79 gs850 popping

[JTGS850GL]

You definitely need to fix the carb #3 rich problem. Could be a float related problem. Check the fuel level in each bowl to verify whether it's leaking or not.

[Chuck Fryer]

Is that as simple as pulling the drain plug and seeing if one bowl has more than the others? I agree the number three problem needs to be fixed but I am not sure whether it is an ignition problem causing the fuel not to burn or the carburetor putting too much fuel in

[Big T]

Well, pull all 4 plugs, lay on the cylinder head and hit the starter button.
They should all spark blue/white. It helps to do this in the dark

To check the static fuel height, you need an adapter and some hose to see the fuel height on the outside of the carb. You can buy one from Z1 Enterprises

You didn't reply to the jet size question. With those Harley mufflers, you're probably lean

[londonboards]

I had popping on one cylinder:

which turned out to be bad carb synch:

You may also have flooding in no.3 due to poor needle valve seat O ring:

You are getting incomplete combustion OR over fuelling on that cylinder. For incomplete combustion problems, make sure the valves are closing and seating (compression testing or leak down test), check plug and leads (try switching plug with another cylinder and then, as a separate test, switching plug leads 2 and 3 - un-plug leads from spark plug on cylinders 2 and 3 and reattach the other way round).

For overfuelling, look at float height, float damage/leaking float, wrong jets or wrong needle clip setting, badly synched carbs (carbs are synched to no. 3 so if it was a bad synch then carbs 1, 2 and 4 are not opening at the same time as no.3), check the working of the petcock (looks like you've done that) and the vacuum hose.

Greetings

[Chuck Fryer]

Thanks. Jets were factory size, as far as the info I found. I bench synched the carbs with a caliper on top of the slides, so they are close, +/- .002 or so. I need to purchase a set of gauges to vac sync. Just finished adjusting valves, all good, #3 exhaust was on the loose side.

[londonboards]

For GS valves, lose is good. That means they are closing. If you can't find a gap then they are still open.

When GS valves wear, the gap closes. So the tighter they are, the more worn they are. Keep on the side of a bigger gap to ensure they are closed correctly and you have built in some capacity for wear.

I have found that bench synching is no substitute for the real thing. When those cylinders are sucking in the air, that's when you need to check the synching.

Greetings

[Chuck Fryer]

So, about the jetting....
I've read they were lean from the get go. What should I change, main? Pilot? Just one size bigger?

[Big T]

Main jets up 3-4 sizes
Raise the needles one notch

[Chuck Fryer]

Thank you, I think I'll order some jets then.

[BC_Rob]

Hi Chuck,

Here is another data point:
1979 GS850G with Vance&Hines 4 into 1, and K&N filter inside the stock air box. I started with moving the main jet up one size to 105 (from stock 102.5) but it still wasn't pulling like my first 850G.

Next was going up one more size to 107.5's - better but not great.

Last adjustment was moving the needle clip down one notch (to the middle slot) and my bike was running perfectly.

Rob

[Chuck Fryer]

Thanks, I'll try raising the needle too, it's free!

[Chuck Fryer]

Problem found! Even though I felt as though I did a thorough job cleaning the carburetors, I found that somewhere in the idle circuit of number 3 there was a clog. The funny thing is I found it when I was looking for an exhaust leak. I was holding my hands real close around the pipes at the head trying to feel for an exhaust leak and noticed that number 3 pipe was cold the other three were hot. Just thought I would add that in case somebody else ran across this thread trying to troubleshoot a similar issue.