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After everything, GS650 bogs slightly on full throttle

  • Thread starter Thread starter sultan
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sultan

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'83 GS650, 23K miles. This season I've replaced the rings, honed the cylinders, cleaned/oiled the air filter, dipped/cleaned the carbs and replaced o-rings, did a full valve job, checked/fixed valve clearance, and balanced the carbs. (Plus a lot of non-engine-related fix-ups.) Compression is good. Bike starts right away with choke. Spark plugs look good. I haven't sealed the airbox with weather stripping or anything, but it seems to have an ok seal as-is. I've gotten great advice in the past from this forum that's gotten me this far, so let me thank everyone who's responded to my posts once again with great and helpful advice. I'm hoping that this is the last engine tweak I'll have to do for a while...

It's sounding and running a lot better (obviously) after doing all of this. It idles around 1200 rpm, the engine seems smoother, and it had very good pickup, with the following exception.

In any gear, around 4,000 rpm (give or take) if I open the throttle wide-open, it bogs down and accelerates slowly for a second or so before taking off again and giving good acceleration, usually around 6,000-7,000 rpm.

Even after taking them apart and rebuilding them, carbs are still somewhat of a mystery to me. Too many chambers and passages, I guess. No where in the manual did I see anything about what to set the fuel needle screw (? the ones on top of each of the carbs that's recessed down in a hole and initially had a cover plate on top...). I've read a couple places that "2 full turns out" from seated is a good general setting. I've seen 2.5 and even 3 turns recommended. I understand more turns=more gas to the engine.

Is this all that I'm missing? Do I just need to adjust the needle valve out half a click, or a full turn, then re-balance the carbs? Or is there something else I'm missing that could be causing this?

Or am I asking too much of my poor bike and I'm shifting too low? In general once I hit about 8.000-9,000 I up-shift, not wanting to rev the engine too hard.

Thoughts? Advice?

Thank you.
 
sultan said:
'83 GS650, 23K miles. This season I've replaced the rings, honed the cylinders, cleaned/oiled the air filter, dipped/cleaned the carbs and replaced o-rings, did a full valve job, checked/fixed valve clearance, and balanced the carbs. (Plus a lot of non-engine-related fix-ups.) Compression is good. Bike starts right away with choke. Spark plugs look good. I haven't sealed the airbox with weather stripping or anything, but it seems to have an ok seal as-is. I've gotten great advice in the past from this forum that's gotten me this far, so let me thank everyone who's responded to my posts once again with great and helpful advice. I'm hoping that this is the last engine tweak I'll have to do for a while...

It's sounding and running a lot better (obviously) after doing all of this. It idles around 1200 rpm, the engine seems smoother, and it had very good pickup, with the following exception.

In any gear, around 4,000 rpm (give or take) if I open the throttle wide-open, it bogs down and accelerates slowly for a second or so before taking off again and giving good acceleration, usually around 6,000-7,000 rpm.

Even after taking them apart and rebuilding them, carbs are still somewhat of a mystery to me. Too many chambers and passages, I guess. No where in the manual did I see anything about what to set the fuel needle screw (? the ones on top of each of the carbs that's recessed down in a hole and initially had a cover plate on top...). I've read a couple places that "2 full turns out" from seated is a good general setting. I've seen 2.5 and even 3 turns recommended. I understand more turns=more gas to the engine.

Is this all that I'm missing? Do I just need to adjust the needle valve out half a click, or a full turn, then re-balance the carbs? Or is there something else I'm missing that could be causing this?

Or am I asking too much of my poor bike and I'm shifting too low? In general once I hit about 8.000-9,000 I up-shift, not wanting to rev the engine too hard.

Thoughts? Advice?

Thank you.
Click to expand...
Check the airbox sealing again.
If they are truely good and tight try raising the jet needles a little bit? The main jets are probably the right size if it goes good once it gets past that bog.
 
sultan said:
'83 GS650, 23K miles. This season I've replaced the rings, honed the cylinders, cleaned/oiled the air filter, dipped/cleaned the carbs and replaced o-rings, did a full valve job, checked/fixed valve clearance, and balanced the carbs. (Plus a lot of non-engine-related fix-ups.) Compression is good. Bike starts right away with choke. Spark plugs look good. I haven't sealed the airbox with weather stripping or anything, but it seems to have an ok seal as-is. I've gotten great advice in the past from this forum that's gotten me this far, so let me thank everyone who's responded to my posts once again with great and helpful advice. I'm hoping that this is the last engine tweak I'll have to do for a while...

It's sounding and running a lot better (obviously) after doing all of this. It idles around 1200 rpm, the engine seems smoother, and it had very good pickup, with the following exception.

In any gear, around 4,000 rpm (give or take) if I open the throttle wide-open, it bogs down and accelerates slowly for a second or so before taking off again and giving good acceleration, usually around 6,000-7,000 rpm.

Even after taking them apart and rebuilding them, carbs are still somewhat of a mystery to me. Too many chambers and passages, I guess. No where in the manual did I see anything about what to set the fuel needle screw (? the ones on top of each of the carbs that's recessed down in a hole and initially had a cover plate on top...). I've read a couple places that "2 full turns out" from seated is a good general setting. I've seen 2.5 and even 3 turns recommended. I understand more turns=more gas to the engine.

Is this all that I'm missing? Do I just need to adjust the needle valve out half a click, or a full turn, then re-balance the carbs? Or is there something else I'm missing that could be causing this?

Or am I asking too much of my poor bike and I'm shifting too low? In general once I hit about 8.000-9,000 I up-shift, not wanting to rev the engine too hard.

Thoughts? Advice?

Thank you.
Click to expand...

I have the G model. You shouldn't really have to seal the airbox like you would an 850. But I guess you should just make sure it's closed all the way. ..

The 4k bump is comin with these bikes. Though I don't notice it too much on my bike, but Duaneage did when riding mine and said it is the same as is. (same bike)


.It's not noticable enough to bother me, and my girl rides pretty daym smooth.... if nothing else, a tad on the lean side...I will prob raise my needles this winter to cure this.

My idle mixture screws are 2.5 out. you will not need to re-synch afterward . . . . this is a post synch thing to do.

and I'm curious as too why you are upshifting at 8k. I feel the need to upshift at around 4-5k for normal riding.
 
seuadr said:
cause 5k is about where these things get fun! :p
Click to expand...

I guess it depends on what I'm doing. Usually I shift pretty low and drive relatively slow. More often than not I'm shifting *at* 4,000 rpm just because I'm not worried about speed or acceleration when just tooling around town. I often find myself in 4th gear at 40 mph without realizing it.

However, when I'm riding for fun/speed/acceleration, I do like to take it off the line a bit and see what she can do. That's when I'm coming much closer to red-lining it, and yes, around 5,000-6,000 is where she picks up the acceleration and shows off a bit. While I'm definitely not doing that at every stoplight, it would be nice to have it there when I wanted to play a bit, and extend that "fun" to a wider range of the tach. ; )

I'll have to check some of the airbox sealing posts to figure out how to do that. It's definitely on tight and seems to have a decent seal, but I know that's problematic with these bikes. I'll up the fuel screw a bit on each carb and see what happens, I guess.

Especially if I don't have to re-synch the carbs, tweaking the fuel screw is easy enough try/test/fix if it works. Good to know. I'll post back in a few days with what I find.

Thanks!
 
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