non starting mower

[lostinthelight]

...Ive modified an old spark plug to perform a leak down test as well or instead of a compression test,these ohv jobbies have a mechanical compression release that may be out of adjustment on the valves?

 

[Burnerman]

I made a similar thing to hold the valves shut on the Ford CVH mill
Worked well when doing the valve stem oil seals! Thought I was a genius
John
I dont think these motors have an automatic decompressor, do they?
J.

 

[jfg]

My new compression test gauge arrived today. the result is 110psi. plenty of compression to start i reckon.

I'm at a loss now.

The plug sparks and the coil is new. The carb is new. The red button squirts into the carb.

I think it's time to revisit the timing perhaps.

The motor pulls over freely every time with the spark plug removed.

It does jam up with the plug fitted every 4 or 5 pulls.

With the new flywheel key locking everything in place and in line, how can this keep happening?

I've read a few similar problems and they point to timing. However if there is only 1 way to fit the flywheel and everything is in line how can it be wrong?

This blastard thing won't win.

 

[Burnerman]

Why is the engine locking up after a few pulls.....what do you do to free it up again?
You should be able to pull the motor over until the cows come home.
John

 

[jfg]

the pull start will jam part way through the pull (nearly tearing fingers off) but then once released it then pulls normally again, until the next jam.

The engine does turn over completely and does not touch the plug electrode.

the valves cycle normally also

 

[Burnerman]

Assuming the motor doesn’t just free up if you remove the spark plug after the freeze, Id guess the lock up is rather a recoil starter jam, do you think?
Anyway, your compression is good.
I did ask if the motor had been in bits before, and you reckoned it hadn’t.....just thinking about the valve timing but really clutching at straws now. I would however go through the 4 stroke cycle, watching the valves open and close according to the piston position.
You have disconnected the flywheel brake cut out when trying?
There’s no low oil warning on this motor I presume.
John

 

[lostinthelight]

the pull start will jam part way through the pull (nearly tearing fingers off) but then once released it then pulls normally again, until the next jam.

The engine does turn over completely and does not touch the plug electrode.

the valves cycle normally also

Did you try the suggestion in post #23 cos I still think it sounds like over advanced ignition with it snatching back?

 

[lostinthelight]

Did you try the suggestion in post #23 cos I still think it sounds like over advanced ignition with it snatching back?

If you pull it over with the plug lead removed and it still snatched back its nothing to do with timing but if it doesn't , it is. After trying this and it still locks, some Ohv engines have auto decompression which can be afected by adjustment of valve clearance but dont know why that would be intermittent if its the cause?

 

[Burnerman]

A great one, this (at least for us )
I fully agree with the advanced timing theory producing kickback - even though the recoil starter mechanism should deal with that.....but if the timing hasn't slipped, what then? We assume the engine has the original flywheel so the timing must be fine.
If the OP found fuel in the cylinder after the lock up then the fault is fuelling - or valve timing but the engine hasn't been apart
I've come across auto decompression a few times, but never on a small engine like this.....they have always been single cylinder pull start of 400cc or over.
For sure, anyone reading this tome will be a Briggs expert by now
Would you be taking the head off - just for the hell of it?
John

 

[Burnerman]

Here's an oddball one.....
Suffolk Colt, horizontal crank, side valve. Ran OK until it got hot.
The eventual cause? The engine had been severely overheated at some point, (no oil I suspect) causing the valve seat to come loose in the alloy block.
When hot, the seat would start jumping about and the engine would stop.
If the seat had settled back into place, the engine would restart but I eventually found the seat holding the exhaust valve open......I peined it back in place and it was fine afterwards.
A real puzzler, that one
John

 

[lostinthelight]

The timing can only be out on a previously running engine, and the rub here is we dont know the history of it, if the key or keyways become damaged after hitting an object The op has replaced the key but needs to be very sure there is no damage to the latter which allows a variation of a few degree on the timing.

 

[lostinthelight]

Here's an oddball one.....
Suffolk Colt, horizontal crank, side valve. Ran OK until it got hot.
The eventual cause? The engine had been severely overheated at some point, (no oil I suspect) causing the valve seat to come loose in the alloy block.
When hot, the seat would start jumping about and the engine would stop.
If the seat had settled back into place, the engine would restart but I eventually found the seat holding the exhaust valve open......I peined it back in place and it was fine afterwards.
A real puzzler, that one
John

Some B&S are a pain for that, I once bought a pallet load of new and used briggs engines that had come from a Karting outfit, every one of the used ones had a loose valve seat

 

[mbertouche]

New to this forum so please be gentle with me if I am posting in wrong section. Currently 'locked down' in France (Covid-19) so away from my UK base and struggling with a Countax C600H ride-on fitted with Briggs 16hp Vanguard engine. To cut an extremely long story short I bought this mower s/h about 2 years ago and it had been built, I think, from several different 'donor' mowers. However, it wouldn't start on the key so I bought a new ignition switch and starter solenoid. Still no joy, only started when shorting out solenoid so did that for a while then about a month ago I decided I should get to the bottom of this. This mower has safety switches for the safety switches and a printed circuit board for the ignition circuit. After lots of different attempts I decided to disconnect all the loom including the pcb and just wire up the engine as though it was in a go-cart or something. It now spins over like a good-un but won't fire. I've connected the fuel solenoid to the spare terminal on the ignition switch and that works. I've disconnected the 'kill wire' loom as the diodes are visible so they may have burnt out, still no good. Found that one plug lead had been chewed by a mouse (found the corpse by the flywheel) but only the outer insulation. Getting a spark, left or right but never at the same time and never reliably - i.e. sometimes one will spark but not the other and vice versa. Also, the plugs are always dry. New fuel filter fitted, cleaned out carb bowl (which was full of fuel) and am now at my wits end. The grass is growing, I have arthritis and cutting half of the grass with a push along petrol mower has put me on my back for two days! Can anyone help please? The ignition switch has M, S, B, L and G terminals. I have connected M to the charge wire coming from the magneto. B to the battery, S to the starter solenoid and L to the fuel solenoid.

 

[Stivino]

It's the right section but, you should really start a new thread.

 

[Burnerman]

I agree a new thread would help, but is this the V twin Briggs Vanguard engine?
John