Hi, I have an Aprilla Area51 to do up that came with a Dellorto PHBN 17.5 carb which was not fitted to the bike. Lokking at workshop manual for the bike, Dellorto carb spec sheets, etc, I can find nowhere that shows me what connector is for what. I have identified the throttle, choke, fuel & water connectors, which leaves me with two.... I know one has got to be the oil feed & one for vacuum..... but this is where I am stuck. One is a small diameter connector, with a brass stepped down screw in fitting, which I suspect is the oil feed & the other is slightly larger & cast into the carb body itself. I think this second one is the vacuum connection .... but for the life of me I cannot find a pipe on the bike anywhere that could go into it, so suspect it may not be used.... If it isn't used, do I need to seal it or just leave it? The two connectors are next to each other on the front left side of the carb.... the suspected vacuum one to the front. Can some kind knowledgeable person and / or Area 51 owner help please? Cheers, Steve
Here's what I've got in the manual about Vaccum lines, etc (if my pics work, 1st time I've tried doing this:
Good thinking Guns, I should have though to attack it from that point of view. From the above, I can't see a split in the vacuum off to the carb. The thing is these scooters are fully enclosed so removing enough panels to verify the above would be a pain. Would there be any benefit / reason to split & provide vacuum to the carb assuming the original system doesn't use it? Cheers, Steve
always, or you will run lean, and overheat/melt the piston. I normally use a spot of aradite, or you put a pipe on, and block the pipe. I know you can get rubber stoppers, but they tend to split over time.
Thanks for your help on this one Guns, I will use the blocked pipe method so I can swap the carb to other bikes if need be. I've just cleaned & serviced the Carb, new gaskets, O rings, float kit, etc. Interestingly, in an unrelated box of bits that came with the bike, I've just found a short pipe blanked off with a screw. It's the correct size for blanking the Vacuum connector off, which is some more confirmation. Hopefully I will give it a go tomorrow. The carb is fitted with a 90 main jet... Area 51's apparently came out of the factory with 78 fitted to a 12mm PHBN carb. With a Leo Vince pipe & stub air filter, I'm hoping a 90 in this 17.5mm will not be far off the mark....a little small to my mind, but the ex owner said he had it running on this set up before. I've got a jet kit to play with assuming I can get it to start in the first place. I've got good compression & a good spark, so hopefully I will get it going. Regards, Steve
I would of thought of up to 80 with an airbox, and anything up to a 100 with an open filter, depending on flow. But I am no dyno expert, just trial and error.
Just a quick update .... I can't get it running on the 17.5mm carb ... it looks to me like the throttle needle slide assembly needs replacing as it's sitting awfully high in the carb & doesn't seem to seat correctly. I used bits from this carb merged with an old 12mm PHBN with an 84 main jet in it (the biggest you can use apparently) I had hanging around & it fires up & runs great. Just swapped in a performance variator & rollers & later will fit new racing adjustable clutch & spring... then a quick service tomorrow ... transmission oil, new plug, pump tyres up, etc & take it on a run... then sort the 17.5mm carb & start some serious tuning & see what I can get out of it. It's surprising what a difference little changes can make. A young lad around my way told me his old 50cc chinese scooter was really slow (it had been derestricted & had an aftermarket exhaust, etc) but he couldn't spend any money on it. I noticed immediately the tyres were really low so pumped them up, changed the transmission oil (it was filthy, I bet 9 out of 10 people never change it ever). I fired it up, was running lumpy so I sprayed around the air intake/carb with some carb cleaner & noticed the air intake was leaking so took it apart, cleaned it all up ( the air filter was grungy as well), tightened it all up correctly & adjusted his carb air screw & idling slightly to compensate. A hour of my time, a few pence worth of oil, etc & it now accelerates well & it's added nearly 10MPH to the top speed + the lad learnt how & when to do some basic maintenance & why it pay off. Cheers, Steve
Forgot to mention I'm fitting a new kelvar belt & polishing up the clutch pully as well... it's surprising how much difference a decent belt can make.
