29mm Smoothbore carbs and vacuum petcock

[weazzor]

I have a 1979 GS1000S and a set of 29mm smoothbores. The problem is that they don't have a tap to hook up the vacuum line for the petcock. I am thinking of using one of the synch screws in the manifold to attach a tube for the petcock. I don't see why it won't work, anyone have some input for me?

[Anonymous]

Smoothbores

Should work.My Scottoiler chain luber works off one of the carb rubbers with no effect on running.

[KEITH KRAUSE]

Re: 29mm Smoothbore carbs and vacuum petcock

I have a 1979 GS1000S and a set of 29mm smoothbores. The problem is that they don't have a tap to hook up the vacuum line for the petcock. I am thinking of using one of the synch screws in the manifold to attach a tube for the petcock. I don't see why it won't work, anyone have some input for me?

The manifold gets really hot. Not too sure of this set up. The diaphragm in the petcock commonly fails. You could start a fire. Also, the hose could expand and contract a lot causing vacuum leaks. A hose clamp would cure that, but the heat would work away at the hose.
If it was my bike, I would buy a Pingel fuel valve. Gets rid of any fire hazard and eliminates leaking diaphragm problems. About $90 including the adapter plate.

[KEITH KRAUSE]

It sounds like you've just decided to install the 29 smoothbores. Let me know how they perform. I know they work well on the 1000. I've heard that parts are getting hard to find, etc, so I'm a little worried about living with them. Have you been able to find basic jetting parts? Mains, needles/needle jets, pilots? Your throttle valve cut-away is a 1.5, correct? There seems to be a little confusion on that recently. I've heard Suzuki and Kawasaki use the same cut-away, but Honda and Yamaha use a different one. There's also supposed to be a paper gasket in the throttle valve assy' that goes bad.(?)
I don't mind the jetting work, I just don't want parts problems. Thanks for any info, thoughts.

[Detman101]

Re: 29mm Smoothbore carbs and vacuum petcock

I have a 1979 GS1000S and a set of 29mm smoothbores. The problem is that they don't have a tap to hook up the vacuum line for the petcock. I am thinking of using one of the synch screws in the manifold to attach a tube for the petcock. I don't see why it won't work, anyone have some input for me?

The manifold gets really hot. Not too sure of this set up. The diaphragm in the petcock commonly fails. You could start a fire. Also, the hose could expand and contract a lot causing vacuum leaks. A hose clamp would cure that, but the heat would work away at the hose.
If it was my bike, I would buy a Pingel fuel valve. Gets rid of any fire hazard and eliminates leaking diaphragm problems. About $90 including the adapter plate.

And well worth every penny!! The reassurance that a working, well designed petcock gives is beyond compare.


Dm of mD

[simon lambert]

Are these 29mm smooth bores the STD equipment as fitted to the 1980 model GS1000s.
The 80 model came out with the bigger slide carbs than the 79 model and I have heard them caled 29mm oval bores and smooth bores..
What is the true name for these things..
Regards Simon

[weazzor]

I'm going to answer a few questions that you guys have posted. I just got a NOS petcock and would like to use it, so I guess I'll have to see if they can be drilled for a vacuum tap. Thanks for the concerns about leaks and fires. I have a set on there now and these are the carbs to use on this bike, the performance is amazing. I bought a nice clean set off E-bay and am replacing mine because I don't want to go through the work of cleaning and repairing them, although I know of a place that does reconditioning, my old set will be up for sale, and offers are welcome. They work, just need a GOOD going over. The 1980 Gs's came with CV carbs which are larger bores, but I beleive designed for emissions and fuel economy, not performance. I appreciate any other input to keep this dialogue going.

[weazzor]

A note for Keith... check out http://www.motorcyclecarbs.com for parts and rebuilding services, they appear to be pretty thorough when it comes to 29mm smoothbores. I haven't had a problem, but mine had to sit for a few years until I got off probation and got my license back, so they deteriorated a bit.

[KEITH KRAUSE]

Thanks! Just wondering, what mod's do you have and what jetting have you selected?

[weazzor]

The bike came with K&N filters, a nice fat Bassani exhaust, and the smoothbores. I'll look into the jetting for you, since I haven't fiddled with the carbs and what they have works. Keep checking back it might take up to a week to get the info for you. Any other ideas what to do about the vacuum line for the petcock?

[Don Lobacz]

I ran a vacuum takeoff for my smoothbores out of the manifold and it works just fine. You can make a nice nipple by drilling through and turning down an extra-long allen bolt (run a nut and o-ring up the threads). You can also use your OEM petcock without vacuum (ala Pingel) by turning it to PRI when running and anything else when not. IMHO, your stock petcock is the best thing to have. I feel the Pingels are more of a problem than they are worth unless you need more fuel flow (top fuel or GSXR 1100).

[simon lambert]

Man what I would do for a Bassani system...

[KEITH KRAUSE]

Don, where are the Pingels a problem? Their operation is much smoother and the stock valve is famous for leaking fuel into the carb or not letting fuel get in because of the diaphragm. The pingel is more peace of mind.

[simon lambert]

And the stock one on a 1000s (without a tap) is bloody expensive to replace.. but its usually the only one that is a straight fit

[weazzor]

Thanks Don, glad to hear someone actually did it. I have a nice fitting for an air line that has the same threads as the manifold screw, so I think I'll give it a go. Simon, I got the Bassani off Ebay, just got lucky, can't wait to fire it up!