TheSamba.com :: View topic - Twin FRDA Dellorto balance pipe and brake servo pipe question

Mon Feb 22, 2021 4:56 am

Apologies for raising this question again but I can't find a clear answer.

I am looking at my twin dellortos and realised that I only plumbed in the brake servo to one side. It runs ok but stutters a bit from low down - all good at higher revs - and brakes work well.
The twin carbs were to replace an odd EMPI central thing. Which in turn sadly replaced the FI and was fitted by a PO.

From what I read, I should have a balance pipe between the inlet manifolds (already tapped).
Is ¼" pipe ok for this?
Can I use the 6mm or 8mm Gates Barricade fuel line for this or should I have a different spec pipe for vacuum servo? Bigger better or smaller better for this section??
I understand that I should T both pipes from the inlet manifolds into the one ½" pipe that then goes to the check valve and on up to the front of the bus. Is that correct?
So I need a ¼" ¼" ½" tee?
And again, what quality of pipe?

Once done I think idle will improve.

Any confirmation or pointers on the above would be greatly appreciated.

Mon Feb 22, 2021 7:10 am

If you have the type of Dellotos I’ve installed then you need to understand that each carb is actually two carbs. Four cylinders and four carbs. If you install a balance tube then you’ll lose the ability to adjust each individual carb. As far as power brake booster vacuum goes, it works very well to tap into a single intake manifold for that. You need to understand that even though vacuum will be tapped off say #3, it remains a closed system and not a constant leak as long as your system is tight. I’ve done it this way several times.

Mon Feb 22, 2021 7:39 am

Before doing anything, clamp off the booster vacuum and tune your carbs to remove the stumble. Then use Gates power brake vacuum hose 15/32” inside diameter all the way to the booster. The gates number is 27231 and can be purchased at finer auto parts stores by the foot. Be sure you install the check valve in the correct direct (sucking towards the engine)

Mon Feb 22, 2021 10:50 am

The Dellortos are the 36 FRDA single barrel into the manifold that then splits in to two branches.
I was under the impression they needed a balance pipe whereas the twin barrel carbs don't. But I am far from being an expert and this was the point of my questions - I can't find the right answer.

Understand that I should clamp or blank off the vacuum tube before tuning as any further airflow into the manifold after the fuel mix will create havoc.

Mon Feb 22, 2021 1:26 pm

You sure those are 36s? All the frds I’ve seen are 34s. Mine do not have a crossover for the brake vac but do have a tee in the distributor vac line. Booster comes from only one carb.

Your stumble may not be the brake vac. Cured my stumble by adjusting the balance @ 1200-1500rpm. None of the snail gauges go high enough so I had to use the hose to ear method.

Mon Feb 22, 2021 2:57 pm

Definitely 36’s.
And I’ll check the balance with the remarkably accurate hose! at higher revs.