No spark - Gordon

gordo2023

gordo2023

Forum Newbie
At wits end with this machine. New here so please bare or bear with me. Briggs & Stratton 17.5 hp engine no start no spark!
Long story short I had adjusted the valves and apparently did not tighten down the lock screw enough and damaged the intake push rod, broke in half. I replaced the push rod and adjusted the valves, setting them at 5, intake, and exhaust 7 thousandths. I get spark to the plug when grounded to the block but nothing when put in the engine. I have used a light to test the coil as well as a multimeter and it tests ok, in fact new. None of the safety wiring has been touched - brake, seat and kill switch.
What can it be??
 
If it fires when touching off to ground , it's firing while installed.
you may have a fuel problem or your key is sheared at the flywheel throwing off your timing
 
I’ve seen units which have weak spark when the air gap is too large. Should be set at .008-.010”. Plus, as Star states try replacing the coil with a known good one. There is no way to test today’s coils without an expensive piece of equipment. I don’t know of any repair shop which even has one.
 
The coil is new, spark plug gap is .30. As I stated, I have a spark with the plug out and grounded but cannot get even a pop with plug in engine. Stater fluid into carb, even sprayed into the combustion chamber and replace the spark plug and nothing!!,
 
Just because it fires out side the cylinder @ .030 does not mean it will fire under compression. To similate compression the gap outside the cylinder has to be at least 1/4 inch.
 
hlw49 said:
Just because it fires out side the cylinder @ .030 does not mean it will fire under compression. To similate compression the gap outside the cylinder has to be at least 1/4 inch.
Click to expand...
Sometimes new parts fail right out of the box (3 times for me this year). Bite the bullet and buy another coil, maybe from a different vendor, install and hopefully it will fire.
 
Come on get it through to your head spark plugs due fail under compression load. I had just proved that to a customer here last month. Nice blue spark out of the engine just means the coil are usually good. The customer brought in his mower that would not start. I did my normal tests and said I needed to go to the parts room to get spark plug and the customer said but the plug is firing. Well when I installed a new known good plug it fired right up.

Plugs can do some strange things too. I had one to cause engine knocking even though it was the correct plug. And one to cause a 2 cycle engine to diesel; it had run away rpms at full throttle. Even had plugs to short out. Plug insulator do crack inside the metal shells. I have personally take plugs apart looking for failure causes.

This why I suggest using a known good plug from a running engine for test purposes.

And as said you can not test these coils that internal triggers with a multi meter. It requires a very expensive tester that nearly no shop has on hand. They are plug and play mag packs that either works or don't work.
 
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