Intake manifolds

Guern

Guern

New member
Location
Guernsey
Hi all, this is my first post here, so apologies if this is a repeat question, I couldn’t find a previous post about it.

I’m 6 months into restoring a 1979 1200, and I’d like to replace these nasty blue carb intake manifolds which (I suspect) aren’t original, and replace them with the stainless trumpet in the other pic.

They’re both 52mm in diameter, but it seems the threads are incompatible. Has anyone experienced this before and can you recommend a replacement trumpet with the correct thread? The one I’ve bought as a sample is a dellorto with a PHF thread. I have no idea what the thread is on the carb itself.

Thanks for your help. I’m not a mechanic and this is my first restoration, so apologies if this falls into the “stupid question” category

Andrew

IMG_0135.jpegIMG_0134.jpeg
 
Ok, please excuse my ignorance, I assumed PHF was the type of thread. Turns out it’s a model of carb, with only the PHF having a threaded spigot.

Still no closer to understanding why the trumpet won’t screw on!

IMG_0137.png
 
PHM is a larger Dellorto carb (38-40mm, and very rare, 42mm) with a M52x1.25 thread for trumpet/bell mouth/intake tube/velocity stack, or whatever you want to call it.

PHB/PHF are 32-36mm and share the same thread for the trumpets, M48x1.25.

Both carb types evolved over the years and both eventually changed from clamp to stub fitment.

piet
 
I would do the following:

a) use longer manifolds. typically longer ones are said to give a bit more torque while shorter ones give a bit more high end HP (which you don't use anyway I suppose on open roads...)
b) no mash is prefered. They reduce air flow and cause tourbulances. Yes, they can also hold flames from burning your bike-frame, however, I would prefere to mount a plate/heat shield there to keep the potential of flames hitting the frame at high revs under controle. Less important on longer ones, more on shorter ones
c) due to the plate that connects all 3 carbs at the rear end, the thread is very short. to avoid turbulances and to make the manifolds seat better against the carbs, I would shorten the thread of the manifolds so that they sit as they should do if there would not be the connecting plate. Measure the length of the visible part of the threads at the rear of the carbs, measure the depth of the thread at the manifolds and remove what's not necessary. Then give them a bit of loctide blue when you mount them so they stay in place.

Personally, I would take the left one, but that's up 2 U

PHF%20(1)-ts1626950191.jpg


Source: www.ducatipaddy.com
 
motoddrob said:
Remember reading somewhere that those screen covered bell mouths rob a heap of HP. Better to leave them open.
If your really worried about dust/rocks better to user K&N or DNA pods.
Click to expand...
Yep. Next to generic pod filters, the gauze would cause the biggest loss on the flowbench. Even the course screen on the plastic Dellortos were rather crappy.

piet
 

Exactly my situation- I live on an island with a 35mph speed limit, so form trumps function every time! Thanks for your assistance
 
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