Newbe GS550 Fuel Issue

[ITim]

Hey all,

First off I am a newbe to all this, so it could just be something simple, please forgive me if it is. Long story short, bought a 78 GS550E in the fall and have been fixing/rebuilding it all winter. Following BassCliffs site and tones of research from here, I have got the bike to an almost rideable state.

I have taken the bike out a couple of times and the acceleration is pretty good, and idles well after ALOT of work. The issue is when I am cruising and keeping the throttle constant to maintain speed the bike feels like it is chugging, it feels to me like its just getting bursts of fuel instead of a constant flow. It doesn't do this when I hold the throttle open sitting still or up on the center stand going through the gears, only when I am on the road.

I think I have followed everything to the letter from BassCliffs site.
- It has a stock air box and filter
- Air and intake boots are still flexible with no cracks in them.
- stock Jets for VM carbs, with a 4 into 1 exhaust.
- I took apart the petcock, cleaned it and replaced the o-ring connecting to the tank as well.
- Dipped the carbs, replaced the Boot O-rings, Replaced all o-rings for the carbs from Cycleorings, bench synced the carbs and used a manometer for fine tuning.
I still have not done a Plug chop test yet, but not sure if I am experienced enough to read it right anyways.

Dose anyone know if this is a jet problem? Air flow problem? or Pet cock Problem? It might be set to rich, but my lack of knowledge make me unsure of it.

Thanks for any help on this. Sorry if this issue has been address before, in my search I couldn't seem to find a post with this issue.

[BassCliff]

Greetings and Salutations!!

Hi Mr. ITim,

Start by making sure your airbox is sealed properly. You want no leaks at all in the air intake system. It seems you've done a good job with the usual necessary maintenance tasks. Good work.

After ensuring the airbox and air intake system have no leaks, if it doesn't run any better, then we can explore what might be happening with the midrange circuit in the carbs. Have you seen the Airbox Sealing and Air Intake Repair guides? Your bike will be a little different but you'll get the general idea.

I'm going to do this anyway.

Let me dump a TON if 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 Rebuild Series, and the Stator Papers. All of these tasks must be addressed in order to have a safe, reliable machine. 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.

Thank you for your indulgence,

BassCliff

[hampshirehog]

I'd start looking at fuel delivery before anything else. Is the hose to the carb clear of kinks and the vacuum hose solid and on tight (no leaks)?

I presume the tap filter is clean. Have you tried running on prime?

Plus it could be the tank vent is blocked. Try riding with the petrol filler cap off (no recommended with a full tank!).

[Nessism]

Stock jetting and 4:1 exhaust are incompatible.

Please check this list, paying attention to #4... http://www.thegsresources.com/_forum...d.php?t=171846

[BassCliff]

Stock jetting and 4:1 exhaust are incompatible.

Oops, I missed that little detail. Yes, you need to re-jet a bit for the 4-n-1 exhaust. What do you think Ed? Go up 2 sizes on the mains to start since the stock airbox is still in place? The needles will probably have to be raised a little to richen up the midrange. Use the "plug chop" method and read the plugs to make sure you don't run too lean and burn up your motor.

And if there's any question about your petcock, it's always a good idea just to get a new one from Suzuki. They may not be cheap, but you won't have to worry about it for another 20 years or so.


Thank you for your indulgence,

BassCliff

[hampshirehog]

Well I'm going to disagree with Ed and Cliff - at least to start off with. All the 550s I've had (and molested) over the years have run ok on standard jets and a 4-1. Note ok - not 100% but ok. Jetting might / might not be needed later but she shouldn't be chugging just because of a 4-1.

I'd start by trying to eliminate all other causes before heading down the re-jetting route or you'll end up chasing your tail.

[ITim]

Thanks guys for all the help so far, I got some things to consider now for sure.
Bass Cliff thanks for the awesome welcome, and the package.

Ooops...don't hate me, the jets are NOT stock. In my defence the PO told me that he cleaned the carbs, and everything was stock in them, and I took his word for it. I still cleaned the carbs and new o-rings, but never gave a detailed check of the jet number. Anyways I am just going to chalk it up to a rookie mistake on my part by not comparing them to the Spread Sheet in detail.

So with that, after a quick check the main is at 92.5 (stock is 80) and Pilot Jet is 15 (stock 15).
Dose the Pilot Jet need to be upgraded as well with the 4 into 1?
The needles are set at half way (3rd slot)

Ed: Lol thanks for the link, gone over the rest of those rookie mistakes and got them all checked off except for breaks, which is on the to do list already.

hampshirehog: I agree with your point it may not be a direct solution to my issue, but since I have put a bunch of work into the bike already, I would definitely make sure the Jets are upgraded as well. Hopefully now that I know what Jets are on it I'm in better shape.

Filter is clean and I have ran it on prime and still the same problem, so I am leaning towards an Air intake problem or Pet Cock.
I'll try running it with no gas cap to see if that has an effect.

It has a new Air filter in it, and I followed the tutorial on weather stripping the air box. I might still order new air box boots to be safe.

[ITim]

Yup all plugs were replaced for this season. I checked the coil voltage and it was just over 12.0V (12.35 or something) on the input side.

It could still be wiring though, I haven't replaced any of the wiring on it yet. There are a few that have burn spots on them that I still have to look at.

Also had it running in the dark without the tank on and saw no sparks

Since I already have some Dip, I think I'm gonna dip and clean the carbs again to see if that has any effect on it. One reason is I just noticed the 4th cylinder wasn't firing, there was plenty of spark, but still wasn't firing which lead me to believe no gas was getting to it. Its either dirty again, or I have it set incredibly lean.

[mlarue472]

Air Screws

Did you try the four little screws that are on the top of the carbs? I have been having the same problem, and I think the "air screws" are the problem.

They are not air screws they are for fuel on our/my bike. (gs550es) If they are turned too far put they pull too much fuel into the mixture causing the overflow.

try this site it says two rotations up from flat out is enough

http://www.iwt.com.au/mikunicarb.htm