I was vacuum tuning the carbs today when I noticed one of the carbs was dribbling fuel.
So I removed the offending carb to check the float valve and float height. I was quite surprised to see ~ 15mm against a manual stated height of ~ 24mm, this explained the overflowing bowl, so I gently bent the float links to get the correct height.
I then checked the other carb to find a very similar float height.
This seems a way out adjustment by a prior owner, or is the Manual stating 23.5 - 24.5 incorrect ?
Interestingly this did not affect the tuning settlings from the vacuum gauges at all.
Thanks, but my manual definitely says 23.5 to 24.5 for the PHF 36, and as it was flooding before and works OK now I will see how I get on with 24mm, but quite a twist on the floats to get it to that from ~ 15mm. BTW the lower the upside down height = higher the fuel level in the bowl.
Fig 13 and Fig14 show how to set two different types of Float. 13 is for a 1 piece Float, 14 for the 2 piece individual Floats. Maybe i should have explained that! Also 18.5 -17.5 is a tolerence not two different settings!
The carb they show is not the same as the PHF36 in the Guzzi manual, and I do realise it is a tolerance measurement not one for each float section. Anyway I will see how it runs at 24mm where I have set them both. The plugs will tell me if it is too lean, but one carb was dribbling fuel with the level set too low (NB too low when inverted = higher fuel level).
Do these have the spring loaded float needles? ie you lift the float and the needle closes the fuel off, but you can still lift it further by pushing against the gentle spring pressure. Measure it at the first point where the fuel supply is closed off.
There’s a lot of justified confusion here because both the Mk1 and Mk2 manuals clearly specify 23.5-24.5 as the float height. My Mk2 manual, which came to me with my Mk1 in 1991, has a beautifully annotated addition, in italic blue/black fountain pen, saying the Mk1 should be 17.5-18mm. BTW, the diagram printed in the manual does specify measuring it the same way as the Dell’Orto manual, and also has the same 24mm setting for the 1000SP etc.
I subsequently managed to get reprints of the Mk1 manual and that also specifies 23.5mm. These are all with 10g floats. 10g floats haven’t been available for a number of years.
It’s possible Guzzi went off-piste with float weight selection and adjusted the float height accordingly; increasing the height lowers the float level, requiring larger jets to get the same mixture. Or perhaps Dell’Orto recommend lighter floats which would ride higher in the fuel and thus need a lower height to achieve the same fuel level. Floats currently supplied are 8.5g generally, so perhaps this is going towards the D’O setting to achieve the same fuel level.
I believe, based on the lack of annotation in my hand, that I’ve been using the 24mm height. I’ve been checking this fairly regularly because of modern fuel issues so I’m fairly confident I’d have made a note if I was using the 18mm setting, as stated by the D’O manual and my machine’s previous owner.
The float height should have no effect on the vac gauges because once the mixtures on both sides are correct the manifold pressures in each side should be the same. Try the 24, see how it works. Let us know how you get on.
Indeed so. Greg’s a trusted resource.
That page is a reprint of the Dell’Orto manual supplied by Eurocarb, so it’s the other part of the confusing picture, vs Guzzi’s own documentation.
I don’t know which is right. I think we just have to find whatever works ( and try to remember it ) especially as the parts change e.g. float weights.
I took the bike out for a brief maiden run the other day, mostly to check the brakes. The RH cylinder was misfiring and popping a bit at lower revs, but this might be because presently the ignition is over retarded to make up for the lazy advance mechanism control springs. Gutzibits have these due in shortly, so once I have these I will reset the timing so the static is closer to the correct marks, plus I am going to set the floats up ~ 18 mm.
If the ignition still over advances at higher revs I am going to have to scratch my head, because increasing the spring tensions will be a bit of a challenge. There is fortunately no slop nor excess wear in the advance mechanism, so I am hoping it is just tired 49 year old / 45,000 mile springs.
