83 GS650, fourth time carbs in!

[ednearls]

Bike is 100% stock, new airfilter, no air leaks anywhere. After a couple or three bouts of carb maintenance I had achieved a perfect low idle and no fuel or air leaks but had a wet plug or two and a cool pipe or two and not always the same ones, and bogging out after some good revs. I had tuned the pilot screws to 2&1/4 turns out using a digital tach. I figured out that a previous owner had reamed the pilot jets out, clearly indicated by comparing the fuel orifice with correct new pilots with a small wire, actually visibly detectable that mine had been enlarged. Today I installed the correct new pilot jets.

Idles like kitten, sounds GREAT for first several revs then bogs out. A noticeable improvement since changing pilot jets but the bigger problem remains of it bogging out. Really sounds super for first few revs. But I should have considered if the guy reamed the pilot jets he may have also reamed the mains! I should have tried to measure the mains orifice. If I shut it off, only briefly, I can reproduce this symptom.

For example, I just ran it again, idled for a minute then held at 6K RPM healthy roar for about 7? seconds then bogged out. Chopped the plugs, all look rich but none wet. For a test, I then removed the air filter, left cover open, similar symptom but a much less healthy roar.

Could oversized mains cause a bog out without flooding plugs? Plugs are clearly rich, but I've seen that plenty of times before, and they are not wet. I think I'll order new mains unless I can measure their orifices well enough to conclude they're unadulterated.

Any other suspicion?​ I have been wondering if an ignitor failure could behave like this, though I think that would produce wet plugs, unless they are drying faster than I chop them

The jets present in the carbs match these measurements; I've been unable to confirm they are correct for my BS32SS but seem to be. [TABLE="border: 0"]
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[TD]N100604-SIZE[/TD]
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[TD]8.0mm Slot head
M5x0.75 Thread
9.0mm Length
5.0mm Thread Length[/TD]
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[jsandidge]

Check to see if your exhaust is clear. Critters can build homes in there.

 

[Suzukian]

Also make sure your valves are adjusted right. If they are tight and aren't closing all the way, the second the bike warms up, it will sputter and fail.

 

[ednearls]

Interesting suggestion, I'll poke a stiff wire in there to try to check but tend to doubt it's the problem. I sourced the exhaust from a cycle salvage business and did notice there is some movement in one muffler, like a loose baffle. We decided it probably becasme dislodged in shipping. I know the "premuffler" is clear. Other than one loose baffle the exhaust is in good shape. Exhaust seems to be blasting out both sides freely. I don't have an issue that's specific to one side. All header pipes are now hot after replacing the pilot jets. I've just removed the carbs again with the main jets in mind. I can't see any machine marks in their orifices but they may have been drilled; the pilot fuel orfices certainly were over spec. Other things I've encountered on this bike included clearly novice efforts (missing long rear axle spacer so rear axle nut cottered hand tight!) so seems reasonable the mains could have been enlarged too.

Yes I correctly adjusted the valve lashes, and have been through the recommended carb tutorial multiple times, confirming passages clear etc

 

[ednearls]

Unfortunately I already removed carbs again but should have tried a little "choke" when it was systematically bogging out when switching to mains
I had tried the opposite because had tunnel vision thinking it was flooding out (tested with no air filter and open airbox which reproduced the "cut out symptom" but didn't think to try it richer with "choke"). I ordered main jets and it will be a few days. If the orifice looks the same I won't reassemble just to test them. The cut out symptom when it's switching over to mains does resemble fuel starvation. Now I'm thinking slide needle may have to be raised.
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[Who Dat?]

Because of the way the "choke" operates, it won't necessarily richen the mixture when the throttle is opened.

If it were an actual choke plate that blocked the inlet of the carb(s), yeah, it would be a valid test, but our "choke" (enrichener system) relies on the high vacuum of a closed throttle to pull the gas through the passages. Once you open the throttle, there is not enough vacuum to suck the extra gas.

 

[1948man]

The mains had been drilled out on the first GS I got. Previous owners do weird things.

 

[ednearls]

thanks guys, yes it occured to me later that the "choke" test might not apply to this type of fuel enrichment starter system. Hoping for the best when new mains arrive. The slides look perfect and I don't see any scratchmarks or indication that the needles were mucked with but I ordered the long reach snap ring pliers in case, and probably have suitable small washers to replace the plastic spacer thinner if it's too lean, does almost sound like fuel starvation which is not consistent with mains drilled. I don't see any indication that they've been drilled, but that wasn't obvious on the pilots either and they were definitely enlarged. She sure conks out in a hurry when try "double rev" the throttle grip. But easing up to 6K just screams for several seconds then conks almost out. I'm also going to try to prove with a digital tach that she's not losing spark from the the ignitor when the transistors are supposed to be supplying advance but still doubt it's electrical. I gave away my old timing light many years ago but figure the tach should work for that.

 

[chris]

Hi ,low float height can cause fuel starvation symptoms. While you still have the carbs out check them. Also make sure your petcock has full flow. It could be taking too long to fill the bowls, that would explain why it starts up well after you shut the engine off.

 

[Grand Rouge]

thanks guys, yes it occured to me later that the "choke" test might not apply to this type of fuel enrichment starter system. Hoping for the best when new mains arrive. The slides look perfect and I don't see any scratchmarks or indication that the needles were mucked with but I ordered the long reach snap ring pliers in case, and probably have suitable small washers to replace the plastic spacer thinner if it's too lean, does almost sound like fuel starvation which is not consistent with mains drilled. I don't see any indication that they've been drilled, but that wasn't obvious on the pilots either and they were definitely enlarged. She sure conks out in a hurry when try "double rev" the throttle grip. But easing up to 6K just screams for several seconds then conks almost out. I'm also going to try to prove with a digital tach that she's not losing spark from the the ignitor when the transistors are supposed to be supplying advance but still doubt it's electrical. I gave away my old timing light many years ago but figure the tach should work for that.

IF your GS is a Canadian spec model, the Needles are adjustable....5 positions I think. third notch most common with stock airbox and stock / close to stock exhaust. Additionally, if stock airbox installed, are the carb intake to airbox runners / boots properly slid in place?

 

[Suzukian]

When I raised the needles on my '83 GS750ES, the choke system became "irrelevant". I have to start the bike by putting my hand over the opening under the seat. It fires right up, and I don't have to do that again, unless the bike sits overnight, or all day. When it did work, I had to ride around with it on for a very long time. It was like that since new. Raising the needle one notch make the bike come alive.

 

[gustovh]

Haven’t heard mention of syncing the carbs, you must sync the carbs for proper running.

V