Newbie Carb and related questions

[bezeee]

Happy Holiday all! I have gs750 project bike that is probably a '79 or '78 (pre CV carb). It has K&N airpods and I'm pretty sure stock exhaust. I'm planning to clean and rebuild the carbs and have a few questions.

1. Is there a benefit to having airpods with stock exhaust?
2. With the airpods, what size jets would be ideal and/or should I get a jet kit?
3. The fuel and vaccum lines were removed before I got the bike. I cannot for the life of me find where to hook them up. I've looked all over especially between carb 2 and 3.

Thanks ahead of time!

 

[Steve]

1. Yes, there is more air available, with the potential for more power.
1a. There is also a bit more noise, as the intake pulses are not muffled.
1b. There can be more sensitivity to side-draft winds and other weather-related events.

2. Jet size will depend on the pods that you get. A "kit" will also depend on which pods you get.
2a. Do yourself (and your bike) a favor, get good pods. Few will debate the quality of K&N, with APE a close second. The problem with them is co$t. K&Ns will likely cost $150 or so, APE will run about half that. Pods are available on eBay that are about $25. Quality on these cheap ones varies greatly, making jetting suggestions rather futile.

3. This one is easy. There is a short line that connects the vent from #1 to #2, a similar short tube connects the vents on #3 and #4. On the left side of #2 and #4 are vent tubes that will get draped over the airbox. They might drop down behind it, they might stay high to a loop under the seat. There is a port on #3 that is the vacuum port that goes to the vacuum port on the petcock. Finally, the T between #2 and #3 is the fuel T that is connected to the fuel port on the petcock.

.

 

[bezeee]

Steve,

Thanks for the reply. However, what I realized last night is that the carb is an RS type (34mm I think) and not the stock VM. That is why I was scratching my head looking for the T between carb 2 and 3 and couldn't find a nipple for the vaccum line.

Would you or anyone be able to advise on the fuel and vacuum line connections on the RS carbs? I'm guessing the pivoting nipples between 1-2 and 3-4 should be connected with lines running to a T and then connect to the fuel nipple on the petcock?

Is there a vacuum line connection with this type of carb? If so, where is the connection for this?

P.S. Luckily the bike came with K&N airpods.

Best,
Adam

 

[steve murdoch]

Probably the best thing you can do is post a pic of the carbs and then we can offer some pertinent help.
It would seem odd to have a set of RS carbs on a GS750 with a stock exhaust.
Have a look at this CV carb cleaning tutorial from Ed. Carbs look like yours? In the last ten pages or so there are some pics of hose locations.
http://zeus.mtsac.edu/~cliff/storage/gs/Mikuni_BS-CV_Carburetor_Rebuild_Tutorial.pdf
Welcome to the site.

 

[bezeee]

Thanks. Here is a pic.

 

[bezeee]

one more.

 

[bezeee]

Thanks. Here is a pic.View attachment 61321

 

[steve murdoch]

RS carb info from Dynoman.
It makes sense to have a performance exhaust and air filtration system to go with performance carbs.

Starts on page 9.
http://www.mikunipower.com/Catalog/MikuniCarburetorCatalog2012.pdf

 

[bezeee]

Thanks.

I actually think that it is not stock exhaust. It's 4 to 1 and the muffler is shorter. It had some rust on it so I assumed it was original (I'm new at this).

Will probably replace the petcock with a non-vacuum one (if I can find one with the holes in the right place) or hook up the petcock vacuum line to one of the vacuum ports (which are all capped off now). Alternatively, may leave all the vacuum ports capped and use the prime setting on the petcock.

Best,
Adam

 

[Rijko]

got any history on the bike, or a seller to ask for details ?
Even with a 4-1 exhaust and K&N filters, RS carbs seem a bit much.
Who knows, sometimes you find a big bore kit in there, cams ...
Why do you want a jet kit, did the PO not jet it right ?

 

[Rijko]

And since the carbs are off, check the ID of the inlet ports.
Have those been enlarged ?

 

[bezeee]

Thanks for the suggestions Rijko. The history is incomplete, however the PO said the cam is upgraded too. The owner before him definitely made some modifications (I just don't know if it was properly done). The PO I bought it from had it running a couple of years ago. He said it wasn't running well and he thought either carb 1 or 4 needed attention. Carbs and fuel system are my first priority for this bike. I wasn't necessarily looking to change the jets, only confirm that they were an appropriate size especially since I don't have the history, but know they were making modifications.