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Rebuilding 1977 GS750 Carbs for cone filters

  • Thread starter Thread starter Spaceecho
  • Start date Start date
S

Spaceecho

Guest
Hello,

I've just started a new project - a 1977 GS750. The bike was running when i first purchased it and shortly after it has decided to not run. I replaced the points and condensers, starter relay etc - so all is good there which leads me to believe the carbs need attention.

Anyway, I know that running these bikes on cone filters can be a major headache so before I start on the carb rebuild I wanted to see if anybody has any tips for float / jet settings which will make the cone transition a little less painful?

Thanks!

-Jon
 
You really can't setup carbs until they are clean, balanced and functioning correctly with stock components as a starting point. Each type of filter is going to be different too so there is no standard off the shelf jetting that will fit all situations. Some cheap filters are very free flowing (Emgo comes to mind) and offer little to no filtering and very limited air restriction and are very hard to setup. It will be a project of trial and error and you may never get it exactly right.

Welcome aboard by the way.
 
Yet another recommendation here to get it running correctly first, then go ahead and make any modifications that you want. Since you are already having problems, it just does not make any sense to make changes toward the 'unknown'. You simply won't know whether any further problems are continuations of your current problems or something new, based on your "upgrades".

As a general rule, keep the float level stock.

For a header, add 2 to 6 main jet sizes, depending on the flow characteristics of the exhaust system.

For pod filters, add 4 to 10 main jet sizes, depending on the flow characteristics of the 'filters'.

If you have pods and a pipe, that would be 6 to 16 sizes up on the mains. :eek:

You usually don't have to change the pilot jets, but you will have to raise the needles.

Good luck, you will soon see why we highly recommend sticking with the stock airbox. :-\\\


.
 
Thanks, happy to be aboard!

I probably should of clarified that I will be using the standard airbox to get it going then transitioning (hopefully) to the cone filters.

The bike came with a brand new Vance & Haines 4 - 1 exhaust, so I'm sure that will have some effect on the way the carbs are set up. I think it might be safe to say that I should order some larger main jets.

Thanks for the tips in advance.
 
Awesome, thanks. Can anyone recommend a good online supplier to grab some larger main jets?
 
There is a pods thread in my signature.

Z1 has the main jets you need. You may also want to go to 17.5 pilots, and Z1 has those too.
 
Ok, quick update.

I rebuilt the carbs with 105 main jets (to compensate for the 4-1 exhaust) and 17.5 pilot jets (there were 27.5 in there??? Isn't stock 15?). The floats were way off so I reset them to 26mm and tried to start the bike with the stock air box. The bike is definitely trying a lot harder to start and i'm getting lots of frequent big exhaust bangs - which I know means the timing is screwy.

Maybe I should move this into a new thread but I did points and condensers a few weeks back and the plugs are are getting spark etc, so I'm just curious if anyone has any advice to what might be going on here? I've went over the point settings a million times and they seem to be right. The bike ran when I bought it but stopped pretty shortly after. Is there an easy wait to test the coils?

Thanks for the help.

-Jon
 
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