Amal carburetter identification

Hi, well I took another look at the markings on the needle jet and believe, that although I agree that it was an attempt to stamp 107, in this case I think the faint line that can be seen, is the result of damage caused by the use of grips to extract the jet! There is a lot of damage on most of the faces, due to improper use of mole grips or similar.

In an attempt to fully understand what should be fitted in a Scott / Jowett Amal carb, I thought I would take a look inside another one, just because I can. The first thing I noted was the underside of the flange, was stamped BC 9, which was again replicated on the main block inside the carb. This is making me wonder, if they really are matched pairs. Also I knew from documentation, the main jet was specified as 110, whereas the previous one above was marked as 100, on this carb the jet is actually marked AMAL and stamped 110 and is a single item, rather than being a two part assembly. Was this a change through the life of the build, or something which happened later, when the engine had been removed from the generator set and was being used as an stand alone stationary engine? The needle jet on this one, is marked 107, as on the first carb but only on one face, possibly confirming the first one was incorrectly marked and then corrected.




The second carburetter under discussion, from a generator set. Note the mark on the round face as mentioned earlier by xulih.




The flange stamped BC 9, these all seem to be individually marked.




And repeated on the main block.




Single piece 110 AMAL main jet.




Needle jet marked 107, same as the previous one.

Hi all, don't know how much interest there is out there for the Scott engine Amal carburetter, due to the limited number of units produced but I thought I should complete my posts on this subject with some details of the mixture adjustment control function. In addition to the normal throttle slide and the butterfly choke, the carburetter is also fitted with a separate mixture control device, which is designed to weaken or richen the mixture. In use the control is set at rich for starting with the choke fully closed, once the engine has started and the choke released, the instructions call for the mixture control to be adjusted towards weak. This is until the engine starts to hunt and the frequency meter swings, then turned slowly towards rich until the engine stabilises, indicating the correct mixture has been achieved. I don't fully understand the operation of the mixture control but it consists of a metal "slug" which slides up and down an external tubular chamber, which has a longitudinal slot cut in it. I assume the position of the slug allows different amount of air to bleed into the the main jet?

One reason I mention this, is in the pictures posted by "xulih", who originally started the posts on this topic, the retaining screw for the mixture control device is shown but the actual component seems to be missing. I don't know how well the carburetter would operate without this fitted. In use, I have not actually noted much difference in the running of the unit whilst moving the air mixture control however I suspect this maybe because there is very little load being presented to the engine, as I'm only using a light bulb to demonstrate the unit's operation.

Hope this is of some interest to you all.

Neil




Mixture control "slug". Note the groove in the adaptor which the retaining screw locates through to hold it in place.




Mixture control knob.




Mixture control connected to carburetter.




Mixture control slug viewed within the slotted chamber.

That's why I also suggested Amal was fitted to the Scammell engine as this does not have a mixture control on the carburettor.

neil (LE) wrote:Hi gents, thanks for your comments. I do feel privileged to own this set, it is one of my favourites, not just because it is unusual but mainly because it is complete, fully operational and in near original condition. Mind you it did take a lot of effort to gently take the rust and corrosion off, without removing all the paint whilst doing so. In some ways it would have been easier to rub it back to bare metal and repaint it but I'm pleased I didn't.

Steve I did wonder what the minimum running speed would be for the Scott engine, as I was concerned I wouldn't be very welcome on the rally field operating the set at 3000 rpm all day. So I had considered removing the drive belt to the exciter, disconnecting the generator plug and running at slow speed for the majority of a rally day. I know what it is like to feel unwelcome, as one of my other engines is a 5 HP oily Petter!

Back to the carburetter question, I have taken another look over the Scott Amal caburetter and I have found the DG 4 stamping found on the intake flange, is repeated on the bottom of the jet block which I removed from the main body. So does this mean these parts are machined as a matched pair during the manufacturing process, or is there another reason for these markings, such as quality control as mentioned previously. In addition to these markings, I took the opportunity to look for other identification marks, in an attempt to prove if the carb in question is from, or could have been adapted to be used, on a Scott / Jowett engine. The first item checked was the slide and this is marked as a number 4, which checks out from some documentation. Then there are the two jets, the needle jet is marked with a 107 on one face and 10 on another, while the main jet has 100 stamped on it, if I've identified them the correct way around.

So the question to xulih is what markings has your carburetter got on these items? If the slide or the jets differ in a significant way, then I would suggest the carburetter is unlikely to have originally come from a Scott / Jowett engine,  especially when the control rod length discrepancy is also taken into consideration. However that does not mean the carburetter could not be adapted to fit and operate on one of theses engines, as the main housing is standard and jets and slides can be changed.

Interesting stuff Neil  thank you. I will strip my carb sometime over the weekend depending if it rains or not and see what markings I can find.

It looks like rain so while waiting to see if it clears I stripped carb. The numbers match those that Neil has found on his carbs. Also the mixture knob pic that Neil posted looks very familiar and I am pretty sure I have come across one very similar in another box of bits but cant remember where.



Number on main block matches that on flange.



Main jet number 110.Looks like it has been cross threaded.



Needle jet marked 107



Number 4 slide.



Found this control lever in the same box that the carb was in.

Hi, sorry I lost my landline and broadband for the last week so I couldn't respond. Looking at xulih's pictures I believe there are so many similarities with a Scott carburetter, that we might be able to accredit it as such. However as blue cat noted, a similar unit was fitted to the Scammell engine, so there is still an element of uncertainty especially as there are a number of unexplained differences. The obvious issue is the "T" prefix on the part number stamping, which perhaps we will never know what that signifies, as all the internals seem to be the same between all of the units. Possibly it could indicate the lack of mixture control feature as suggested by blue cat but if xulih believes he has one of the control knobs, then that again points to it being identical to a Scott carburetter. One other issue I noted, was the difference in the actuator rod length on the throttle control, which could indicate a different use. However there are possible answers as to why this length could be a different but still be associated with the Scott. The first option could be related to the fact that the operating lever arms are clamped to spindles so they could be fitted at almost any angle, in which case the rod length would vary to suit the actual position used. I must admit I'm not happy with that suggestion as I would have presumed that all engines would have been built the same and set up with actuator rods of the same length. The other possibility could be that as there are two similar rods used on the Scott engine these have been mixed up and swapped over at some stage. Unfortunately I haven't been able to measure the two rods on the engine, to see if this could explain the different lengths as identified between the my carburetter and the one xulih has. I will try to measure these soon, to see if there is a difference.

As far as the the Amal control lever is concerned, these are often used to operate the choke, and/or the mixture control on engines which have been separated from the generator set housings. If xulith finds the mixture control knob, then the lever could have been for the choke. as this was just a pull knob on the sets. The knob was held up against a spring until the engine started and then released, so an alternative method of operation is necessary for stand alone engines.

Neil




The two actuator rods, possibly of different length, which could explain the difference on xulith's carburetter.




The spring loaded choke control which needs to be operated by some other means when engine is removed from generator.




The straight pull choke control as fitted. It has to be held on and can't be left in position. If a replacement control lever is used it should not be left on, once engine has started.

I think that after studying many images of the Scammell fire pump carb that although it is similar to the Scott-Jowett carb there are a number of differences. The slide linkage is different and it and the choke if there is one are on the opposite side and the fuel supply pipe is a solid pipe where as the Scott one is flexible. I guess I will never know for certain if my carb originated on a Scott-Jowett gen set but I think it would be close enough to be suitable replacement. Thank you to everyone for your input.

xulith, just to finalise your investigation, I think I can add to your assessment that the carb is from the Scott-Jowett generator set. I have managed to measure the side control rod mentioned above and it is indeed shorter, with my one having an overall length of 6 5/8" so it is possible that the rod linked to you throttle control is actually the one for the governor output linkage, on the side of the engine. Perhaps you will discover the other longer control rod amongst your boxes of bits.

If you're looking for a new home for it, I can find it one!

Neil

neil (LE) wrote:xulith, just to finalise your investigation, I think I can add to your assessment that the carb is from the Scott-Jowett generator set. I have managed to measure the side control rod mentioned above and it is indeed shorter, with my one having an overall length of 6 5/8" so it is possible that the rod linked to you throttle control is actually the one for the governor output linkage, on the side of the engine. Perhaps you will discover the other longer control rod amongst your boxes of bits.

If you're looking for a new home for it, I can find it one!

Neil

I will be listing it on ebay but if you're interested drop me a PM

xulih,

PM sent.

Neil

I found another mark on the underside of the choke today that I had not noticed before. At first sight I thought it was perhaps a war department broad arrow but I don't think so now, at least not one that I have come across before anyway.

Hi,

I had a quick look to see if there were similar markings on a couple of my carbs. I did find markings on both which were similar to those on the one above. I don't believe they represent the War Department arrow but I cannot say what they do mean, possibly they are foundry casting marks, but that is just a guess. Interestingly both of the marks on my carbs have the same number inside the triangle but in my case 25 is stamped, rather than 27 as above.



Marking on the first carb.




And the same on the second.

Thank you Neil, its interesting that you have two with the same number. As you say could be casting numbers or maybe date stamp.

Just seen it on eBay

StuartTurnerSteve wrote:Just seen it on eBay

Yeah, I'd expect the whole Bofors set for that price

blue cat wrote:

StuartTurnerSteve wrote:Just seen it on eBay

Yeah, I'd expect the whole Bofors set for that price

Indeed.