'80 550L Gutter on Decline: Petcock?

[GSinDC]

When I first got this bike, riding it in city traffic (With many stops, many abrupt) I noticed that at a stop the idle would drop quickly and could gutter out. Giving it a hit of throttle with the clutch in would prevent it from guttering. This doesn't happen all the time, or predictably, but whenever it does a hit of throttle clears it up.

Today I pulled into a steep decline (going into a underground parking garage), and almost immediately the bike guttered nearly to a stall. Hitting the throttle hard (and maintaining for a few seconds) kept it going, but it was like the problem I described above on steroids. I had just filled the bike up with gas.

I know one of the recommended service things for a newold GS is a petcock replacement. Could a faulty or struggling petcock be the culprit here? Gas shifting in the tank away from the intake (excuse me if I am using the wrong terminology here), with a weak petcock, causes the fuel flow to slow?

If so... does the petcock #4357 at http://www.crc2onlinecatalog.com/petcock_suzuki.htm include everything I would need to replace? Is this something a newb without a lot of repair experience could do?

Or other theories?

 

[spyug]

First things first. When were the carbs last cleaned? If they haven't been done in recent memory they likely need a strip dip and rebuild with new o-rings. The petcock could be an issue but the carbs get the fuel into the cyclinders and if they're gummed up its not going to run right and issues will occur.

Start there. Cleaning carbs is not hard and the tutorials take you through it step by step.

Good luck,
Spyug

 

[cowboyup3371]

After doing what Spyug suggests make sure you do the valve adjustment, PROPERLY synch your carbs (both bench and on the bike), and then adjust your mixture screws by the highest idle method.

 

[GSinDC]

Thanks for the advice gentlemen. I seem to recall the previous owner saying he had the carbs cleaned and the floats redone, but I think that was before the bike went basically into storage on a battery tender for about a year. I'm sure it could stand doing again.

The page I found that I think is the carb cleaning process is http://www.thegsresources.com/gs_carbrebuild.htm.

This looks like disassembly, cleaning, and reassembly. This looks like a complicated (and high risk, for someone with a running bike and low tech skills) procedure to me. Is all of this required for cleaning? I don't have a garage and don't have a store of tools, so it would be quite an undertaking for me to do this one. I'd also be concerned about not getting my bike back up and running, particularly as it is one of my primary modes of transport!

Any thoughts? Is there a simpler carb cleaning procedure I've missed somewhere? I am so green to this... the tutorial above starts with the carbs already off the bike. Just removing the gas tank and draining all the necessary fluids is a daunting procedure for me!

 

[cowboyup3371]

Yes this is what is required and NO it's not that difficult. Get the can of Berryman's, order the orings from www.cycleorings.com, and get yourself some jars or an egg carton to store the things you take out. Give yourself 24 hours FOR EACH CARB and you'll do fine.

Honestly, if you don't do it this way you will be looking at continuous problems for some time to come. Take the time now and do everything right the first time.

 

[Gonzo]

I just did my first carb clean and honestly it's not hard at all. It looks daunting because of so many parts that you need to keep track of and keep with the respective carb they came from, but it's honestly not hard at all. Prep work will go a long ways into making the process much easier. That's where I screwed up. Not planning out just what I needed, so nearly everyday I find myself ordering some small part or making a trip to the parts shop for something that I should have seen coming.

Idk what to do about the garage, but as far as tools, if you plan on owning that bike for any amount of time, get some. Otherwise you'll have nothing but problems that need solving and a bike shop likely will not do it right and they will charge you your first born to do it wrong too. Tools are an investment. If you never need to use it after the first time, that's great. Nothing has broken. But if you need it, well, you have it.

 

[cowboyup3371]

Yea, tool wise you'll only need a set of screwdrivers, metric socket set, 1/4" drive ratchet to start but I'd recommend getting both a 3/8" and 1/2" for other jobs, and a pair of pliers.

 

[BassCliff]

Hi,

This looks like a complicated (and high risk, for someone with a running bike and low tech skills) procedure to me... I don't have a garage and don't have a store of tools, so it would be quite an undertaking for me to do this one.

OK, let's be real. So you bought a 30 year old motorcycle that hasn't run in a year? It's an old machine that needs maintenance. To be honest, you'll have to learn how to fix your motorcycle or sell it and buy something new that needs no maintenance for a while. You don't even want to take your bike to a shop for an oil change. There have been a dozen horror stories just this week about how bike shops and dealerships have messed up a lot of members' bikes.

Tell you what, dump a half a can of Sea Foam in a tank of gas a couple of times. See if that clears up your carbs a little bit.

But if you don't learn how to fix your bike, it won't run for very long. Download a manual, read the information on my website, arm yourself with knowledge, and seek the experience of the community here. Then you will be able to enjoy your classic motorcycle. See this thread: Top 10 Newbie Mistakes

And have a look at Mr. Nessism's new carb rebuild tutorial:

[FONT=Verdana, sans-serif]Mikuni BS(CV) Carburetor Rebuild Tutorial
[/FONT](by Mr. Nessism)


Thank you for your indulgence,

BassCliff

 

[GSinDC]

Alright team. I'm convinced. I've got the Clymer manual, the original manual PDF, two different and equally awesome tutorial PDFs from the forum.

I've got my dad's garage and all his (ancient) tools, plus the hand tools I already own (more for carpentry than engines, but a screwdriver is a screwdriver).

In the next couple weeks I am going to block out some time and do this. I'm assuming I need to drain the bike dry (oil and gas) before I take the fuel tank and the carbs out?

After reading through several times, the only part that still flummoxes me is setting the float. I think syncing the valves seems doable, as does tearing apart and rebuilding. I guess part of the problem is that I don't really understand what the float *means*. I certainly understand why the valves need to be synced, but the float evades me.

Thanks for your support. I've already put a few hours into working on this bike (did my first oil change myself! and it was dirty but worked, took apart rear brakes, etc) and I really enjoyed it, so I'm hoping to enjoy many more hours. Hopefully this will eventually be old hat!

 

[BassCliff]

Hi,

That's the spirit!

The "floats" in the carb do just that, they float on the gas in the bowls. When the fuel level in the carb bowls gets high enough for proper operation they close a little valve that cuts off the flow of gas from the fuel line. Then as the gas gets atomized and drawn into the cylinders for combustion, the fuel level in the bowls goes down. Then the floats go down, and the float valves get opened to allow more fuel into the bowls.

The proper fuel level needs to be maintained in the bowls so that the carbs are able to provide an uninterrupted flow of fuel/air mix to the cylinders.


Thank you for your indulgence,

BassCliff

 

[tom203]

Basscliff said.....(maybe sarcastically)

"Tell you what, dump a half a can of Sea Foam in a tank of gas a couple of times. See if that clears up your carbs a little bit. "

Bike sat for a only a year- nothing to lose by trying the Seafoam- it sometimes improves things and afterwards further running might help. You can always dive in later, when you have no other options!

 

[BassCliff]

Hi,

Basscliff said.....(maybe sarcastically)

"Tell you what, dump a half a can of Sea Foam in a tank of gas a couple of times. See if that clears up your carbs a little bit. "

That was a serious suggestion. I use Sea Foam occasionally as maintenance. Although I've read where the Amsoil "Quickshot" or "Performance Improver" products and the BG44K fuel cleaners work better, I've been happy with Sea Foam. But none can really do as good of a job as physically disassembling and dipping the carbs.

Thank you for your indulgence,

BassCliff

 

[Gonzo]

On the screwdriver is a screwdriver comment, this is a half truth in the case of our old bikes. There is a Japanese philips screwdriver that fits the screws on these bikes properly versus what we are used to using. I stripped out a TON of screws before I found that out. If you plan on reusing them old screws, I suggest you get one so you don't turn them into cheese. Lots of the members here have made/are making the switch to allen bolts however. Just a lil tip that you didn't ask for but should know.

 

[don]

My idle on my 550 would drop when I had the bike running on the center stand then pushed it forward to knock it off the center stand. Problem was simple, Floats were set just a smidge too high. Gas would splash up into the system and temporarily drown the bike.

If a complete cleaning is a bit out of your reach at the moment, start with a small task like resetting the floats to factory settings. You don't have to take the carbs all apart, but it will get you used to taking them off.

 

[cowboyup3371]

On the screwdriver is a screwdriver comment, this is a half truth in the case of our old bikes. There is a Japanese philips screwdriver that fits the screws on these bikes properly versus what we are used to using. I stripped out a TON of screws before I found that out. If you plan on reusing them old screws, I suggest you get one so you don't turn them into cheese. Lots of the members here have made/are making the switch to allen bolts however. Just a lil tip that you didn't ask for but should know.

+1. At the very least use a number 3 phillips...that's about as close as you'll get.

 

[GSinDC]

My idle on my 550 would drop when I had the bike running on the center stand then pushed it forward to knock it off the center stand. Problem was simple, Floats were set just a smidge too high. Gas would splash up into the system and temporarily drown the bike.

If a complete cleaning is a bit out of your reach at the moment, start with a small task like resetting the floats to factory settings. You don't have to take the carbs all apart, but it will get you used to taking them off.

This sounds exactly like my problem. Truth be told, guy who sold it to me said something about "carbs.... floats.... when i got it...", but at the time I didn't even know what those things meant (even less than I do now, if you can imagine it) so it just made no sense to me.

Its possible he got the carbs cleaned and assembled, or had the float set a little too high... the quote above sounds exactly like my problem.

My Clymer guide doesn't give a lot of detail about setting the floats- is there a guide for that somewhere? Outside of doing a complete carb rebuild?

 

[mike_of_bbg]

There are a few potential causes for the old "idle stumble". Let me offer a few suggestions - though you should clean your carbs and check your float heights (do some forum searches on the subject of float height - you can use a thin clear sharpened tube shoved in the bowl drain plug threads). You should also verify the proper operation of your petcock - particularly that there is no fuel in the vacuum tube.

Check your voltage at the coils. The stator puts out less power at idle, and the bike voltage can drop because of it. If you're already low at the coils you can get weak spark. The ever-so-common coil relay mod is an easy fix. Go through the whole stator papers test procedure. Maybe it's just me, but the smaller 4 cyls seem to charge high, and this can cause burned out ignition components; particularly ignitors. You'll want to head that off if you can. You should also check the resistance on your plug caps. Stock ones ran about 10k ohms, most of the NGKs we use as replacements are 5k ohms. When they go bad the resistance can jump up into hundreds of thousands of ohms and really restrict your spark.

You need to do a vacuum sync (when was the last valve adjustment? if it's time that needs to be done first). At idle the butterflies are BARELY open. Just having them off a little bit can cause one of your cylinders to be too far closed, suck in too much fuel and foul out. Pull your plugs and have a look (feel free to post your pics here and have the masses take a look). If the insulators are turning charcoal grey this is a good bet. Combined with a rich mixture this gave me headaches (plus low coil voltage, which didn't help the stumble and made the bike a bear to re-start). This will be more pronounced too when the air is hot and less dense.

If only the #2 plug seems very rich that could definitely indicate petcock issues.