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D1 carburettor replacement with modern Dellorto PHBG 18AS
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Cornish Rooster
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April 5, 2012 - 9:51 am
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Here is my latest project fitting a modern Dellorto carburettor to my D1, ordered it on wednesday afternoon turned up nine o'clock thursday morning and fitted that afternoon. Obviously some work is going to be involved setting it up to get the carburation correct but I have had the bike running and went for a buzz around so can't be too far away like it is, and it started ok.

Here it is out of the box,

Phil

http://i1125.photobucket.com/albums/l585/bsathunderbolt/DellortoCarb1.jpg

BSA Bantam D1 "150" in use regularly often as general purpose transport, quite a few other bikes as well. Cornwall Area Rep. 

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April 5, 2012 - 9:55 am
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Being a modern carb this has a pilot circuit as well as the main jet/ needle combination and of course a throttle stop to set the tick-over. Endless combination of jets/slides/needles available even for the pilot circuit so with some tests, time and patience hopefully I can get a good result.

http://i1125.photobucket.com/albums/l585/bsathunderbolt/DellortoCarb2.jpg

BSA Bantam D1 "150" in use regularly often as general purpose transport, quite a few other bikes as well. Cornwall Area Rep. 

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April 5, 2012 - 9:59 am
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This is the first hurdle to cross, it comes with two nylon sleeves, one 24mm and one 25mm, with the stub being one inch (25.4mm) I couldn't use either of these, so made a shim out of some thin plate (cut up an empty Gunk can) its still not as tight as I would like so a bit more work required here.

http://i1125.photobucket.com/albums/l585/bsathunderbolt/Dellortocarb3.jpg

BSA Bantam D1 "150" in use regularly often as general purpose transport, quite a few other bikes as well. Cornwall Area Rep. 

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April 5, 2012 - 10:04 am
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Here it is fitted, there were a few different air filters available but I knew there is not a lot of space on these D1's so opted for a small bell mouth with a mesh end, and it just fits.

This carb has a choke for cold starting, the little black piece on the top, a push and lift arrangement though there is an option to change it over to a lever.

http://i1125.photobucket.com/albums/l585/bsathunderbolt/Dellortocarb4.jpg

BSA Bantam D1 "150" in use regularly often as general purpose transport, quite a few other bikes as well. Cornwall Area Rep. 

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April 5, 2012 - 10:10 am
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You can see the choke arrangement, and mixture/ throttle stop screws on this side. The standard throttle cable fits with no modification required. Complete with the intake trumpet this lot cost £120 which sounds a bit pricey but seeing complete D1 carbs are going for around £75 on Ebay and still you are buying a fifty year old plus carb maybe thats not so bad ?

http://i1125.photobucket.com/albums/l585/bsathunderbolt/Dellortocarb5.jpg

BSA Bantam D1 "150" in use regularly often as general purpose transport, quite a few other bikes as well. Cornwall Area Rep. 

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Charlie
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April 5, 2012 - 11:02 am
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That looks like an excellent job,  perhaps if someone had their engine dismantled it might then be possible to remove .4 of a millimetre from the stub to allow use of the supplied sleeve.

 

Charlie

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April 5, 2012 - 11:18 am
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Going to measure the diameter of the inlet side of the carb this morning which I think is 26mm, if it is I will get some 0.5mm PTFE sheet and cut a sleeve to get a better fit, it's reasonably ok now with my tin plate sleeve but would prefer its really tight on the stub. Yes taking off a wee bit of the stub down to 24 or 25mm would be the ideal solution but I reckon I will get over this one way or another. Took it for another spin this morning and running well, nice throaty sound from that intake trumpet !!

Looked at the Dellorto site this morning for spares for these carbs and they do a clear plastic float bowl, now that would be useful to see if any sediment is finding its way through ?

Phil

BSA Bantam D1 "150" in use regularly often as general purpose transport, quite a few other bikes as well. Cornwall Area Rep. 

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April 5, 2012 - 4:36 pm
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Managed to clamp it down on the stub a big tighter today using a 8mm socket and its secure enough on the stub but have ordered some 0.5mm PTFE sheet as that should work out perfectly, the bore on the inlet side of the carb is 26mm, so 25.4mm on the stub plus 0.5mm will give 25.9mm, close enough, and should get a good seal using the PTFE.

Also ordered a metal float bowl which has a drain plug (always useful) the plastic one at present does the job ok but seems better with a drain plug, also ordered the flip up lever choke kit should be less fiddly than the lift and twist one there at the moment. next job is to do a "plug chop" to get some sort of idea which way the carburation is, rich or weak. If anything I would guess its too rich, the needle has four positions and its second from the top at the moment, main jet is an 82, I was running a 75 on the original Amal we will see ! Still thinking about ordering the clear plastic float bowl, what a good idea especially with us rusty fuel tank crowd.

Phil

BSA Bantam D1 "150" in use regularly often as general purpose transport, quite a few other bikes as well. Cornwall Area Rep. 

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Steven
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April 7, 2012 - 11:13 am
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Nice work. I did something similar to my old Batavus moped. The Encarwi carb is a bit of a leaker so I got a larger intake a put a Dellorto 15.15 on her.

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April 7, 2012 - 11:34 am
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Great work and write up Phil !

For your PTFE sheet - won't it add 1mm in total ?  ie 0.5 on both 'sides' of the stub as it wraps round ?

Looking forward to the first full road test report. 

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April 7, 2012 - 11:47 am
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Got a good secure fit by using some brass shim with my "Gunk Can" shim, seems ok now. Metal float bowl with drain plug turned up this morning together with the flip lever choke modification.

http://i1125.photobucket.com/albums/l585/bsathunderbolt/Dellortofloatbowlandchokekit.jpg

BSA Bantam D1 "150" in use regularly often as general purpose transport, quite a few other bikes as well. Cornwall Area Rep. 

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April 7, 2012 - 11:51 am
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Next job get a few spare spark plugs and do a "plug chop" and get an idea on how far off it is, not too concerned about the pilot circuit as I reckon on these bantams it doesn't spend to much of its operation on that. Hopefully another test this afternoon.

http://i1125.photobucket.com/albums/l585/bsathunderbolt/Dellortofittedwithnewfloatbowl.jpg

BSA Bantam D1 "150" in use regularly often as general purpose transport, quite a few other bikes as well. Cornwall Area Rep. 

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April 7, 2012 - 4:44 pm
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Out on test this afternoon, running weak when up to speed could feel the engine being held back, and this plug shows its a weak mixture as the electrode is white !

Raised the needle one notch and tried again, better but still a bit hesitant at around full throttle, will try raising another notch on the needle and after that will probably start increasing the main jet size.

http://i1125.photobucket.com/albums/l585/bsathunderbolt/Plugchop.jpg

BSA Bantam D1 "150" in use regularly often as general purpose transport, quite a few other bikes as well. Cornwall Area Rep. 

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April 7, 2012 - 4:46 pm
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On the positive side I think I can get a good result with this carb, the bike is going well through most of the carb operating range and holding top gear better than with the Amal.

BSA Bantam D1 "150" in use regularly often as general purpose transport, quite a few other bikes as well. Cornwall Area Rep. 

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April 7, 2012 - 5:11 pm
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Thoughts just occurred to me .... how do you kill the throttle on the bantam when you are doing a plug chop ?

I'm used to doing it on a Japanese bike where you hit the kill switch and pull the clutch in and then coast to a stop.

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April 7, 2012 - 6:10 pm
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I just coasted to a stop and let the engine die, there was not enough slow running to worry about the mixture effect on the plug colour for those few seconds. Plus I can tell its weak at the moment without even looking at the plug.

I still have the throttle stop adjusted so the engine can be stopped on the twist-grip position, one thing to think about in the future is to use the throttle stop to set the tickover, fortunately with the Rex Caunt ignition system there is a lead from the coil that can be used for an ignition cut out and it just needs a switch fitting with a wire that goes to earth, we will see. Found an excellent carb set up guide on a Ducati site, very good for any carb, explains the theory on how the carb works and how to go about adjustment.

Phil

BSA Bantam D1 "150" in use regularly often as general purpose transport, quite a few other bikes as well. Cornwall Area Rep. 

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April 7, 2012 - 6:17 pm
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Perhaps you could post up a link Phil - that sounds good!

 

Did you read how I accidentally connected the Rex Caunt kill switch wire to to my main loom instead of using the 12v feed? Not only the headlight switch worked as a kill switch but so did my back brake .....

embarassedout-a-here

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April 7, 2012 - 6:19 pm
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This is a very good site for carburettors in general.

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BSA Bantam D1 "150" in use regularly often as general purpose transport, quite a few other bikes as well. Cornwall Area Rep. 

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April 7, 2012 - 10:15 pm
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Hmm could make things interesting putting the back brake on and the engine stopping !

BSA Bantam D1 "150" in use regularly often as general purpose transport, quite a few other bikes as well. Cornwall Area Rep. 

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April 9, 2012 - 11:36 am
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No testing today but next plan is to try raising the needle another notch. Have been looking through the available needles and jets a vast selection of possibilities main jets are in increments of one, starting at a 30 and going up to 198 and there are 26 different needles available !! One way or another I should find a combination that works well.  

BSA Bantam D1 "150" in use regularly often as general purpose transport, quite a few other bikes as well. Cornwall Area Rep. 

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