Carb balance-pipe - REALLY necessary?

Hi, I have 3 Strom CD150's on my GT6 (1998cc) which sit on 3 seperate home-made manifolds fabricated by the previous owner. He has drilled holes in the top of each and brazed a balance pipe between them (copper elbows, short SS pipe sections and rubber couplers to account for any severe vibration - a neat job). Yesterday while being a little 'vigorous' with a spanner I managed to knock one of the pipe sections off. As I didn't have tools or time to re-affix the part, I removed it from all three manifold sections, and blanked off the holes.
Now the engine starts better than it did, but backfires quite regularly. In fact it sounds like it pops fuel BACK through the carbs and out of the filters.

So.. my questions are, what does the balance pipe do? DO I REALLY need it? Have I done, or will I do damage to the engine by driving it like it is?

Cheers for any info, thoughts, ideas... Ben

The more cylinders you have pulling on the manifold, the more even the vacuum. With a street engine at low idle, the vacuum would be very irregular with only two cylinders per carb. I suspect the balancing tubes would make the carbs function much better. You could probably see this if you put a vacuum gage on the manifold with and without the balance tubes.

Hi Craig,
Thanks for the response, so when you say "function much better" can you say in which way that would be? Economy, throuput, power, responsiveness.
I'm deffinitely noticing a difference in 'pull' while accelerating. I used to have a problem with very low power when pulling away but it was ok past about 2k revs. I put this down to the differnt cam in there. But since doing away with the balance pipe, it has WAY more pull at low power. In fact it'll start to pull itself along on the flat if I up-clutch slowly in first gear with zero accelerator - Before if I'd done that the engine would just die.

Cheers,
Ben

I would think you should check the ignition timing, backfiring through the carbs might mean you're too advanced which could damage the intake valves or the carbs/air filters if bad enough or prolonged.
Try backing it off a few degrees, see if that helps.

Oh ok thanks, I'll try that and see if it makes much difference.

I know Craig has touched on it, but anyone else got any thoughts on whether I actually need a balance pipe?
I know Triumph included one in all their manifolds on 2 carb systems, but does anyone really know WHY that was?
I've been talking to Mini and Porsche mechanics and they think the balance pipe is useless.. Triumph MUST have had a reason though...

cheers

I wonder if one of the Balance pipes had a vacuume leak, that could have caused the symptoms you described. and eliminating them eliminated the leak.

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...
I've been talking to Mini and Porsche mechanics and they think the balance pipe is useless.. Triumph MUST have had a reason though...

cheers

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Although we often may think otherwise, all these things that are on cars were put there by some highly paid engineer that the bean counters approved. That balance tube is there for a reason. I tried to find out what exactly it is there for, and as the name suggests, it is there for "balance". This site on MG's gives some info on the reason it's there and the effects of it not being there. The discussion about the balance tube starts at about the third paragraph down./ubbthreads/images/graemlins/driving.gif

Here's another tidbit:

https://www.teglerizer.com/mgstuff/a_stumble_at_cruise.htm

Although this author was convinced the K&N filters were "bad", the real problem is the pulsing pressure in the carb. By changing back to a more restrictive air filter, these pulses were diminished and his car ran better. It is unclear if he had any kind of balance tube on his setup...

Aha.. yes so its possible that since owning the car (3 months ish) I've always had a leak there, and now I've covered it up the power is more even throughout acceleration.
And this pulsing effect is exactly what it feels like.. even sounds like that. I was calling it 'punch'. I was telling the people the engine sounded more 'punchy'. Pulsing is better /ubbthreads/images/graemlins/smile.gif

Thanks guys, thats given me more info to play with.

I think I'm going to re-make the balance pipe. I shall probably make it from 1/2" fuel unions if I can find any that big, if not then some 1/2" (or close) air-line fittings. I plan to 'fine' tap the 3 manifolds (using the existing holes opened out more) and connect the unions/couplings with some 'fuel' proof hose. Any thoughts on this setup?

Ben,

That's a beautiful GT6! Please keep us updated on the balance pipe fix.

Cheers! I will... i have asked about this on another forum and its looking like I might try running without the pipes for a while. A guy here in the UK thats a bit of a 'carb guru' seems to think the balance pipe is basically an excuse for lazy tuning.