vacuum ports

Dumb question, perhaps. Two of my carb holders (#2 and 3) have what are obviously vacuum ports for synchronizing...they are capped. Are the ports on #1 and 4 that feed some kind of emissions thing (I assume they are drawing blow-by into the combustion chamber) also to be used for this purpose? Begs the question, would it be a good idea to disassemble that stuff, since it's a potential source for vacuum leak?

Your assumption is incorrect. You have vacuum lines on 1 and 4 that activate the vacuum switch that opens your reed valves on your valve cover. In any case, you can remove the hoses and cap the vacuum fittings. You will have to remove all the associated hoses and put some sort of cover or plug the holes on the valve cover. One of the hoses will also go to your airbox and the hole in the airbox should be plugged. You should also have a vacuum hose connected to either the #2 or #3 carburetor going to your petcock which on an 80 ST is vacuum actuated. Look at the petcock. If it has TWO nozzles with one smaller than the other, the smaller is vacuum. The larger is gas. If the smaller is not connected, the petcock can't work as it should and you would be forced to ride with the petcock in the PRI (prime) position.

Yes, #3 has the vacuum port for the petcock. And thanks for the correction on the emissions. I just did some more research and discovered that the #1 and #4 vacuum ports are used to shut off the air 'injection' during deceleration. Also that there's no real reason to disable it. True? Obviously, hoses must be verified to be in good condition or leaks will ensue.

So there's 1 vacuum port on #1, 1 on #2, 2 on #3, and 1 on #4, all of which could be used for synchronizing?

Yes, #3 has the vacuum port for the petcock. And thanks for the correction on the emissions. I just did some more research and discovered that the #1 and #4 vacuum ports are used to shut off the air 'injection' during deceleration. Also that there's no real reason to disable it. True? Obviously, hoses must be verified to be in good condition or leaks will ensue.

So there's 1 vacuum port on #1, 1 on #2, 2 on #3, and 1 on #4, all of which could be used for synchronizing?

Oh, and another thing while I'm at it. I'm hearing on one hand that I should be able to use 1/4" fuel line (and filter) but I can't seem to make that work without some serious grunt work. 5/16" works much better. Problem is I can't seem to find a 5/16" filter anywhere.

Post edited by: rckz, at: 2007/09/13 15:19

The fittings on the carb holders are used for synchronizing the assembly.

As far as the utility of the emissions system, it causes the bike to backfire on decelleration and adds un-needed complexity in that it is only more stuff to go bad and adds clutter. I remove them immediately just to clean up under the tank. I don't know how effective the system works as far as emissions go... I doubt they make a difference.