carburettor setting

[Dave487]

I got the 400-4 engine running last after week after a complete overhaul. I hooked it up to a small temporary fuel tank and all seemed ok initially, it ran on all cylinders although idling was a bit lumpy, however after playing with the air bleeds I settled 2 turns out and went on to balance them with vacuum gauges and it didn't take much adjustment to get a good balance.
After this the engine ran much smoother although there seemed to be a bit of a flat spot on the transition from idle jet to main. I checked the ignition timing with a strobotorch and decided to leave it at that until I get it on the road.
However two of the carburettors started to drip fuel which was really annoying as I was careful to set the float levels at 22mm so I decided to remove the carb's in order to re-check the float levels but after reading some older posts on this forum regarding carb' problems I decided that the floats might not all have the same buoyancy after 40 years so I made a set of adapters to fit into the bowl drains with short clear plastic tubes in order to see the actual fuel level in each bowl.
It was found that on the 2 which were dripping from the drains the level gradually rose whilst the others remained constant and therefore the problem was leaking needle valves, this turned out to be tiny pieces of cotton fluff where I had used a cotton cloth to wipe out the temporary tank and hadn't fitted a filter into the line. Lesson learned, and a quick trip to the local garage for a 2 quid in line filter should resolve the problem.
After checking all the needle valve were free of dirt I re-filled the bowls and this time they were remarkably consistent and settled at about 3mm below the joint so after leaving them for a couple of hours I am satisfied that all is well and I can now re-fit them and prepare for the MOT test.

What I take from this is that it's easy to blame faulty components for some of our problems but in my case it was a very small almost invisible foreign bodies that were to blame.
 

[petermigreen]

Thanks for sharing, what did you use for the little float bowl adapters?
Peter

[Dave487]

They're made from bowden cable threaded adjusters. I have a small lathe so machined a undercut at the base to fit an 0ring seal and inserted a piece of polythene tube in the open end. The adjusters are fine thread M6 x 0.75 as drain plugs are not the standard M6 x 1mm

[petermigreen]

Ah not easily accessible then.
Thanks, Peter

[Orcade-Ian]

Well, I'll go to the foot of our stairs!
I have just come out of the workshop for a well earned brew after making 4 adaptors for the float bowl drains and just saw your post!  I had a die of the correct size and some hex brass rod, so no big deal really.  I was surprised that the drain screws were not listed separately in my parts book - perhaps they were never available?  I have a few spare sets of carbs and could have adapted (butchered!) a set but if they are made from unobtainium, best to make my own.
Anyway, you have set your floats at 22mm and that has given you a level about 3mm down from the joint face - have you run it at that without the flat spot?
I'm still finding disagreements about whether they should be 22 or 24 mm and I'm about to do my spare 400 but my 350/4 runs fine on 24mm.

It's strange how these carbs seem finicky on float height - my old man used to switch the fuel off on our BSA Golden Flash outfit at the top of the road and it ran well on a diminishing float height right to the house - ah, for a simple life!

Ian

[Dave487]

Ran it today and just had a little potter down the road before it started raining but never got out of second gear. It seems to run ok and picks up from idle without a flat spot, but as it doesn't have MOT or Insurance yet and 'plod' lives a few doors away I can't give it a real run. Best of all 'no drips'.

[Orcade-Ian]

No drips or flat spots must be a good result - I'll try 22mm on mine and see how it goes.

Ian