Villiers F15 with Amal carb - is this a good idea?

My F15 with new Amal carb continues to drive me bonkers. It is ridiculously tempremental and now is almost unstartable. It behaves like there are fuel problems but I have done everything to try to improve it but still I have trouble.
The thing is that the F15 manual doesn't mention Amal carb so I wonder how suitable it is (on Allen scythe). Would a Villiers carb be better?
Are Amal carbs troublesome?

My F15 manual has Amal & Villiers carbs shown, this is the Amal page.

Thanks for that. It confirms what I suspected, namely that for an exgine that operates on a governor and thus never idles there are no adjustments that will affect it.

So how do they compare to the Villiers carburetters?

One of the big problems I had with the Amal is that there was no air filter for it and I could not see how it was possible to nicely fit a filter.
Do you have a picture of the filter assembly?
I had to make my own and tie it on with cable ties - or risk grass clippings being sucked into the engine.

I have always been worried that while the engine seemed to work on on the bench, when mounted on the scythe with the engine now at a slight angle, it has been an absolute pain. This is why I wondered if it was suitable.

Amal 519 info







I don't know how they compare to the Villiers carbs, I can't access my F15 so don't know which type of carb is fitted.

Thanks again. That is really useful.

I just had a breakthrough - I think I can answer my own question now...

The reason the Amal carb is trouble on the Allen Scythe is indeed because the engine axis slopes downwards.
The Amal main jet seems to pick up its fuel quite near the bottom of the float chamber. Now add in the slope and the smallest drop of water or any bit of crap is funnelled straight into the main jet.

I hadn't expected so much condensation in such a short time!
Having rebuilt the fuel pipes and filter I fuelled it and ran it. It had stalled and at this point the starter broke.
So a day elapsed and I came back to it with the starter fixed, and now it just won't run. In that brief time about 1ml of water had condensed in the tank and ended up in the carb. It starts, but the vibration immediately makes enough waves on the water layer that it gets a mouthful and stops, with the plug now all wet.

It looks like I must implement a water separator!

I've had similar problems with two-stroke garden tools, especially after winter storage. In the end I moved to Aspen Alkylate Petrol ( no ethanol which attracts moisture) - but probably a tad pricey for all day rally use.

Look at super unleaded fuel (97 RON) but check the pump as they should display E5 if it has Ethanol in, Esso super is Ethanol free, but Shell V power isn't so check first.

Water in fuel is certainly a nightmare for equipment stored in ambient external conditions.
Our Ferguson TEA20's Zenith carb has a simple way to drain out crap and a bowl-filter to catch water before it even gets there.
I have been contemplating whether to add a drain to the Amal, but I am not sure the best way to do it so it doesn't just leak or have the drain screw fall out all the time.

But now I come to think about it, I never actually saw any water collect in the tractor's filter until this year.
And something else... I used a container that is OK with white spirit to run out some fuel, and it surprised me by dissolving like in cellulose thinners!

All this makes me wonder if there has been a significant change to petrol formulation in the last year or so.

OK, things are still not good.
Having sorted out dirt and water issues it still will not run.
It starts and goes Brmmmm  Brmmmm and then stops.
One significant thing, I found that opening the adjuster screw (#4 above) to maximum extent improves it greatly - it splutters along for several seconds if I am lucky.

The engine ran OK on the bench, but that was mainly with it just idling or running with no load.
In the scythe the load is always significant, and also it runs on the governor so it starts with the throttle wide open and then closes down somewhat on running.

So it looks like there isn't enough fuel getting in when running on significant load.
Any suggestions?
This carburetter is NOS and has never been seen to work on load, ever. I have no way of knowing if it even has the right jets installed.

I'm not exactly sure what air cleaner you are using or how well fitted.

It needs to be a good close fit to the carburettor and have the correct element. or oil (if it's an oil bath type).

If incorrect it could be giving either:- a rich mixture; if too much of a restriction,
or, a weak mixture if not enough restriction.

The air cleaner is the one used on Honda GX100 engines, adapted to fit.
There is very little resistance to the air flow.

I am fairly sure the problem is not lack of air, it is too much!

If opening the air bleed screw (weakening the mixture) improves it it would suggest it's flooding? Is the float height correct? Is the float needle valve seating correctly?

The "pilot air adjusting screw" is a mystery to me as it is such a tiny little tapered needle control that it is hard to imagine what effect it could possbly have except at almost zero air flow. It is documented as affecting the idle mixture - and my situation is nothing like idling!

If weakening the mixture was helping then opening the choke would help in spades, and yet opening the choke the smallest amount means it won't go at all.

I am wondering if something very bad is going on.
I now have the carb back on the bench so I will try to see if something is blocked - but some bits of it are so small that it is hard to tell.

This is a good one for us not the owner.
Is the main jet the size the book says. No 11 95c.
With running on choke and stalls of choke. Sounds like it's running lean.
Andrew

The  main jet says "AMAL 95"
Is that good (enough) ?
And how big should the hole be?

And another thing - what is the strange brass rod that sticks down into the main jet do exactly? (Apart from ripping the float chamber gasket when you remove it and forget about it, of course)
(I do not see it on the parts diagram)

Update: Now on the bench, I see no fault with the carb. The tiny passages are not blocked, and it works as expected.
I note that the so-called "pilot air adjusting screw" actually communicates with the main jet fuel passage - in that if you take the screw out and blow up the main jet passage it comes out of the adjuster screw. I think this is a clue - if something is not right about the main jet then opening this screw provides an additional route for fuel to get in.

Are you sure the problem is with the carb? The general rule with any engine is the carb is the last thing you adjust when setting it up.

Are the valves OK, not sticking or burnt and clearances correct? Are the points clean and gapped correctly, and the same for the plug? Is the timing set correctly? Head gasket not leaking? No air leaks between the carb and engine?

Not trying to teach you to suck eggs with the above, BTW...

The general rule with any engine is the carb is the last thing you adjust when setting it up.

That general rule makes a hidden assumption - that the whole installation used to work, but now it doesn't.

I am in the situation that the old Amal carburettor was so grotty that I bought a "new" one. The new carburettor has never been seen to work - ever. Except it seemed to. As I said, I had the engine on the bench to work over all the usual stuff. I had it running OK-ish, but entirely off load.

I also managed to buy a very manky-looking spare engine fitted with a gas carburettor - but sadly the regulator was a bit past it. I thought its magneto was a thing to try, but annoyingly I found there are two kinds of Villiers F15 (it doesn't mention that in my book). The flywheel and magneto assemblies are different enough that one cannot swap individual parts between them, in spite of looking similar.

I have been fighting all kinds of stupid problems. I seem to run into this a lot. The "it can't have worked" issues. One was the governor spring - it was totally wrong. I could not understand how it could possibly work and eventually managed to buy a replacement that was way different - and that did work just fine. The magneto seemed very hard to get a good output. There were possible reasons for this, but to avoid having too many things wrong at once I fitted a coil run from a  battery - massively improving the spark and thereby elliminating any marginal issues on that score (I have a concern that the magneto magnets have lost their strength). Also the original starter spring was broken, but I was able to fit the entirely different starter from the spare engine but have a concern that the pawl things are only just engaging (which I discovered when a cover bolt came about 1 turn loose, and it stopped working as a result of the extra clearance).

So when I stuck the engine back on the scythe I expected a good result - but it has hideously tempermental and never ran for long enough for me to reach the choke and try varying the setting. Thinking this was a fuel-feed issue I decided that the fuel tank (the wrong kind BTW, like on the 2-stroke scythe, not like a normal Villiers F15) was too low, so raised it and fitted a filter too. The tank needed a load of work, so that had to be cleaned and sealed with epoxy sealer stuff for tanks. When it still didn't go properly I assumed I hadn't raised the tank enough so raised it up to the point that there would be no argument about fuel feed.

I have pulled the starter rope so many times that the starter is wearing out! I think it needs to fit further inside the cup-thing on the engine - but this was a transplant so may need some work. When bench testing I had mainly spun the engine up using a power drill - and it did seem to be rather hard to get it to go.

I do not think there is an issue with valves, ignition, or timing and the engine has roared away for a couple of seconds, as if all was well. So it can run!

BTW I am shocked to look back at my records to see I bought this thing in 2016. It was advertied as "good working order" (yes, I did get a discount when I discovered how bad it was - but not enough by a mile had a realised).

The engine is back on the bench.
The carb all checks out OK - I can't see a problem with it.
I had the thought that the problem could be with the inlet valve.
I vaguely remember that when the engine spluttered to a halt, I often saw a very small puff of white smoke/vapour blowing away in the wind. I once thought I saw it emerge from the air filter, maybe.
It occured to me that if something causes the inlet valve to stick open very briefly as the rpm builds up then this could explain everything.

On opening the valve compartment I was disappointed to not see a broken spring or a deformed tappet etc.
It all looked really good, everything oily, all working nicely.
BUT - I notice that while the exhaust valve stem is dripping in oil and both springs are oily, and lots of oil on the tappets and pretty much everywhere, there is absolutely no oil on the top part of the inlet valve stem from the the spring retainer and upwards. It is absolutely bone dry and shows signs of tiny marks of corrosion. It is like the inlet retainer has entirely shielded the valve stem from any oil splashing about.

So how exactly is this area lubricated? How does oil normally reach the valve stems?
Although oily it is very black - like old oil - not the fresh stuff currently loaded.

Well it may be that there is so much fuel from a flooding carburetor, that petrol is running down the valve guide, and washing any oil from the valve stem.