Datsun Roadster Forum-311s.org

david premo wrote: ↑Wed Jan 31, 2018 9:17 pm FYI you can NOT use Weber soft mount! Big vacuum leaks.

Dave is the issue on the manifold side or the carbs themselves ? if its the carbs wouldn't he be fine since he's using OERs?

Pictures!!!!

The Mikuni's have the air bleed on the back, and Mikuni softmounts have a bump out to compensate. I was under the impression that some of the newer soft mounts worked, but David would know much better than me.

Have 2 intakes sitting in garage let me know what you need
ps have a digital read out on my mill for measuring

I want the intake to be universal for all, i.e. Solex, Webber, OER, is there anything that needs to be added to the carb flange.
Thanks

From what I can see the Mikuni insulators have an O ring with a slight bump to seal things up which the Webers don’t need

so this would mean if you’re using Weber or OER you can use the Weber insulators but if you’re using Mikuni it has to be the Mikuni insulators and The manifold is the same regardless
Would that be correct ?

Mikuni insulators

These pics don't seem to show any special changes from a Webber insulator.

IIRC, the flat ones work fine. The O rings have to clear the vacuum port - hence the bump in the O ring on the Mikuni insulators. I was under the impression that some of the Weber ones had the O rings wider to accomodate either.

BBF Roadster wrote: ↑Fri Feb 02, 2018 7:50 pm These pics don't seem to show any special changes from a Webber insulator.

Maybe these will show the difference better

For clarity on my post

With Mikuni carbs you need to take care that you do not create vacuum leaks by exposing the starter port to atmosphere. The Mikuni O-ring insulators and the Nissan insulators do a good job of covering the port. Some times the manifold if designed just for a Weber will also present a problem as they do not have sufficient material on top on the inboard side and can cause vacuum leaks. Attached are a few photos that I hope will shed a little light on this. Note that the two gaskets though similar in looks are a bit different in shape. The Mikuni gasket has a bit more bulk to it to cover the starter port. Also not the witness marks on the carb pictures, someone install the insulators upside down. You will also note the factory Mikuni insulator has a bulge for the starter port which is not on the Weber insulators.

Dave

Thanks Guys
This area will be added to the carb flanges so that Mikuni O ring insulators can be utilized for a better seal.
Your pictures and explanation really highlighted this issue, many thanks Dave, spl310, pjackb.

This drawing shows the addition to the flange.

Well I finally was able to pickup the 3D models so I could check final fit.
I took some time today to run to the shop and fit them on the engine.
The fit was perfect and I was able to temporarily mount the OER's with filters.
Now I can finalize the linkage fitment, I will post pics when I have that done.
Thanks to everyone for all your help.
PS. the carb flanges are not the new design that will match the Mikuni carbs.

I'm fascinated by the 3D-printing phenomenon. We have one at work for clinical imaging stuff. I'm curious about a few things with the manifold:
1) If you mounted the carbs and ran the engine what would happen first? Would the manifold melt from heat/fuel mist? How long would that take?
2) How do you go from the 3D intake to an actual metal piece? Will it look exactly like the 3D part shown, made with a machine or hand made?

Neat stuff!

The PLA filament would melt quickly on the head, heat has always been the biggest challenge for 3D prints.
The intake flanges will be waterjet cut and hand finished.
Tubes will be hand fitted and welded internally to the flanges.
A jig will be used to maintain uniform parts.
I can't wait to have the first one completed and test it on my car.