5000 rpm "wall" .....

[jaywelchy]

Hey all,

I am new to the forum, yet have read many tech articles to get some info.

Be patient .. long post, its my first to describe

I have a 1980 GS 550, that like most I picked up neglected but workable. All original, and carbs recently "rebuilt", as the owner wanted it running.

It ran decent, started and idled bad, and at idle would pour fuel out the back of the carb where it met the intake boot. And fouled the plugs very quickly at idle.

The Previous owner paid a shop to do the carbs, and was discouraged by the "wall" at 4000 rpm. The bike wont rev out.

I did my carb rebuild, with good results. Idle .. great .. 1100 rpm all day.
Starting .. great. Hot or cold.
Runs smooth, seamlessly to ... 4000 rpm. The "wall".
( I replaced the pilot jets with factory size .. previous owner went up a size)

I took in to my local bike shop .. owner worked at Suzuki as mechanic in late 70's to mid 80's. Perfect!

After 3 carb overhauls(!), the bike runs like a dang swiss watch ... till 5000 rpm. He even got discouraged, and we split the charges due to the lack of it getting fixed.

He mentioned a vacuum problem ... maybe .. or main jets may have been drilled out. I called it off, as I dont want a 1000 or more repair bill at this point.

I have not replaced O rings throughout carbs .. diaphrams are good.

I have a set of 92.5 jets on the way ... for giggles. Doubt it will change the runability issue. The factory 92.5's are in it now .. may have been drilled out.

I could go on, but at this stage, the bike is a blast ... and I am getting more and more attached to my first old school GS. Put almost 100 miles on it today, with a top speed of 64ish .... Would like to fix it.

So ... any ideas??

And, can I buy some standard slide 38mm Mikunis (new) and convert from CV to standard with good results??

Thanks all!!!

Jason
Salem, Oregon
new GS owner

[bietau85]

if you havent got the bike past 5,000 rpm's you havent had a blast yet, The bike is very happy at 5,000 to 10,000 rpm's. Change ur O-rings man, good reason why you hit a wall mostlikely. including your leaks. I Do not believe that your carbs were re-built the right way if your overflowing your carbs either. Bench sync your floats. Hell tear em off and rebuild them the right way by replacing everything you didnt buy yet. And then bench sync the rail. The butterflies (seq cyl- 3, 2, 1, 4) <--I think thats right. And measure your floats. You will get your welcome into here soon that will explain all that jazz in detail. Oh and I have an 81 550. I pull 2nd gear to 85mph in a blink of an eye. (my sprocket ratio is not stock) Im telling ya you got work to do. Plus You are Very most likely in need of a valve adjustment. Heck when you start it up let it run for about 45 seconds and kill the motor. feel each header pipe. if any are cold you arent firing. If theres a variable temp difference in them thats your carbs and/or valves not set correctly. I bet you will have it 100% by spring though. Takes time, Bloody knuckles, and patience.

[TheCafeKid]

Ok, stick your money back in your pocket. The only way to assure the carbs were rebuilt right is to do it yourself. If the Orings inside weren't replaced, they weren't done right.
Get yourself an Oring kit from:

https://Www.cycleorings.com

Maybe $15-ish bucks shipped.
38mm flatslides are way too much carb for that lil thing.
So get that out of your mind right now

Also, theres some info we need from you:
Stock airbox or pod filters?
Stock exhaust or four into one or aftermarket?
If youre using the stock box, does it have the stock filter?

All these things make a huge difference in how we can help.

But lesson one is:
Wrench it yourself, learn the ins and outs, cause eventually you'll have to.
The sooner the better.

[1_v8_merc]

Is there any vibration at this Wall?
Any noises?

Some inline fuel filters can cause walls if they are too small in diameter.

maybe the carbs needa be sync'ed properly?
Petcock problem or other fuel supply problem?

[jaywelchy]

just downloaded the carb tutorial from Basscliffs site...

Bike is all stock ... has stock:
airbox,
air cleaner,
exhaust.
Jets are 40 pilot, 92.5 main.

the carbs were "rebuilt" 3 times by local bike shop ... (in 2 weeks time)
and they were synced.

There is NO fuel filter in the line ..

Petcock seems to work fine ... runs the same on fuel, resrv, and prm.

Now was it done properly?? I sure dont know ... I know NO parts were added, as there is no charge for parts on my reciept.

When I fire the bike up, all 4 header pipes get hot .. and again, it starts, idles, and runs up to 5000 rpm super smoothly ...

O rings are cheap, I found that site too ... placing order today, got factory main jets coming, and my knuckles are already bloody'd up so time to clean the bench, print out the tutorial and get back in there ...

CafeKid ..... diggin your ZRX??? We have had lots of bikes at the house through the years (wife rides too occasionally), and the ZRX has been in my mind for about the last 2 yrs.

[MisterCinders]

On top of the info that CafeKid noted, what throttle position are you in when you hit this "wall"?

Carb jetting follows throttle position, not RPM. If your jetting at the mains is bad, then you will hit a wall at WoT, which might explain your problem at high RPMs.

[jaywelchy]

On top of the info that CafeKid noted, what throttle position are you in when you hit this "wall"?

Carb jetting follows throttle position, not RPM. If your jetting at the mains is bad, then you will hit a wall at WoT, which might explain your problem at high RPMs.

WOT is possible, as long as the rpms are below the wall of 5000. I can roll onto WOT in any gear, and it pulls smooth and hard till 5000, then its a matter of feathering on/off in tiny increments on flat ground to maintain 5100.

Once I hit the 5000 rpm area, no matter throttle position, it wont push farther ... Its like pulling the choke out all the way. Matter of fact, I pulled the choke out fully when it was at the wall, and nothing changed .. sputter, powerloss, no weird noises just no power ..

As soon as I back off throttle, dip under 5000 rpm it goes again ...

Its like a built in governor!! (would make a great first bike .. ha!)

[trippivot]

does the timing advance work correctly? Get an inductive timing light and witness that event for sure.

Is the exhaust completely clear of hidden obstructions

Rev the engine , shake the bike and feel the exhaust to see if something is hidden inside the muffler getting thrown up when hi flow is needed. like a flap of rusty metal.

same thing in the intake no flaps or gloves on top of the air intake snorkel.

I know it seems off track but these are good ideas that have not been mentioned about being checked and verified.

[salty_monk]

You might also want to check out the ignitor or replace it with a Dyna S... if rebuilding the carbs properly doesn't fix it & the advancer is working fine.

I chased carb issues for months on my 80-1000g only to eventually find out it was an ignitor going bad. Dyna S was the fix.

[BassCliff]

Greetings and Salutations!!

Hi Mr. jaywelchy,

Sorry I'm a little late with this. Before I get to it, let me offer one more possible scenario. If it's not carbs, timing, igniter, etc, I have heard where mis-timed valves can cause the engine to "hit a wall". If a cam is one tooth off, it won't be opening/closing at the proper time.

Anyway, let me dump a TON of information on you and share some GS lovin'.

I just stopped by to welcome you to the forum in my own, special way.

If there's anything you'd like to know about the Suzuki GS model bikes, and most others actually, you've come to the right place. There's a lot of knowledge and experience here in the community. Come on in and let me say "HOoooowwwDY!"....

Here is your very own magical, mystical, mythical, mind-expanding "mega-welcome". Please take notice of the "Top 10 Common Issues", "Top 15 Tips For GS Happiness", the Carb Cleanup Series, and the Stator Papers. All of these tasks must be addressed in order to have a safe, reliable machine. This is what NOT to do: Top 10 Newbie Mistakes. Now let me roll out the welcome mat for you...



Please click here for your mega-welcome, chock full of tips, suggestions, links to vendors, and other information. Then feel free to visit my little BikeCliff website where I've been collecting the wisdom of this generous community. Don't forget, we like pictures! Not you, your bike!

Thanks for joining us. Keep us informed. I will put you on my prayer list.

Thank you for your indulgence,

BassCliff

[hampshirehog]

Try running it with the petrol cap off - could be a vacuum is forming in the tank and she's not flowing enough petrol as a result.

[jaywelchy]

Pictures ..! Man I just about forgot ... I am a picture hound myself, so here is before and as it sits now. Not going to go too far with changes, just a fan of clean and simple.


Did some seat .. "work", cleaned and painted a few really discolored parts, and overall just took off anything I found offensive. Went through all the parts, wheels, swingarm, etc and cleaned, greased and such. Just having fun with it.

[jaywelchy]

Ok .. here we go ... when I brought it home.


Pic looks decent ... everything was so weathered on the bike, I felt so sorry for it. All aluminum is severely etched and discolored, all cables were rotten ... but it was all there, and I new I could bring it back and have a fun little ride.

[jaywelchy]

Wow!! Thx so much for the welcome Basscliff ... holy cow, the info is overwhelming in a great way.

I got some work to do .. and will hold off on more silly questions until they are valid.

My GS has 22,000 miles on it ... and without knowing the history, and of course how I found it, I think its wise to go through from head to tail following the information provided in here.

Forums like this keep things alive ... awesome to see.

I am also building an aircraft, that without the forum we have there, wouldnt be possible.

Super happy to be here.

Jason

[AJ]

I bet this is carbs, not ignition, probably not valves either (shim over buckets, right?). Not terribly high mileage. I put 55,000 miles on my 1977 550e before selling it with a spare motor that the new owner never even picked up.

Assume this is CV carbs. Are these the weird "siamesed" carbs of the later 550? I know a lot about those.

Others have given you good advice about replacing the o-rings and such.

Look to see that the the larger passageway at the air-intake side of the carb to the underside of the diaphragms is not blocked. This is the oval port at the top of the tube on the airbox side. I have seen carbs where someone incorrectly put a rubber plug in that port, which keeps the slides from lifting and keeps the carb from transitioning onto the main circuit.

Another thought is to check the needle positions. Some bikes actually put a rubber o-ring under the needle clip. When that o-ring goes, the needle drops down and checks the fuel flow for the high-speed circuit.

Patience. You will get this working and when you find out what the problem was, you will be happy.