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  • Jets and carbs for Hawkstone

    Hi i have a Greeves Hawkstone 250cc iron (round) barrel motocross bike. Does anyone have any suggestions for carb and jet sizes? Its got an Amal Concentric carb on it now.

  • #2
    Hawkstone carbs/settings

    According to Greeves (Carrick & Walker)
    24SAS with 31A engine
    Amal 389 1 3/16" (monobloc) Main jet 480/560; pilot jet 25; needle jet .109 needle groove 3; throttle slide 3

    24SCS with 34A engine
    same carb; 370 main jet: pilot jet 25; needle jet .109; needle groove 3; throttle slide 3 1/2

    Presumably these settings would be the same for an Amal Concentric of same size, but jetting may have to be a case of trial & error depending on exhaust set up as above would be with open megga.

    Comment


    • #3
      Hi,
      Settings on the Concentric are very much different to the Monobloc....which took me a while to sort on my dads MDS when I switched carbs

      I run an Iron Barrel - on an MDS - and race it in the pre 60 class. It is fitted with an Amal mk 1 - 932 (32mm) concentric carb...but you may well have a 930 (30mm inlet) - jets would be similar........and unless your engine has been ported/tuned - you are probably better off with a 930

      I would start with a 106 needle jet, middle groove on the needle, I think Carb slide cutaway is 3 and pilot 25..........(will card slide cutaway and pilot size on mine in garage tonight and confirm) . Main Jet will be in the 250 to 300 main jet range. Start at the rich end (300) and work down - as better to be rich than lean....and get it right with plug chops before you pin it at high revs..a seized piston is costly!

      Some riders in the Greeves Hawkstone class run a 107 needle jet (very rich mid range) - but a smaller say 240 to 250 main jet to compensate ...so that is also a combination you could try. These guys have a suck through exhaust - so if you have a standard pipe - I would stick with the 106 for starters

      Also - Caution - based on experience....If it is a new supplied carb - you need to check you have been supplied with correct needle.....and also that the carb is set up for a 2 stroke - not a 4 stroke....as quite often they get it wrong (as suppliers are more used to shipping carbs for 4-strokes). Check that the brass delivery tube on top of the jet body - that feeds the fuel/air mix into the carb engine body/inlet has a shamfered edge facing towards the engine inlet port - and also that the main jet holder has no bleed hole. If it is an old carb - you are probably ok......

      Send me a private message if you have any follow up questions.........I can always cross check with other greeves motocross riders as well. Cheers Kim
      Last edited by Kim275; 15/03/2011, 12:37 PM.

      Comment


      • #4
        Carb settings

        Well put Kim, I didn't realise you were so well versed in Amal carbuerettors, I know where to ask now if I have problems in future.
        Certainly I have to agree on the needle jet size, I've no idea where the 109 figure came from that's listed in Villiers handbooks unless it was necessary for open mega's! It is far too large for the period expansion chamber on my own machine, in fact I've gone as small as a 105 to obtain "clean" carbueration at times. Admittedly this is with a 389 Monobloc. I hadn't realised, and the suppliers were unaware, of what the numbers 106, 109 etc referred too when I enquired with them. I don't know if it's a coincidence but the sizes do relate to the diameter of the jets in thousandths of an inch. ie 106 = 0.106". I used Pin gauges from work in an effort to understand the difference between them and this was the result. Over a long period of time a Needle jet will wear, not so much from the fuel passing through it but from the fluttering of the Needle which mates with it.
        I've no knowledge of modern exhausts but had noticed that some machines fitted with this type can have problems with starting, despite electronic igniton and seemingly correct carb setups. The phrase "Suck through exhaust" perhaps suggests a clue to where the problem lies!
        Of course running on Points ignition and a Monobloc carb I am hardly qualified to comment further. But I suspect that the originator of this thread would do far worse than to follow Kim's seemingly sound advice. Adrian335


        Originally posted by Kim275 View Post
        Hi,
        Settings on the Concentric are very much different to the Monobloc....which took me a while to sort on my dads MDS when I switched carbs

        I run an Iron Barrel - on an MDS - and race it in the pre 60 class. It is fitted with an Amal mk 1 - 932 (32mm) concentric carb...but you may well have a 930 (30mm inlet) - jets would be similar........and unless your engine has been ported/tuned - you are probably better off with a 930

        I would start with a 106 needle jet, middle groove on the needle, I think Carb slide cutaway is 3 and pilot 25..........(will card slide cutaway and pilot size on mine in garage tonight and confirm) . Main Jet will be in the 250 to 300 main jet range. Start at the rich end (300) and work down - as better to be rich than lean....and get it right with plug chops before you pin it at high revs..a seized piston is costly!

        Some riders in the Greeves Hawkstone class run a 107 needle jet (very rich mid range) - but a smaller say 240 to 250 main jet to compensate ...so that is also a combination you could try. These guys have a suck through exhaust - so if you have a standard pipe - I would stick with the 106 for starters

        Also - Caution - based on experience....If it is a new supplied carb - you need to check you have been supplied with correct needle.....and also that the carb is set up for a 2 stroke - not a 4 stroke....as quite often they get it wrong (as suppliers are more used to shipping carbs for 4-strokes). Check that the brass delivery tube on top of the jet body - that feeds the fuel/air mix into the carb engine body/inlet has a shamfered edge facing towards the engine inlet port - and also that the main jet holder has no bleed hole. If it is an old carb - you are probably ok......

        Send me a private message if you have any follow up questions.........I can always cross check with other greeves motocross riders as well. Cheers Kim

        Comment


        • #5
          Originally posted by Kim275 View Post
          Hi,

          Also - Caution - based on experience....If it is a new supplied carb - you need to check you have been supplied with correct needle.....and also that the carb is set up for a 2 stroke - not a 4 stroke....as quite often they get it wrong (as suppliers are more used to shipping carbs for 4-strokes). Check that the brass delivery tube on top of the jet body - that feeds the fuel/air mix into the carb engine body/inlet has a shamfered edge facing towards the engine inlet port - and also that the main jet holder has no bleed hole. If it is an old carb - you are probably ok......
          Cheers Kim
          Couldn't agree more with what has been said here - I ordered a MK1 from Amal which arrived with the wrong main jet, 4-stroke spray tube and needle jet.
          Maybe not that surprising from a company who can't even spell "Carburettor"!
          Everywhere on their website its written as "carburetter"!

          Cheers,
          Andrew

          Comment


          • #6
            Amal Carbs

            I assume we are talking 'BFS' here. This is not the first criticism I have seen on this company who are supposed to be manufacturing to original Amal spec, & own the right to the Amal & SU carburettor names.
            These carbs are basically of simple construction & if they have the original tooling, drawings, & spec sheets, with modern NC machines the carbs should be spot on. They are continually making a 'song & dance' in their adverts about 'pattern sub standard' Amal parts.
            As you say Andy, if they cant spell CARBURETTOR correctly it does not give a good impression. Not sure if they actually manufacture them themselves but there was an article in OBM some time ago which said they did, & showed carbs being made. Of course the pics could have been taken anywhere!.

            Comment


            • #7
              Looking at the spark plug it is black and running quite rich so was wondering if i should look at changing the air filter. Is there a particular one you could recommend.

              Originally posted by Kim275 View Post
              Hi,
              Settings on the Concentric are very much different to the Monobloc....which took me a while to sort on my dads MDS when I switched carbs

              I run an Iron Barrel - on an MDS - and race it in the pre 60 class. It is fitted with an Amal mk 1 - 932 (32mm) concentric carb...but you may well have a 930 (30mm inlet) - jets would be similar........and unless your engine has been ported/tuned - you are probably better off with a 930

              I would start with a 106 needle jet, middle groove on the needle, I think Carb slide cutaway is 3 and pilot 25..........(will card slide cutaway and pilot size on mine in garage tonight and confirm) . Main Jet will be in the 250 to 300 main jet range. Start at the rich end (300) and work down - as better to be rich than lean....and get it right with plug chops before you pin it at high revs..a seized piston is costly!

              Some riders in the Greeves Hawkstone class run a 107 needle jet (very rich mid range) - but a smaller say 240 to 250 main jet to compensate ...so that is also a combination you could try. These guys have a suck through exhaust - so if you have a standard pipe - I would stick with the 106 for starters

              Also - Caution - based on experience....If it is a new supplied carb - you need to check you have been supplied with correct needle.....and also that the carb is set up for a 2 stroke - not a 4 stroke....as quite often they get it wrong (as suppliers are more used to shipping carbs for 4-strokes). Check that the brass delivery tube on top of the jet body - that feeds the fuel/air mix into the carb engine body/inlet has a shamfered edge facing towards the engine inlet port - and also that the main jet holder has no bleed hole. If it is an old carb - you are probably ok......

              Send me a private message if you have any follow up questions.........I can always cross check with other greeves motocross riders as well. Cheers Kim

              Comment


              • #8
                Hi Kayjay,
                Yes - it is a waste of time tuning an engine with a blocked or dirty air filter. I use and would recommend a two part foam motocross filter - with filter oil or spray - (wide bore outer foam and narrow inner)...such as Twin Air .. I use a cylindrical shaped one that has a rubber tube end that slides over the carb intake.
                If you are a traditionalist or want an original look it is hard to keep the original air box and get a decent foam motocross filter - so not sure what you would use (Adrian has a lot of experience here and may have some tips ) . The original bikes would have run paper filters, I remeber my dad always changing his paper filters for every new race meeting. Infact whatever your filter you should do the same.

                In terms of tuning your carb - always start with a clean air filter as your first job.

                Then try and get your main jet close with Plug chops (big field - full throttle in at least 3rd - and hit the kill switch) - then inspect the plug. Should be an even tan colour - (white or grey too lean, increase your main jet - and black too rich reduce your main jet) ......

                Then you can take a look at bottom and mid range.........As I remember the Amal carb comes with a tuning guide which is quite helpful.

                It is worth getting this right ....I was tuning my 250 griff last sunday after a rebuild and new carb ...and have not yet got it running correctly yet. It started too rich and ended up too lean - as I was using the standard 310 main jet and tuning on the needle only....so I need to like you go back to basics and follow the above main jet procedure - which is a pain but I need to be patient and only change one setting at a time !!
                Cheers Kim

                Comment


                • #9
                  Can't add much to your words of wisdom Kim, but for what it's worth I run my Hawkstone with the standard airbox of the day and a foam filter cleaned after each meeting and Castorl R at 25:1. I'm not very confident with air filters sealing properly on the outer faces. I know you can apply grease to these but I have seen them collapse over the course of a meeting therefore bringing into doubt the integrity of the seal. I tend to go to Hitchcocks of Birmingham for my Amal spares, they offer a good service and also supply the tuning sheets that Kim mentioned. Certainly when ordering carbueretor parts you do need to state whether they are for a two or four stroke. Good luck with your setup. Adrian

                  Comment


                  • #10
                    Ahh!! castrol r, the stuff that dreams are made of........, can`t get enough of it?, i`ve even been known to throw a dab behind me ears for a trip to the pub!.....
                    I hope you use it in g/box as well adrian?.
                    But going back to jw`s comments on bfs, i`ve always found them to be very helpfull & have dealt with them numerous times, last week i ordered some parts & fair play to the guy, he spent ages trolling & cross referencing numbers for an item that was only a fiver, i was quite impressed, so i bought a few extra items & £50 & one week later all the parts i didn`t order turned up! but hey! everyone has a bad day.
                    Every other time they have been spot, so i`ll keep using them. dave.

                    Comment


                    • #11
                      Originally posted by ADickerson View Post
                      Can't add much to your words of wisdom Kim, but for what it's worth I run my Hawkstone with the standard airbox of the day and a foam filter cleaned after each meeting and Castorl R at 25:1. I'm not very confident with air filters sealing properly on the outer faces. I know you can apply grease to these but I have seen them collapse over the course of a meeting therefore bringing into doubt the integrity of the seal. I tend to go to Hitchcocks of Birmingham for my Amal spares, they offer a good service and also supply the tuning sheets that Kim mentioned. Certainly when ordering carbueretor parts you do need to state whether they are for a two or four stroke. Good luck with your setup. Adrian
                      Hi Adrian - On my QUB Griffon - I use the original airbox - with a large and small foam air filter on the LH and RHS - your mention of appling greese on the edge that touches the inside face of the airbox is a really good tip for these types of filter arrangements - essentially the same as on a modern motocross bike.....where equally a good seal is essential - Infact a lot of modern motocross guys do the same.......Another issue I had with Foam filters when I started using them - and also a good tip - is to avoid over oiling them - especially with modern - very sticky filter oil. Make sure it is used sparingly - squeezed out and the filter aired and dried before use (an airing cupboard over night is ideal !! - Your use of presumably petrol castrol R mix - would I think avoid over oiling and achieve the same once dried out and petrol evapourated ...with the added advantage of not upsetting the Missus !)

                      Comment


                      • #12
                        Oooops!!!
                        Apologies all, the reference to Castrol R at 25:1 refers to the mix in the tank, not the air filter, where I do use modern filter oil! And yes Dave, as well as behind the ears and in the gearbox I also put it in the clutch too, against the majority of recommendations to use something with the viscocity of Maidens water! Saves me using more than one type of oil and getting them muddled up! Doesn't usually take much in my case.


                        Originally posted by Kim275 View Post
                        Hi Adrian - On my QUB Griffon - I use the original airbox - with a large and small foam air filter on the LH and RHS - your mention of appling greese on the edge that touches the inside face of the airbox is a really good tip for these types of filter arrangements - essentially the same as on a modern motocross bike.....where equally a good seal is essential - Infact a lot of modern motocross guys do the same.......Another issue I had with Foam filters when I started using them - and also a good tip - is to avoid over oiling them - especially with modern - very sticky filter oil. Make sure it is used sparingly - squeezed out and the filter aired and dried before use (an airing cupboard over night is ideal !! - Your use of presumably petrol castrol R mix - would I think avoid over oiling and achieve the same once dried out and petrol evapourated ...with the added advantage of not upsetting the Missus !)

                        Comment


                        • #13
                          This may sound a little bit of a daft question but how do you know the the difference between a 250 and 200cc engine?

                          I tried the jets as recomended but had no luck. We tried a 190 main jet this weekend at Marks Tey and seem to cure it.

                          We were wondering if the engine is actually a 200cc or the carb maybe a bigger size??

                          Comment


                          • #14
                            Originally posted by kayjay283 View Post
                            This may sound a little bit of a daft question but how do you know the the difference between a 250 and 200cc engine?

                            I tried the jets as recomended but had no luck. We tried a 190 main jet this weekend at Marks Tey and seem to cure it.

                            We were wondering if the engine is actually a 200cc or the carb maybe a bigger size??
                            Remove the cylinder head & measue the bore. If it is 200cc (197 actually)
                            it will measure 59mm dia & 250cc (247cc) 66mm plus any oversize due to rebore which is usually stamped on piston

                            Comment


                            • #15
                              Scs 932 amal mk1 concentric

                              Hi all
                              Can any one help me with the correct jetting for the above as I have 30 270 107 needle position 3 and it has trouble picking up from low idle unless I keep the revs up. I would like to get this sorted as want to ride it this year along with my 36MX4 67
                              Thanks
                              Ray
                              Ps I have lots of original jets and floats needles etc even a spare 389 carb although a little tired.

                              Comment

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