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20 MPG!! Need Carb Help.

  • Thread starter Thread starter jstump63
  • Start date Start date
J

jstump63

Guest
I recently installed a vance and hines 4 into 1 on my 77 GS750B. I did as the paper said with the jetting.(115 main, 20 idle, and move the needle up one notch) I have bench synced the carbs, but not synchronized with the engine running. I've already checked the point clearance, valve clearance, put fresh plugs in which it keeps fouling. They don't foul to the point the bike is unrideable, but they are extremely black. What belittles me is the bike runs great. No misses and it pulls hard all the way to redline. When I'm cruising below 3500 or 4000 the bike surges a little. I have tried pulling the air filter to lean it out but it didn't seem to help. Thanks to everyone in advance.
 
1. Lean the needles 1 clip position. 2. Go 5 numbers smaller on the main jets. (If they are 115, go to 110s.) 3. Adjust the mixture screws in or out with the bike RUNNING till it idles the fastest on each screw setting. 4. Make sure the float heights are correct. 5. Install a DYNA ignition & get rid of the points. 6. Do THIS first, make sure you have NO vacuum leaks & that your manifolds aren't cracked & the O rings behind them are good. Let us know how it goes after these things. Ray.
 
gday mate, what was the pilot jet, that you pulled out,as rapid said, you need to lean it, in the mid, but more info would help, regards.
 
The pilot jet is 20. I had 17.5s in it before and it acted too lean. Even with the 20s now, it wants to die when I try to adjust the pilot screws on the side of the carbs. I have them all the way in as rich as they will go. I really wouldn't think that I need 22.5s with an uni filter and 4-1. I also forgot to ask what the mixture screws on the bottom of the carbs control?(idle circuit, mid-range, all over or what?) Does turning them out lean or richen the mixture? Does anyone know what the stock settings are for the '77 GS750B. I have already replaced the intake boot and carb o-rings too. I forgot to mention that in my previous post.
 
gday mate, pilot screws all the way in will be lean, your mixture should be around 2 turns out, to start,and adjust idle to get it running, then do what rapidray said, to fine tune, mixture screws affect low down revs, up to about 2500, but your needle and other jets also influence to a certain extent, regards,
 
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