Cylinder 2 and 4 issues.

[brutaldm]

1982 gs650glz 33k miles


I'm having an issue with cylinders 2 and 4 on my bike. When I turn the idle mixture adjusting screw on either carb 2 or 4, the engine does not respond Turning the idle mixture screw in or out all the way does nothing to the rpms on the engine. (I was able to get a correct air fuel mixture with colortune on cylinders 1 and 3.)

I have a colortune and checked out cylinder 2 and 4 using it as well.

Colortune Cylinder 2: blueish white flame, does not change when mixture
screw is turned, occasionally flashes yellow when throttle is opened

Colortune cylinder 4: very weak blueish white flame, does not change when mixture screw is turned, does not flash yellow at all, even if throttle opened. The flame on cylinder 4 is barely visible.

I removed the idle mixture screw from carb #4 while bike was running and sprayed some Carb cleaner in there. the cleaner was immediately sucked in and rpms increased on bike. After 2 seconds or so, the rpms relaxed back to normal idle (~1100 rpm) Each plug is sparking the same. (laid plugs on head and tapped start button to verify spark)

Currently plug 2 and 4 have idle mixture screws set at 2 turns out.

Pinching off vacuum line to Carb #2 does nothing to engine rpms.

I swapped the ignition coils positions (left to right, right to left) and I still had the same problem..


I had no issues getting a solid carb sync on this bike. Idle is very steady, so I don't think I have any air leaks. (tested with carb cleaner and didn't find anything)

I'm using 87 octane gas with 10% ethanol. Petcock seems to be fine. Res, Prime and Run all work properly.

Bike is semi-street worthy. Took it out for a spin. Got up to 65 mph with no issues. Bike stayed running the entire ride. No issues with stalling or loss of power. I went about 70 miles and burned up almost an entire tank of gas. I know my GS should be getting at least 150 miles/fillup. Also, bike does not back fire and idles smoothly + consistently. Hard to start when cold (i'm in massachusetts), but starts up no problem once engine is warmed up.


Where do I start troubleshooting this problem?




here's what I have done on the bike so far:
Carbs dipped (72 hour dip/body) rinsed in kerosene and dried with air compressor.
Carbs synced with Motion Pro carb syncer
Air-intake boot orings and screws replaced
Airbox-to-Carb and Carb to Head clamps replaced.
Plugs (NGK D8EA) and caps (NGK VD05F/XD05F) replaced
New throttle, choke, and clutch cables. (all oem)
OEM handlebars put on (po had cafe handlebars on it)
Air box sealed with weather stripping
Air filter cleaned and oiled using K&N cleaning kit.
Camshafts journals regreased with suzuki moly-paste
Timing reset
New brake calipers + pads
New piston+cup in front master cylinder
Left and Right switches disassembled, cleaned and reassembled.
Inline fuel filter installed
All hoses and fuel lines replaced.
New valve cover gasket
All valves adjusted using spreadsheet.

 

[BassCliff]

Hi Mr. brutaldm,

That's quite an extensive list of maintenance items that you've covered so far. Well done! All I can do is offer a couple more suggestions.

While you had the carbs apart, did you verify that all the jets (pilot, main, needle, etc) were stock sizes? Have you adjusted the valves? If a cylinder is not "breathing" properly you might not get a good blue flame with your Colortune.

If nothing else, I will have bumped your post back up to the top so that the real gurus might see it.


Thank you for your indulgence,

BassCliff

 

[Guest]

Did you change the o-rings in the carbs?

 

[brutaldm]

Did you change the o-rings in the carbs?

yes, all orings in the carbs were changed with a kit from cycleorings.com

 

[brutaldm]

While you had the carbs apart, did you verify that all the jets (pilot, main, needle, etc) were stock sizes? Have you adjusted the valves? If a cylinder is not "breathing" properly you might not get a good blue flame with your Colortune.

I did not verify the jet sizes when I had them disassembled.

The valves were adjusted. Four of the eight valves needed new shims, the other 4 were in spec.

And thank you for the bump!

 

[Steve]

If you get no change when adjusting the mixture screws, I would suspect a tip broken off in the carb body. :-k

Remove the carbs from the engine, run your finger into the throat, just under the mixture screws. If you can feel a point sticking through, it's likely stuck and broken off the screw. I have used the side of a Phillips screwdriver to roll it over the tip and pop it back up. You can then turn the carbs over and let the tip fall out. You can also verify by removing a screw from #1 or #3 for comparison. There should be a very fine tip on the end of each screw.

.

 

[ardbeglily]

same problem with 2 and 4

same problem with 2 and 4

Thanks STEVE for the answer. I have done a ton of work to my bike, like Brutaldm and have hit the same issue with cylinders 2 and 4. I am hoping your advise helps me too. Is there some link internally in the carbs between #2 and #4 ?? Thanks