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Collection, Preservation and Display of Old Lawn Mowers

Ransomes Marquis- difficulty starting

Hi everyone

I am a new member and have been renovating a Ransomes Marquis 4A which had stood in the garden of the house I lived in for at least 10 years. I have done the following:-

cleaned head and put on new head gasket but not removed or reground valves, removed and sharpened cylinder, stripped and cleaned/reassembled Amyl 379 carburettor, stripped and cleaned clutch, reattached clutch cable, purchased new/used throttle cable, replaced coil/points and condenser and reattached flywheel, purchased new/used pull starter which was missing, changed oil and new spark plug.

 

When I turn the engine over it shows no sign of firing. I have checked and there is a spark from the plug and the fuel is getting to the carburettor - float seems ok in the chamber but I am wondering if I need to fiddle with the mixture. Should I be giving it full choke, should the air intake cover be open/closed, and should I change the setting on the needle inserted into the mixture jet to get a better mixture (which stop should it be on)?

many thanks

 

Forums

wristpin Mon, 21/12/2020

Welcome to the club.

As a matter of course with an unknown F12 Sloper engine I would always do the valves but if you are happy with the compression we will assume that they are seating and the clearances are ok.

I think that your problem may be with the carburettor.  The air cleaner on your carb is not correct for the application; it should be an oil bath unit. Also it looks as though someone has done some modifications in the area where the carb clamps to the inlet manifold so the engine could be ingesting air and upsetting the air to fuel mixture.

If you take an aerosol of flammable carb cleaner and squirt it directly into the carb intake or even the manifold, and the engine fires, just briefully , it will prove the point. It will then be a matter of finding a correct carburettor or modifying yours to the correct configuration and specification.

richardM Tue, 22/12/2020

Thanks very much for your advice Wristspin.

I tried switching to my spare carburettor (also without oil bath but doesn't have manifold modidification) and no joy so no easy fix there but I take your point about the oil bath. I will try your cleaner spray tip and have sourced a correct carb with oil bath on ebay so will keep you posted.

wristpin Tue, 22/12/2020

Carburettors with the type of air filters in your original image are more usually found on two stroke engines so it’s possible that the jets may be incorrect for the Sloper . There are also Amal’s that look the same but have a different diameter venturi .  What is the 379 /xxx number stamped into your carbs adjacent to the manifold clamp ? From memory /121 is usual on a Sloper.

richardM Wed, 23/12/2020

thats interesting

But both mine are 121's so should be ok from that point of view?

How do you get to the valves- I presume you need to take the cylinder head off?

wristpin Wed, 23/12/2020

Yes, head off. If you are careful / lucky you may get it off without destroying the head gasket. Then take the valve chest cover off.  Depending on the age of the engine the valves may be retained with pins through the stems or may have keyhole slots in the spring cups.

The job is easier done with the engine removed from the chassis.

Unless it is obviously low on compression, I would try the carb cleaner direct into the engine before going down the dismantling route.

Gaskets from Meetens or Jon at the Hailsham Mower Centre.

 

DJD Sat, 26/12/2020

Was the HT coil of the Siba type? I do remember looking after a few of these lovely sounding and easy to use heavy machines, a true idea of the cylinder compression is partly hidden by the heavy flywheel assisted start. Good compression is essential, even on old engines, removing the plug and putting your thumb over the hole if you haven't got a tester, is a good 'rule of thumb' test. Spark needs to be blue and some can easily be heard by younger folk, fresh fuel is a must. I think I have one of the tiny Amal carbs somewhere too.

The strangler on the air filter is the choke. These engines run on the tiniest amounts of fuel on tickover.

Can you hear a slight hissing noise? A head gasket will occasionally blow partly, but will lose most of compression.

richardM Wed, 30/12/2020

thanks DJD

I will look into your suggestions

 

DJD Sun, 03/01/2021

I managed to find my little Amal carb, I took some pics of it and will reproduce them here if it helps, maybe my main jet is different? A white plastic float used on mine too, so maybe a bit later than the brass type ones

Plastic carb

 

DJD Sun, 03/01/2021

I don't understand why the text I put in the boxes under the pics never appear? I forgot to note the numbers on the main jet sorry.

wristpin Sun, 03/01/2021

Have you tried the carb cleaner straight up the manifold? If you get even a single fire there you will at least know that the engine has the makings before you spend time on jet sizes etc.

richardM Thu, 21/01/2021

Hi,

Have had a bit of a break from this but now back on the case.

I have now got a proper carburettor with oil bath etc but before fitting I have tried your trick with the carb cleaner and there was no sign of a fire up. So I am now assuming a compression problem and will take the head off the engine and explore further.......

DJD Thu, 21/01/2021

Excuse my interruption, but all carb. cleaners are not the same, can't be, some won't even begin to clean a carb. let alone get an engine to fire due to thinners etc content, the cheap ones are a con.

'Taryl fixes all' Youtube poster uses good quality stuff in the USA that he regularly starts many different engines with, when needed. I enjoy that site.