GS550 won't rev past 6000 RPM

[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.

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[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.

[erki52]

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/bik...e-carburetors/

[JohnnyL]

Just went for a quick ride. It is much better in the mid-range but still a slight hesitation crossing 6000 RPM. Is it possible I would have to remove all the washers above the needle? Currently have one washer.

[Steve]

So I removed the carbs this morning. Found that I had two washers on top of the needles as spacers.

Just to be clear, that is ONLY two washers above the e-clip?

No nylon spacer, just the two washers?

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[JohnnyL]

Just to be clear, that is ONLY two washers above the e-clip?

No nylon spacer, just the two washers?

.

Yes. That is correct.