Trying to Start a B (GOT IT STARTED!!!)

The manual that I linked says compression pressure is 94 to 115 pounds for various variations of the B/C gas or low octane fuel engine. It doesn't give any details about making the test. I'm sure that it is crucial to make sure the choke and throttle are full open. Then take the pressure as it builds, usually in my experience it stops rising after 5 or 6 compression strokes. The highest pressure reached is considered the proper reading.The starter or cranker work faster if all the plugs are out and the clutch pedal is pushed even with the transmission is in neutral.

Checking for ignition power by looking at a plug removed but grounded is not a good test of ignition. At atmospheric pressure it takes a lot less voltage to spark than it does at 100 psi or so for a normal compression. A system that sparks a plug at atmospheric pressure may not fire at the higher pressure. A more conventional test is to expose the end of the plug wire and hold it between 3/8" and 1/2" from the block or head. A good ignition system will spark that gap at atmospheric pressure. The spark has to be fat and blue. A skinny or yellow spark shows problems in the ignition system. A bad coil probably won't get voltage to jump any gap. A bad condenser will make the thin and yellow sparks and the engine won't run well with a yellow spark.

When preparing to set the timing it is important to set the point gap first because changing the point gap changes the timing.

Gerald J.

    Hey Thas great,,,,but,,,,when are Ya gonna break out the Black Label,,,,,????

I did mention upthread that the plugs looked old. The wires probably could be replaced too. When you feel rich I'd go with new points, rotor, cap, wires and plugs. That pretty much takes care of the ignition system.

AJ,
You did very good with a lot of good instructions! I have had similar issues with tractors. and Its just a lot of checking! for spark, compression and gas. If they have those things they should run, Maybe not very well but they should fire and try to run.
So taking number 1 plug out and grounding to the block and looking for spark might have given you a lead on the problem sooner. That's what hind site is good for!
 Glad you got the B running. I bet the compression is better now too?
Regards,
 Chris

The question isn't why it would start on some and not others, it's what would prevent it from starting. Spark plugs are doing a seemingly simple job, but it's not that simple of a situation.

The concept is to provide a spot for a spark to form, and create enough heat to ignite fuel. In order to have a spark, you have to have an open circuit... meaning, the insulation between center electrode and outer exists. If the insulator has carbon built up on it, electricity will leak across the carbon, preventing a spark from forming.

There is a reason why spark plugs come in different 'heat' ranges. It's obvious to most why you'd not want to 'hot' a plug... 'autoignition temperature' is the temperature AND PRESSURE at which point a volatile mixture will just ignite. IF a plug's electrode was so hot that it was glowing red, you wouldn't need a spark to cause the fuel/air mix to touch off... as soon as the compression pressure is high enough for the fuel... and that hot spot... to light up, you'd have fire... This is exactly how 'hot bulb' diesel engines work... but in a gasoline engine, we call it 'pre-ignition'.

(it's bad in gasoline and gaseous-fuel engines because the flame speed and expansion/pressure rate is really high compared to 'heavy oil' engines)

So what about a 'cold' plug? Well, fuel burns... it's called a 'chemical reaction'... and in any chemical reaction, you start with one thing, get some energy out or in (exothermic or endothermic), and when that's done, there's always stuff left over.

If it was a pure fuel, and the mixture was ABSOLUTELY PERFECT, you'd have a very predictable basket of leftovers. In the case of a hydrocarbon fuel, the results of a 'perfect' burn are MOSTLY carbon dioxide and water... but usually some carbon monoxide, and some other nasties, and leftovers of whatever dust, dirt, crud, corrosion, etc., found it's way in through the intake, fuel system, whatever. Aluminum oxide from the inside of the carb bowl, bits of bug guts, some oil through the rings and valve guides, a little iron dust... 'yknow... crud.

And to make for clarity... NO engine I've ever seen, manages a 'perfect' burn. If you feed it ordinary pump gas, you ain't gonna get one... because it's a mixture of hydrocarbons... and frequently a carbohydrate (ethanol), and of course, crap and water.

So what happens, is the leftovers of the burn accumulate in places where they 'like' to stick. Typical barnyard carbon likes to stick to hot surfaces... it kinda likes to 'coat' them, and the spark plug electrode is one of those places. Carbon ain't much of an insulator... matter of fact, it's really handy for making resistors (electronic parts). It actually conducts electricity, but not very well... but enough so that it'll 'bleed off' your spark energy before the VOLTAGE across the plug electrodes reaches high enough to 'excite' the atoms between the gap... and the result, is no sparky arkey.

Remember that there's 'water' as a leftover? Well, wet carbon turns into a dead-short really fast. Lots'a guys will check for spark by lifting a wire off the terminal of a plug, and see a nice blue flash... but that doesn't mean you're getting a flash across the electrode inside. You can also pull the plug and watch it spark on the outside, but once it's threaded into that dark hole, and there's watery oily used-to-be-gasoline in there, it'll be just another dead-short.

So putting three new plugs in, made those three fire. What about the fourth? Well, once the engine's turning fast and warmed up, the mere presence of airflow through, and a rise in temp, will eventually clean up that one plug enough so it'll start to pop, then run.

Cleaning up the old plugs may very well result in them working fine, now that the engine's been fired up, warmed up, and happy. Matter of fact, now that it's been warmed up and cooled down a few times, a socket on that last plug, and light tap from a hammer on the side of the socket may break those threads loose and back it out nicely.

Thanks for the input- a lot of good advice and wisdom in what you say.

DaveKamp wrote: Finally... it's important to remember that when you're foiled by an engine that won't run... even after you've checked EVERYTHING... It's not that you've overlooked something... It's that you ASSUMED that something you HAVEN'T overlooked... is actually as you thought. These machines' spirit exists within YOU. You work on them, and you learn their story... and they vex and challenge you. They torment you, and when you finally get them alive, they warm you, they sing you their song. But remember- they are just machines. If you think they hate you... if you think they're evil demons that poke you with electrified, hot spears in jest of all your blood, sweat and tears, they're just machines. This is why it's best, when put to the test, to put the tools down and grab the phone, call a friend over to visit your home. Tell them nothing of what you've tried, just hand them a beverage and tell 'em you're fried. Stand back and watch, but keep your mouth shut, give them a chance to drag you out of your rut.

PURE POETRY!  Thank you!

Yeah, I'm guilty-as-charged... between work, taking Nick to work (For some strange reason, school permit doesn't allow a responsible kid to drive to his job and back...) and taking Libby to soccer games... and working towards getting foundation laid for the new workshop, and bicycling and motorcycling... boating and more work...

I've been kinda missing from this, and other forums (Smokstak, Practical Machinist, WeldingWeb)...

How's the line go... "I'm Sorry Spanky, I guess I just hafta live my own life..."   

One of these days, I'll get back to Schwartz... get the steering cylinders and column done, get the loader fitted, engine running, controls operational...