Tecumseh BVS 143 (Mountfield Empress) - Won't start, oily spark plug, stiff jerking pull

[ilmiont]

Hi all, new here,

We've got a mid-80s Mountfield Empress 16 with a Tecumseh BVS 143 engine. Solid machine which ran flawlessly until a few years ago when it got progressively more tricky to start and ended up being retired due to inheritance of another machine.

Cut a long story short, I want the Mountfield back as it's built to last and becoming a classic, and does a much finer job overall than the newer machine (a B&S Sovereign with a fiddly height adjustment system, a safety pull bar and no roller).

Over the past few years, the Empress has been seen by several local repair shops with varying results; each time it has come back improved, done a few mows and then proven impossible to start next season. Last year, it was taken to a local mechanic, who again did a service on it and got it running acceptably. It did a few cuts and then failed to start later in the season. We recall that he had mentioned the flywheel needed attention but we cannot recall exactly what was wrong.

It's my dad's mower but I'm now hoping to take this on as a project. I am inexperienced and generally piecing things together as I go, from vaguely similar online discussion threads and from this manual:

http://www.servicelink.org.uk/sites/default/files/Manuals/16%20empress.pdf

With that in mind please exercise patience as required, and clarity in responses, wherever possible.

The historical detail is provided to paint as accurate a picture as possible but I must stress I have drawn a line under it and am working from the present state, as multiple mechanics and repair shops have so far failed to satisfactorily remedy what we see as the main problem ("it fails to start") for any significant duration of time, and because we cannot recall all of the particulars which we have been told at various points with respect to specific components.

Therefore here is the situation as of today:

Attempted to mow yesterday but failed to start as expected. Cue me committing to getting it running again!

It sounds as though it's cranking and about to start but never actually turns over.

The pull cord is stiff at particular and repeatable points in its motion - approximately the first few centimetres are stiff, then there's a strong distinct tug and further stiffness over the next quarter (approximately), then it runs generally smoothly with a few more stiff points. This is not due to the pull cord itself (which is relatively new) and I confirmed this today - with the pull cord removed and cranking the engine by hand, it remains stiff and resistant as described.

Things which have been checked or adjusted:

- Engine oil was low and has been topped up to the level
- Fuel was old and low; it has been topped up with fresh fuel to a reasonable level
- Air filter was dry and dirty; it has been cleaned in water and lightly saturated with engine oil
- The carb mixture screw has been adjusted using the guidance in the manual linked above - close, open by three quarters of a turn
- The throttle cable has been checked and adjusted using the guidance in the manual linked above.
- Cranking the engine is stiff at particular points in its motion as described above
- The engine does crank and can often sound like it's about to start
- The spark plug (replaced by a mechanic last year with a lightly used part) was wet with what seems to be oil
- With the spark plug removed, the engine cranks completely smoothly - all of the resistance described above is completely gone. As soon as the spark plug is inserted, whether cable connected or not, there is resistance to cranking as described above
- There appears to be damp behind the carb and there is a smell of fuel in the air after attempting to start

After cleaning the spark plug today, I succeeded in starting the engine a couple of times by using a tip I found online: pulled the cord three times with the throttle in choke position (failed to start each time), and then retry with the throttle in fast idle position. On the first attempt in idle, it coughed and almost started. After repeating the entire choke/idle process again, on the second attempt, it did indeed very reluctantly start and run.

I then managed to repeat this success several more times and on a few occasions it was possible to start on the first attempt in the choke position. The engine was running reasonably smoothly. Each time, the engine abruptly and spontaneously slowed down and then cut out within 15 seconds of starting, irrespective of throttle position. After sitting for a while, I could not repeat the success again using any method, and even having removed, cleaned and reinserted the spark plug again, I've not had it start again in a while and have put it away for the day. When it did start, on several occasions, there was a very violent kickback/recoil of the pull cord.

Any advice at all to get us on the right track would be much appreciated. I am happy and able to provide photos of any component to help clarify what's going on.

Many thanks indeed.

 

[Romore]

Have you checked the oil level? It may be contaminated with gas which points to a carburetor problem. Was the plug wet when you removed it?

 

[bertsmobile1]

Welcome
Small engine course 101
Firstly from your high school physics , only gasses can burn, so the fuel has to e turned into a vapour inside the engine or nothing is going to happen.
Second compressing a gas requires energy, in this case from you via the starting rope.
Working out if the stiffness is too much or too little is what you pay people like me the big bucks for ( I wish )

To start & run an engine needs:-
fuel & air in a combustable ratio ( about 1:14 )
Compression above 65 psi
a spark at the right time.

Keep this in mind all the time and things become easier to understand.

To provide compression you have 2 valves that open & close at a prescribed time and this is set by the cam shaft.
Over time cam shafts wear out so the valves open latter, close earlier and do ont open as far so less fuel gets in.

The carburettor turns the fuel into tiny droplets which heat from the engine convert into a gas for the spark to ignite.
When an engine is very cold we put a lot more fuel into the engine in the hope that enough will become a gas to get to that magic 14:1 ratio & the engine will start.
Most of the excess fuel will blow strait out the muffler unburned or as partially burned soot which we see as black smoke.
As the engine heats up , there is enough energy for the fuel to fully vapourise so the amount of fuel entering must be reduced or we will exceed the magic 14:1 ration and the engine will flood & stall out .

To provide the spark at the right time you have a magneto that is keyed onto the crank shaft.

The full repair manual for your engine is TECUMSEH-SERVICE--REPAIR-MANUAL-3HP-TO-11HP-4-CYCLE-L-HEAD-FLAT-HEAD-ENGINES-69250..> available from K & C parts warehouse whee you will find a lot of other useful downloads relating to your engine.

Now the easy things to check first.
Pull off the cover on the top of the engine, including the pull stater and visually inspect the key.
1/2 of it is in the fly wheel & 1/2 is in the crankshaft .
If the key is intact the 2 halves should sit together and look like a square .
Pull the spark plug out and rotate the engine by hand.
When the piston is closest to the spark plug hole the magnets on the flywheel should be under the legs of the coil and the space between the magnets & coil should be 0.010"
If not adjust it .

Now because you have a side valve engine commonly called a flat head or L head, all means the same everything else will require removal of the carburettor.

Way way back, petrol was distilled from oil
If you put a jar of petrol out even in the feeble UK winter sun, it would evaporate in a few hours leaving the jar bone dry
Now days "fuel" which is nothing like petrol will not evaporate to leave a bone dry carb.
It will reduce to a foul smelling sticky gum that will not redissolve into fuel so has to be removed with other solvents.
If a mower has been left with "fuel" in it for extended time the fuel will leave this gum every where and block off all the tiny holes in the carb.
You will find detailed cleaning instructions with photos & explainations at the Outdoor Power information site .


While the carb is off remove the valve chest cover and check the valve gap as per the instruction to be found in the manual previously linked to.
When not used for long times valve stems rust so they get stuck in the guides and do not fully close every time .
And after a long time of use the gaps get too small so need to be adjusted.
Very few repair shops will do this to your engine as the time required to do it will exceed the cost of the engine.
For fun download the repair times chart from the K & C site then multiply the time by the hourly charge the workshop billed you .
To use it you add up the times for each step , so just checking it will cost you £ 20 .

Best of British luck to you old chum.
Feel free to come back as many times as you feel the need to we are all here to help .
Photos of stuff you do not understand are always appreciated

 

[ilmiont]

Hello, thank you for the welcome and useful information!

A quick update of the morning's work.

Got the mower out the shed this morning. First got the air filter cover off again and checked the air filter to see if it was oversaturated. Didn't seem to be.

Took the pull cord assembly off the top again to get photos which will post later.

Took the spark plug out again, it had some oil around it once again, which I cleaned off and reinserted it.

Possibly relevant - the mower had been sat in the sun for about 20 minutes prior to starting work.

After reinserting the spark plug, attempted start and decided to try without choke (we'd normally always start in choke position). It immediately started, first time, with very little resistance to the pull - altogether a very enthusiastic start.

Repeated this success multiple times with no failure yet. I suspect therefore that I've been flooding it through use of the choke position.

Problem far from solved yet. The engine seems to be running extremely fast and there is nonexistent throttle control - it's either running, fast, or it's off. It smells and puffs blue at points but at least it's now starting on command.

Referring to that very helpful manual you linked to hopefully now start adjusting the carb and getting throttle control back.

I have photos/videos to post later.

 

[ilmiont]

Some photos prior to the starts this morning - the spark plug is oily as removed this morning.

One thing I forgot to mention - the owner's manual/maintenance guide I linked above shows a round gasket inside the air intake in the air filter cover; it's missing. Not sure if it's an issue or not. I noticed this morning there was dust and dirt around the sides of the air intake and I've now cleaned that out.

Started again many times successfully since my earlier post, always in the idle position (not tried in choke yet for fear of flooding it). The only real change since yesterday is that it's sat overnight and I tipped it forwards this morning with the spark plug out (forgot to mention in the earlier post) in the hope of getting any oil out of the cylinder, but I didn't see anything come out. The only other change is starting in idle instead of in choke position.

It starts every time, extremely enthusiastically, and does not cut out; it runs very fast and with no throttle control whatsoever (but the cable and lever are moving and in the correct positions).

 

[bertsmobile1]

Just be a little wary of allowing these engines to over rev.
Most spin at 3,000 to 4,000 rpm without much hassel but at 5,000 rpm it is exit piston , sage right,,, through the crank case.

 

[ilmiont]

Just be a little wary of allowing these engines to over rev.
Most spin at 3,000 to 4,000 rpm without much hassel but at 5,000 rpm it is exit piston , sage right,,, through the crank case.

I'm not too sure what to look at next.

Starting enthusiastically every time but I can't get the revs down. Carb mixture and idle screws don't seem to have an effect. Throttle lever looks like the linkages are moving OK but revs remain constant all the way to stall.

 

[ilmiont]

Here are some photos with the throttle lever in idle position - as previously stated, revs remain constantly high irrespective of throttle position:



In the final image I have highlighted some areas of interest (to me):

- The red boxes, I'm not sure what they are, they rotate when pressed and I presume are used to control fuel/air inlets in some way. The silver metal pin above the right one, connected to the throttle lever, engages with the right one when the throttle is near the choke position, moving it around, and I presume reducing the air intake. I'm not sure I can observe the left one being moved by the throttle lever.
- The yellow box - the gasket/rubber seal for the air intake side of the carb has some corrosion and there are slight gaps in it, it doesn't quite seal completely I think, whereas the fuel one does.

Not sure if any of this shows anything relevant to the current problem, which seems to be complete lack of throttle control with no obvious cause (to me).

 

[bertsmobile1]

Go back to that manual and read the chapter on governors
The governor SLOWS down the engine and works against the throttle lever via a spring
Either the gvernor is not connected, badly adjusted or broken.

 

[ilmiont]

Got there via help on another forum - the basic owner's maintenance guide I had been reading said to turn the idle screw in and then back out by one turn when resetting the carb screws. Turns out that should be more like 4+ turns out...

Although I'd been adjusting it either way (with no real observable change), I'd never have got to turning it out that far based on my prior knowledge and what I'd been reading.

Now running at about 5-6 turns out on the idle adjuster and we're back to a nice slow idle. Also still starting reliably and enthusiastically every time, although the stiff resistance remains through the first quarter or so of the cable pull (I pull that section out slowly, avoiding starting, wait until it's passed, and then pull the rest to start - the cable/crank is however completely smooth without the spark plug). There's still also the occasional kickback.

Seem to have made it to a serviceable state though... seems to be starting reliably and the throttle issue turned out to be a basic mistake, although the solution seems to have come from experience I simply don't have. Whether it will start again at the weekend to actually mow the lawn remains to be seen!