Zenith 24T2

[sidevalve5]

Have recently got another Trusty, I think its a 1959 model with a Jap 6 engine, 3 speed and reverse box. It does not look like its done much work and has been stored in covered yet damp conditions for decades. There was a lot of freeing up and small jobs to do before it was running. The exhaust valve was stuck open, freed it with a tap at the end of the stem, but still no real compression. Had to take the head and barrel off to deal with the corrosion damage. It does go really well, put to work yesterday evening and all OK except the clutch shoes are a bit sticky and is obviously running too rich.

Which is the point of this post. It has a Zenith 24T2 carb and a fixed jet. Do have another carb with an adjustable needle and was wondering if anyone had removed the blanking plug on a fix jet model, then fitted the needle. Did clean the carb thoroughly and noted the main jet had the right hand side of the slots well rounded. Which suggested to me it was difficult to put in even at the factory. Removed the other jets with the aid of some heat, but the main jet would not budge. Have tried to remove the main jet from a couple of other Zenith’s, with no joy either. Does anyone know if the tapers to the needle and jet are the same. I would have thought it was, but if anyone know’s for definite, that would be great.

Also have a Jap 5 with a Zenith 24T2 which I fitted years ago as a replacement for the worn out Jap carb. The Zenith has never been 100% perfect, despite a new throttle spindle. Had it ultrasonically cleaned, which made a bit difference. Think there was some corrosion I could not get to in the between the main jet and the discharge nozzle. Possibly blocking the emulsion holes. But does anyone know the correct choke size for a Jap 5. The Jap 6 tickover is much steadier, the Jap 5 is OK, but not quite as reliable of the 6. When using a Trusty find good carburetion vital for slow manoeuvring.

Have a Zenith service sheet which may be of use to somebody, so have uploaded it. When I got it I could see the emulsion holes and therefore where a problem may occur.

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[davidbliss]

I would have though the jet would be larger so would go from rich to weak, Think I have a good 24 T carb minus the adjustable bits as they fitted a teens to twenty’s bronze zenith, if you need spare bit could try and fing it.

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[andyfrost]

24t2s with fixed jets are ok provided there is very little to no wear in the butterfly shaft , and your engine bore/valve set up is also ok , this is especially so for any application that requires smooth tickover and smooth pickup of revs.
I would always go down the route of changing fixed to adjustable , it eliminates all the USUAL problems with the fixed jet , I had a Coleby a few years back that was a comlete pain until I changed to adjustable.

Andy.

[sidevalve5]

Many thanks for the replies. My old Trusty Jap 5 has now done its time, the transmission is worn out. Had rebuilt the engine and it was working very well before the transmission system broke. Have a Clifford Mk1a, so am going to put the engine on that and scrap the Trusty. The Jap 6 Trusty has a graunching sound from the very slack primary chain hitting the casing. Had this problem before so at the weekend am going to see if a half link will fit. Put some new clutch springs available at the club shop on my old Trusty, they made a big improvement. So at the weekend, if the Jap 6 clutch shoes have less resistance that the Jap 5 one, will take them off and fit them on the more recent machine. Will be saving the springs anyway, have two Douglas engine Trusty’s awaiting restoration.

The Jap 5 has the adjustable carb needle, so am going to put it on the Jap 6 and see how it goes. Have nothing to loose and can always return it back to the fixed jet. Many thanks for the offer David, but have a spare Zenith carbs with an adjustable needle. When I get round to restoring the Gravely D I might have a go at fitting a modern carb to it. Think the Zenith is too big so such a small slow reving engine. But thats for another day.

[sidevalve5]

An update, the adjustable tapered screw does work very well with Zenith 24T2 carb that has a fixed jet. The Jap 6 in my newly acquired Trusty was obviously running rich. Had to take the head a barrel off as part of the re-commissioning and there was a lot of sooty type deposits. It was not hard baked on carbon, which I would have expected if it was burning oil. I set the fuel/air mixture with a plug chop and after a couple of efforts with doing adjustments, I have the plug with the correct brown coloured deposits on the end. The engine sounded beautiful and pick up from tickover was smooth. But currently only scuffling with 7” diamond feet on 5 legs, with at 2” deep in ground I have already gone over both ways with ducks feet at 3” in clay soil that was padded down well. So did not need much power on the already roughed up ground. Find when I put a SV engine to harder work and if I have the correct brown colour on the plug, I get a bit of a hunting type misfire. A tweak to richen the mixture usually cures it, even though the plug colour changes more to a charcoal shade.

The Zenith carb on the Jap 5 was taken off a Trusty that must have been left outside uncovered for decades. It had thick corrosion deposits inside and out, could clean off what I could and blew everything through with an airline. Have also recently had it ultrasonically cleaned. But the air mixture screw makes no difference to the tickover, unlike to carb on the Jap 6. Where I could adjust both main and idler jets. I think that the blind holes and passageways still have corrosion deposits in them and was thinking of soaking it in something like drain cleaner or caustic soda. Would be interested if anybody has any advice as to what is the best solution.

[andyfrost]

If it’s a carb I’m relatively familiar with , and I know there are no hidden/unknown rubber seals etc., I use a little drain cleaner in the ultrasonic , in your case it would definately work fine , as in a 24T2 there are no hidden “dangers”. A 15min cycle in mine with a little drain cleaner will rid the white corrosion deposits , make sure to drop it into some fresh boiled water , and finish by blowing dry with airline.
Glad you had success with the adjustable jet , it’s the only way to go.

Andy.

[sidevalve5]

Just done a quick google search about things to use for removing corrosion from ali. What ever you use, its got to be acidic, not alkaline. So caustic soda if definately a ‘no no’. Will be getting an ultrasonic cleaner at some point. Its good to know what cleaning fluids I can use with it. Have some brick cleaning acid, so may give that a go if the parts are corroded.

[andyfrost]

Despite what you have read on the internet , my early experiences taught me the hard way that acid “CAN” damage very fine threads ,and I managed to ruin a carb , and it wasn’t because of a too rich mixture of acid. I took experienced advice from a good friend and went over to drain cleaner , and have had no problems since.

Andy.

[sidevalve5]

Think before I use something I am not sure about on a carb I will trial it with some scrap material. Some carbs are made from different alloys, so need to be careful.

[andyfrost]

That’s a good idea , and you’re spot on about differing types of alloy used to make carbs.

Andy.

[davidbliss]

Just by accident one day found washing powder and boiling it in a saucepan, in several cases the brown sticky mess goes whitish and when dry even small airways can be blown out with an air line. However remove the float before putting into hot water, without thinking one day just dropped a part carb still with the float into boiling water, in only count of two float burst and thru hot water out everywhere as had bit of petrol in. it took some time teasing the distorted float back to work again.

[charlie]

Float probably burst due to rapid expansion of the air inside due to heat of boling water.

[sidevalve5]

When I have recovered carb’s that have been left outside for years, found the opposite affect to expansion on the float. Some have crumpled due to the action of contraction in extreme cold. Put one into a cup of boiled water to see if it would recover its shape, but bubbles came out instead.

The ultrasonic cleaning did improve the Zenith’s performance at tickover on the Jap 5, but it was not perfect. After looking at the sectional drawing of the carb, I just get a feeling that some of the blind passageways still have a partial blockage due to corrosion deposits leaving an uneven surface.

Finished scuffling with the diamond feet yesterday using the new Jap 6 Trusty, it went like a dream. Raining this morning, so am sorting out a shed to fit it in. Will not need it now until the December ploughing. Now have a reserve gear can back it in, can even move it around on a hard surface because of the rubber tyres. Its a different world to the old steel wheeled Jap 5 Trusty. Used to leave that outside all year under a steel bath, just like most of the Trusty’s were kept around the Vale of Evesham. Gong to dig out the Davis toolbar this morning to use as a counterweight on the Trusty. Wonder if anyone had heard of one and know what it is.

[davidbliss]

When I dropped the carb into boiling water I should have known what was going to happen. When a float has a pin hole in and has sunk with petrol in thats how I get rid of it by firstly unsoldering the pin hole that all floats have then just warming it a few times will soon empty the petrol, with a cool float I then solder the pin hole up. This is how I find any holes that can’t be seen, placing under in warm water and watch for bubbles, clean and before soldering the leak unsolder the the breather hole. solder the leaking hole and again cool and then solder the pinhole and test in warm water again. With some floats with the manufacturing process of drawn metal to cause stress cracking all over, would clean and tin all over, if done properly doesn’t cause any detrimental weight increase, a friend used to electro plate floats, I could see how a float would implode like Sidevalve mentions, in full sun things can get very hot indeed and one day left a jug with petrol in out in full sun, as I went to pick it up noticed the petrol was boiling away quite well and thats the same as air expands, thats how water gets into seemingly sealed parts like gearboxes, rain water cools and then is sucked into a part. If the carb had a bit of water in and the float had the smallest hole air would escape but if cooled water wouldn’t get drawn back in and would then implode.as not very structurally sound with pressure on the outside.

[sidevalve5]

Brilliant advice, especially about water getting into gearboxes. Have a Toyota Hiace and have to have the gearbox oil changed every year because it has water in it. No one who has looked at it could understand the reason why, but now David has explained it. As air cools it becomes denser and reduces in volume. Its why the float contracted then crumpled under severe cold and water around the Hiace’s gearbox was drawn into it. Have seen it as low as -14oC on more than one occasion. On a Zenith float would try to pull out the creases with heating, but if that did not work, de-solder it and knock out the dents from the inside. Or go to Villiersparts and buy a new plastic one. If I ever get a float thats just leaking and not malformed, will follow David’s method.

Many thanks

Grahame

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