Fuel Taps

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frankfast
Posts: 140
Joined: Wed May 05, 2010 12:35 pm
Location: New York (upstate)

Fuel Taps

Postby frankfast » Sun May 17, 2020 7:06 pm

My '71 350 Scrambler has dual petcocks with 6mm outlets yet the 29mm VHB carb has a dual banjo with 8mm inlets. I'm suspicious that either the tank

(or petcocks) or the carb is not original to the machine. Or is that the way Ducati did things back then?

Ventodue
Posts: 627
Joined: Mon Mar 08, 2010 3:23 pm
Location: Montpellier, France

Re: Fuel Taps

Postby Ventodue » Tue May 19, 2020 11:15 am

Sounds like it's the taps that are too small, Frank. See photo below (1972 450 SCR, btw). The caliper jaws are over the outlet spigot, of course.
Attachments
SCR tap.jpg

frankfast
Posts: 140
Joined: Wed May 05, 2010 12:35 pm
Location: New York (upstate)

Re: Fuel Taps

Postby frankfast » Tue May 19, 2020 11:38 am

I think you're right. It's reasonable to assume that the 350 and 450 Scramblers had the same size taps. I'm not sure that having a smaller tap would cause a problem with feeding the carb, especially because there are two. Getting a fuel line to accommodate both is the issue.

amartina75
Posts: 339
Joined: Tue Aug 21, 2012 1:13 am
Location: Cincinnati, OH. USA

Re: Fuel Taps

Postby amartina75 » Tue May 19, 2020 6:00 pm

The 450 uses 12 mm threaded taps 250/350 uses 10mm threaded taps
The barbs on the bigger taps are 8mm and smaller taps are 6mm although they may have made later small taps with 8mm barbs they are available at Guzzino
Dellorto also made fuel inlet fittings with 6 and 8mm barbs

The carb on your bike may have came from a 450 or something was swapped over the years. Your 350 scrambler probably originally had an SSI29D on it. It’s hard to say without seeing several pictures of the bike to see better when it was produced.
1966 250 Scrambler
1970 450 Jupiter

frankfast
Posts: 140
Joined: Wed May 05, 2010 12:35 pm
Location: New York (upstate)

Re: Fuel Taps

Postby frankfast » Tue May 19, 2020 8:03 pm

The information I have reads that the earlier 350 Scramblers had the 29mmSSi carbs while the later models, '70 to '74, had the square slide 29mmVHB. Since I don't have the history of the bike it could be that the taps or the complete tank were not original to the bike. Since I believe the barbs on the carb to be correct at 8mm, I probably should change the taps on the tank. So that the lines don't leak, I have to crank down hard on the hose clamps over the 6mm taps in order to keep them from leaking. Eventually they will cut into the fuel line and start leaking.

amartina75
Posts: 339
Joined: Tue Aug 21, 2012 1:13 am
Location: Cincinnati, OH. USA

Re: Fuel Taps

Postby amartina75 » Tue May 19, 2020 11:59 pm

Yeah it’s hard to say for what it’s worth I have a VHB on my NC 250 Scrambler and I was able to fit new 6mm Tygon tubing over the 8mm carb inlet (it’ll never come off but that’s ok)
You can buy new 8mm petcocks that might be the best route depending on the condition of yours. If they are original I’m surprised they aren’t leaking. The old rubber seals don’t like the ethanol in modern gas.

Good luck sorting it out
Aaron
1966 250 Scrambler
1970 450 Jupiter

Ventodue
Posts: 627
Joined: Mon Mar 08, 2010 3:23 pm
Location: Montpellier, France

Re: Fuel Taps

Postby Ventodue » Wed May 20, 2020 7:48 am

amartina75 wrote:The 450 uses 12 mm threaded taps, 250/350 uses 10mm threaded taps. The barbs on the bigger taps are 8mm and smaller taps are 6mm although they may have made later small taps with 8mm barbs <snip>

That's good info, Aaron! Who would have guessed? Thanks!

Jordan
Posts: 983
Joined: Fri Dec 24, 2010 11:29 am

Re: Fuel Taps

Postby Jordan » Wed May 20, 2020 11:31 am

The size difference could be even worse.
I measured some barbs on various Ducati tanks and carbs, and the range is from 5.5mm to 8.5mm.

It might be worth considering making some mid-line adaptors that can accept two different sized hoses.

frankfast
Posts: 140
Joined: Wed May 05, 2010 12:35 pm
Location: New York (upstate)

Re: Fuel Taps

Postby frankfast » Wed May 20, 2020 3:21 pm

If what you're saying is true, then my tank, taps and carbs could all be original equipment. Can't believe Ducati could have used 6mm barbs at the tank and 8mm barbs at the carb. Then again.... Or is what you are saying the range of barbs are on different models.

amartina75
Posts: 339
Joined: Tue Aug 21, 2012 1:13 am
Location: Cincinnati, OH. USA

Re: Fuel Taps

Postby amartina75 » Wed May 20, 2020 4:45 pm

Keep in mid Ducati didn’t make any of those parts, they sourced what was available from Italian companies at the time. Even the gas tanks were outsourced as far as I know. Don’t remember who produced them but I’ve seen pictures of a makers mark inside gas tanks.

Also parts are swapped over time with whatever works and is available.

I think what Jordan is pointing out is that the tolerance between parts were pretty loose.
1966 250 Scrambler
1970 450 Jupiter


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