#4 cyl not firing

[Jonesz]

First a disclaimer "I am not a carb guru" Have had the carbs out twice on my 79 GS850 and tried my best to clean them. Bike had sat for 20 years before it came to its' new home here. Used a fine guitar string, ultrasonic cleaner etc. Also had to get a new pilot fuel screw and install that as the tip had at some point broken off and wedged in the orifice . Set the new fuel screw to one turn out from being lightly seated Undid the bowl drain screw and there is fuel getting to the bowl. Still have a problem with #4 not coming online. The only way I can get it to fire is to put my hand over the carb throat. When I do that and remove my hand the # 4 cylinder comes on stream for a short time until it uses up the fuel drawn in and it then reverts to popping/lean then quits firing. Has anyone got a suggestion as to what my problem is?
Any help appreciated
Jonesz

[Nessism]

Did you remove the broken fuel screw tip from the carb body? Remove the pilot jets and hold them up to a light to make sure they are open? Replace the intake boot O-rings? Adjust the engine valves?

[Jonesz]

Hi Ed
I did remove the broken tip from the carb body. Will get the carbs out again and give another good inspection. Have not adjusted the valves yet but the compression test shows # 4 to be approx the same as the other cylinders. The bike has just over 10,000 miles on it.

[Jonesz]

So life got in the way and I was not working on the bike for a few days. Pulled the carbs this aft and took the bowl off # 4 carb. Checked all the jets etc and all appeared clean and redid them gently with a high E guitar string. Pulled the carb connector off the head and the o-ring was very flattened/shiny. Replaced it with a new oring and reassembled. Fired up the bike and # 4 carb came online and the header heated right away. I am thinking #4 must have been drawing air through that oring. Thanks Nessism you called it right, thanks a bunch. Will be ordering 4 new orings and installing them before installing the airbox etc. Winter is here and I have lots of time.

[Jonesz]

Was wondering if I should use some kind of sealant when installing the new intake Orings? The ones on the bike appear to have some type of sealant (kind of elastic & brownish) on them but could have been done by the PO. I am not used to having to put sealant on Orings other than a slight bit of lube to hold some in place when doing the install.

[Brendan W]

Shouldn't need sealer if the faces and grooves are clean.
Was thinking that the 850 would need a G string

[Jonesz]

Shouldn't need sealer if the faces and grooves are clean.
Was thinking that the 850 would need a G string

Yep I hear you . Just after I posted the ? found the Bikecliff site and see that he used no sealant either. Must have been the PO trying to fix my bike without buying new Orings! Not the only weird thing I have come across when doing the restore on it.

[Brendan W]

Yep I hear you . Just after I posted the ? found the Bikecliff site and see that he used no sealant either. Must have been the PO trying to fix my bike without buying new Orings! Not the only weird thing I have come across when doing the restore on it.

Fancy that. A PO taking shortcuts. Whatever is the World coming to

[Jonesz]

Does anyone know the proper size for the intake pipe Orings. Sounds like I might have to wait awhile or order stateside. The one I used to test # 4 cyl was a bit thick although the right circumference. Was thinking of going to a local supplier and trying to find 4 compatible Orings and change them all before reassembly. Hard to judge by the old ones as they are so flat & shiny after 40 years!

[Brendan W]

Robert is the O ring guru.

https://www.thegsresources.com/_forum/showthread.php?262414-O-ring-sizes-as-promised

[Jonesz]

Robert is the O ring guru.
https://www.thegsresources.com/_foru...es-as-promised

Thanks for the info will print and keep this handy. Thanks and best wishes to Robert as well

[Jonesz]

Does anyone have a source for the intake pipe Orings on a 1979 GS850G.Ordered today from Partzilla and they are on backorder. Showed as available but they are not in stock. Also tried my nearby Suzuki dealer before Partzilla and they are on backorder he says they could be 2 months or longer. Part # 09280-32006. They fit a whole gamut of machines so am left wondering.

[Jonesz]

Finally (most suppliers were initially out of stock)received my new carb intake O rings and was wondering about how tight to torque the intakes on my 79 GS850. Have looked in the manual but have only been able to find a general value for 6mm bolts of 3-5 ft lbs? I am switching to metric bolts to get away from the JIS heads on the oem fasteners. Seems a bit low to me but also realize that too much pressure might slightly warp the mounting flanges. Any info appreciated

[Grimly]

6mm bolts into alloy max 7lbs/ft. As you say, there might be a risk of flange warping, so 5 would be good. The right o-ring should accomodate that perfectly well, though.

[Jonesz]

Thanx Dave appreciated