple plug engines ( 4 cyl ., 6 cyl. , etc. )you need to pull more than one plug out to make sure that their firing , at least it wouldn't hurt . On a 1 cylinder engine replace plug with a know good one or a new one .

Whizkid

P.S. As always when working with spark plugs and wires be careful that you don't electrocute your self or start a fire somehow from gas squirting into an " open " cylinder .

For a gas engine to run there are 3 components necessary, not 2 as you stated. 1)gas---2)spark---3)compression.

If you can t/s fuel and spark, you will cover most likely causes. Yes, I am aware that you need compression, yet, if you factor out the two I mentioned, Which most can do with the most basic tools, you will be far closer to fixing the problem, and compression is rarely the cause of a no start. Far more often, loses of compression will be indicated by a lose of power. I know that most of us can relay the rare account that an engine had lost enough compression that it would not start, yet, in most cases, even with low compression, the engine will start. It just will not have much power and will stall under any load. Long before it reaches the point where the engine will not start, other issues will have developed, such as large plums of blue smake. I've taken engines down for rebuild that were pushing clouds of blue smake, yet, would start, and found the rings weren't even making contact on all sides of the cylinder wall because of the wear, yet the engine had not been a no start. But yes compression is needed for an engine to start, technically.

You could break each one of those down with # 1 A B and C's. Like A-gas, B-gas with water, C-gas with dirt. # 2 A-spark, B-spark weak, C-spark at the right time. # 3 A-compression on all cylinders, B-compression on some cylinders. ^D LOL.

73 and not retired, still keeping 20 some tractors that all set outside running without asking any how to questions.

Unfortunately there are way more things that can cause an engine not to start than just those you mention, and even the checks your talking about don't alays mean anything. Like another post said just because you have spark doesn't mean the plug is actually firing as it can be fouled, the ceramic can be broke allowing it ground out, etc, etc, etc. I've seen starters that had been rebuilt and turned the engine the wrong direction, ignition systems that didn't have enough energy to fire the plug when under compression but would fire the plug in open air, plugs that would fire when you took them out but not when installed and tightend, a distrubutor cap that had a hairline crack that wasn't visible that was causing one plug to misfire on occasion, etc, etc etc. I've seen an updraft carb that the siphon tube that put gas into the airstream had unthreaded itself, gotten sucked up into the intake manifold and eventually wound up under an intake valve. In that case the engine had just shut down unexpectedly and absolutely wouldn't restart. In other words the engine was 'getting gas to the carb, it had spark, etc, etc. Basically there was nothing visible externally, and the only way I found the problem was to pull the carb and look.

I guess what I'm trying to say is that, yes, your saying that troubleshooting a basic, non electronic gas engine is basically 'a simple matter' is a bit presumptious. The thing is that for those of us that do this kind of thing for a living we do tend to get a bit presumptious, complacent, or whatever on occasion and as a result we occasionally fall prey to making the assumption that the problem we're running into will always fall into one of the catagories of an 'easy fix'.

Unfortunately just when we think that every problem stems from one of the tried and true 'easy fixes', just when we think that we've seen it all, something new pops up. When this happens it's our job to stop assuming, recognize that the problem is something new, learn from it, and add the new problem to our troubleshooting knowledge for future use. If we can do that then we ultimately end up as better mechanics, if not then we're nothing but 'presumptious idiots' who have no right to be called a real mechanic.....But that's just my humble opinion as someone who has made my share of assumptions over the years and wasted way to many hours trying to figure out what "should" have been a simple problem and as a result tended to be blind to the fact that the problem wasn't as simple as it appeared on the surface.....and as a result have learned alot and continue to learn more and more every day I go to work........

Like my grandpa used to tell me, " A day spent without learning something new is a wasted day". I think Grandpa was a really smart fellow.....

Engine with blue smake ? What's blue smake ? I think that you mean blue smoke ? You are right about the two problems though about fuel and fire and ruling either one of those out when the motor won't start . But there is also compression needed to make a motor run and you'd be suprised how many small engines ( still gas powered so same rules apply )people bring in to be worked on because they won't start and it turns out to be no compression.

Whizkid

I think you might have forgotten the 4th one F.B. The 3 must also be at the proper time. Just my thoughts, Kieth