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Mixture setting on early Bantam
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Bola
Swindon
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May 7, 2019 - 7:40 pm
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I think my D3 is running rich, or at least the the plug is sooting up on tick over and killing the spark.

I know with the later carbs there is setting to easily adjust the mixture getting to the engine. With the older bikes with 523 carb is it as simple as moving the position of the needle? I thought the standard setting was 2nd notch from the top?

Where is the line between running lean and not cooking the engine as I also heard rich mix cools the engine?? 

I haven’t seen anything on the archive section however I’m sure I’m not the 1st to ask. Maybe someone can give me a quick guide, plug / needle position pictures would be nice as I’m not sure what a correct mix plug should look like!

 

Thanks

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Mags 1
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May 7, 2019 - 10:02 pm
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You might still not be able to get a decent weak mix with needle in top position, a sixty plus years old carb can't really be expected to do so, even if it did when brand new, doubtful in my opinion.

The D3 carb doesn't even have a tickover or idling jet to my knowledge.

I wonder if you've considered fitting a modern flange fitting Italian Del'Orto carb, as advised by the Cornwall rep (Cornish Rooster) a while ago? They definitely do have all the correct jets and passages fitted and the jets are all available too.

Four now on the road and at least several in bits.

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cocorico
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May 8, 2019 - 8:08 am
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Mags 1 said
...The D3 carb doesn't even have a tickover or idling jet to my knowledge.

I wonder if you've considered fitting a modern flange fitting Italian Del'Orto carb, as advised by the Cornwall rep (Cornish Rooster) a while ago? They definitely do have all the correct jets and passages fitted and the jets are all available too.  

That's right, no luxury adjustments on a D3 carb! The Dellorto carbs are available with stub or socket fittings, so you don't need to alter your cylinder at all.

** Please log in to view **

The Bantam Club Forum - all the answers are in there. If not, Google may.

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Mags 1
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May 8, 2019 - 10:42 am
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** Please log in to view **

The article is here.

Four now on the road and at least several in bits.

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Bola
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May 8, 2019 - 7:43 pm
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Thanks guys, interesting article. 

I really want to keep mine as standard as I can.

Having said that it would be nice to get it starting and running well with out the worry I’ll be walking home 🚶🏻‍♂️ 

So at least there shouldn’t be much to go wrong, all jet sizes are standard. Needle in correct poison. Fuel mix 20:1 as running it in. I will change to 25:1 after 100 miles. That might help fingers-crossed

Was it this much trouble in the 50’s? 🧐

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Cornish Rooster
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May 13, 2019 - 9:00 am
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If the engine is running very rich on tick-over or small throttle openings it's worth checking the needle on the float, you may find it's passing and the rich mixture is caused by too high a level in the float chamber.

Also check that the locating hole for the lower pin on the float is crud free (in the bottom the float chamber), If you are careful you can lightly lap the taper on the top of the pin into the float chamber cover (use something like Brasso or other metal polish). There is plenty of info on a long post I put up some years ago in the FAQ section "** Please log in to view **".

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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