1977 GS550 Huge flat spot in power range w/ pods and pipes

[Guest]

Hey all,

I'll try to be as specific as I can with my setup. Carbs just cleaned, all o-rings and gaskets replaced, new o-rings for the carb boots which are still healthy, added pod filters and Emgo shorty mufflers. Subsequently upped the main jets from stock 80 to 110's and after messing with raising the needle I ended up back at the center position. All valve clearances are in spec, new points installed, new plugs, new battery. Prior to all of this the bike was stock, and not running well. It was a classic hard to start / took forever to warm up and idle scenario. It starts right up and runs great now, revs through the entire range smoothly with no bogging. I am still in the middle of getting the fine tunings done on the carbs with the pods and pipe but I feel as though I am pretty close with the settings.

Current carb settings: 110 main jets, stock pilot jets, idle mixture screws 1 1/4 turn out, pilot fuel screws 1 turn out. Pulled plugs after a short ride and they are a little sooty but not fully covered. This seems surprising because I thought for sure the pods would make for a super lean mixture rather than the opposite.

When I take the bike for test rides around the block, I notice a huge loss of power in the 1/4 to 3/4 open throttle range. The bike revs smoothly but it isn't translating to the wheel. I have read about others running very similar setups and settings to mine with great results, but the difference in parts could be making these settings incorrect for my bike. Admittedly, the pods I am using are the cheapos (possibly Emgo?) but could that be a reason for such a huge loss of power? Since I mentioned my plugs are still a little sooty could it be that the mains jets are too big now and its not getting enough air in the mix with the throttle rolling open? I haven't done moving plug chops yet but I'm just curious if there are any tell tale signs I am missing ahead of time.

Thanks!

[tkent02]

GS 550s are strange engines. Very gutless at low RPM, the pipe and pods make it worse, even well tuned with pipe and pods it's almost unridable until about 5,000 or so. After that it starts to get good, from 6,500 or so the power increases to well past the red line. That's just the way they are. Pretty fast bike if you keep it between say 8,000 and 11,000, a real dog below that. If you are not familiar with the 550 you may be mistaking the way they naturally are for a tuning problem, although you probably have that going too.

Lose the Emgo Sand Sifters, they don't flow much air, don't filter much of anything and they are very difficult to tune. They also block the air jets in the back of the carb somewhat. Ape make a good one, a lot cheaper than K&Ns.

It sounds like you do need to make jetting changes. With VM carbs you tune from the bottom up, so get the idle right, pilot jets, then the mid range with the jet needle, worry about the main jet and full throttle last. It will take a lot of plug chops to get it right. Where are your pilot fuel screws set? And the pilot air screws? How did you set them?

[HogsRear]

GS 550s are strange engines. Very gutless at low RPM, the pipe and pods make it worse, even well tuned with pipe and pods it's almost unridable until about 5,000 or so. After that it starts to get good, from 6,500 or so the power increases to well past the red line. That's just the way they are. Pretty fast bike if you keep it between say 8,000 and 11,000, a real dog below that. If you are not familiar with the 550 you may be mistaking the way they naturally are for a tuning problem, although you probably have that going too.

Lose the Emgo Sand Sifters, they don't flow much air, don't filter much of anything and they are very difficult to tune. They also block the air jets in the back of the carb somewhat. Ape make a good one, a lot cheaper than K&Ns.

It sounds like you do need to make jetting changes. With VM carbs you tune from the bottom up, so get the idle right, pilot jets, then the mid range with the jet needle, worry about the main jet and full throttle last. It will take a lot of plug chops to get it right. Where are your pilot fuel screws set? And the pilot air screws? How did you set them?

Thanks for the reply tkent. My sole basis for comparison is my buddy's GS that also resides in my garage, same exact year and model. His has stock pipes and pods but pulls considerably harder in the aforementioned range, which leads me to believe something is off.

My current carb settings are 110 main jets, stock pilot jets, idle mixture screws 1 1/4 turn out, pilot fuel screws 1 turn out. Plugs lightly sooted after a ride around the block. From what I've read from people who have done similar mods with success, they typically leave pilot jets stock, so I did the same.

I did adjust the needle up (lowered the clip to 4th position down, then all the way down and it was bogging badly) but now it's back in the center spot. I even tried running with the filters off and it was the same power situation. I'm wondering now if my pilot fuel screws are too far out.

[tkent02]

Probably. I usually start with 1/2 turn out, but I'm tuning for 6,000' elevation. I think 5/8 or 3/4 is a good spot to start for sea level. You will of course be fine tuning it from there. Do NOT bottom the fuel screws to count turns, they are very easy to break the tips off of, tiny needles made of soft brass. Then you are screwed. Take the carbs off, look inside the bore and screw the screw in, when you see the tip visible in it's little hole go just a little bit more, a very slight increase in drag is as far as you want to go. I go as far as removing the rubber o ring and the spring from the screw and finding the bottom, it's easier to feel it without going too far that way.

It's very common to find fuel screws with broken tips on VM carbs, they never work right that way. That's the first place I look at for idling problems, and usually the last place I need to look...

[HogsRear]

Probably. I usually start with 1/2 turn out, but I'm tuning for 6,000' elevation. I think 5/8 or 3/4 is a good spot to start for sea level. You will of course be fine tuning it from there. Do NOT bottom the fuel screws to count turns, they are very easy to break the tips off of, tiny needles made of soft brass. Then you are screwed. Take the carbs off, look inside the bore and screw the screw in, when you see the tip visible in it's little hole go just a little bit more, a very slight increase in drag is as far as you want to go. I go as far as removing the rubber o ring and the spring from the screw and finding the bottom, it's easier to feel it without going too far that way.

It's very common to find fuel screws with broken tips on VM carbs, they never work right that way. That's the first place I look at for idling problems, and usually the last place I need to look...

Just pulled the pilot fuel screws out. All were straight and pointy except for in carb #3, which looked like it had been turned in too hard. Slightly crooked/flattened tip. I will order a replacement.

[tkent02]

OK, look in the hole it came from, shine a light on the other side. You should be able to see a pinpoint spot of light in it, coming through the tiny port. If not, there's a broken off tip stuck in it. #3 you say?

[HogsRear]

The more I ride it the more I'm seeing that the adjustments I'm making aren't affecting my lack of power and I think I figure out what's going on. It relates nothing to the carb, I think it's actually my clutch is slipping. It's the exact symptoms I have seen online, and for all I know this clutch has never been changed. Does this sound like it might be what's going on?

[tkent02]

Might be, if the engine revs up without the bike moving faster it's the clutch slipping. Usually it's the springs are too short from age, stick with stock Suzuki springs.

[HogsRear]

Might be, if the engine revs up without the bike moving faster it's the clutch slipping. Usually it's the springs are too short from age, stick with stock Suzuki springs.

Well, I made a small adjustment to the cable and noticed a difference instantly, I mistook the slippage for a lack of power. Sad thing is I think I had a decent tune on the carbs earlier this morning, then ripped them up and tweaked things trying to solve my "problem." Back off they come tomorrow, I guess you live and learn. By the way your points are still very valid and now I can really focus on tuning the carbs right without worrying something is way off. Thanks again.

[tkent02]

Have you adjusted the lower clutch adjustment? The one in the sprocket cover?

[HogsRear]

Have you adjusted the lower clutch adjustment? The one in the sprocket cover?

I haven't, and sadly I think that section of my Clymer manual fell out so I've been trying to find info online about how to properly adjust it.

[HogsRear]

Found it in my service manual and I think I have it set where it should be. Now back to tuning the carbs....