Carb float level setting

[Alpine Daimler]

Hello

Before refitting the carbs on my V8 saloon I have stripped them down to examine the condition of the parts and renew the float chamber needle valves.

I was surprised to discover that the float level setting was way off spec on both carbs and by the same amount, 15mm instead of 11, using the method described in the manual, quite a bit!
All the more surprising as the engine has run very well under all conditions since the summer of 2015.

Unless I am having a senior moment I think this will cause the floats to close the needle valve and fuel supply early leaving too little fuel in the chambers and jet causing a lean mixture, the removed plugs do not confirm this.

I am very reluctant to set the floats to the correct setting and possibly introduce problems I have not until now experienced.........unless someone here can convince me otherwise!

All the very best over there.

Rob C.

[daimlersteve]

hi all,
the best way to set the float level ht. is to see where the fuel level is in the jet.
Over the years i've seen various effective hts. of the float needle valve assembly, so if it works for you and the jet adjustment is 60-90 thou down from the bridge , no problem . Any lower than that it needs sorting.
Cheers Steve ,
in isolation ,
but with another SP to rebuild i'm busy .Steering converted to Rack , Engine freshened up and fully assembled, body repaired, Vinyl Ester undercoated , faired, engine bay repaired and about to be hi build undercoated today. Gearbox later this week. I just cant get the paint to complete the engine bay so i can replace the power unit, bugga .

[Jez]

There's a fairly wide tolerance on the float setting which will still allow the mixture to be set correctly and the engine run well. A low float may starve the engine on sudden deceleration whereas a high setting is more likely to cause overflow. Actual effect on mixture in normal running is limited so long as the float level is there or thereabouts.

Cheers - Jez

[Christopher Storey]

Rob : IIRC from my flying days, Munich itself is about 1500 feet above sea level, and of course if you go much south of there, the ground level is significantly higher. Therefore, you will always need a weaker setting than would usually be the case in e.g. the Netherlands and the UK . It may be that someone has achieved this by setting the float level to shut off at a lower level than would normally be the case . If it ran well for you, I should leave it as it is

[Sydsmith]

Rob I thing this is a case where "if it aint broke don't try to fix it" applies, mine are likewise not as per the book, but they have never let me down.

As has been made clear here, there has always been a difference of opinion as to how to set them, but as I say if you don't have a problem with them I would personally leave well alone. Syd

[Fossil]

A very quick rough guide to the float chamber fuel height that I've resorted to for many years is to remove the dashpots and pistons one at a time and blow a quick strong puff of air at the jet. If the level in the jet rebounds sufficient to send a trickle of fuel down towards the butterfly I assume the float height is about right. If no fuel after puff, level too low; if fuel leaks when piston removed, level too high. Often you will see the fuel level just a mm or two below the jet orifice and then you don't need to apply the puff.

It works and avoids the need to take off the float chamber tops only to find that they don't seal properly when replaced.

Regards

Fossil

[daimlersteve]

Yep, couldnt have said it better,
steve ,
be safe out there

[Alpine Daimler]

Thank you all for your responses.

You have, of course, convinced me to leave well alone and see how it runs when the time comes and allows.

@ Christopher : We are up at a tad over 1700 feet above sea level here on average in Munich, the old Riem airport is just a stones throw from where I live. It never occurred to me the float level heights are set to take into account the rarified atmosphere and reduced air pressure and density we enjoy here but quite plausible.

@ Fossil : Thanks Geoff, I remember you gave me this tip before and I had not forgotten and I intend to try it out when everything is back together and hopefully up and running.

Thinking of you all over there.

Rob C.

[Fossil]

Rob, thanks for the mench. I hope that you succeed in sorting it all out. You are slightly higher than the highest village in Scotland, which I think is Wanlochhead at 1500 ft approx, an old lead mining village; to my regret it doesn't register on the cheap & cheerful altimeter I bought when touring the Western USA and reaching the top of Pike's Peak at 14,110 ft (and no crash barriers). Mountain air is lovely even when you look blue.

However I digress. I'll check my SU carb reference book and see if a weaker needle is quoted and at what altitude.

Steve, thanks for the compliment, we never did seal the deal for a pair of your special TR6 front suspension conversion stub axles! However not now, I must get the other SP completed. If/when that is achieved I'll come back, but don't hold your breath, slow progress is now the order of the day, one task per day, perhaps it's just laziness, or retirement.

Best regards, wash your hands and keep your distance!

Geoff

[Fossil]

Rob

Indeed there is a recommendation in SU's HD6 information, including the booklet I received with repair kits. It says that a weaker needle is recommended at altitudes of 1800m, 6000ft, or above. Which may suggest that you would be safe to set the floats at the standard recommended height of 7/16 inch if you wish to. Unfortunately I cannot find a recommended weaker needle for the V8 saloon, or SP250, but in this instance it does not appear to be an urgent matter.

I'm about to adjust the Dauphin's HD6s after a major operation to re-seat the exhaust manifolds following a minor contre-temps. [I reversed into an old tree stump which sealed the tail pipe so completely that the manifold gaskets blew, fortunately they were not cracked, but they had to come off anyway]. HD carbs are so easy to live with, and on the "if it ain't broke....." principle I rarely touch them, unless of course they have to come off to remove the exhaust manifolds. But this time I put them to one side and then replaced them after several months a few days ago, without further adjustment; she started immediately and is running v sweetly, as before the prang, although not yet on the open road. I will check the balance and mixture before concluding the exercise. The Dauphin is a MkI Century so it came with H6 SUs, The conversion to the MkII's HD6s isn't simple but is extremely worthwhile for any MkI Century if you don't like the smell of petrol and you can find a MkII donor. Highly recommended!!

Apologies everyone for yet another digression.

Good luck.

Geoff