GS550 won't rev past 6000 RPM

[JohnnyL]

I think you have 2 separate problems going on here. First, It looks like you are too lean on the main jet. Second, I would make sure your 2-3 coil is properly grounded. May as well be sure the other one is too while your under there. Plug 2 looking ok, while 3 looks like it isn't firing sounds like a ground issue to me. Try that first and see if it improves the rpm issue, then address the jetting.

Grounds are good. Is there a way to tell if I am getting adequate spark at a specific plug? I pulled #3 plug and touched it to a bolt and see spark but how do I know if it is good spark? Is there a way to test the voltage at the end of the plug wire?

[Big T]

How about the spark plugs caps?

A known failure point. Ohm test them

[JohnnyL]

I think you have 2 separate problems going on here. First, It looks like you are too lean on the main jet. Second, I would make sure your 2-3 coil is properly grounded. May as well be sure the other one is too while your under there. Plug 2 looking ok, while 3 looks like it isn't firing sounds like a ground issue to me. Try that first and see if it improves the rpm issue, then address the jetting.

Wait...if the 2-3 coil wasn't grounded well then how would plug #2 look good and # 3 look like it isn't firing?

How about the spark plugs caps?

A known failure point. Ohm test them

Not sure what you mean by "spark plug caps". I have tried numerous spark plugs in the bike and it runs the same no matter what set is in there. The spark plug wires are resistance wires and they all show 1.3 ohms.

I have re-seated the spark plug wires into the Dyna Coils. They're a bear to get in with the rubber cap. Just hard to get to. It's possible that #3 wasn't seated all the way into the coil but I doubt this is the problem. It just doesn't explain why the bike will rev out to 10-11,000 in neutral but not when in gear going down the road.

[Zaos]

Just a few thoughts. Is your charging system working as it should? Theres a quick test to check in the forum somewhere.

If it's any help, on my gs850 I had to go up from a stock 115 jet size to a 130 before it ran right. (Pods and exhaust)

One thing I've see happen is an aftermarket gauge cluster causing the problem. Some wire into the ignition to measure the rpm and cause issues from.

[JohnnyL]

One thing I've see happen is an aftermarket gauge cluster causing the problem. Some wire into the ignition to measure the rpm and cause issues from.

Bingo! I wondered about that! I do have the tach wire connected to the 2-3 coil. I think I’m going to remove it and just wrap it around one of the spark plug wires.

[cowboyup3371]

You can replace the spark plug boots themselves by unscrewing the ends, clipping off about 1/8"-1/4" of the wire, and screwing new ones on

[JohnnyL]

You can replace the spark plug boots themselves by unscrewing the ends, clipping off about 1/8"-1/4" of the wire, and screwing new ones on

I don’t have the screw on type boots. They’re crimped on.

[Cipher]

I don’t have the screw on type boots. They’re crimped on.

IS this an oem ignition if it is aftermarket it might have some vile default rev limiter setting.

shot in the dark.

The pods may be impacted by cross winds as well. Although I know of no way you could temporarily shroud them.
My 550 in sever croos winds gets a starved for fuel feeling but thats high winds.
perhaps even the wee bit of vacuum in the slipstream is thwarting you.

Mind you my bikes inlet on the stock airbox is super small and shielded uner the seat and has a snorkel as well.

[JohnnyL]

IS this an oem ignition if it is aftermarket it might have some vile default rev limiter setting.

shot in the dark.

The pods may be impacted by cross winds as well. Although I know of no way you could temporarily shroud them.
My 550 in sever croos winds gets a starved for fuel feeling but thats high winds.
perhaps even the wee bit of vacuum in the slipstream is thwarting you.

Mind you my bikes inlet on the stock airbox is super small and shielded uner the seat and has a snorkel as well.

I have a Dyna-S ignition on the bike.

I'm going to remove the speedo tach pick-up from the coils and just wrap it around a spark plug wire. I'm willing to bet money that being connected to the coil is affecting the spark on 2-3. It's supposed to be chilly here today but I am going to take the bike for a spin later today and see if that solves the problem. Will post results.

[Spyder]

I have seen coils with a bad ground spark one cylinder stronger than the other on the same coil. I really don't know the technical reason why. Just know it can happen. I have also had an after market tach (in a car) short out the coil. Car wouldn't start, pulled the tach lead off the coil, and it fired right up. I agree that that valve will not be the reason for your rev issue, but needed to be fixed anyway for overall performance, and efficiency. I have followed your whole build, you are persistent. You'll get this...

[JohnnyL]

Holy Smokes! Eureka! The bike finally runs just about right! It's 41 degrees out and my son and I just went for a quick ride to test my bike. My son was on his 69 CL350. My bike is finally alive! Hit 70mph in 3rd gear and probably still had more. The tach isn't working but I know it was way over 6000 RPM. So here's what I did:

1. Discovered a leak on #3 intake. Lapped the valve and re-tested with no leaks.
2. Instead of relying on the coils being grounded to the frame through their mounting brackets, I ran a dedicated ground wire from the mounting brackets to the frame.
3. Removed the tachometer pick-up wire from the 2-3 coil and just wrapped the wire around the spark plug wire. Acewell gauge instructions state that this can be done. Since the spark plug wires are shielded, I don't think I'm picking up the correct RPMs. Needle is bouncing around and not responding with revving the engine. Pretty sure this was the problem all along. I'm wondering if I can put a resistor inline for the pick-up wire and reconnect to the coil. Or maybe a need a one way diode? Not sure what to do here.
4. I removed the 100 main jets I had in the carbs and replaced with 112.5 mains. Seems to run pretty damn good with this main in here but I need to do some plug chops once the weather is a little warmer. I also have a flat spot at about mid throttle. Raise needles? Currently raised by one washer I think. Can't remember if I put one or two in.
5. I replaced the little filters in the carbs where the fuel comes in. Still had old ones in. Could have been restricting fuel.
6. I removed the inline fuel filter I had between the tank and carbs. Could have contributed to the problem.

I can't believe how this bike feels after 6000 RPM. The pull is insane. I still need to mess with the mixture screws. The bike was somewhat warmed up before I left and the bike was idling pretty good at about 1300(guessing) but about halfway through the ride, the bike was idling much higher. Couldn't get it to calm down. I think this is a mixture screw problem. I have 92.5 pilots in I am currently 3-1/2 turns out on the mixture screw.

Please offer your suggestions for the mid range flat spot, the mixture screw adjustment and if you have any ideas for the tach...I'm open to all suggestions!

Thank you guys for all your help on this thread. I kept looking at the tach wire connected to the coil and wondered if that was the problem. When Zaos posted he has seen that be a problem with aftermarket gauges...I knew that was probably the problem. The rev limiting at 6000 felt like an electrical problem and not carburetion.

[Rob S.]

As Mr. Spock would say, "I rejoice in your success." BUT...

Do you know for sure which of the many changes you made fixed the problem? That mid range flat spot can be a tricky one. But if you change the main, the needle and the screw at the same time, you won't know which was responsible for what.

Make sense?

[JohnnyL]

As Mr. Spock would say, "I rejoice in your success." BUT...

Do you know for sure which of the many changes you made fixed the problem? That mid range flat spot can be a tricky one. But if you change the main, the needle and the screw at the same time, you won't know which was responsible for what.

Make sense?

Nope! There is no way to no for sure which change allowed the bike to rev over 6000 RPM unless I connect the tach wire back to the coil and it goes back to not revving over 6000. I'm pretty confident that that little wire was the culprit.

I'm going to start by trying to figure out how I can get my tach to work. Then I am going to take it for a spin. If the tach works, then I will move onto adjusting the mixture screws. After I get the mixture screws adjusted, then I will move onto the mid range(needle adjustment) if necessary. Lastly, I will do plug chops at full throttle to check my main jet.

[Rust_to_Redemption]

Nope! There is no way to no for sure which change allowed the bike to rev over 6000 RPM unless I connect the tach wire back to the coil and it goes back to not revving over 6000. I'm pretty confident that that little wire was the culprit.

I'm going to start by trying to figure out how I can get my tach to work. Then I am going to take it for a spin. If the tach works, then I will move onto adjusting the mixture screws. After I get the mixture screws adjusted, then I will move onto the mid range(needle adjustment) if necessary. Lastly, I will do plug chops at full throttle to check my main jet.

I've always heard to do carb adjustments almost exactly backwards from how you're doing it. Do main jets for top end first, then needle shimming/clip moving for midrange, then low range by float height, then idle by mixture screws last. Cant recall where I picked this up, but it has always worked really well for me to do it in that order. Perhaps someone more knowledgable can chime in on the order/reasons why.

[Rijko]

3. Removed the tachometer pick-up wire from the 2-3 coil and just wrapped the wire around the spark plug wire. Acewell gauge instructions state that this can be done. Since the spark plug wires are shielded, I don't think I'm picking up the correct RPMs. Needle is bouncing around and not responding with revving the engine. Pretty sure this was the problem all along. I'm wondering if I can put a resistor inline for the pick-up wire and reconnect to the coil. Or maybe a need a one way diode? Not sure what to do here.

I wonder if this was the issue, it only measures pulses and
should not interfere with coil operation.
(It was connected to the trigger wire, right ?)
Reconnect the wire, easy confirmation if it was the problem.
If not the issue ... rev counter function restored