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Post by BritPete on Apr 21, 2021 20:03:07 GMT
When I tried to start SME tonight - Carbs flooded - out of the overflow, nearside carb
Stripped them off cleaned the nearside float needle (Changed float bowl screws for hex)
Put back together flooded out the other one
Suspect the floats may be knackered so I bought a set of 250 carbs and they have the same plastic floats
Looking at the parts book the N NA and NB 250 and 400 had the same floats by part no
The NC also had the same - The 250NDc had different floats - Why
So plan tomorrow is change the floats and Needle while the carbs are still on the bike
Currently they dont over flow as I have had the bike started
Should I leave them - booked for MOT Friday
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Post by comstar on Apr 21, 2021 21:41:07 GMT
Okay...so here's the drill.
Firstly, have you renewed the float needles and cleaned the needle seats with some fresh fuel and a cotton bud Pete?
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Post by BritPete on Apr 21, 2021 21:43:17 GMT
Okay...so here's the drill. Firstly, have you renewed the float needles and cleaned the needle seats with some fresh fuel and a cotton bud Pete? The float needles in the carb pack did not fit so no Carb was fully cleaned as were needles |
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Post by comstar on Apr 21, 2021 21:43:49 GMT
From the NB models on (may have been midway through the NB run, need to double check again) the floats and subsequent needle assemblies changed to the yellowy looking floats (from the adjustable black ones). The needles on the non adjustable floats did away with that fiddly spring and the float needles sat on a little square plate.
Be careful with these as I have discovered that there is a part number error in the books which has caught me out before....
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Post by BritPete on Apr 21, 2021 21:45:33 GMT
From the NB models on (may have been midway through the run, need to double check again) the floats and subsequent needle assemblies changed to the yellowy looking floats (from the adjustable black ones). The needles on the non adjustable floats did away with that fiddly spring and the float needles sat on a little square plate. Be careful with these as I have discovered that there is a part number error in the books which has caught me out before.... It’s the ones with the plate I have 4 new ones with springs |
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Post by comstar on Apr 21, 2021 21:47:56 GMT
And this is the thing. The NDC floats are also actually the correct ones for the NB/NDB, from memory the part number ends 751.
This is the error in the parts book.
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Post by comstar on Apr 21, 2021 21:48:49 GMT
So are your floats the black adjustable tang type or the yellow non adjustable? It follows that the floats and needles cannot be interchanged.
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Post by comstar on Apr 21, 2021 21:52:41 GMT
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Post by comstar on Apr 21, 2021 22:00:56 GMT
Reading between the lines and I think what will solve your problem is simply to have new needles which fit your floats.....whichever ones you are using. So you are going to have to get different floats that fit your needles or visa versa. It follows (again) that if you install the adjustable floats that you must adjust the metal tang / height correctly to insure no overflow / starvation issues with that....
Can you exchange those needles for the other type? ...guess maybe not as you've used them.
In a nutshell, I think new correct matching floats to float needles will solve your issue as it looks like you have an intermittent problem due to one or both of the floats being worn. chances are it might now be okay.....but could leak again at any time if they are worn. Keep an eye and use the 'off' function on your petcock during this period....and don't trust it being turned to 'on' overnight....otherwise you'll have a lovely damp patch and aroma in your garage in the morning.
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Post by BritPete on Apr 22, 2021 6:55:01 GMT
Reading between the lines and I think what will solve your problem is simply to have new needles which fit your floats.....whichever ones you are using. So you are going to have to get different floats that fit your needles or visa versa. It follows (again) that if you install the adjustable floats that you must adjust the metal tang / height correctly to insure no overflow / starvation issues with that.... Can you exchange those needles for the other type? ...guess maybe not as you've used them. In a nutshell, I think new correct matching floats to float needles will solve your issue as it looks like you have an intermittent problem due to one or both of the floats being worn. chances are it might now be okay.....but could leak again at any time if they are worn. Keep an eye and use the 'off' function on your petcock during this period....and don't trust it being turned to 'on' overnight....otherwise you'll have a lovely damp patch and aroma in your garage in the morning. Silvers show the older style valve only - emailed them |
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Post by BritPete on Apr 22, 2021 9:32:26 GMT
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Post by buster on Apr 22, 2021 11:49:57 GMT
just out of interest, was it the first time since the rebuild that the carbs had petrol in them? they often need a gentle tap just to seat the float valves properly the first time and can be fine after that
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Post by BritPete on Apr 22, 2021 14:26:21 GMT
just out of interest, was it the first time since the rebuild that the carbs had petrol in them? they often need a gentle tap just to seat the float valves properly the first time and can be fine after that Its done it a couple of times |
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Post by BritPete on Apr 22, 2021 19:07:33 GMT
So an update Donor set of carbs 250 ones - part of a £10 box at Kempton - Low expectations but when I opened them up very clean  Float needle and Float into SME No leaks Going to order a new set of float needles though Put these on last night - changed the float needle very easily on the bike - recommended but not for the purists I know  |
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Post by bawbag on Apr 22, 2021 20:35:40 GMT
They are a good mod, makes getting the bowls off soooo much easier.
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