I am in need of some advice from the carb gods. Got my GS400 (yes 400, not 500) running for the first time since buying it. Cleaned the carbs, checked the diaphrams etc. One cylinder is spitting from the carb on idle, it pops every now and then through the exhaust and that same carb side the exhaust is runnimg red hot on idle. It also bogs on fast throttle openings.....where do I start looking?

Hi, Im no expert, learning a little on my old gs .. but I would  check the pilot jet on the spitting side to be sure its clear , I would check for air leaks around the carb inlet boot , i would look at the valve timings . Sounds like youve got ignition in the exhaust  but what do i know , I expect people with more knowledge will be along soon .. good luck

Quote from: jackinacabin on February 10, 2021, 10:53:27 AM
Hi, Im no expert, learning a little on my old gs .. but I would  check the pilot jet on the spitting side to be sure its clear , I would check for air leaks around the carb inlet boot , i would look at the valve timings . Sounds like youve got ignition in the exhaust  but what do i know , I expect people with more knowledge will be along soon .. good luck

Motor is freshly rebuilt, so valve timing and shims etc. are all sorted, I will check the rest you suggested again as well, thank you. I realised that I never checked the pilot screw setting yesterday, so that is also on the list for today

Under the diaphram cap is a small o-ring that is easy to lose so check to make sure both are still in place.
A glowing exhaust pipe is normally a sign of a very lean mixture so check all jets and passages are clear and that the float level is in spec. Popping from the exhaust is a sign of a possible vacuum leak which will make the mixture lean.
The way the bike runs changed after you took the carbs off to clean them so be patient, thorough and remember with carbs the small details count. It might take a couple of goes at it but you'll get there

So.....I took the carbs out again today, cleaned them again, replaced the pinched diaphragm on the right-hand side (Damn expensive), turned in both pilot screws, and backed them out again 2 turns each, needle clip is on the 2nd notch from the bottom on both carbs. It now idles rather good, only spit back through the left side carb once or twice, still popping through the exhaust at idle and now she will not rev at all, not even with slow throttle openings. I nearly lost one of those pesky little o-rings the first time I opened up the carbs, so to make sure I changed them out with new ones.

Long story short, the glowing exhaust seems fine now, but I suspect way to rich conditions now, as the plugs are black and soot-covered after today's test run.

un-shim the needles. Check the float level. Might be jetted way too rich. Also two turns out may not necessarily be the right pilot mixture setting. You have to set all of this correctly with a procedure on a running bike, not just with counting turns.

I might have found something.... In the Left hand side carb that has the spitting issues when I removed the slide guide and emulsion tube, the little white ring that seats the emulsion tube that should be attached to the guide came out along with the tube. I suspect it is creating an air leak. There are rubber gaskets at the bottom of the guides, does anyone know if they are supposed to be flat, or if they are supposed to be o-rings?

This just keeps on getting better. Is the pilot screws not supposed to have springs and O-rings in them?

Pilot jet is not supposed to have spring, washer and O ring in that order. Pilot jets are inside the float bowl, they're the highest jet in the bowl as it sits in the bike. They're made of brass.

Air mixture screws which are in front of the float bowl and can be adjusted without removing anything off the bike are supposed to have them. They're also supposed to have a brass cap over em, but we usually remove those. Screw is made of steel. As is spring and washer, O ring obviously nitrile.

Sorry I wandered in the middle of this conversation, I got no idea what's going on.

Cool.
Buddha.

Hi Buddha,

It is the mixture screws that I am referring to. I suspect in the absence of the orings etc, it is causing a vacuum leak.

missing o-ring will cause a fuel leak ... like way too much fuel at idle. It would likely drip fuel from the bottom of the carb. But in any case the carb can't be adjusted to idle correctly without these parts intact.

You can replace the whole needle, spring, washer and o-ring in a complete kit. Probably easiest way to get the right parts. Those o-rings are tiny and I have only been able to source them from Suzuki dealers.

Quote from: mr72 on February 12, 2021, 10:34:57 AM
missing o-ring will cause a fuel leak ... like way too much fuel at idle. It would likely drip fuel from the bottom of the carb. But in any case the carb can't be adjusted to idle correctly without these parts intact.

You can replace the whole needle, spring, washer and o-ring in a complete kit. Probably easiest way to get the right parts. Those o-rings are tiny and I have only been able to source them from Suzuki dealers.

Since the first startup it has been giving different issues everytime. Recon I am going to get the missing parts on Monday, we have a local guy that has a ton of older Suzuki spares, hopefully he can help. The Suzuki dealers are crazy with part costs, so I try avoiding them where possible.

Once the missing parts are installed I will deal with whatever the next symtoms are.

My dad bought a cheap rebuild kit for his DR200 carb that included the whole pilot needle, spring, washer and o-ring assy. along with the ordinary rebuild parts. I am sure a cheap rebuild kit from somewhere will supply all of this cheaper than buying the pieces one at a time from a Suzuki dealer.

It's no suprise then that you had to bring the bike home on a trailer when you bought it...
If you hadn't already started buying carb parts mr72's advice on buying a kit would be the best option. Hopefully there are just one or two bits in the carbs to replace now.
Keep at it. Before long you'll be commuting to work on it with increasing smiles per mile!

Quote from: Henrico123 on February 12, 2021, 08:08:58 AM
Hi Buddha,

It is the mixture screws that I am referring to. I suspect in the absence of the orings etc, it is causing a vacuum leak.

A bigger problem than the air leak IMHO could be that its not mathematically useable in terms of how many turns you are at. I dont think it will suck much air out of that fine and tight fitting threads between the body and the air screw.

But, when we say 3 turns from lightly seated - well that thread pitch is very fine, the needle has a taper and you're short the thickness of the O ring, which may be as much as 2 turns thick.
Besides your PO may have tightened it without the O ring, and wallowed out the passage. You're gonna need to get the O ring, and tune it by ear and feel and plug pull and examination of the hole and fuel passage for damage.

Cool.
Buddha.

It makes a lot of sense, I also thought of that. The other thing that I found was that instead of replacing the intake boot o-rings, the PO put paper gaskets in between the intake boot and the motor along with the old flat o-rings. Ths to me does not make sense at all, correct me if I am wrong, but there should not be paper gaskets in there? The O-ring should seal against the intake seat face?

Quote from: moe_tunes on February 12, 2021, 10:56:37 PM
It's no suprise then that you had to bring the bike home on a trailer when you bought it...
If you hadn't already started buying carb parts mr72's advice on buying a kit would be the best option. Hopefully, there are just one or two bits in the carbs to replace now.
Keep at it. Before long you'll be commuting to work on it with increasing smiles per mile!

Carb rebuild kits are ordered from Suzuki, as expected I had to sell a kidney. I tried BMW as the GS650 uses the same carbs, but they are even worse on pricing. I basically got the bike with the vales and halve of the top end in a plastic bag, that's the reason for the trailer, so I knew I was buying a risk, but I also refused to pay the selling price for it, which helped a lot.

Carb boot to head has no paper, O ring which should obviously be o not l.
But I have also used that purple gasket maker and copper spray gasket helper along with the O ring to "help".
The purple stuff I like, it stays pliant and also takes up oil and its really good. Copper colored spray ... meeh no idea ...
Cool.
Buddha.

Check also that there is no air leak from petcock vacuum hose to the cylinder. That can also cause the unsync!

Carbs rebuilt today, all the missing parts are now replaced, including new o-rings on the intake boots and I blocked off the vacuum port on the lefthand side. Went up to a 140 main jet and a 40 pilot jet. It had a 110 main in, could not see what the pilots were, bit with the airage pipe and no airbox I suspect it was way too lean. The popping at idle as well as the carb misfire is gone finally!

The bike still bogs when you open the throttle, however, if I restrict airflow slightly with my hand over the carb, she revs great, so I suspect it might just be a case of it needs some filters. I am in Cape Town, South Africa and there is literally no K&N filters available for the GS in SA, so it seems I will be stuck with the cheap cones.