98VTRrider

I went to do a carb sync today after a recent valve adjustment, and I found that the vacuum line the previous owner had set up for carb synchronizing went to the front carb where the PAIR valve signal was, instead of the capped vacuum fitting on the front head below the front carb where the manual says you should get the front vacuum signal from.

Is it possible to get an accurate setting using the vacuum signal from the PAIR valve?

I did the carb sync with a homemade two-bottle setup I made, it worked great and I adjusted it using the vacuum line as described above. The bike ran much smoother and felt a lot better than before, but I wonder if the results would be different if I used the other vacuum signal for the front carb. thoughts anyone?

thanks

mikstr

Funny you should post about this as I was just wondering the same thing (as I contemplate using this vacuum feed for the vacuum relief valve/compression reduction system I will be installing in the coming weeks/monts).

Looking forward to hearing what the opinions are....

98VTRrider

What's a vacuum pressure relief/compression reduction system all about?

I have another Superhawk I'm putting together that I will need to sync soon as well. I think I might pull a vacuum fitting off another spare I have and put it on so I can do the sync from the correct vacuum source on this one.

Side question, what is the best source for the vacuum fitting used to do the carb sync? It is a 5mm threaded vacuum fitting.

mikstr

It's simply a pressure relief valve set to react to vacuum as opposed to positive pressure (simple matter of reversing the order of the spring and ball). Engine braking is the result of an increase in intake vacuum when the throttle is closed. By allowing air to bleed into the cylinder, you reduce this vacuum and, in so doign, decrease engine braking. This basic set-up has been used on four-stroke snowmobile engines for a few years now to great success. Of course, the engines using it are fuel-injected but there is no reason it can't be used on a carbed engine (the only possible issue would be excessive heat from a leaner mixture but if the bleed-off setting is set fairly high, it would only kick in just before the rear wheel locks, which is very seldom so hte heat issue would be largely inconsequential).

One of the chaps on the vtr1000.org site tried it and reported it to work (he used two small relief valves; I plan to use a single larger valve and hook up both cylinders to it with a Tee). It is relatively easy and cheap to set up so I will give it a go. I have all the parts, just need to pull the tank off and "get at 'er".....

8541Hawk

The main question would be are the pair valve vacuum ports metered or straight.

If they are metered then you could have problems with a false signal.

If I get a chance I'll take a look at my extra set of carbs and see if I can figure out what kind of signal you get from that port.

CrankenFine

Any Honda dealer would have this. It's pictured on the exploded parts diagram for the front cylinder head at any online Honda parts dealer.

JOINT, BOOST Honda p/n#16214-MB0-000

Hollister Honda lists it for $2.61 but you have to figure shipping vs tax if it's just this one item you need.