More confusion on Dellorto float heights

[Frenchfrog]

So...been experiencing fuel starvation when accelerating at motorway speeds and thinking it could be due to the float heights.
The carbs are new PHF 36's and fearing the kind of trouble encountered by quite a lot of you ,  I retrofitted my old black 10 grm floats instead of the white 8.5 gms that they were sold with.
Previously , the black 10 grm  floats were used for many trouble free miles in a set of PHF 30's.Never had to reset them as they ran fine.
This is where the fun starts:
-all the online figures relating to float heights show that the PHF's should be set at 17.5 to 18.5 mm...no details of variations according to float weight.Same info from the Dellorto carb setting book.
- Having the factory workshop manual and Haynes manual circa late seventies /early eighties the figures shown are 23.5 to 24.5 for the 10 grm floats.
Now I haven't had the opportunity to road test the bike with the white 8.5 grm floats so I'm not sure if it will cure my problem....but I'm confused and I'll add to that confusion by remembering that there was a change to the float cut out needle about 30 years ago.
Can someone confirm  the correct  heights for the white 8.6 grm floats ,black 10 grm ones and confirm that the newer needles don't change anything if used with the old black floats...

[guzzisteve]

You use the 17-18 height, it's not the float weight it's the carb body that controls height.  If you are running out of fuel at that height you go to a larger needle size. From a 250 to a 300 say. The needle also has a spring inside, the pin head wears on the crimp on needle and gets longer. This shuts your fuel off sooner. Many used ones are this way.
I went through all this w/sidecar rig in the 80's. Look at new ones compare to used ones.
The smaller the needle the more it works the spring pinhead the faster it wears.

[Frenchfrog]

Thank you Steve !
I'm going to try out the white 8.5 's...hopefully there wont be any issues.They are set at 18mm.
I'm still surprised that the older black ones are supposed to be set much wider according to the two contemporary sources and that no one makes reference to this setting now....If the whites leak I'll try the blacks again and like you suggest make sure the valve is adequate.

[Frenchfrog]

Everything is brand new in the carbs ...except the black floats which have worked perfectly for more years than I can remember!I never realised that there was a variation in the valve needles....even old monkeys learn new tricks!

[guzzisteve]

My Cal2   would shut off at 65mph, slow down to 60 and it come back on. The pin on needle was worn from working too much. No problems since.          I haven't had any luck w/white floats, to adjust them individually you have to heat the plastic arm, junk.

[Frenchfrog]

That's not good news Steve.....
I'm right in understanding that your running 10 grn black floats in 36mm dells  ?

[SED]

I've used all 3 types of floats white, black, brown and used the white ones, since they have no adjustment, to confirm height of others.  I also replaced the needle and seat (size =300).  Have had the white floats in my LMIII and, as of a couple days ago, have no liquid in them.  One white float did hang up on its pivot due to a little casting flash.

I'm not sure how much difference the 10g vs. 8.5g weight makes because the gasoline density can vary by quite a bit (0.71-0.78g/cc IIRC) and because the heaviest part of the 10g floats is the steel pivot and arms which are primarily supported by the pivot pin.

To confirm starvation you might open the chokes when it starts to falter.  It's not much more fuel, but I remember being able to detect the difference.

[guzzisteve]

Cal 2 has 32's on it & black floats, LM3 has 36's and black. I used to sell DelOrto's and put them on BMW, Guzzi's, Triumph's and jet them to go. My favorite carb. Float needle is 300 in all mine, 250's work too much if on the gas getting power.

[Frenchfrog]

Thanks for the info from both of you !I've got carb mounted chokes on the bike at the moment so I may change that back to standard if the problem persists...not sure what size the float valve is ...supposed to be 300 according to the spec so I'm assuming that they are correct. With 30mm's I never had this problem and I've also disconnected the accelerator pumps .

[SED]

I tried disconnecting the accelerator pumps on the LMIII (PHF36s) and it would bog if I opened the throttles quickly.  Reconnecting the accelerator pumps eliminated the problem.

[Frenchfrog]

No had that problem SED.She's still running in so I'm not pushing it but apart from the fuel apparently running low after a few seconds she runs really well....and fuel consumption is really good too.