Vacuum ports joined?

[Bob Maynard]

My new to me Sport has a piece of fuel line joining the left and right vacuum ports together. Any advantages to this setup? I’ll disconnect this to balance the tb’s, but wonder if it’s worth putting back on. The PO went to trouble of installing with a clamping tool instead of regular hose clamps, makes me wonder if he may have known what he was doing. TIA

Bob

[Lucky Phil]

2 hours ago, Bob Maynard said:

My new to me Sport has a piece of fuel line joining the left and right vacuum ports together. Any advantages to this setup? I’ll disconnect this to balance the tb’s, but wonder if it’s worth putting back on. The PO went to trouble of installing with a clamping tool instead of regular hose clamps, makes me wonder if he may have known what he was doing. TIA

Bob

Pointless, get rid of it and plug the holes. Its just a convenient way of isolating the holes without plugging.

Ciao

[68C]

I have often wondered if linking the two manifolds would help low throttle balance.  Many parallel twins do, perhaps the uneven firing order of our v- twins mean this would not be of any benefit.

[Lucky Phil]

16 minutes ago, 68C said:

I have often wondered if linking the two manifolds would help low throttle balance.  Many parallel twins do, perhaps the uneven firing order of our v- twins mean this would not be of any benefit.

All it does is introduce another variable you dont need. Ducati did it for a while in the 851 days along with a vacuum connection to the fuel pressure reg then wisely deleted it.

Ciao

[Chuck]

Back in the day, I had them joined on the Centauro.. many did. I tried just capping them off and didn't really see any change.

[GuzziMoto]

As Phil said, it is really just another option vs plugging the holes. I don't really see a problem with it, but I also don't see it as any sort of benefit. It brings nothing to the table, no improvement or advantage except it is a way of closing the ports without actually closing the ports, allowing for easy access to the ports when needed. But how often do you need access to those ports, and when you do it is really that big a deal to re-install or open up the ports? The only real risk is if the hose gets damaged and develops a leak. But aside from that it really won't make a difference. I do think it is simpler to just plug the holes. On some bikes I actually remove the ports and replace them with a screw. On others the port is a nipple set into the manifold and all you can do is block it off with a vacuum port plug. It is the latter, the permanent ports, that using a hose to connect the two ports makes the most sense, as you can't remove those ports, and a vacuum port plug is just as prone to issues as a hose connecting the two ports is.

[Bob Maynard]

1 hour ago, GuzziMoto said:

On others the port is a nipple set into the manifold and all you can do is block it off with a vacuum port plug. It is the latter, the permanent ports, that using a hose to connect the two ports makes the most sense, as you can't remove those ports, and a vacuum port plug is just as prone to issues as a hose connecting the two ports is.

Thanks all for the advice, quote above is my situation, and I’ve decided to wait until spring, remove the crimped on clamps and hose, then do a decent tuneup and replace with caps. Riding time is getting shorter now, need to enjoy before you know what starts falling.

[68C]

I thought the idea of connecting the manifolds was to help keep the carbs/fuel injector bodies balanced at closed or almost closed throttle, once you open the throttle it makes little difference.  We used to blank the balance pipe off while setting up and synching the carbs then reconnect.  Probably a 360° parallel twin thing.

[GuzziMoto]

If you properly balanced the cylinders with the ports blocked off, how does connecting the ports "balance" the two cylinders?

I would say that if you properly balance the two cylinders, no additional "balancing" is needed. I also doubt that little hose could flow enough air fast enough to actually balance the two cylinders. It is too small and too long. By the time a differential is detected and pressure starts to flow from high to low the differential is gone and likely now it is trying to flow in the other direction.

Maybe on a parallel twin where the distance is much less.

[68C]

As you say, on a parallel twin maybe it helps.  

Have you ever contributed to a thread then after a few turns kind of lose interest in continuing the story.

[thumper]

My Ducati 996 was the same connected.