1981 GS650G sat for almost 20 years

[KiwiAlfa156]

Darryl, I know you’re “down under” but I’m sure you meant to say that the ignition cover is on the RIGHT side of the engine. We always talk about Left/right and cylinder/carb #’s 1234 from the POV of sitting on the bike.
We don’t want him taking off the stator cover just yet.

and I know this is off-topic and nothing to do with getting this bike running, but could we see some pics of the 750S, maybe in another thread. We (I?) never ever see those.

Thanks Rich, water does go down the sink the 'wrong' way down here. And we do ride on the 'wrong' side of the road. But yes the cover on the right. Sorry for the confusion . To confirm the RIGHT HAND side of the engine.

And as not to hijack the thread. Here's some short vids of the 750S rebuild.

https://youtube.com/playlist?list=PL8uxA1sXaolrpS91MUFBqWrKyCsEpDKq0&s i=OMR-j1-2x8CSHAUz

[Rich82GS750TZ]

Thanks for that, a fun watch. No fluff, just the highlights. Hard to believe Suzuki made that bike the same year as my 750T. The S is like the T's evil twin. Beautiful job.

[bbrad1775]

Mad some solid progress today. New plugs and oil. Got the petcock freed up but still not sure if it's actually working though. I did get the bike to run for a couple seconds but that is it and then it won't start again.

Once again I have questions.

I set the petcock to prime to fill the bowls. At what point should I switch this to on? Also, when should I pull the choke?

how can I test the petcock?

Had fuel over flow from the far right carb. What does this mean? Is it just flooded?

While trying to start I noticed the positive side on the battery cable was getting pretty hot. I think this may be from extended attempts to start but could this be a sign of something else?

I figure the next is to pull the carbs and clean them. Is there a good write up on how to pull the carbs out?

[KiwiAlfa156]

Mad some solid progress today. New plugs and oil. Got the petcock freed up but still not sure if it's actually working though. I did get the bike to run for a couple seconds but that is it and then it won't start again.

Once again I have questions.

I set the petcock to prime to fill the bowls. At what point should I switch this to on?

The PRIME position by-passes the vacuum-tap and fuel will flow without the engine running (and creating vacuum in the no. 2 inlet tract which is connected to the petcock and opens the tap). You can leave the tap in PRIME until it starts, or if you have a fuel overflow problem (as you mention below) you can turn it to ON as soon as the carb bowls are full.

Also, when should I pull the choke?

The choke should be put to full BEFORE you hit the starter button. DO NOT open the throttle with the choke applied. The 'choke' is actually a separate cold enrichment circuit (a mini carburetor) that requires full vacuum from the cranking engine to work. If you open the throttle you destroy the vacuum to the enrichment circuit and it doesn't flow fuel.

How can I test the petcock?

Run a long hose to the fuel tap outlet into a suitable container, run another to hose the vacuum spigot. Test the tap. PRIME - fuel should flow. ON - no fuel unless you suck on the vacuum hose, stop sucking on the vacuum hose the fuel should stop flowing. Repeat this in the RES position. You should get the same result. If you get a mouthful of gasoline, the diaphragm in the tap is shot.

Had fuel over flow from the far right carb. What does this mean? Is it just flooded?

First positively identify the source of the leak. Is it from a vent hose? Is it from the carb bowl gasket or is it from the junction pipes (fuel gallery) that connect no.3 (RH inner) and no.4 (RH outer) carbs? If its the pipe, its likely to be the o-rings on the junction. If it from an hose or weeping around the bowl gasket, its likely to be the needle valve -either worn or stuck open. Fixed by replacing or cleaning.

While trying to start I noticed the positive side on the battery cable was getting pretty hot. I think this may be from extended attempts to start but could this be a sign of something else?

Starter draws a lot of current hence the thicker gauge wire. Prolonged cranking can cause heating on old positive starter leads. If the lead gets hot without cranking it will be shorting somewhere and that should be fairly obvious.

I figure the next is to pull the carbs and clean them. Is there a good write up on how to pull the carbs out?

If its the standard airbox some wrestling will be required. In broad terms, the procedure is to remove the tank and anything that will get in the way. Disconnect throttle and choke cables. Loosen the hose clamp between the air filter box and the plenum chamber that contains the 4 hoses feed air to the carbs. This 'should' allow the plenum chamber to slide backwards (alternatively you could remove the air filter and box). Unbolt the plenum chamber mounts and loosen (all the way) the hose clamps between the plenum hoses and the carbs and pull the plenum box backwards away and off the carb set bell-mouths to gain the meagre clearance afforded. Next is to loosen all the way the inlet hose clamps between the head and the carbs. The rubber hoses on both sides of the carbs are likely to be colder and harder that a Nuns heart on a Sunday, so trying to make everything rubber a little more pliable with a hairdryer (don't use a hot air gun unless it can be turned down very low - these are for burning and melting things). Next you need to pull the carb set from the inlet hoses. This is likely to not to be an easy task after all these years.



Once you get the carbs free from the inlet hoses, you will discover there isn't enough room between the front and rear hoses easily pull the carbs out the side of the bike. They will come out, but it takes some tilting of the carb set and deformation of hoses (hence the hairdryer) to get them out - and back in. You will be left sweating, but if you take it methodically and look where the carbs are catching on the hoses you will eventually get them out. Just the effort of doing this, should ensure that you do a surgical cleaning job on the carbs. Only a sado-masochist finds joy in pulling carbs from a bike with a standard air box. On the plus side it does get easier the more often you do it. Just on other tip, the bracket that holds the throttle and the one that holds the choke cable can be removed easily as they are only held in with one or two screws that hold the diaphragm covers on. Removing them before pulling the carbs gives you more clearance for extraction and refit.

[bbrad1775]

The PRIME position by-passes the vacuum-tap and fuel will flow without the engine running (and creating vacuum in the no. 2 inlet tract which is connected to the petcock and opens the tap). You can leave the tap in PRIME until it starts, or if you have a fuel overflow problem (as you mention below) you can turn it to ON as soon as the carb bowls are full.



The choke should be put to full BEFORE you hit the starter button. DO NOT open the throttle with the choke applied. The 'choke' is actually a separate cold enrichment circuit (a mini carburetor) that requires full vacuum from the cranking engine to work. If you open the throttle you destroy the vacuum to the enrichment circuit and it doesn't flow fuel.



Run a long hose to the fuel tap outlet into a suitable container, run another to hose the vacuum spigot. Test the tap. PRIME - fuel should flow. ON - no fuel unless you suck on the vacuum hose, stop sucking on the vacuum hose the fuel should stop flowing. Repeat this in the RES position. You should get the same result. If you get a mouthful of gasoline, the diaphragm in the tap is shot.



First positively identify the source of the leak. Is it from a vent hose? Is it from the carb bowl gasket or is it from the junction pipes (fuel gallery) that connect no.3 (RH inner) and no.4 (RH outer) carbs? If its the pipe, its likely to be the o-rings on the junction. If it from an hose or weeping around the bowl gasket, its likely to be the needle valve -either worn or stuck open. Fixed by replacing or cleaning.



Starter draws a lot of current hence the thicker gauge wire. Prolonged cranking can cause heating on old positive starter leads. If the lead gets hot without cranking it will be shorting somewhere and that should be fairly obvious.



If its the standard airbox some wrestling will be required. In broad terms, the procedure is to remove the tank and anything that will get in the way. Disconnect throttle and choke cables. Loosen the hose clamp between the air filter box and the plenum chamber that contains the 4 hoses feed air to the carbs. This 'should' allow the plenum chamber to slide backwards (alternatively you could remove the air filter and box). Unbolt the plenum chamber mounts and loosen (all the way) the hose clamps between the plenum hoses and the carbs and pull the plenum box backwards away and off the carb set bell-mouths to gain the meagre clearance afforded. Next is to loosen all the way the inlet hose clamps between the head and the carbs. The rubber hoses on both sides of the carbs are likely to be colder and harder that a Nuns heart on a Sunday, so trying to make everything rubber a little more pliable with a hairdryer (don't use a hot air gun unless it can be turned down very low - these are for burning and melting things). Next you need to pull the carb set from the inlet hoses. This is likely to not to be an easy task after all these years.



Once you get the carbs free from the inlet hoses, you will discover there isn't enough room between the front and rear hoses easily pull the carbs out the side of the bike. They will come out, but it takes some tilting of the carb set and deformation of hoses (hence the hairdryer) to get them out - and back in. You will be left sweating, but if you take it methodically and look where the carbs are catching on the hoses you will eventually get them out. Just the effort of doing this, should ensure that you do a surgical cleaning job on the carbs. Only a sado-masochist finds joy in pulling carbs from a bike with a standard air box. On the plus side it does get easier the more often you do it. Just on other tip, the bracket that holds the throttle and the one that holds the choke cable can be removed easily as they are only held in with one or two screws that hold the diaphragm covers on. Removing them before pulling the carbs gives you more clearance for extraction and refit.

Awesome! Thank you for all of that great info. Might have time to tear into it more this weekend.

Probably just going to do a full rebuild on the carbs since I have them pulled off. What carb rebuild is everyone using?

Here is what I am thinking:

Pull carbs and rebuild.
Go ahead an replace petcock since I will already be there.
Check for any dry rotted air or fuel lines.
New UNI air filter.
Test charging system.
New shocks.
New tires.
Check brakes and change fluid.
Change fluid in both gear boxes.


Is there anything I am missing?

[Pewpew82]

What carb rebuild is everyone using?

https://www.thegsresources.com/_forum/forum/consumer-information/gs-parts-and-services/1703182-mikuni-bs-cv-and-vm-o-ring-kits#post1703182

[tom203]

Get a new petcock…..Georgefix has got them…made in Japan ..about $55…skip the Chinese copies
get a new air filter element UNI -2440 fits the 650 shafties..about $25….hopefully your old filter element still has internal plastic cage…avoid losing it! It’s aD-shaped element ..
without properly cleaned carbs, starting will be difficult, decent running impossible !
As mentioned, for starting, full apply “choke” but NO throttle as you crank…if “choke” passages are clear, fuel will get sucked up into carb throats and revs should take off….then you fiddle with “choke” to control revs. What fun!

[bbrad1775]

Get a new petcock…..Georgefix has got them…made in Japan ..about $55…skip the Chinese copies
get a new air filter element UNI -2440 fits the 650 shafties..about $25….hopefully your old filter element still has internal plastic cage…avoid losing it! It’s aD-shaped element ..
without properly cleaned carbs, starting will be difficult, decent running impossible !
As mentioned, for starting, full apply “choke” but NO throttle as you crank…if “choke” passages are clear, fuel will get sucked up into carb throats and revs should take off….then you fiddle with “choke” to control revs. What fun!

I will check the old filter. Thank you for the advice.

[Nessism]

Probably just going to do a full rebuild on the carbs since I have them pulled off. What carb rebuild is everyone using?

Here is what I am thinking:

Pull carbs and rebuild.
Go ahead an replace petcock since I will already be there.
Check for any dry rotted air or fuel lines.
New UNI air filter.
Test charging system.
New shocks.
New tires.
Check brakes and change fluid.
Change fluid in both gear boxes.


Is there anything I am missing?

If you haven't done so already, go into your profile, and turn on "view signatures". Then you can see the carb rebuild tutorial link in my signature (also on Basscliff's website)

Regarding the brakes, you have to break down the calipers and master cylinders, in order to clean out the system. Inspect the pistons and master bore for corrosion pitting. Replace parts are needed, and be sure to replace the brake lines, since they are sure to be filled with scale, which doesn't come out by flushing the system.

When replacing the tires, inspect the driven spline inside the rear wheel. They often fail due to a heat treatment problem on Suzuki's part. During reassembly, get some high moly (50%) lubricant, and coat the splines. This is critical to making the parts live long term.