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Collection, Preservation and Display of Old Lawn Mowers

Villiers Engine

I have an early 1950's JP Simplex powered by a Villiers Midget, 98cc 2-stroke engine with a "Junior" carburetor. The engine drives both the cutting cylinder and the rear roller. I've got it running very nicely, producing very little smoke from the 32:1 petoil mix, with more than enough power to pull it and me around the garden.

There's only one problem - the engine runs at its best with the choke closed instead of open. This is contrary to all that I know of 2-strokes and runs against the advice in both the engine and mower manuals. Obviously the engine must be pulling enough air from somewhere because at the slightest attempt to open the choke, the revs die off and the engine runs poorly.

Have any of you had this "problem"? 

Forums

wristpin Sat, 13/09/2014

That suggests a fuel flow problem so start with a thorough fuel system check and clean beginning with the tank vent and working through from there.

jpsimplex14 Sun, 14/09/2014

Thanks for getting back to me.

I stripped down the fuel line, Tap, and Tank earlier this morning. The Tap had what looked like tiny pieces of plastic inside and both the Tank and copper fuel line contained quite a lot of debris in the form of  small pieces of grit like crud. I cleaned out all three, reassembled, cleaned up the Spark Plug contacts and put fresh petiol into the tank.

I'm sorry to say that my efforts made no apparent difference to the way the engine runs so I can't say I'm any further forward. There is black fluid escaping at the exhaust port and I will seal that later this week. I didn't mention that before because I didn't think that that was a contributing factor.

wristpin Sun, 14/09/2014

You make no mention of cleaning the carburettor ?​ That's the next step. Until  you know that the whole fuel system is spotlessly clean don't worry about your black fluid , it's probably just a mixture of combustion products and  the oil/fuel mixture. Possibly indicates incomplete combustion and the general condition of the engine.

jpsimplex14 Mon, 15/09/2014

I hadn't mentioned the Carburettor because I dismantled it and cleaned it out a fortnight ago. There may still be a problem in there with worn parts or perhaps  the original factory setting of the needle valve has been altered. I'm now at the stage of considering replacing the Carburettor as I've pretty much tried everything else. The Lodge spark plug is fairly old but seems to work fine. I could try replacing that with todays equivalent but it might have no overall effect. Air must be getting in somewhere somehow otherwise the engine wouldn't run so well. All the nuts and bolts around the engine, manifold and Carburettor are tight. What else is there to try?

wristpin Mon, 15/09/2014

I know that you cleaned the carb' but since then you found all the crud in the fuel pipe etc - are you sure that none has found its way into the carb'?

Only running on choke is a classic sign of a weak mixture, either due to a restricted fuel supply or a correct mixture being diluted by the ingress of air. so work through the likely causes.

Restricted fuel supply from the tank., incorrect float level, incorrect jetting (both fixed and adjustable), dirt/gum in the jets, air leaks from warped flanges of worn main bearings.

By all means try another carb' but make sure that it is "known good" and has been running another engine satisfactorily and that you aren't importing another problem! 

 

gtc Tue, 16/09/2014

Wristpin has nicely summarized the likely culprits, but if you are still seeing crud from the tank then it's indicative of a problem.

Fuel tanks that have gone rusty internally, and/or which have accumulated a coating of varnish from evaporated stale petroil mixture can keep on supplying crud for a long time after any attempt to clean them out. The crud tends to stick to the internal surface in small patches here and there and only moves when it wants to.

I would suggest replacing the fuel line temporarily with a plastic one with a fuel filter in it until the filter remains clean.

 

wristpin Tue, 16/09/2014

"see through" pipe and a filter is a good idea but just make sure that the filter is one designed to work with a gravity and not a pumped system. Those specified for use on a pumped system are often finer and can starve the engine of fuel if used without the pump.

If you use a long enough bit of clear pipe and form it into a U bend between tank and carb' you can see the crud accumulating in the bottom of the U.

I have recently been experimenting with electrolytic cleaning for the interior of steel fuel tanks and although the "chemistry " of the process is for rust removal it seems to bring out a goodly amount of other corruption along the way.

jpsimplex14 Thu, 18/09/2014

Well, as it 'appens, I took another look at the condition of the fuel entering the Carburettor a couple of nights ago. What prompted me to do this was after applying exhaust sealant paste to the engine outlet, I ran the engine for a little while to bake the paste and produce a good seal. While doing this I opened the choke and for a few seconds, the engine ran okay - after which the revs began to die. This encouraged me to believe that the fuel flow was compromised in some way. Disconnecting the fuel pipe to Carburettor joint revealed a quantity of red/brown particles - surprising really because I'd cleaned out the Tank, Tap, pipe, and Tank during the last fortnight. This contamination was held and prevented from getting into the Carburetor by a filter which was showing sins of getting clogged. Further investigation revealed the Tank to be a source of sludge and red/brown flakes and particles contaminating and affecting the fuel flow. I'll now concentrate my efforts into cleaning the Tank out. The tank on this mower is made from a casting in aluminium which I wouldn't have thought of as a source of corrosion.

gtc Thu, 18/09/2014

As I mentioned earlier, petroil/corrosion deposits can remain lodged in a tank despite your best efforts and they continue to emerge long after attempts at cleaning. Hence the suggestion of a filter.

wristpin Thu, 18/09/2014

Aluminium is attacked by water and usually forms a jelly or white powder. perhaps rust has been introduced from a contaminated fuel can. I presume that electrolytic corrosion removal will work with an ally tank but it will need someone who paid more attention in physics and chemistry at school to confirm how..

 

 

jpsimplex14 Sat, 20/09/2014

I removed the Tank, Tap, Copper Pipe, and Carburettor. I tackled the cleaning of the Tank first by partially filling with small Alpine Granite stones and shaking violently until my arms ached. Once all the wee stones were removed, I flushed the Tank out with detergent and very hot water, rinsed it out thoroughly with clean water and allowed to air overnight. I cleaned through the Tap and Copper Pipe and stripped the Carburettor. It had some dirty fuel inside.

When all was assembled, I filled the Tank with fresh fuel. The inside of the Tank looks shiny and clean. I opened the Tap over a small container and the fuel flowed strongly and clean.

The engine runs fine but with the choke only very slightly moved from the closed position. So, despite having a nice clean fuel supply, I'm almost back at square one. There is however one thing I've not yet tried. The Carburettor allows for the adjustment of the Taper Needle which should provide a correctly adjusted mixture at all throttle settings . I'm tempted to make small adjustments to the Taper Needle to see the effect.

wristpin Sat, 20/09/2014

Sounds like progress of a sort ! Does the tapered needle have small radial grooves at the top engaged by a small (and easily lost!) circlip. If so, try raising it by a groove at a time.

Useful tip to avoid spending time on all fours with a torch looking for an escaped small  flyaway component is to get a large clear poly bag and "operate" inside that so if a circlip or spring "pings" it will be constrained from flying across the workshop.

 

jpsimplex14 Sat, 20/09/2014

Progress indeed. I adjusted the Taper Needle inside the Carburettor to increase the richness of the mixture by turning the adjustment screw counterclockwise - a half turn at a time, (in keeping with the manufacturers instructions). I soon found I was able to run the engine with the choke out and as I reached the best position for the Taper Needle, the engine run better and better. Unfortunately, the Carburettor must be partially stripped to make each adjustment to the Taper Needle position, so it took a while. The Taper Needle is set at the factory so I'd put off trying this solution to my dilemma as I didn't want to risk damaging the engine and I wasn't altogether sure that such an adjustment was the answer. You learn something every day. 

Anyway, alls well that ends well and at least the whole fuel line system got a good clean out. Thanks for all your helpful suggestions.

wristpin Sat, 20/09/2014

That's good news. Your faith in the factory setting could be misplaced due to to wear and tear and even a previous owner having a fiddle - round here we call it "finger blight"!  However. with all the cleaning that you've done the lean mixture could just be down to the viscosity of your petrol oil mix . Much has been said and argued over the issue of whether vintage engines should be run on a vintage mix; ie using a straight SAE30 or 40 oil  or whether it's OK or beneficial/detrimental to use a modern semi or fully synthetic oil giving a "thinner mix".

Personally I favour an old mix for an old engine, but the main thing is that you've cracked the problem.

.

gtc Sat, 20/09/2014

Good to know that it's now running.

I have recently done the "gravel martini shake" on a brass Atco Standard tank.