Slight roughness/stumble off idle- GS1100E with Kerker, APE pods, and DynoJet Stage 3

[dweller]

1982 GS1100E with stock carbs (BS34SS). Kerker four into one, APE pods, DynoJet Stage 3. I've been able to dial this combo in almost perfectly. Had to raise the needles two positions from DynoJet's baseline recommendation. Increased pilot jet size from 45 to 47.5 to 50. All of these changes were done separately and each change helped. I did attempt to raise the needles one more position which hurt off-idle rideability, so I reversed that change. The latest change has been the 50 pilot jets (fuel screws 3.0 turns out) and this is the best yet. The only issue currently is a very minor but sometimes annoying roughness/stumble just off idle, with the throttle barely cracked open. If I roll the throttle open somewhat quickly, the bike responds instantly and leaps forward in any gear or rpm. If I barely crack the throttle very slowly, it stumbles slightly then responds.

Things that I have personally done on this bike (I'm a skilled mechanic for all manner of vehicles): Valves adjusted, carbs completely broken down and rebuilt (all seals, including throttle shaft seals), new intake rubbers, Accel ignition coils and wires (including the recommended wiring changes found on this forum), carbs synced at about 2500 rpm using Carbtune, that's all I can think of that might be relevant to this issue. Just don't want anyone to go down an unneeded path regarding ignition, valse adjustment, etc.

Would appreciate any feedback from header/pod users that might have experienced the same issues. Would rather not go down the "put your stock exhaust and airbox back on" road. Right now, even with the slight stumble, the bike runs better and sounds way cooler than stock.

Thanks

 

[Rob S.]

That slight roughness/stumble sounds like how Cycle World described the 11E brand new.

 

[salty_monk]

How accurate is your tach? The GS ones aren't super accurate. You may just need to raise the idle a couple hundred RPM... I would say what you're seeing has to be in the pilot circuit. It's either a bit rich or a bit lean. You could also mess with the float level but it's pretty sensitive once you get out of the stock range in my experience. Even between the stock tolerances produces a noticeable difference. Maybe go up to the richer end of what is stock & try again....

Also to note is that the fuel enrichener valves (Chokes) might be leaking and making that circuit run richer than it should... there is a post from a guy in the UK who repairs them to order. All of our bikes prob suffer from that to a certain degree at this age!

 

[dweller]

How accurate is your tach? The GS ones aren't super accurate. You may just need to raise the idle a couple hundred RPM... I would say what you're seeing has to be in the pilot circuit. It's either a bit rich or a bit lean. You could also mess with the float level but it's pretty sensitive once you get out of the stock range in my experience. Even between the stock tolerances produces a noticeable difference. Maybe go up to the richer end of what is stock & try again....

Also to note is that the fuel enrichener valves (Chokes) might be leaking and making that circuit run richer than it should... there is a post from a guy in the UK who repairs them to order. All of our bikes prob suffer from that to a certain degree at this age!

Thanks for the feedback. I was thinking about the float level height and how that might affect the pilot circuit. I've been playing with fuel screw settings with the 50 pilots. I've tried from 2.5-4 turns out and the slight stumble is there regardless but is minimized at the middle of that range. So I was thinking of perhaps raising float height to see how that might change things.

Interesting about the tach. I've been setting idle at 1200 rpm (as noted on stock tach) on fully warmed engine regardless of all carb changes. Perhaps I should try 1300-1400 instead and see if that helps?

I should note: after prolonged idling, spark plugs still look lean to me.

 

[bonanzadave]

Would rather not go down the "put your stock exhaust and airbox back on" road.

I did it to a KZ 650 and never got it as smooth as stock. Im glad I never did it to my EZ. I don't expect throttle response to ever be as good as an injected engine....

 

[dweller]

I did it to a KZ 650 and never got it as smooth as stock. Im glad I never did it to my EZ. I don't expect throttle response to ever be as good as an injected engine....

It's surprisingly good the way it is. The slight stumble that sometimes occurs is a minor annoyance. I like tinkering with it so will likely keep at it until I get it 100% perfect.

 

[gustovh]

Try dropping the idle to 1000. Then do a lean best idle adjustment.

V

 

[dweller]

Try dropping the idle to 1000. Then do a lean best idle adjustment.

V

I will try that.

Does anyone thing there is value in resynching the carbs at a lower rpm?

 

[KEITH KRAUSE]

I think synching the carbs at about 2,500 rpm's is fine. You may have noticed that you can synch them very evenly at a certain rpm and then see the levels change a little when you lower or raise the rpm's. You could go nuts trying to make them perfect at various rpm's. Synching at a higher rpm just makes the bike run hotter while synching.
As for you experimenting with idle rpm's, I'd stay with whatever the factory manual says. Setting it at 1,300-1,400 rpm's just wastes fuel, makes it run hotter at stops and requires more brake pressure and brake wear to stop or slow down.
I don't have nearly as much experience with CV carbs and pods as I do with the VM's and pods, but I've always been very picky how my '79 GS1000 runs, with V&H pipe/K&N ovals. I developed a stumble a couple years back that sounds similar to yours but mine was pretty annoying. Only way I could stop the stumble was to open the throttle faster, which can be hazardous in some situations. Like you say, rolling the throttle on normally created the stumble. I played with everything I could think of but nothing helped. Then I got to thinking if the K&N's were possibly too dry from not being re-oiled lately. With the VM's, I've found that if the filters are too dry, there's not that small amount of resistance when the throttle is cracked open just above idle. The pressure changes too suddenly and my bike stumbled for just a quick moment before recovering. As soon as I re-oiled the filters, just a single moderate layer, the stumble was completely gone. So, with the filters not so dry, it eliminated that sudden pressure change and the stumble.
I knew all along that the stumble was related to something I'd never experienced before, like simply falling behind on re-oiling. My pods looked clean but somehow I just didn't think to re-oil like I have in the past. Getting older and having my mind on health issues has messed up my maintenance routines. On the flip side, I have, over 42 years, a couple of times made one to many passes with my K&N spray can and created a very bad bog as soon as I tried to open her up from around 3,000 rpm's or so. It's surprising how easy it can be too over or under oil them.
I do know the CV carbs are, based on a million owners statements, much more finicky when set up with pods. They can be difficult to dial in when changing how they take in air. Short story long, be sure the pods are oiled properly and with the correct oil.
As for your lean plug reads after prolonged idling, my opinion is plug reads after excessive/prolonged idling are generally innacurate. Suzuki, like everyone else, had to focus on leaning the carburetion to pass emissions, especially at lower rpm's. I would expect less coloring on the plugs. And of course, pods running a little dry would add to any lean plug reads.

 

[dweller]

I think synching the carbs at about 2,500 rpm's is fine. You may have noticed that you can synch them very evenly at a certain rpm and then see the levels change a little when you lower or raise the rpm's. You could go nuts trying to make them perfect at various rpm's. Synching at a higher rpm just makes the bike run hotter while synching.
As for you experimenting with idle rpm's, I'd stay with whatever the factory manual says. Setting it at 1,300-1,400 rpm's just wastes fuel, makes it run hotter at stops and requires more brake pressure and brake wear to stop or slow down.
I don't have nearly as much experience with CV carbs and pods as I do with the VM's and pods, but I've always been very picky how my '79 GS1000 runs, with V&H pipe/K&N ovals. I developed a stumble a couple years back that sounds similar to yours but mine was pretty annoying. Only way I could stop the stumble was to open the throttle faster, which can be hazardous in some situations. Like you say, rolling the throttle on normally created the stumble. I played with everything I could think of but nothing helped. Then I got to thinking if the K&N's were possibly too dry from not being re-oiled lately. With the VM's, I've found that if the filters are too dry, there's not that small amount of resistance when the throttle is cracked open just above idle. The pressure changes too suddenly and my bike stumbled for just a quick moment before recovering. As soon as I re-oiled the filters, just a single moderate layer, the stumble was completely gone. So, with the filters not so dry, it eliminated that sudden pressure change and the stumble.
I knew all along that the stumble was related to something I'd never experienced before, like simply falling behind on re-oiling. My pods looked clean but somehow I just didn't think to re-oil like I have in the past. Getting older and having my mind on health issues has messed up my maintenance routines. On the flip side, I have, over 42 years, a couple of times made one to many passes with my K&N spray can and created a very bad bog as soon as I tried to open her up from around 3,000 rpm's or so. It's surprising how easy it can be too over or under oil them.
I do know the CV carbs are, based on a million owners statements, much more finicky when set up with pods. They can be difficult to dial in when changing how they take in air. Short story long, be sure the pods are oiled properly and with the correct oil.
As for your lean plug reads after prolonged idling, my opinion is plug reads after excessive/prolonged idling are generally innacurate. Suzuki, like everyone else, had to focus on leaning the carburetion to pass emissions, especially at lower rpm's. I would expect less coloring on the plugs. And of course, pods running a little dry would add to any lean plug reads.

Very good point on air filter oiling! I was messing with the bike just a bit ago and it crossed my mind to pull, clean, and reoil my APE pods. I will try that and let you know.

One thing I did tonight is turn the mixture screws out to 4 turns (which is wide open on the 50 pilots for all intents and purposes) and then put masking tape over about 1/3 of each pod filter to block some air flow. Went for a ride and the stumble was almost completely gone. Of course the bike did not run well at larger throttle openings, but at the idle and off-idle range that I'm trying to fix it was much improved. From this I can only surmise that I need to go at least one more step up on pilot jet size. So I'm going to order some 52.5 pilots and maybe even some 55s just in case.

But before I do that, I'm going to redo my filters as suggested and try that.

 

[salty_monk]

Do you have Air correctors in that DJ kit? If I remember rights the one for the 1000 carbs had a glue in restrictor bush but as it happens the hole is about the same size as the stock on the GS1100E carb.....

 

[Rob S.]

"Throttle response is good but there is a small amount of lean surge at steady-state cruising speeds and low throttle openings. It feels as though the carb pistons are undecided as to where, exactly, they want to position themselves. At higher road speeds, during hard riding, or in the fast-slow transitions of daily riding no carb problem is evident and the throttle is quick and responsive."

Cycle World, July 1982

I have APE pods, V&H pipe and DynoJet stage 3, and my bike runs very nicely. An accomplished builder/tuner did the jetting on his dynamometer. When I installed the pods, I had to cover about 80% of them with tape just to get the bike rideable until I could get it to my mechanic.

 

[KEITH KRAUSE]

Well, by applying some tape and increasing the restriction, you would obviously change how air enters the filters and how that effects pressure. We often are short sighted and think that the least restriction at the filters is best. But there needs to be SOME restriction to avoid sudden pressure issues. So taping your filters, though a crude test, is effecting the carbs in a similar way that adding some oil to the filters does. Of course, what you did would also change the air/fuel ratio and your problem could be simple lack of fuel in the ratio. But being certain your filters are oiled properly is a basic maintenance thing and should be done anyways.
In my opinion, the mixture screws won't further effect the mixture after 4 turns out, possibly 3 turns? Also, again, I have less experience with CV carbs but with the VM carbs, stage 3 jetting kits don't change the pilot jets for basic quality pipe and pod filter mod's. The freer flowing intake and exhaust simply has no significant effect at idle/smaller throttle openings, so the stock pilot jets are adequate and generally only need some richer tuning at the pilot fuel screws to make the pilot circuit run well (usually 1 additional turn out or less). At these smaller throttle openings, I would think the same applies to the CV's? Wish I knew more. I do know that with ANY carbs with only "mixture" screws, you must adjust the screws using the "highest rpm method". On the center stand, with the motor at full operating temp', throttle cable(s) adjusted correctly and the idle set to the factory recommendation...start at any carb (unless the factory manual says otherwise), slowly adjust the screw in or out and listen for the highest idle you can achieve. Reset the idle to the factory base rpm, if it changed, by adjusting the throttle pulley adjuster. Repeat this procedure to each carb until done. Adjusting the mixture screws at higher rpm's than factory recommended will compromise the tuning.

 

[dweller]

Do you have Air correctors in that DJ kit? If I remember rights the one for the 1000 carbs had a glue in restrictor bush but as it happens the hole is about the same size as the stock on the GS1100E carb.....

The BS34SS kit comes with an optional pilot air jet that can be used to lean it out if your pilot circuit is too rich. But I was definately way lean with the 45s and the 47.5s so I didn't use it.

 

[dweller]

"Throttle response is good but there is a small amount of lean surge at steady-state cruising speeds and low throttle openings. It feels as though the carb pistons are undecided as to where, exactly, they want to position themselves. At higher road speeds, during hard riding, or in the fast-slow transitions of daily riding no carb problem is evident and the throttle is quick and responsive."

Cycle World, July 1982

I have APE pods, V&H pipe and DynoJet stage 3, and my bike runs very nicely. An accomplished builder/tuner did the jetting on his dynamometer. When I installed the pods, I had to cover about 80% of them with tape just to get the bike rideable until I could get it to my mechanic.

I applied the tape per the DynoJet tuning guide. They advise either adding tape or removing filters completely to diagnose the carb circuit you're working on as a quick way to go in the right direction without pulling carbs to rejet each time. It's a good idea, I like it!

 

[dweller]

Well, by applying some tape and increasing the restriction, you would obviously change how air enters the filters and how that effects pressure. We often are short sighted and think that the least restriction at the filters is best. But there needs to be SOME restriction to avoid sudden pressure issues. So taping your filters, though a crude test, is effecting the carbs in a similar way that adding some oil to the filters does. Of course, what you did would also change the air/fuel ratio and your problem could be simple lack of fuel in the ratio. But being certain your filters are oiled properly is a basic maintenance thing and should be done anyways.
In my opinion, the mixture screws won't further effect the mixture after 4 turns out, possibly 3 turns? Also, again, I have less experience with CV carbs but with the VM carbs, stage 3 jetting kits don't change the pilot jets for basic quality pipe and pod filter mod's. The freer flowing intake and exhaust simply has no significant effect at idle/smaller throttle openings, so the stock pilot jets are adequate and generally only need some richer tuning at the pilot fuel screws to make the pilot circuit run well (usually 1 additional turn out or less). At these smaller throttle openings, I would think the same applies to the CV's? Wish I knew more. I do know that with ANY carbs with only "mixture" screws, you must adjust the screws using the "highest rpm method". On the center stand, with the motor at full operating temp', throttle cable(s) adjusted correctly and the idle set to the factory recommendation...start at any carb (unless the factory manual says otherwise), slowly adjust the screw in or out and listen for the highest idle you can achieve. Reset the idle to the factory base rpm, if it changed, by adjusting the throttle pulley adjuster. Repeat this procedure to each carb until done. Adjusting the mixture screws at higher rpm's than factory recommended will compromise the tuning.

I did try the highest RPMs method with the 50s two days ago but in the <4 turns out range I was not getting a valid test (couldn't get the idle to go down due to excessive richness). Which seems to support the idea of moving up one more pilot size so that the mixture screws have some effect. But first! Today I'm going to pull the pods, clean, dry and reoil and try that. I agree that it's likely to have a positive effect!

Thanks for the discussion all, much appreciated. Great thing to play with on a cold rainy day!

 

[dweller]

Alright guys, an update on this issue. I went up to 55 pilots and no change. I procured an infrared thermo gun and sampled the header temps at the exit of the exhaust ports. Cylinder 3 was less than half the temp of the other cylinders at idle. Aha, I thought, there's an obstruction in the #3 carb pilot circuit! So I pulled the carbs and broke down number 3 and did not seem to be getting carb cleaner through the various ports of the pilot circuit. So I started blocking off outlets and alternating between air and carb cleaner until I was getting flow everywhere (I thought). Bear in mind that the first thing I did to this bike when I got it was strip all the carbs and do a very thorough full rebuild on them, including a couple days in the Berryman's solution for each carb. Tank is perfect inside, petcock is brand new OEM. Float bowls have never had any debris in them each time I've done jet swaps. I figured maybe there was something in that carb all along that never came out. Anyway, got it back together and same deal, stumble off idle and number 3 running much cooler. Did the 2/3 plug wire swap and the problem stayed with 3. Tried closing the number 3 pilot screw completely and running it out 4 turns, with no discernable difference in how the bike idled or rode. Seemed clear that number 3 simply wasn't getting gas through the pilot circuit.

I just pulled the carbs again and noticed that the throttle blade for 3 was closed and the others were cracked. This was the result of syncing at 2500 rpm with my carbtune and I hadn't noticed that number 3 throttle blade position was significantly different than the others. The blade was obstructing the pilot bypass ports. So I bench synched the carbs and put them back on. Runs a bit better and now the temp on that header is 100 degrees warmer, but still 250-300 degrees shy of the other cylinders. Bike runs better but still has a stumble at idle and just off idle. I'm perplexed.

I guess I'm now thinking that perhaps one or more of the pilot bypass ports might be clogged. There are three tiny holes. I'm thinking this could cause the issue and also explain why adjusting the pilot screw doesn't have any effect.

Any thoughts or suggestions at this point? Thanks!

 

[dweller]

So I pulled the carbs again last night and went through number 3 completely and verified that all three bypass ports were open. One of them may have been at least partially obstructed. Test rode it this morning and it's much improved. Still an occasional stumble off idle but far better than before. Checked the head pipe temps after the ride while it was idling and now 1 and 2 are at 550 and 3 and 4 are both at 400. I'm guessing that is because I wasn't right on with my bench synch on the final step matching 1/2 to 3/4.

Hopefully after I go through pilot adjustment and carbtune synch, all will be well.

On a positive note, I'm getting really fast pulling and reinstalling the carb rack! I can have the carbs off in less then five minutes!

 

[CincinnatiKid]

I came to the forum to look into this same sort of symptom on my 81 1100. A small dead spot on the 1/8 to 1/4 throttle zone. Great power once you get the revs up into the power band I have quality pods (unbranded...), 4-2-1 exhaust and a DJ stage III kit installed. I have the notes about whats inside the stock BS34 carbs somewhere but not close by.

I have been generally happy with the state of tune, though I am also constantly searching for that little extra, as are you. cheers. I like to take off fast from stoplights when I ride (in the city of Chicago, the best defense is a quick takeoff), but it requires some clutch work to get the power through to the rear wheel at low throttle openings. bring up the revs to ~4k ish (no instruments on the bike), then disengage clutch, revs drop, but it requires more than steady throttle in order to keep the bike making good power to the ground to get a quick takeoff. I have to twist it up to about 1/2 throttle in order to keep accelerating.
It's not an issue when trying to putt around in a leisurely way, but I rarely ride like that. My other ride is a 510cc KTM single, and the difference in low end torque is about as different as it comes, so I try to keep my expectations in check. I recall having seen Rob S's Cycle World quote before when pursuing this same line of performance increase, and try to keep it in mind. It's not a FI engine and won't react like one.

I will stay tuned here for your updates, and re-check my filters for proper oiling. I think i had them well oiled at the end of last season, and didnt ride too much this winter.
The bike needs a good servicing for the new season, so I will also come back with any updates that I find.

 

[dweller]

I came to the forum to look into this same sort of symptom on my 81 1100. A small dead spot on the 1/8 to 1/4 throttle zone. Great power once you get the revs up into the power band I have quality pods (unbranded...), 4-2-1 exhaust and a DJ stage III kit installed. I have the notes about whats inside the stock BS34 carbs somewhere but not close by.

I have been generally happy with the state of tune, though I am also constantly searching for that little extra, as are you. cheers. I like to take off fast from stoplights when I ride (in the city of Chicago, the best defense is a quick takeoff), but it requires some clutch work to get the power through to the rear wheel at low throttle openings. bring up the revs to ~4k ish (no instruments on the bike), then disengage clutch, revs drop, but it requires more than steady throttle in order to keep the bike making good power to the ground to get a quick takeoff. I have to twist it up to about 1/2 throttle in order to keep accelerating.
It's not an issue when trying to putt around in a leisurely way, but I rarely ride like that. My other ride is a 510cc KTM single, and the difference in low end torque is about as different as it comes, so I try to keep my expectations in check. I recall having seen Rob S's Cycle World quote before when pursuing this same line of performance increase, and try to keep it in mind. It's not a FI engine and won't react like one.

I will stay tuned here for your updates, and re-check my filters for proper oiling. I think i had them well oiled at the end of last season, and didnt ride too much this winter.
The bike needs a good servicing for the new season, so I will also come back with any updates that I find.

What you're describing sounds to me like a needle issue. Try raising your needles one position (lower the clips one slot down on the needle). I think that is going to help you. I had to raise my needles two position from the initial setting recommended by Dynojet.