Float height/weight?

B

Bunyip1

New member
Location
Cumbria
Evening all,

Mirage TS, Eng/Vin 2845,  42000km

I?m working through the carbs, replacing O rings etc.  After reading through the old threads and your collective thoughts it seems most of the jet sizes are standard/ok though mains at 145 are probably at the upper limit.  Not too worried by them at the moment.

I am wondering about the floats. The ones fitted are Black 7450.1 10gr. As found they were set at 19.5 - 21mm and have now been reset to 18ish.  The DellortoUk site shows some alternative floats but I haven?t found any other mentions in the Laverda books etc. for a specific float.  Are the float weights critical?

Generally it was ok, started easily with some choke and when warm settled into a steady idle. As bought it had no air filter fitted and fitting an element made it better/smoother at from half throttle upwards. At low steady speeds however it is harsh ? ok on the over-run and when accelerating gently but trying to ride at steady 20 - 40mph is a no no.  The carbs were all nice and clean inside though some of the O rings were quite brittle.

Now I haven?t been into the inlet stubs/valves/cams/chains/ignition etc. yet and know they can contribute to the roughness. Compressions, cold and WOT, are all 160.

A spare head and some sets of pistons came with it, possibly from this bike, possibly just unrelated spares.

Anyway, I gave up work today so at last have some time to play with the bikes.
Sorry Terry, beat you to it!

Cheers,
Peter
 
Joined the ranks of the unwashed unemployed or became an 'old age pensioner'? :D
 
A couple of points, the float weight will alter the float height and the real problem most people have with running and carbs is wear in the slides and bodies so check that. Wear equals air leaks and rough running..
Congratulations on you retirement :)
 
Terry Dymond said:
Joined the ranks of the unwashed unemployed or became an 'old age pensioner'? :D
Click to expand...
Bit of both really - now self-unemployed and a month away from OAP status!

Paddy said:
A couple of points, the float weight will alter the float height and the real problem most people have with running and carbs is wear in the slides and bodies so check that. Wear equals air leaks and rough running..
Congratulations on you retirement :)
Click to expand...

Thanks. Yes, aware of problems from leaks & wear. Just trying to get near standard settings before looking for other problems.  It already seems quite rich with sooty plugs and some fouling after a 2 mile downhill stretch, so not expecting a raised float level to help that.  Possibly the PO lowered floats to cover up other/wear problems.

Peter
 
Apparently the newer white plastic floats (8.5gr?) are giving lots of trouble and people have been advised on this forum to avoid them and use the old black ones.
 
Sounds like its wrong on the needle phase ie 1/4 turn.
obviously its Keihin but have a read of this, its a bit "in general" but it might give you a clue about the needle phase.

http://www.duncanracing.com/TechCenter/KeihinCarbJetting.pdf
 
I have Mirage TS 2829. 170,000kms. It's been a brilliant motor and just finished a total rebuild. The head is now fucked and needs replacing so having a spare may come in handy. :D
 
If you want to be cock-on, float heights are a real PITA on Dells. Float weight is certainly a factor.

Here's what I do to test for that. (Triple)

Carbs off - float bowls off - fuel lines still on - prop upside down (or near to) - block a fuel pipe - blow into other fuel pipe - listen/look for which float jet blows first - make adjustments accordingly. By touching them lightly you can tell which ones are very near to blowing. Get them as near to blowing at the same time as poss.

HTH, Paul H
 
Interesting procedure Paul. I've never heard of that one before. I'm still trying to figure out what it actually achieves in relation to float height.

If you want to get pedantic, it's not float height or float weight that you need to be concerned with. The only reason we set float heights is that it's something that is easily measured, and hopefully achieves the result we're after.

What we're really trying to set is the liquid level in the float bowl. You could conceivably set all float levels the same, but if there's a slight variation in float weights, the fuel levels in the bowls will all be different. The only way you can be 100% sure of the fuel level is to measure it directly. The simplest method is to connect a clear plastic tube to the float bowl, bend it up alongside the carb body, turn the fuel tap on and see where the level settles. Having said that, don't ask me what the "sight glass" level should be - I've never done it!

You can also get clear plastic float bowls for Dellorto carbs. Might be an idea to get a set for setting fuel levels. I've heard that they suffer from UV degradation in the long term, so I wouldn't leave them on the bike indefinitely.
 
I know it came up in a thread some time ago , but interesting letters thread in theTimes about Miss Shillings Orifice. Helped Spitfires having carb issues when diving after 109s, who had fuel injected engines. Jeez, if they had them back then, why didn't everything since? Today's letter says she became head ofRoyal Aircraft establishment mechanical engineering department, and rode bikes! First woman to lap Brooklands at over 100mph...must google and find out what she rode.off to kill myself in squash game now..
 
sound like everybody is getting a bit too technical for their own good, yes we should pay attention to float heights and be sure that they are all the same weight, and (important this) free to move through out their whole arc, but don't get too hung up on it, important also is nice clean filters in both the tank pet cocks and the carb banjos. I have always stated and still do that the best thing for a tuned and hard used motor (triples) is to have three taps in the tank, each one feeding its own carb, but linked across all three as well, together with float valves (not needles) which will flow adequate fuel, but if you really want accurate float heights then a single remote float chamber, feeding all carbs is what you need and what we all used to do in sidecar racing with twins triples and fours both two and for stroke a long time ago.
CLEM
 
Hey Clem, we like a 'bit too technical'. Gives us something important to think about during the humdrum workday.

You know the old engineer's jokes.... 'If it ain't improvable, it ain't get enough features yet'.  :D  Do most of these tiny mods make a sod of difference? Of course not!

Hi Cam, the blowing achieves nowt with regard to true float height. It is just to establish if any floats are heavier (and/or the pivot is goosed) and to enable a slight height offset carb-to-carb. Its just a little overcheck. In terms of displacement, Archimedes would have said that these tiny amounts resolve to bugger all when the density of the displaced fuel is considered anyway.

Those little springs in the float needles aren't very accurate in their rate either.....


 
Ah yes, I can see it now. Archimedes fanging around the streets of Syracuse on his Laverda, his toga flying in the breeze. Would he have ridden anything else? I doubt it.  :D

I'm off to make a fuel manometer to check my float fuel levels.
 
Now you've done it. I cant see the word Manometer without starting to sing the Muppet theme tune....

Manometer do doooo do do do
Manometer do do do do do
Manometer do dooo do do do do do do do do do do do do do do duh duh duh duh

That's in my bloody head all day now.
 
It would have stuck in my head too Paul. But you had one too many "do"s in line 2 and several too many in line 3 which buggered up my mental rhythm.

I can sign off safe in the knowledge that my mind is a complete blank. I trust it will remain that way.

Cam
 
I did have a lot of problems with a set of new white floats...not sure of the weight difference though. When it. Went to Keith one time, he just junked them and put black ones back.but do they still supply those new...I thought not?
 
I use a ?go ? no go? gauge to set my float heights ? if the floats don?t go through the 17.5mm setting , but the 18.5mm passes over them ? that?s Ok. It?s handy for checking that both floats are equally set too ? Regards - phil





 
I wonder how important float hight really is ? Its going to alter with lean angle, acceleration and deceleration. In my world of bevel ducati's the float hight is given as an exact but TBH the front carb is angled at about 45 degrees and leaning on its side while the rear is horizontal and level.
what is really important is the fuel level in the emulsion tube which being in the centre of the float bowl (ish) will remain pretty constant, for this reason some sort of manometer would be the answer, some Dellorto's do have a drain plug that can be used to attach a manometer tube.
 
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