GS550 won't rev past 6000 RPM

[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.

 

[Guest]

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

 

[Steve]

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.

EVERYTHING in the carb is based on float height. If you tune for top end, then change the float height, you will have to re-tune for top end. Same for the needle.

Start with the proper float height. Verify that with and actual check of fuel level with a clear tube held against the carb.

After that, I have heard conflicting reports on the order to tune, but my (semi-)logical mind says to do the idle circuit first. Why? Not too many people are able to start a bike and immediately go to wide-open throttle to check the main jets. Somewhere, you are going to have to use partial throttle to get down your driveway to the street, then get to your testing area. Unless, of course, you have the luxury of doing your jetting checks at a drag strip or a dyno room.

Your pilot jets don't really care what the main or needle jets are. They are the smallest, most-restrictive jets. Yes, they happen to get their fuel through the main jets, but you could remove the mains without affecting pilot operation. The needle jet also draws fuel through the main jet. However, it is much smaller than the main jet, so it also doesn't care what the main jet is, or even if it's there.

<My> preference is to tune from the bottom up. Set the fuel height. Get it to idle. Get your low-throttle and mid-range operating properly so you get get to your main jet testing area. Then get your mains dialed in.

My opinion. Could be wrong. You are getting your money's worth.

.

 

[Rijko]

I'm confused why no one is commenting on my leak down test. #3 intake valve was leaking. Isn't this a BIG problem?

No, up to 5% is considered a healthy engine.

Did you check the width of the contact area on your valve and head ?
Those look wide but hard to tell from a picture.

 

[JohnnyL]

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

Well now I am at a loss as to what was causing the problem. I reconnected the tach wire to the coil(yes trigger wire) and the bike ran fine. Ran over 6000 RPM and up to 11k. However, when putting the tach wire back on the coil, I remember one thing that I forgot to mention...when I had the bike apart, I noticed the trigger wire has a ring terminal on it and it was rotated so that it was very close to the grounding bars on the coil. Is it possible that it was close enough to arc to ground? I don't know but when I removed the tach wire from the coil, I made sure to rotate it away from the ground bar. Maybe this was the problem?

I still have a flat spot at about 5-6k. It struggles to get past this point and then it's a kick in the pants from 6k-9k! Gotta get this figured out. I'm thinking it's needle position but maybe someone can point me in the right direction before I remove the carbs for the 887th time.

 

[Rijko]

4-1 exhausts have a flat spot.
I do not know how bad yours is, but wrapped headers lean out the mixture and the muffler may not be optimal. Not saying that's the issue but it may be a factor.
Happen to know anyone with a AF ratio meter ? Or an original exhaust to compare ?

 

[Rijko]

My guess would be the inline fuel filter you removed played a big part.
Those usually restrict gas flow.

Revving is short term will run from full float bowls, but riding will
empty the bowls which may not be filled in time to sustain higher
revs.

 

[Spyder]

I'm still sticking to the bad ground theory. My bet is needle adjustment for your stumble. You shouldn't have to remove carbs to get at your needle. Though you aren't exactly a stock bike anymore, so maybe you do... I would think that one notch / washer isn't high enough for pods and a pipe.

In my experience, and everything I have read from experts such as Factory Pro. You dial carbs in from the Main on down. Now, of course you have to have all circuits somewhat close so it will run, but fine tuning should be, main, needle, floats, pilot. Just the way I have always done it. But, I also tend to ride that way. I am on my mains more than average I guess. It is here that I envy people with pods. Pulling carb with an airbox SUCKS ! ! !

Glad you're getting her dialed in. Hopefully get to see this beast in person this summer in Brown County...

 

[JohnnyL]

At this point, I really don't care about what solved the issue. I am just really happy that the bike now revs out like it should. I will be working on raising the needles today but I won't be testing it today. It's 41 degrees here and rain and snow are on the way. Yuck....Looking forward to sun and 60 this weekend. Will be doing a lot of fine tuning this weekend. I purchased more plugs and will be doing some plug chops to zero in on that main jet.

 

[JohnnyL]

By the way...I was taking the bike off of the lift yesterday and the bike fell off on it's side. Amazingly, the only thing damaged was the bar end turn signal. I don't know how it didn't incur anymore damage. I ordered a new turn signal at $74.
I thought for sure when I picked it up there would be a huge dent in the tank. That would have killed me.

 

[Guest]

buy yourself 2 lottery tickets! send me one then we can both win.

 

[JohnnyL]

So I removed the carbs this morning. Found that I had two washers on top of the needles as spacers. I removed one and will see how it performs this weekend when it gets a little warmer. It's supposed to hit 47 today so maybe I'll get out yet today.

So here is where I am currently with the carb:
42.5 pilot(stock)
3 turns out on the mixture screws
Needle shimmed with one washer
102.5 Main jet

I found a good article on tuning carbs. It suggests following their steps which start at the pilot circuit. https://www.cycleworld.com/story/bikes/kevin-cameron-explains-how-to-tune-carburetors/