Float Weights

So...my 10Gr floats are heavier, therefor less buoyant and require a higher level of gas in the bowl , which is not so far to suck up and will lead to a richer mixture throughout the rev range....I think :-\
 
I have no idea of PHF settings for an SF2 but 10gr floats are standard in PHF 36s for Guzzis. According to my Dellorto tuning manual the 2 weights suitable for PHF 36?s are 10 and 14gr.

My strong guess is that 10gr was standard for yours.

Your summation of float height to fuel mix is correct. PHFs should have a float height of 17.5-18.5mm. Too big a height and the mixture will be lean, too small and it will be rich but take care. There is a limit to how far you can raise the float (reduce the height) before the float will hit the roof of the chamber. This will mean the needle valve will not effectively close and you will have more of a flowing situation rather than just rich.

The only times I have found the float height to be outside these bounds is when there is something wrong and a PO has done it to get around that particular issue. I always return the height to standard then jet to suit.

Cheers

Rod
 
Thanks for the confirmation. These carbs were bought used from a Guzzi dealer so I had changed all needles jets etc but am still having some issues so thought I would check weights. The float jet is a 300, and I beleive 250 is stock but heard that wouldn't make  much difference.
130 mains
60 pilot
K2 needles
New emulsion tubes
chokes working properly
slides opeing fully

new spark plugs and leads


This is a project comp;letion form a 70% complete bike. Motor rebuilt by Scott Potter, so no issues there, but cannot rev out in 4th and 5th gear. Baselined everything else, valve adjustments, timing, new points. Running Conti replicas and stock airbox.
Had some issues with the PHF 36's having the male coupling at the front so used Wolfgang's rubber connector and some cut down inlet manifiolds but the airbox rubber boots protruded into the airbox about 3/4". I just trimmed them down so will test later.

 
Bigger float valve? Shouldn?t matter really being bigger as it just means the float will fill faster. A good idea if you ever remove the pumps.

No all PHF 36?s are the same for jetting. If you look into the venturi at the needle aperture if there is a little brass shroud around the port then it is a ?lean burn? type. These can be pressed out but there is no need to if you understand them.

PHF 36?s were fitted to all mid valve 850?s and some 949?s (1000) that had mid sized valves. Later Cali III?s, some Stradas and maybe Mille GT?s but it isn?t important. The only models that didn?t have the lean burn feature were the LM I and II. They look the same fro the outside but the jetting you need is completely different.

Without knowing what atomiser you have the K2 needle looks a bit lean at wider openings.

My LM III (Lean burn) uses K18?s. Being a 850 the jetting should be just a tad smaller than for your 750 due to the slower air velocity in the venturi on yours.

I run:

Main 120
Idle 56
Needle K18/3
Atomiser AB268 (265 OEM)
Weight 10gr
Slide 60/3

Yours shouldn?t be too far away from that if the shroud is in place.

Best I can guess.

Have you checked the full advance on the ignition? The advance curve on the Alpino is a shocker. I don?t know SF?s so I?m hoping it actually has a curve, not a step.

Rod

 
Rod, yes the shroud is in place so I have the lean burn type.  Have been asking advice based on stock 750 but it sounds like this will be different for the lean burn so maybe I have been going wrong in this respect.

Atomiser is 265.

I have checked the advance mechanism manually and with a strobe and all appears well there.

Am going to try it with the modification to the air box rubbers first as I want to rule out restricted airflow before I change any more jet or needle settings though.

Cheers
 
You say stock airbox, but what kind of air filter?  The filter area is very small and if you use anything with any sort of restriction (ie an oiled foam uni-filter type thing) it does not flow enough to rev out.  Pop the filter out completely (or even quicker just pull the airbox boots off the carbs) and see if it makes a difference.
 
breganzane said:
You say stock airbox, but what kind of air filter?  The filter area is very small and if you use anything with any sort of restriction (ie an oiled foam uni-filter type thing) it does not flow enough to rev out.  Pop the filter out completely (or even quicker just pull the airbox boots off the carbs) and see if it makes a difference.
Click to expand...

Yes stock airbox from Wolfgang with the green foam filter that I have not yet oiled. I already popped off the rubber boots and the bike revved considerably better (90mph easily instead of 80mph) but still not quite right at WFO, so I figured my previous adjustments , leaning the mixture with 130 mains and needle on highest clip might be starving it at top end. So I moved the needle up to middle clip position, stripped and cleaned carbs, checked float height. While doing this I noticed the issue with the rubber connector at the inlet manifold (old Guzzi carbs so rubber hose conection from Wolfgang) was pushing the carbs further back and the rubber boots were protruding into the airbox. I cut 5mm form each inlet rubber to move the carbs forward and clear the frame better. Also trimmed the rear of the rubber boot for a better airtight seal in the airbox and a minimal protrusion of about 6mm.

Then I warmed the bike up to balance carbs and noticed the left pipe starting to yellow. Checked plug and it shows a weak mixture on that cylinder, other is fine. I balanced carbs at low throttle openings, tickover and 3000rpm so suspect an air leak from trimming the inlet rubber. Any other suggestions where to look would be appreciated. I have been fighting this for months.

 
Not sure what else you have done or your experience working on these carbs, here a few things I have come across over the years:

Did you check for air leaks in the inlet track by spraying the carbs/manifolds with WD40 or something similar while the engine was running?
Slides actually being pulled all the way open by throttle?
No little washers left in the idle jet orfices after rebuild so you actually end up with more than one in there? (would not affect top end though)
Set it up without the air filter as a start to eliminate it as a possibility.
If you have points ignition still, make sure no points bounce from a worn mechanism and advance is working 
 
laverdaskidoo said:
Not sure what else you have done or your experience working on these carbs, here a few things I have come across over the years:

Did you check for air leaks in the inlet track by spraying the carbs/manifolds with WD40 or something similar while the engine was running?
Slides actually being pulled all the way open by throttle?
No little washers left in the idle jet orfices after rebuild so you actually end up with more than one in there? (would not affect top end though)
Set it up without the air filter as a start to eliminate it as a possibility.
If you have points ignition still, make sure no points bounce from a worn mechanism and advance is working 
Click to expand...

Checked all the above including fitting new points but not sure how to check for points bounce.
 
It's been awhile since I sold my 750 SFC but if you wiggle the cam that opens the points and find it moves up and down, you can imagine as it spins at higher rpms centrifugal force and vibrations would cause it to move out and open the points more, causing change to gap......at least that is the theory in my mind. With timing inconsistent it could affect perfomance.....not sure it would cause your symptoms,  but something you want to fix if it is a problem. I'm sure more knowledgeable members than me can provide a better response. The fix is either a new mechanism or better yet an electronic ignition from Wolfgang.
 
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