GS550 Acting Over-Jetted

[leecatd8209]

Hey all!

My recently acquired GS has a pretty nasty part throttle high speed misfire. It's been well kept, and was recently gone through quite extensively. It starts fine, idles great, and runs like a raped ape all the way up to the top of 4th gear. After that it gets quite sluggish, and sometimes struggles to recover, then develops a hard start.

It's been rewired, has new carb boots, plugs look normal, and I'm not getting too many fuel smells or anything.

The PO gave me a copy of the ad from when he purchased it, and it states that it's been jetted (haven't confirmed, I really don't want to tear into the carbs), and has a K&N intake (It for sure has a K&N filter in the stock location). The PO and I have very different riding styles, so I doubt if he ever even came across this issue.

After reading, and digging around a bit, it seems like it could possibly be over-jetted, especially since it's still sporting the stock exhaust. I have a Kerker 4-1 laying here that I would like to put on sometime, but I'm wondering how likely it may be to at least somewhat correct my problem?

She's got 8400 miles, and I hope to enjoy many more

 

[Steve]

Even with a K&N insert in the stock airbox, your jetting needs should not have changed. Your pipes appear to be stock as well, so no changes there, either.

One way to confirm your jetting is to put it in fourth gear at a relatively low speed (20-25?) then open the throttle all the way. When it starts feeling "bad", hold it there for a few more seconds, then hit the kill switch, pull the clutch and coast to a stop in a safe place. Pull your plugs and check the color.

It's also possible that the problem might be electrial, not fuel-related, checking plug colors will be the first step in determining that.

When you put the Kerker on, you might have to re-jet a bit, how much will depend on how loud the muffler is.

.

 

[leecatd8209]

An electrical issue seems somewhat likely the more I dig into it. The plugs are a perfect light grey, and it just runs so well everywhere else in the range. This sounds like it's gonna be fun to track down.

 

[Gumpster]

I had a similar situation and it turned out to be the petcock. Check the fuel flow and the vacuum line. Just a thought.

 

[leecatd8209]

I've been meaning to look into that anyway as this one is a bear to turn. Thanks for the tip!

 

[fbody_mike]

I had a plugged gas cap cause that exact problem. After a fast pace it would die and not restart. It wasn't till I was checking if there was gas in the tank did I hear the whoosh from the vacuum that had formed.

 

[leecatd8209]

A quick update. After a busy day I cleaned the plugs and put them back in, gassed her up, and took it out for a spin.

It ran bad, worse than other times I've ridden it. Still started fine, and idled well, though. I tried applying the choke at throttle to varying degrees, with no change. I also tried running it in prime, and reserve on the petcock with no change. There's an inline filter from the petcock to the carbs, it's clean, but I'm wondering if maybe it's restricting flow.

First I'm gonna take the ignition switch apart, and see what there is to see in there.

 

[leecatd8209]

SOOO. I messed around with the inline fuel filter. Blew through it, and noticed it was installed backwards. I reinstalled it in the correct orientation, and saw a marked increase in performance, but the problem didn't really go away.

My test drive revealed a new issue. At higher RPMs the turn signals will start flashing MUCH faster, so it looks like I'll be getting the DVOM out sooner than I had hoped.

My dreams of riding this thing for the Summer are slowly fading away.

 

[Steve]

I would suggest ditching the fuel filter. :-k

There is a filter inside the tank at the petcock and another filter at the inlet for each carb.

Also, consider that many of the aftermarket filters that are found on bikes are actually made for cars. What's the difference? Virtually all cars on the road today are fuel injected. They run a rather high fuel pressure (40-50psi), MUCH higher than our bikes have, which is just the force of gravity in about a one-foot drop. There simply isn't enough pressure to force the fuel through the rather restrictive filter media. If you feel that you really MUST have a filter, get one for a lawn tractor. Most of them have gravity-fed fuel systems, too, so should work reasonably well.

.

 

[Mr.humbucker]

I am not to the level of many here but I have two of the same bikes that I have restored and two more 550L models as well. Kind of fell into a familiarity rut restoring them ... nonetheless I have torn the carbs down for each one and was glad I did as 37 years is a long time for these gas drinking bikes to be on the road. Most had their carbs overhauled to some degree, some were better than others. I have had NO problems with any of these bikes once I cleaned the carbs. Each time I did I checked the specs (see photo/cahrt) for the jets etc to ensure they were the proper stock items. Clean what you have if they're the right ones, don't bother getting new ones, old but clean ones work just fine. My suspicion is that if you do this and ensure your airbox is clean, tight and that you have the proper seals (new) on your manifolds aka boots, as well as a clean petcock in your tank my bet is your problem will be no more. E sure to tear them right down but do not take out the throttle plates .... they're impossible to put back in for me at least. There are a few good You Tube videos on how to and a lot of very good sets of instructions here.

if the is chart is too small you can find it on the forum or through Google.

Try this link ... http://gsarchive.bwringer.com/bikecliff/images/carbspec_float_height.html#A01

 

[tkent02]

What Mr Humbucker said. I have never found an old bike with questionable maintenance that didn't have something wrong inside the carbs. Something clogged, something adjusted wrong, something worn out, something broken, something jetted wrong, something leaking, something hardened, something cracked, or more likely a little bit of each... Take it apart and see what's inside.

 

[cornishgs]

It could be worth doing a coil relay mod as others have done .
sometimes voltage to coils can be iffy on old wiring looms and its difficult to distinguish from carb faults fueling.
symtoms such as misfires, bad starting, no revving can all be down to voltage to coils being bad

 

[leecatd8209]

Alright, I decided to dig into it further, and I've got the carbs out without too much trouble. I want to have the rebuild parts on hand before I decide to tear them down. However, I'm having some trouble finding stuff to fit the BS32s. Seems the early bikes get all the support.

I guess while it's torn down and still early in the season I might tear into the wiring, and upgrade that, probably go to electronic ignition at the same time.

Any advice?

 

[Guest]

Read this: http://gsarchive.bwringer.com/mtsac/~cliff/storage/gs/Mikuni_BS-CV_Carburetor_Rebuild_Tutorial.pdf

Written by a member here, and the best guide I've ever seen for these carbs. Also note the reference in the guide to 'cycleorings', supplied at a very good price by another member.

If you're lucky, you won't need anything else. If you find the wrong jets have been fitted (http://gsarchive.bwringer.com/bikecliff/images/carbspec_float_height.html#A01), ask here and someone should be able to help, or point you to a supplier.

 

[leecatd8209]

Read this: http://gsarchive.bwringer.com/mtsac/~cliff/storage/gs/Mikuni_BS-CV_Carburetor_Rebuild_Tutorial.pdf

Written by a member here, and the best guide I've ever seen for these carbs. Also note the reference in the guide to 'cycleorings', supplied at a very good price by another member.

If you're lucky, you won't need anything else. If you find the wrong jets have been fitted (http://gsarchive.bwringer.com/bikecliff/images/carbspec_float_height.html#A01), ask here and someone should be able to help, or point you to a supplier.

You're the man! :beer:

 

[Mr.humbucker]

Here are a few good Youtube video's that will help guide you. https://www.youtube.com/watch?v=aidJvpMTiIo This guy is quite interesting and plays some funky tune overtop of the work.
Here's another .... https://www.youtube.com/watch?v=dD3UWtLfzX4
And the last good one ... https://www.youtube.com/watch?v=TGqUAtsP3_o

I use an ultrasonic cleaner, simple spray carb cleaner and and a good JIS screwdriver (phillips style) Japanese Industrial Standard I believe. They're different than the North American philips screwdriver. The other KEY is a new 3/16th long shaft screwdriver worth about $5 at a half decent hardware store. This will be the key to removing the pilot jet. Those little buggers can be a bit of a challenge. Heat up the surrounding part of the carb where they're sitting if you experience much resistance. This 3/16th screwdriver are also perfect for the air/fuel screw removal. Make sure you clean out each little passageway. The bottom of the pilot jet is tiny - a wire from a bread bag/twist tie is usually the right size. Be patient, take the time to clean it all including the passageway in the float bowls as they get clogged and you may miss this in a superficial cleaning. Be sure to blow compressed air through all passages when you finish to ensure they're clear and free of water ... it doesn't burn well

I always get my O Rings from Cycle O Rings (mentioned here) and I get new plugs off ebay:
https://www.ebay.com/itm/Suzuki-carburetor-CARB-RUBBER-PASSAGE-PLUGS-gs1100-gs1000-gs850-gs750-gs650-oem/292243134260?hash=item440b0c5734:g:sx8AAOSwt0tZd-7p

Lastly I replace the screws with stainless caps screws cuz they're easy to work with and look nice 40 of these https://www.boltdepot.com/Product-Details.aspx?product=6408 and 8 of these https://www.boltdepot.com/Product-Details.aspx?product=6417

Good luck - you'll be glad you did this as long as you take your time and don't "force" anything - that's when I usually bugger up a jet... I got a lot of help from the fine folks here

 

[leecatd8209]

Awesome, thank you for the advice. O-rings are on order, and then once I get them apart it'll be time to order jets. I've rebuilt a few quadrajets in the past with varying degrees of success, but I attribute some of the to them just being worn out.

My biggest fear is the throttle shafts leaking when I get done, but hopefully I can tune most of that out if it does occur. I'm not looking for peak performance, it'd just be nice to have the option to pass somebody if I need to, haha.

 

[Guest]

Awesome, thank you for the advice. O-rings are on order, and then once I get them apart it'll be time to order jets. I've rebuilt a few quadrajets in the past with varying degrees of success, but I attribute some of the to them just being worn out.

My biggest fear is the throttle shafts leaking when I get done, but hopefully I can tune most of that out if it does occur. I'm not looking for peak performance, it'd just be nice to have the option to pass somebody if I need to, haha.

You don't need to take the throttle shafts out unless the bushings are worn. At 8,400 miles I doubt they are.

 

[leecatd8209]

Tomorrow's the big day, the last of the parts arrived, hoping I can take it for an evening cruise.

Wish me luck!

 

[leecatd8209]

I got the carbs all cleaned up, and put back on. I seem to have a vacuum leak between the carb boots and the head. The boots, as well as the O-rings are new and installed tightly.

Any common stuff I should hunt for?

Edit: Big vacuum leaks fixed. It still comes down tonidle a little slow, though.

Now it won't start once It's hot, and I got a couple backfires through the exhaust. Time to play with the valves I suppose.