Vacuum Port/Carb Sync

[accidentprone315]

I would like to sync my CL450 carbs, and plan on installing these ports from DCC. I was just checking in over here to see if anyone had any advice about installation.

http://www.dimecitycycles.com/vintage-cafe-racer-caferacer-bobber-brat-chopper-custom-motorcycle-carburetor-parts-5mm-vacuum-intake-tuning-port-adaptors-dcc-08-0013-2.html

Where exactly should these ports be installed? DCC recommends installing a line between the two of them after syncing them. Is that necessary?

Thanks.

 

[carnivorous chicken]

I'm curious to know about the line as well. Capping them is obvious, but connecting them?

 

[dualitymike]

My 550 has threaded ports from the factory with a 5mm bolt in them. You remove the bolt to attach the manometer and then replace the bolts once you're done. In any case, as long as they're installed between the carb and the head you're good. Make sure you make them finger tight. Don't use a socket or wrench or you're likely to strip them. If the port is hard to reach to put in the brass tube, you can cut a short piece of rubber tubing, slide one end over the brass tube and the other end over a hollow tube from a bic pen, then use the pen to turn the brass tube in. Let the engine cool before you try to remove the brass tubes. They tend to stick a bit when hot.

 

[carnivorous chicken]

My 550 has threaded ports from the factory with a 5mm bolt in them. You remove the bolt to attach the manometer and then replace the bolts once you're done. In any case, as long as they're installed between the carb and the head you're good. Make sure you make them finger tight. Don't use a socket or wrench or you're likely to strip them. If the port is hard to reach to put in the brass tube, you can cut a short piece of rubber tubing, slide one end over the brass tube and the other end over a hollow tube from a bic pen, then use the pen to turn the brass tube in. Let the engine cool before you try to remove the brass tubes. They tend to stick a bit when hot.

Right, that's how you're supposed to do it. But a lot of bikes didn't come with ports to screw in the sync tool. What the DTT kit is suggesting is tapping a hole, screwing in the brass tubes, and leaving them in with a line connecting the them. Why connect them? Why not cap them (like your 550, which has bolts that screw in to the holes to plug them)? That's the question.

 

[hillsy]

Right, that's how you're supposed to do it. But a lot of bikes didn't come with ports to screw in the sync tool. What the DTT kit is suggesting is tapping a hole, screwing in the brass tubes, and leaving them in with a line connecting the them. Why connect them? Why not cap them (like your 550, which has bolts that screw in to the holes to plug them)? That's the question.

You can do either, but the theory with connecting them is that it smooths out the carb pulses between the intakes. Yamaha did it (inside the head) with their YICS system on their XJ bikes from the 80's.

The real difference (if any) is at idle and low RPM. Jury's been out on whether it works or not for many years.

 

[carnivorous chicken]

You can do either, but the theory with connecting them is that it smooths out the carb pulses between the intakes. Yamaha did it (inside the head) with their YICS system on their XJ bikes from the 80's.

The real difference (if any) is at idle and low RPM. Jury's been out on whether it works or not for many years.

If I'm not mistaken, the YICS system was for more efficient combustion and better fuel economy (but synching carbs with YICS was a pain in the ass that needed a special tool bought or made). YICS bikes could idle at lower rpms. And that simply connecting the two holes used for synching carbs isn't exactly the same thing. If it was such a great and revolutionary thing, it raises the question why it didn't become standard (and why I've gotten along for years with capped synch ports, and nobody has suggested to me that I connect the two (or four)). Anyone else have any ideas about this?

 

[Flugtechnik]

I put mine in the intake manifolds........here:

There is a metal base that extends out a little into the tubular part. I drilled and tapped that.

When I'm not using them, I put bolts in the holes with sealant.

I have also seen some people drill and tap their heads, just forward of the manifold. I chose to do it in the manifold in case I screwed it up.

There are a couple discussion about this over on hondatwins.net


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[hillsy]

If I'm not mistaken, the YICS system was for more efficient combustion and better fuel economy (but synching carbs with YICS was a pain in the ass that needed a special tool bought or made). YICS bikes could idle at lower rpms. And that simply connecting the two holes used for synching carbs isn't exactly the same thing. If it was such a great and revolutionary thing, it raises the question why it didn't become standard (and why I've gotten along for years with capped synch ports, and nobody has suggested to me that I connect the two (or four)). Anyone else have any ideas about this?

Connecting the vacuum ports together is like a "poor mans YICS" as an XJ'er once described it to me. IMO the YICS system didn't work that well - and the performance gains were negligible. You could balance the carbs without the YICS being blocked off - it was just a bit harder to get right.

If anything, connecting the ports can smooth out idle/lower RPM running - there's not a bunch of HP locked away waiting to be untapped by thowing a piece of tube on your manifolds. And no one does it anymore (YICS) because it costs too much to cast/machine it into the head.