# Briggs and Stratton 6.75 hp mower not starting



## fishboy

I pulled the carb and cleaned it, checked the plug and it will not start. I did a compression check and only got 30psi. But I read somewhere these engines have a compression letoff or something so it may not be valid. Below is the model number and it is on Troy bult 220 mower...


125k02-0243-e1 04010759


----------



## Basementgeek

B&S uses(used) a system called easy spin. It modified the exhaust valve cam.

Spin the engine backwards to get a more accurate compression reading.

BG


----------



## fishboy

I spin the blade backwards and nothing registered on the gauge? Any ideas?


----------



## Basementgeek

When the engine was running was it smoking a lot? That would indicate a problem with rings/cylinder.

B&S does not publish compression readings.

Here is what my old BS repair manual says on checking compression:

Remove the spark plug wire first.

"Spin the flywheel counterclockwise (flywheel side) against the compression stroke, a sharp rebound indicates satisfactory compression. Slight or no rebound indicates poor compression.

Loss of compression will usually be the result of the following

1. The cylinder head gasket blown or leaking

2. Valves ticking or not seating properly

3. Piston rings not sealing, which would also cause the engine to consume an excessive amount of oil"

BG


----------



## fishboy

Thanks I will ask the owner about the smoke. It belongs to a friends mother.


----------



## MrChooks

Hi Fishboy - just a quick question - was the mower working OK before it stopped - can you give us a little more info on what it was that made the mower stop working - was it burniung oil / blowing blue smoke?

If it was going OK but has just stopped working - then carb and or ignitiion problems are more likely to be the cause. Very often a thorough carb / jet cleaning and a check on the spark / ignition will pinpoint / correct the problem

If it is a really tired old unit and was burning oil and or had a history of lousy compression - then the engine's internals need to be looked at


----------



## fishboy

I will have to check on the oil burning issue. I think it was getting harder and harder to start. I did rinse out the carb with cleaner and the plug is new...


----------



## MrChooks

maybe the next step is to give the carb a thorough clean out - don't forget to remove the main jet and clean the orifaces and carb body ports


----------



## fishboy

Thanks i will do that!


----------



## fishboy

I pulled and cleaned the carb this morning and tried a different plug to no avail...


----------



## Basementgeek

If the compression is not there, it will not run.

BG


----------



## MrChooks

If you have spark in correct timing, fuel & compression – the engine JUST HAS TO START – but without all 3 – it will never start - so something is still missing.

As BG said – if your engine has no compression – it’s in a bad way and will need some pretty serious work on its internals. But before tearing it apart – maybe worth a last check of spark & fuel.

If you pull the plug and lay it across the head so the plug body is touching the head and pull the engine through – you should see spark jumping across the plug’s electrodes – if not then you need to look closely at what is wrong with your ignition. 

If you have spark – then try tipping about a teaspoon of fuel down the plug hole – put the plug straight back and pull the engine through – see if it fires at all or maybe even runs a bit before quitting – then you will know you still have a carb / fuel delivery problem.

If after all this you are confident you have spark & fuel and it still won’t go – and you have low / no compression - you will need to decide why and whether or not the engine is worth the effort to strip down to fix.


----------



## fishboy

Thanks I will certainly follow your advice! Thank you very much.
David


----------

