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Over the last few months, I had started to notice that my GS850 was developing a lean stumble in situations where it develops a higher amount of intake vacuum.
For example, when strafing a tight set of twisties in second gear at 6,000 - 8,000 rpm, I couldn't roll back into the throttle gently after entering a turn. As soon as I'd get my corner speed and angle all nice and set up and add a smidgen of throttle, the engine would pretty much fall flat until I yanked the throttle open further. This led to an unwelcome surge of power from the engine room, and a distinct lack of panache.
Basically, any transfer from higher-rpm engine braking to partial throttle was met with burbling, stumbling, and uneven firing rather than the expected smooth flow of power. Boo.
It was also starting to have the lean stumble at steady interstate speeds at 1/4 throttle or less.
So the hunt was on for intake leaks...
What I found was two things:
1) The airbox on my bike, a 1983 GS850G, is made in two halves bolted together. After taking it apart, it was painfully obvious that the sloppy hardened rubber seal between the sections was only doing the most casual job of sealing. A little cleaning and a bit of weatherstripping applied to the top half of the airbox, and this was quickly sorted out. I used a thinner foam weather stripping for this, 1/4 or 3/8 inch thick, I think.
2) The foam weatherstripping I had used to seal the end covers on my airbox about five to seven years ago had hardened quite a bit. Actually, I think it was still sealing OK, but I went ahead and splashed out the four bucks for a roll of nice squishy new weatherstripping. Cost is no object in the pursuit of perfect carburetion. I also renewed the similarly hardened weatherstripping seal on top of the air filter cage.
The result? Perfect carburetion once more. Now I can once again dive into high-rpm corners with confidence that I can start feeding in power when and how I wish. No stumbling on the interstate or street.
The moral of the story is that if you have a GS850/1000/1100 with a two-piece airbox, go ahead and take it apart and seal the halves. To get the front two bolts, you have to remove the outer two carb/airbox boots and go in with a large screwdriver at a small angle.
For everyone else, just make sure your airbox is only slurping in air where it's supposed to. I've outlined the symptoms above, so if your bike is doing something like this, try to figure it out.
There are about a zillion GS airbox designs, but the nice thing about airboxes is that foam weatherstripping and duct tape are cheap and easy solutions. You don't need a lot of precision or absolute watertight perfection.
Also, try to figure out what your airbox is supposed to look like. A frustrated poster a while back was having no end of problems because the rubber "snorkel" on the back of his GS850 airbox was missing. He had no idea it was supposed to have a snorkel, and there's no way to tell from the fiche or manual.
A friend of mine had a GS1100E with similar symptoms. In his case, the airbox lid was missing entirely. Since he hadn't examined a stock 1100E in detail before, he hadn't noticed that the airbox wasn't supposed to have a big hole in the top. A few strips of duct tape sorted that one out quickly. The bike runs great now, and he'll probably make a replacement from sheet metal or plastic someday.
For example, when strafing a tight set of twisties in second gear at 6,000 - 8,000 rpm, I couldn't roll back into the throttle gently after entering a turn. As soon as I'd get my corner speed and angle all nice and set up and add a smidgen of throttle, the engine would pretty much fall flat until I yanked the throttle open further. This led to an unwelcome surge of power from the engine room, and a distinct lack of panache.
Basically, any transfer from higher-rpm engine braking to partial throttle was met with burbling, stumbling, and uneven firing rather than the expected smooth flow of power. Boo.
It was also starting to have the lean stumble at steady interstate speeds at 1/4 throttle or less.
So the hunt was on for intake leaks...
What I found was two things:
1) The airbox on my bike, a 1983 GS850G, is made in two halves bolted together. After taking it apart, it was painfully obvious that the sloppy hardened rubber seal between the sections was only doing the most casual job of sealing. A little cleaning and a bit of weatherstripping applied to the top half of the airbox, and this was quickly sorted out. I used a thinner foam weather stripping for this, 1/4 or 3/8 inch thick, I think.
2) The foam weatherstripping I had used to seal the end covers on my airbox about five to seven years ago had hardened quite a bit. Actually, I think it was still sealing OK, but I went ahead and splashed out the four bucks for a roll of nice squishy new weatherstripping. Cost is no object in the pursuit of perfect carburetion. I also renewed the similarly hardened weatherstripping seal on top of the air filter cage.
The result? Perfect carburetion once more. Now I can once again dive into high-rpm corners with confidence that I can start feeding in power when and how I wish. No stumbling on the interstate or street.
The moral of the story is that if you have a GS850/1000/1100 with a two-piece airbox, go ahead and take it apart and seal the halves. To get the front two bolts, you have to remove the outer two carb/airbox boots and go in with a large screwdriver at a small angle.
For everyone else, just make sure your airbox is only slurping in air where it's supposed to. I've outlined the symptoms above, so if your bike is doing something like this, try to figure it out.
There are about a zillion GS airbox designs, but the nice thing about airboxes is that foam weatherstripping and duct tape are cheap and easy solutions. You don't need a lot of precision or absolute watertight perfection.
Also, try to figure out what your airbox is supposed to look like. A frustrated poster a while back was having no end of problems because the rubber "snorkel" on the back of his GS850 airbox was missing. He had no idea it was supposed to have a snorkel, and there's no way to tell from the fiche or manual.
A friend of mine had a GS1100E with similar symptoms. In his case, the airbox lid was missing entirely. Since he hadn't examined a stock 1100E in detail before, he hadn't noticed that the airbox wasn't supposed to have a big hole in the top. A few strips of duct tape sorted that one out quickly. The bike runs great now, and he'll probably make a replacement from sheet metal or plastic someday.
/
I will keep my receit handy so I may regain entry into the "House of Stainless". I might even raise you two endcap screws and one cover screw.\\
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