The thing doesn't want to run

[brainrush]

1978 Suzuki GS 550 E. I got some used carbs yesterday as the old ones had the fuel screws stuck in the carb bodies. even with the new(er) carbs, I can't get it to idle without choke, static timing is dead on, good spark, compression is a little low across the board, about mid 90's (worn rings) but even if I put a touch of oil in the cylinders to bump up the compression a bit it doesn't want to idle without choke. When the throttle is pulled, sometimes it'll rev, most the time it will just die, plugs 1&2 are sooty, plugs 3&4 are wet, I can't find any air leaks. I haven't touched the carbs yet other than screwing the air screws to 1.5 turns out. it's got an old 4-1 exhaust and pod filters so I'd expect it to run a little lean but not this lean.

The carbs are Mikuni VM22SS's

Help!

 

[Big R]

You'll get a much better answer in the morning, but here goes: turn the mixture screws out a little bit more. Are 3 + 4 wet with gas or wet with oil?

If 3+4 are wet with gas, check to make sure that 1+2 are getting gas.

 

[hillsy]

First thing you should do is check the valve clearances. A couple might have closed up and this will affect the idling / running / compression.

Second, pull apart the carbs and clean them FULLY. Then bench sync them (make sure the butterflies all open at the same time).

Now, you'll probably need larger main jets with the 4-1 and pods, so check these while you have the carbs apart (you probably have stock sizes and need to go a couple of sizes up on the mains), and probably lift the needles up a notch or 2.

After this you should be able to get the bike to idle by turning out the idle mixture screws - start with 2 1/2 turns and go out by 1/4 turn on each carb until it idles.

If all this fails to get it to run, you'll probably need to re-ring.

 

[brainrush]

#3 seem wet with oil/gas, #4 seems wet with gas. since #3 is inboard it could be left over from when I checked the compression... I think I found the problem the tips of the fuel screws were all broken off inside the carb bodies, exactly why I needed new carbs in the first place...sonovabitch!

 

[brainrush]

After some boiling water I used most of it to mix with murphy's and detergent (I used the rest to make ramen) I set the carbs in there, I didn't have much luck with the old carbs, so I tried the new carbs, (this time the rest of the boiling water went to some late night hot cocoa!) and with a sharpened staple and a bit of luck it popped right out! no visible scratches either. I re-assembled the carbs moving the jet needle to the richest position in anticipation of the aforementioned pods&pipes my engine came with. Now for some fuel screws...

i'm guessing the wet/sootyness is from the choke, that would explain a lot.

 

[brainrush]

perfect music for my mood atm--> http://www.youtube.com/watch?v=MjG6F4vh_n0

I got the carbs installed and they seem to be doing the trick!, still doesn't like the upper half of the throttle, and is pretty unpredictable in power delivery, which means plenty of carb tuning to come, but at least I have a baseline, it sounds wonderful! slow to return to idle and does the occasional backfire, but it RUNS!, I took it out around the block with the new seat temporarily taped in, and it feels great! it pulls HARD when it can, and it feels dead everywhere else, so I know I'm getting somewhere. the bump-stop is in the perfect place for now, we'll see if I need to move things around when the clubmans get here and we'll see about where rear-sets will feel right.

 

[Makr]

Did you replace the o-rings on the manifolds? Mine were completely dried out. Made a huge difference on my GS.

Did you just boil the carbs, or rebuild them?

 

[HerrDeacon]

With compression numbers that low, it'll never run like it should. I don't know the spec numbers for a GS 550 but I'm betting is much higher than 90, probably north of 150. You need to find out the cause of the low compression and fix it. It may just be something small like the valves, check the valve clearances and adjust if necessary, then recheck the compression.

Did you do the compression test with a warm engine? Choke off (i.e. open)? Throttle on full?

 

[brainrush]

After searching the GS Resources, I found a couple threads that sounded familiar, I'm going to order some ASAP as I remember when I had the head off, I thought the o-rings were plastic! as for the carb's internals, all the o-rings and gaskets look/feel brand spanking new, when removing the one super stuck carb, I took it completely apart and let it sit in the hot water/soap for a while, the murphy's soap oil left a tacky residue that came off nicely with carb cleaner, all the passages cleaned themselves out so I didn't need to get in there with a bristle.

The motor started with 40k miles on the clock and a frozen cylinder, I cleaned what I could, re-used what I had available, did a mild hone and buttoned thing up with new gaskets. I know it needs new rings as adding a little oil brings up the compression to the 130's, and in retrospect I should have changed the rings. I hate how hindsight is 20/20 while foresight is legally blind. lets just call it a learning experience.

 

[crazypj]

You got 'new' carbs but did you clean them?
Sounds like blocked pilot system.
GS 550 has shim over bucket tappets, dead easy to adjust if you have correct tool.
You will have to get shims from Suzuki dealer, they are still available as GS500 twin used exact same ones.
Get a new cam cover gasket, it will probably break and using silicon usually leads to destroyed cylinder head when it gets in oil-ways.
Awesome motor, I built a 170+mph one about 30 yrs ago (720cc conversion, cams, exhaust, etc)
Clearance is only 0.001" to 0.003", set them 'loose' if they haven't been checked for a few years as they will bed in.

 

[Makr]

After searching the GS Resources, I found a couple threads that sounded familiar, I'm going to order some ASAP as I remember when I had the head off, I thought the o-rings were plastic! as for the carb's internals, all the o-rings and gaskets look/feel brand spanking new, when removing the one super stuck carb, I took it completely apart and let it sit in the hot water/soap for a while, the murphy's soap oil left a tacky residue that came off nicely with carb cleaner, all the passages cleaned themselves out so I didn't need to get in there with a bristle.

The motor started with 40k miles on the clock and a frozen cylinder, I cleaned what I could, re-used what I had available, did a mild hone and buttoned thing up with new gaskets. I know it needs new rings as adding a little oil brings up the compression to the 130's, and in retrospect I should have changed the rings. I hate how hindsight is 20/20 while foresight is legally blind. lets just call it a learning experience.

I have a four into one and one big pod filter. I went up two sizes on the main jet. with the filter opening blocked about halfway it runs perfect.

With a rehone, you may just need to let the rings seat. May work, may not. 90 psi is on the low side, but it is serviceable. I had about the same on mine, but was getting quite a bit of blowby, so I re-ringed.

 

[brainrush]

You got 'new' carbs but did you clean them?
Sounds like blocked pilot system.
GS 550 has shim over bucket tappets, dead easy to adjust if you have correct tool.
You will have to get shims from Suzuki dealer, they are still available as GS500 twin used exact same ones.
Get a new cam cover gasket, it will probably break and using silicon usually leads to destroyed cylinder head when it gets in oil-ways.
Awesome motor, I built a 170+mph one about 30 yrs ago (720cc conversion, cams, exhaust, etc)
Clearance is only 0.001" to 0.003", set them 'loose' if they haven't been checked for a few years as they will bed in.

170+!!!!! I've heard of the elusive 720cc kits, but I didn't know they were that potent! that's about double my top speed goal.

The PO used silicon sealant on said gasket, super annoying to remove, he got it all over the cams and there was plenty of it in the oil screen when I dropped the pan. Lacking a reliable source of compressed air makes cleaning the parts all the more annoying. when some money heads my way I was planning on doing another more thorough rebuild. I'm pretty sure my valves could use some adjusting, I hear some ticking (valve noise?) possibly coming from the #4 intake, which makes sense because that was the valve that was open letting in all the water into the cylinder (enough that I siphoned it out). :-[

new oil filter is on its way so after about 50 miles, I'll give it an oil change and re-torque all bolts and see if it feels better.

I'm going to have to say it's bad o-rings because with all the same settings, the left two cylinders are running rich, while the right two (exposed to sunlight) are running way lean.

 

[Rocan]

You got 'new' carbs but did you clean them?
Sounds like blocked pilot system.
GS 550 has shim over bucket tappets, dead easy to adjust if you have correct tool.
You will have to get shims from Suzuki dealer, they are still available as GS500 twin used exact same ones.
Get a new cam cover gasket, it will probably break and using silicon usually leads to destroyed cylinder head when it gets in oil-ways.
Awesome motor, I built a 170+mph one about 30 yrs ago (720cc conversion, cams, exhaust, etc)
Clearance is only 0.001" to 0.003", set them 'loose' if they haven't been checked for a few years as they will bed in.

*gags*

170... holy fuck pj... pics? info?