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Too much fuel? 1981 GS400S

  • Thread starter Thread starter 400s
  • Start date Start date
4

400s

Guest
Hi,

So I have enjoyed a 1981 GS400S now for a few weeks and have addressed issues as they arise. Yesterday I passed my skills test (which in BC means you can drive with no constrictions other than no passengers and during nighttime), so I've been driving faster than I have so far. And by that I mean I have finally adventured into 3rd gear and beyond. Now I have a real problem which should be easy to fix but I dont know what screws to turn. My engine seems to get more gas than it wants. It sounds like it's drowning when I hit the throttle and it does not accelerate well. When I drive over 50 km/h for more than a minute it drowns and dies (this is what I think). Earlier I attributed my engine dying to airleaks, and I did fix an airleak and replaced airfilter but this is different. It is almost as if the engine was happier with the airleaks. What I'm asking is simple but the GS400S model seems to be different than other 400 models of the same era and I can't find what to adjust to reduce the gasflow, or even increase the airflow. I am happy to play with both. Does anyone with a 400s model have any wisdom they would like to share? I should add that after the engine dies when driving above 50ish for a while it takes a long time for it to restart. Like it is cooling down or needs gas to drain from the carburetor.
 
Next time it dies, pull over someplace safe and pull the spark plugs.
Let us know what the colors look like on the tips.
That will tell you how it's running.

.
 
I actually did this today. They look fine, a bit wet. I just replaced them last week.
 
A bit wet means incomplete combustion. There is a whole littany of places to start looking. I guess for me the first indicator is that it was running better with an air leak, which means you are probably running rich. What colour are the plugs? You say fine, but does that mean black, or the nice dry brown you should be getting? Do they look the same?

Does the 400s have the siamese carbs?

You certainly will have to synch your carbs. Have you done the valves yet? Once that is done you can get down to figuring out how strong the spark is and whether the triumvirate of spark/(air/fuel)/pressure is being completed.
 
Based on the body style of the bike in your avatar, it looks to me like you actually have a GSX400S. I think your bike should have Mikuni carbs, BS34, and they should have an air/fuel mix screw located centrally and at the intake manifold (forward) end of the top surface of the carb. This is what you should be using to do a highest rpm carb adjust.
 
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