Saimese carbies

[erjeff]

Hi guys,

What a great resource this sit is! I recently bought an 83 550L that sat in a shed for many years. Put new tires on it (fork wipers are disintegrating so I suspect I have a fork seal job in my future too), changed the oil and filter and slapped in a new battery. It starts right up with full choke but idles erratically and you can't take the choke off, even a smidge, or it'll immediately die. This happens even when the engine is hot. On the road, it performs OK (still with full choke) until it warms up a bit. Then whenever I pull in the clutch and let go of the throttle at a stop or turn it will immediately stall unless I give it a little gas until it stabilizes. If it does die and I'm still moving, I can pop the clutch and it'll take right off again.

So I suspect that the carbs are all varnished and gummed up and there is probably no flow through the pilot jets. It certainly seems totally reliant on the flow through the choke circuit for gas at idle.

I know I need to pull the carbs and tear them apart for cleaning and probably a rebuild. I also suspect that the carb boot O-rings are completely trashed as well. While I'm an old hand at working on gas, diesel and even steam engines, I'm a newb with motorcycles. Any advice or pearls of wisdom would be appreciated.

Most of the stuff here refers to the gang of four, CV or VM carb setup. Mine has two duplex (Siamese) carbs. Manual says they are Mikuni BSW30, twins. Does anyone have any info or advice specific to these? I'd like to have everything I need before I tear into them. What parts am I likely to need and who is the best vendor?

I really like this old bike and would like to get her on the road while there is still some summer left.

Thanks!!

[JEEPRUSTY]

Thes carbs are effective two carbs in one body. All internals are regular Mikuni, jet, valves etc.

The carbs were made this way to allow for a narrower middle point in the bike which translates to more legroom.

They really only share Diaphragms, floats and needle valves on each carb the rest of the system is two seperate carbs.

Robert Barr has a kit but you will end up with twice as many o-rings which is not a bad thing. Again these rings are standard sizes as used int he other carbs on GS bikes.

[victorgallas]

Besides dipping the carb in a carb cleaning solution overnight to clean all of it and also cleaning all of the jets. Do make sure you syncronize the carbs after reinstalling and then if youre carb has it, adjust the mixture screws. Most of the times start with 2 1/2 turns from bottom.

Also do pay attention on the jets. Cylinders 1 and 4 have the same jets, while the 2 and 3 have another sizing. This is due to the airflow trough the air filter box and carbs.

Another little trick i had an issue on mine was with the variable venturi assembly. Essentially the sliding barrels that move up and down inside the carbs with the diafram on the top. When you assemble it. make sure it can slide up and down freely. If it gets even a little stuck it will cause issues.
Sometimes a light sanding on the sliding saft will help. Do this very carefully thou.

Thes carbs are effective two carbs in one body. All internals are regular Mikuni, jet, valves etc.

The carbs were made this way to allow for a narrower middle point in the bike which translates to more legroom.

They really only share Diaphragms, floats and needle valves on each carb the rest of the system is two seperate carbs.

Robert Barr has a kit but you will end up with twice as many o-rings which is not a bad thing. Again these rings are standard sizes as used int he other carbs on GS bikes.

[BassCliff]

Greetings and Salutations!!

Hi Mr. erjeff,

In addition to the previous excellent advice, let me dump a TON if information on you and share some GS lovin'.

There are a couple of carb rebuild guides on my little website. Sorry they are not specific to the siamese carbs but they will give you a lot of pertinent information. See http://cycleorings.com for the necessary internal carb O-rings and other handy parts.


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. 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

[erjeff]

No joy

After cleaning the carbs things are actually much worse. The bike had been running fine on the road except at idle and I had to keep it choked. Now it'll only start with full choke and will idle irregularly. The second I take the choke off or give it any throttle it'll immediately die.

I completely stripped and soaked the carbs. Cleaned the jets, needles, passages and put in all new O-rings. I bench synched the throttles as close as I could. Put in new boot O-rings. The boots and airbox are all standard and in good shape and I couldn't find any major vacuum leaks. Checked the fuel level in the bowls and they are OK. The needles had originally been 2.5 turns out but I've tried all different settings on those with no change at all.

Any ideas? I don't know what to try next.

[erjeff]

Seems to be running exclusively on fuel from the choke circuit. The minute you give it any throttle it leans out and stalls.

[JEEPRUSTY]

Can you check that your choke plunger are moving in and out freely without binding?

If the springs do not fully close one or both then that could definitively cause problems.
The cables can get dirty and the plastic nuts can get packed with dirt.
The plungers can get sticky too.

Did you blow out all the orifices? Soaking but not doing this may leave you with something plugged.
You did remove all jets and valves in the carb body and soak separately yes?

[JEEPRUSTY]

Y'all Y'all do have the airbox on?

[erjeff]

Yes, air box and filter are on. No cracks or obvious air leaks. Choke plungers are moving properly and I did blow all the passages out with compressed air after soaking. Squirted all the passages with carb cleaner to insure good flow through them also. Removed and cleaned everything. The pilot jets had been plugged up as I originally suspected, so I thought I had the problem solved.

[JEEPRUSTY]

It is quite easy to block the pilot air jet with the intake boot.
Check to see if the lower part pf the boot is correctly oriented.

[erjeff]

I even took the boots off and reinstalled them to be sure it wasn't something like that. I did start it up with the boots off just to see if it would make a difference and it seemed to run about the same.

[elrico]

erjeff,if the motor runs and is well warmed up,as it is still runnig at say 2000+rpm fairly stable ,reach under and adj large knurled knob between carbs:the idle speed adj screw some call it.Turn it counterclockwise slowly and notice engine rpm speed increase,now cut back towards close position with choke setting,keep this process going to eventually have chock fully closed and the idle speed screw/knob set to control idle speed totaly.Back off choke,increase idle speed w/idle speed screw knob.It can be tricky,on this hot running motor,wear thin tight fitting glove to avoid burnt/cut hand/fingers or shop rag as you reach under/between carbs you should try using your left hand fingers as this is your"tool") .Normal idle rpm @1100-1200. Use finess..good luck

[erjeff]

The idle adjustment screw does nothing. I really think that it's only getting fuel from the choke. I can bring the rpm's down by starting to close the choke just a little. Any more and it'll die.

I really don't think that I overlooked anything but I sure can't figure it out. Hate the thought of pulling the carbs and tearing them down again but I may have to. Anyone else here ever have the same problem?

[JEEPRUSTY]

If it is only getting fuel from the enrichment circuit then other circuits would be blocked/

[elrico]

siamese carbies

erjeff,spray WD-40 or your choice,all around/about air box,all boot/clamp fitting points esp.at engine intake stubbies,have engine running at somewhat lower rpm,does rpms rise while spraying? Did you change Orings at intake stubbies...also ,please,how is the electricial/charging situation...also where did you set the 4 idle circuit needle/screws,turns out from bottom,just need data to try to be helpfull.