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Throttle Response

Dave8338

Dave8338

Forum Sage
Past Site Supporter
I picked up a 1982 GS 650 L with 6000 miles on it. The bike had been sitting for 14 years, so I knew that there was plenty that would need to be done to make this a road worthy machine again. I cleaned, recleaned, and then rebuild the carbs and did a bench synchro on them to get them close. The bike starts and runs fine at an idle. When I open the throttle to rev it, it wants to stall out. Just die. No popping, misfire, nothing. This isn't the first machine that I've worked on, but the way it's going, it may be the last. I've checked fuel flow, and looked for vaccume leaks. This seems like a classic fuel shortage issue, however, I set the floats to spec with gasket on and flow from the petcock is enough to run three times the engine that is in this bike.

Q. Anyone have a clue as to what I'm overlooking?

Dave
 
Shooting in the dark here but did you physically remove the diaphragms and slides? Are the diaphragms ripped? With the carbs together but on the bench if you introduce a regulated small amount of air into the small upper port at the top of the airhorn, does the slide on that carb raise then lower slowly? It sounds like the slides aren't rising when you open the throttle plates.
Or.....you have an ignition problem that is causing the spark to go away. But I doubt that.
 
Dave8338 said:
I picked up a 1982 GS 650 L with 6000 miles on it. The bike had been sitting for 14 years, so I knew that there was plenty that would need to be done to make this a road worthy machine again. I cleaned, recleaned, and then rebuild the carbs and did a bench synchro on them to get them close. The bike starts and runs fine at an idle. When I open the throttle to rev it, it wants to stall out. Just die. No popping, misfire, nothing. This isn't the first machine that I've worked on, but the way it's going, it may be the last. I've checked fuel flow, and looked for vaccume leaks. This seems like a classic fuel shortage issue, however, I set the floats to spec with gasket on and flow from the petcock is enough to run three times the engine that is in this bike.

Q. Anyone have a clue as to what I'm overlooking?

Dave
Click to expand...
Is it stock with the airbox on and sealed properly?What happens if you try to put the choke on?Does it stall out instantly?What do the plugs look like?Are the air needles capped off or did you adjust them in any way?
 
In response to the slides being stuck or hanging up, they were completely removed as were all other materials befor the "soak" and rebuild. They were in great shape, not cracked or torn anywhere...

As for the Airbox issue that was raised, yes it is the stock unit however, someone had replaced the stock filter with a "unifit" high flow filter. I was in the shop last night and installed the filter that was in it, which is a poor fit at best and somewhere, someone lost one of the slide clips for the airbox cover.
After this, I again started the bike...and...I now have throttle control through the 1,100 to 3,800 RPM range. We're gaining :shock:. It sounds as though I should pick up a stock filter and another slide clip and work from there. I do not know if the setting on the slide needles was changed with the installation of the Unifit Filter. Where are they supposed to be set with a completely stock bike?
 
Dave8338 said:
In response to the slides being stuck or hanging up, they were completely removed as were all other materials befor the "soak" and rebuild. They were in great shape, not cracked or torn anywhere...

As for the Airbox issue that was raised, yes it is the stock unit however, someone had replaced the stock filter with a "unifit" high flow filter. I was in the shop last night and installed the filter that was in it, which is a poor fit at best and somewhere, someone lost one of the slide clips for the airbox cover.
After this, I again started the bike...and...I now have throttle control through the 1,100 to 3,800 RPM range. We're gaining :shock:. It sounds as though I should pick up a stock filter and another slide clip and work from there. I do not know if the setting on the slide needles was changed with the installation of the Unifit Filter. Where are they supposed to be set with a completely stock bike?
Click to expand...
I would get a regular filter and that clip first.Do you have the plastic peice that the filter goes onto?Then oil the filter and grease the box where the filter rests in it and make sure the lid is on good and tight.Check your clamp from the airbox to the air intakes that hook on to the carbs and check those clamps too.Then clean your plugs cause they are probably fouled and reset your idle once it is warmed up and choke is off then we will go from there.You need to sync your carbs once you get it going better.Do you have a fuel filter on it?is there any sign of a vacumn leak?
Does it idle up after it is warmed up?
 
tconroy;

It seems as though you've steered me in the right direction. Last night I again went to the shop to see if I could get to the bottom of this issue. The only fuel filter that is on the bike is on the petcock. Though I've not picked up the new filter or clip yet, I zip tied the cover of the air box to the frame so that everything was tight, replaced the plugs for the third time, and after the bike had warmed up, reset the idle to 1,100 rpm. I once again checked all the fittings on the intake side, on the airbox side, and at the petcock (of which I ordered a new one so as to completely eliminate this potential) and all are tight. I took it out on the road and have strong pull up to about 1/3 throttle now. Then it seems to bog down. However, if I open it up...it bogs slightly and then kicks in to the point that it will almost pull the fornt end up in second gear at around 5500-6000. Mid range rpms are still weak. I sure appreciate the help, as this bike feels as though it will be one fun little cruiser once it is running right. Any more thoughts?
 
Dave8338 said:
tconroy;

It seems as though you've steered me in the right direction. Last night I again went to the shop to see if I could get to the bottom of this issue. The only fuel filter that is on the bike is on the petcock. Though I've not picked up the new filter or clip yet, I zip tied the cover of the air box to the frame so that everything was tight, replaced the plugs for the third time, and after the bike had warmed up, reset the idle to 1,100 rpm. I once again checked all the fittings on the intake side, on the airbox side, and at the petcock (of which I ordered a new one so as to completely eliminate this potential) and all are tight. I took it out on the road and have strong pull up to about 1/3 throttle now. Then it seems to bog down. However, if I open it up...it bogs slightly and then kicks in to the point that it will almost pull the fornt end up in second gear at around 5500-6000. Mid range rpms are still weak. I sure appreciate the help, as this bike feels as though it will be one fun little cruiser once it is running right. Any more thoughts?
Click to expand...
What are the plugs gapped at and also when you cleaned your carbs how did you set the pilot screw and the air screws? I take it you have the bs 32 ss cv carbs?Air the air screws still factory set?How did you set the floats with or without the gaskets on?We will get this thing running if i have to get on a plane and come over there LOL !!!!! Where are you anyway?
 
Same Problem....

Same Problem....

Im kindda new to not only the motorcycle world but also forums so plz bare with me. I just bought my first bike, 1981 GS750, that according to the previous owner sat for a copule of years up until last year which he only rode a little bit and had tune up work done by one of his buddies (which i dont tust cuz it looked like he half assed it). Im assuming it did sit for a while becase it only has like 6500 miles on it. Anyways the bike runs pritty good except for the fact that i have the same problem you are having... Whenever u give it gas too fast it boggs down ALOT and ALMOST dies but if it doesnt die, it works just fine if you can get past somewhere around 3000-4000 rpm then it almost nocks me off the bike because of the power increase. i will try to make sure all of the air box connnections are tight and as best as possible tonite, but if theres anything else you think might work plz let me know...
 
Minnesota. With a short riding season, this thing has me itching!!! You are correct with the MIK carbs being 32 ss cv. I wish that I could say that I was the first person that touched this bike, if I had been, I may not be having these problems. The screw caps were missing (adjusted?) I did seat them before removing them and repalcing them with new ones. They were all set at 1 1/2 turns out. After searching this site I thought that this would at least get me close, so reset at 1 1/2 out. Floats were set with the gaskets (new uncompressed) on. I never pulled the jet needles to see where the clips were set, but I do have new ones to replace them if needed. And yes, this thing will run...I've yet to be stumped by a fire-breather...this one will not be the first!
 
throttle response

throttle response

i've got a 82' gs300lz that does the same thing, when it's cold untill it really gets warmed up.
i've set and checked everything except the cam timing and adjust the valves.
on the last outing i heard a popping on the left exhaust when decellerating.
and am suspecting valves need adjusting , to be done this week.
 
Dave8338 said:
Minnesota. With a short riding season, this thing has me itching!!! You are correct with the MIK carbs being 32 ss cv. I wish that I could say that I was the first person that touched this bike, if I had been, I may not be having these problems. The screw caps were missing (adjusted?) I did seat them before removing them and repalcing them with new ones. They were all set at 1 1/2 turns out. After searching this site I thought that this would at least get me close, so reset at 1 1/2 out. Floats were set with the gaskets (new uncompressed) on. I never pulled the jet needles to see where the clips were set, but I do have new ones to replace them if needed. And yes, this thing will run...I've yet to be stumped by a fire-breather...this one will not be the first!
Click to expand...
You need to reset them by running your idle up to the highest you can get out of each screw and then restting your idle screw to 1000 or 1100.Then you need to sync them with a sync tool.Does it idle smooth?I think your getting too much air and that causing your bogging before it takes off.Try 1 to 1 1/4 out on your air screws.Dont forget to oil you air filter too!
 
popeye0088 said:
Im kindda new to not only the motorcycle world but also forums so plz bare with me. I just bought my first bike, 1981 GS750, that according to the previous owner sat for a copule of years up until last year which he only rode a little bit and had tune up work done by one of his buddies (which i dont tust cuz it looked like he half assed it). Im assuming it did sit for a while becase it only has like 6500 miles on it. Anyways the bike runs pritty good except for the fact that i have the same problem you are having... Whenever u give it gas too fast it boggs down ALOT and ALMOST dies but if it doesnt die, it works just fine if you can get past somewhere around 3000-4000 rpm then it almost nocks me off the bike because of the power increase. i will try to make sure all of the air box connnections are tight and as best as possible tonite, but if theres anything else you think might work plz let me know...
Click to expand...
It sounds like you need to clean your carbs and sync them.Make sure you oil your air filter and have no leaks.Does it idle good when its warm? Have you checked for intake leaks around the boots?
 
scott hamm said:
i've got a 82' gs300lz that does the same thing, when it's cold untill it really gets warmed up.
i've set and checked everything except the cam timing and adjust the valves.
on the last outing i heard a popping on the left exhaust when decellerating.
and am suspecting valves need adjusting , to be done this week.
Click to expand...
That popping could also be a lean fuel mixture/Let me know how the valve adjustment comes out.
 
Greetings:
Was again in the shop until 12:00pm checking...rechecking...and changing. I am closing in on the issue. I know that the displacement of this bike (GS650L) is rather small but I can't get over how much tiny air leaks and poor adjustments make dramatic changes in its performance. With new filter in and sealed as 'tconroy' suggested, tightened intake fittings (I should really get new ones they're stiff from age) and adjusting pilot screws to 1 7/8 turns out, I hit the road at Midnight. Not advised! In this case, the bike was all but final synchroed and I could tell that it wanted to run and I was ready to ride. What a trip!!! Great little bike, put on 56 miles last night and rolled in at 1:10 am. I still have a slight flat spot between 3800 and 4500...slight...but am sure that it will balance out after the sync. Keep you posted.
 
Dave8338 said:
Greetings:
Was again in the shop until 12:00pm checking...rechecking...and changing. I am closing in on the issue. I know that the displacement of this bike (GS650L) is rather small but I can't get over how much tiny air leaks and poor adjustments make dramatic changes in its performance. With new filter in and sealed as 'tconroy' suggested, tightened intake fittings (I should really get new ones they're stiff from age) and adjusting pilot screws to 1 7/8 turns out, I hit the road at Midnight. Not advised! In this case, the bike was all but final synchroed and I could tell that it wanted to run and I was ready to ride. What a trip!!! Great little bike, put on 56 miles last night and rolled in at 1:10 am. I still have a slight flat spot between 3800 and 4500...slight...but am sure that it will balance out after the sync. Keep you posted.
Click to expand...
The gs 650L has a lot going for it and it is a great all around bike.I ought to know, I have one too!Have you checked your intake boots for leaks yet?While the bike is running spray some wd-40 around where the boots go onto the heads and see if you notice a change in the idle.If its been sitting a while you may need to replace the intake boot o-rings,there probably trashed.Do you notice it idleing up after the ride? If so you have an intake leak at the boots or bad o-rings.Let me know how you are progressing on the bike.I think your almost there!
 
tconroy;

I will do the wd-40 trick tonight (if time permits) and let you know what I find. It seems as though it's pulling air from somewhere...as I stated, the intake boots are very stiff and when rebuilding the carbs, the o-rings were beyond bad, it wouldn't surprise me if the intake o-rings look the same way, I've never had them off. AIR AIR AIR...seems to be the main issue with this bike. One might assume that it is not only this bike that has a lean burn tendency. I know that everything that I've done to ensure that all intake fittings, air box fittings WITH STOCK COVER, vacuum lines, and petcock diaphragm, are all sealing tightly, have made huge strides in getting this thing back on the road.

For those of you who have joined in on the issue, before giving up hope, spend the time it takes to check all of these conditions first. It will save you time and money in the long run!!
 
Dave8338 said:
tconroy;

I will do the wd-40 trick tonight (if time permits) and let you know what I find. It seems as though it's pulling air from somewhere...as I stated, the intake boots are very stiff and when rebuilding the carbs, the o-rings were beyond bad, it wouldn't surprise me if the intake o-rings look the same way, I've never had them off. AIR AIR AIR...seems to be the main issue with this bike. One might assume that it is not only this bike that has a lean burn tendency. I know that everything that I've done to ensure that all intake fittings, air box fittings WITH STOCK COVER, vacuum lines, and petcock diaphragm, are all sealing tightly, have made huge strides in getting this thing back on the road.

For those of you who have joined in on the issue, before giving up hope, spend the time it takes to check all of these conditions first. It will save you time and money in the long run!!
Click to expand...
The boots may not look bad or cracked but look closely around the metal to rubber part that connects onto the engine.When I took my carbs off the boot seperated from the metal flange that holds them to the carbs.If you have an air leak at the intake your idle will go up when the bike warms up.
 
Air

Air

Air DEFINATELLY makes a HUGE difference..... i havent had much time to work on my bike because of work and weather (i dont have a shop) n e ways... yesterday i tighted up all the boots, air box, and air filter the best i could... it made a HUGE difference i can now actually ride. Its the best its ever ran...
 
popeye0088 said:
Air DEFINATELLY makes a HUGE difference..... i havent had much time to work on my bike because of work and weather (i dont have a shop) n e ways... yesterday i tighted up all the boots, air box, and air filter the best i could... it made a HUGE difference i can now actually ride. Its the best its ever ran...
Click to expand...
COOL!!! im glad to hear that.I like heraing about one more GS on the road! Have fun and be careful!!!!
 
tconroy;
Back at it. Took the wd-40 to the base of the intake boots last night and could notice no increase in the RPM's. Not to rule this out...I grabbed the starting fluid off the shelf and with the straw in place, again took after the boots. BINGO!!! We have a winner. There is a slight increase when sprayed on the #2 boot and slightly more when aiming at the #4 boot. I think that the straw was the trick. I'm off to the dealer to order new intake orings for the whole team. Also, thought that I'd ride it to work today...FUN BIKE...and when I pulled into the parking lot, I noticed that the idle was sitting at 1400, not the 1,100 that it has been set at.

Are WE getting close?
 
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