Help with stumble

[JTsGS650]

Hi all. I'm having some drivability issues with my '82 650G. I seem to have a stumble at about 1/8 throttle. It's especially noticeable when in say, 4th gear at aroung 4K RPM and I roll on the trottle.

Over the past few months I've checked and adjusted the valve clearances, completely stripped and dipped the carbs with new orings, new intake orings and have also installed new spark plugs and caps. I checked out the spark plugs and they appear as follows: #1 is black and sooty, #2 looks rich (possible leaky petcock), #3 and #4 look perfect. I checked the spark for both cylinders 1 and 2 and they were both good blue sparks. I also rechecked float height, which were all spot-on, and synched the carbs.

The stumbling also gets worse as the bike warms up. When I first start out and leave the driveway it is almost nonexistent, but after 20 miles or so it's stumbleing like a drunken sorority girl. After it's warmed up, I feel like it may also be missing when I'm cruising along at around 40 or so, which, along with the plug reading makes me believe that I have an intermittant spark in cylinder #1. Everything else seems good, twist the throttle and go.

This is my first street bike and I don't have alot of experience, so I was wondering if some of you more knowledgable folks could offer me some advice and maybe throw some ideas at me. TIA.

[catbed]

what did you set the pilot mixture screws at? a good point to start out is 2 turns out.

[GSJohn]

I am just getting started with working on these bikes but from what you described it initially sounded like a carb problem. But I think you should first eliminate the "leaky petcock" possibility first. Then I would make sure it is not a spark issue. When electronics heat up they can start to act flaky. Would it be possible to swap the coils or more simply the wires from right to left to see if a different spark plug is affected? Good luck with troubleshooting...I hope someone else has some more suggestions. I have noticed my bike starting to run a little rougher and popping more when decelerating. It also is getting more "buzzy" or it is just annoying me more LOL. How is your fuel mileage? Mine did an honest 58 mpg the other day on a ride at speeds of 50 up to 70 mph....so I think that indicates it is pretty healthy.

[JTsGS650]

what did you set the pilot mixture screws at? a good point to start out is 2 turns out.

Pilot mixture screws were set for highest idle, which worked out to be two turns out from lightly seated.

I am just getting started with working on these bikes but from what you described it initially sounded like a carb problem. But I think you should first eliminate the "leaky petcock" possibility first. Then I would make sure it is not a spark issue. When electronics heat up they can start to act flaky. Would it be possible to swap the coils or more simply the wires from right to left to see if a different spark plug is affected? Good luck with troubleshooting...I hope someone else has some more suggestions. I have noticed my bike starting to run a little rougher and popping more when decelerating. It also is getting more "buzzy" or it is just annoying me more LOL. How is your fuel mileage? Mine did an honest 58 mpg the other day on a ride at speeds of 50 up to 70 mph....so I think that indicates it is pretty healthy.

You're right John. I should definitely take care of the suspect petcock first. I have also thought about switching the plug wires for 1 & 4 to see if 4 would be affected, I'll have to try that on the way home.

As far as your buzzyness, I think once you adjust your valves and sync your carbs you'll be all set. And as far as mileage goes, I've only been getting around 30-35, however I don't do any highway driving really and I like to get on it alot. 8-[ My bike is also running rich with this stumbling issue and I think my mileage will improve once it's sorted out.

[bwringer]

How's your airbox?

If air can get in anywhere besides where it's supposed to, you will get a lean condition that will cause your exact symptoms.

I don't know what a GS650 airbox looks like, but on the 850s, you have to seal the end covers, the airbox halves, and the surface where the air filter mounts with foam weatherstripping. There's also a snorkel on the back of the airbox that must be in place.

On bikes with a plastic airbox, the lid must be in place.

Just throwin' out some ideas -- as I said, I don't know what a GS650 airbox looks like, but the principle is the same -- air should only get in where it's supposed to get in, and the air filter must be sealed so air can't bypass it.

[JTsGS650]

How's your airbox?

If air can get in anywhere besides where it's supposed to, you will get a lean condition that will cause your exact symptoms.

I don't know what a GS650 airbox looks like, but on the 850s, you have to seal the end covers, the airbox halves, and the surface where the air filter mounts with foam weatherstripping. There's also a snorkel on the back of the airbox that must be in place.

On bikes with a plastic airbox, the lid must be in place.

Just throwin' out some ideas -- as I said, I don't know what a GS650 airbox looks like, but the principle is the same -- air should only get in where it's supposed to get in, and the air filter must be sealed so air can't bypass it.

The 650 airbox is a different animal than the 850. I know about the sealing that is required with the 850s but the 650 airbox is basically just one cover. The cover is held on by two sliding clips. The air filter is foam over a plastic skeleton that clips into place inside the airbox. I checked the filter because I thought it may have been dirty or over oiled. Everything looked good.

I'm also thinking that it's a spark issue. Spark plugs look good on cylinders #3 and #4. I believe that cylinder #1 is what is giving me the issue. The plug on #1 is black and sooty. #2 looks a bit rich which, may be a leaky petcock. I rebuilt the petcock last year with a new diaphragm and orings and it seemed to be working fine. A few weeks ago when I was putting the carbs back on, I noticed a tiny bit of gas in the vacuum line. It also smells rich and the exhaust looks rich in the left hand side exhaust on startup. Anyway, I ordered a new petcock last Friday.

I'm going to switch the wires from #1 and #4 today, go for a ride and see if the issue switches cylinders. Thanks for responding guys.

[JTsGS650]

No progress

No real progress to report. Received my new petcock today and will install this afternoon. I'm also going to check the airbox as suggested and cleanup any connections around the coils. I actually drove the car to work today . Ugh.

[maro]

Did anything come of this issue. I think I have a similar problem, but with spark 4. let me know, thanks

[JTsGS650]

Nope

Still dealing with my stumble. New petcock installed, checked the airbox and cleaned up the coil connections. I've also been fiddleing with the air screws based on the plug readings. It's still there. What's weird is it's not there consistently. Sometimes it will be there and is obvious and other times I'll try and make it stumble (just to make sure it hasn't cured itself 8-[) and It'll be gone but then back again two minutes later. I'm planning on messing around with it again this weekend.

[maro]

How did you clean up your coil connections? Just wondering, as I'm going to sort through it tonight? I can feel it stumbling during idle, and my #4 pipe get barely hot.

[twistedwankel]

Over the past few months I've checked and adjusted the valve clearances, completely stripped and dipped the carbs with new orings, new intake orings and have also installed new spark plugs and caps. I checked out the spark plugs and they appear as follows: #1 is black and sooty, #2 looks rich (possible leaky petcock), #3 and #4 look perfect. I checked the spark for both cylinders 1 and 2 and they were both good blue sparks. I also rechecked float height, which were all spot-on, and synched the carbs.

This is my first street bike and I don't have alot of experience, so I was wondering if some of you more knowledgable folks could offer me some advice and maybe throw some ideas at me. TIA.

You have alot more experience than alot of us in tackling what you all ready have...good for you\\/ I can tell you a couple things that the other GSers told me to do that made all the difference in the world with similar issues. Put a really good charge on your battery overnite as even tho' you can spin the starter and it runs you need higher voltages to fire the ignition properly. Put in different spark plugs as I had a bad one in the last new batch. I finally believed them and replaced the clean old bullet connectors on my Stator with new blade connectors and my idle voltage immediately increased to 13.8 from 11.8VDC. My 81 is totally stock original ignition and RR so I know they are reliable

[JTsGS650]

How did you clean up your coil connections? Just wondering, as I'm going to sort through it tonight? I can feel it stumbling during idle, and my #4 pipe get barely hot.

I pulled off my tank and cleaned the spade-type connections from (I guess )the ignitor (?) to the coils with a wire brush and applied dielectric grease. This didn't make a difference, as they already looked pretty good.

You have alot more experience than alot of us in tackling what you all ready have...good for you\\/ I can tell you a couple things that the other GSers told me to do that made all the difference in the world with similar issues. Put a really good charge on your battery overnite as even tho' you can spin the starter and it runs you need higher voltages to fire the ignition properly. Put in different spark plugs as I had a bad one in the last new batch. I finally believed them and replaced the clean old bullet connectors on my Stator with new blade connectors and my idle voltage immediately increased to 13.8 from 11.8VDC. My 81 is totally stock original ignition and RR so I know they are reliable

Thanks. I like to think that I'm fairly mechanically inclined . I'll throw the battery on a charger overnight tonight. I have tried different plugs with no change. I have been meaning to replace the bullet connectors with the spade type or eliminate them all together. Looks like I have another project over the long weekend. :-D

[JTsGS650]

I tweaked the mixture screws again last week to try and lean out the pilot circut and it made the stumble worse. Richened it back up and it's better, but still there. So now I'm beginning to think it's electrical? So, based on yous guys recommendations, I went to Radio Shack and bought a multimeter. Played around with it a bit this weekend and found that my battery was only around 12.0V and would only charge at 12.9V @ 4K rpm. After soldering my three stator wires the voltage is now at 13.9V @4K RPM. According to the Stator papers it should be higher than that. Do you guys think that 13.9V @4K is okay? I also installed another ground from the R/R earth direct to the battery earth (which I've been meaning to do) Haven't been able to ride her yet to see if these things made any improvement though . Going to test my coils/wires/caps next to try and diagnose this damn misfire. If everything tests okay, then I guess I'll pull the carbs (again) and adjust the floats in #s 1 and 2 to lean them out a bit.

[Steve]

Do you guys think that 13.9V @4K is okay?

Actually, anything over 12.6V is going to charge a 12 volt lead-acid battery. The question is how well and how quickly. 13.9 volts is perfectly acceptable.

Just for your own education, start with a fully-charged battery. It should read 12.6-12.8 volts with no load. Start the bike, let it idle. Note the battery voltage at idle. Increase the engine speed to 1500, 2000, 2500, 3000, note the voltages at those speeds. You will likely find that somewhere around 2000 rpm the voltage will peak, then slowly come back down. That is the point where the regulator starts to kick in. Now that the regulator is doing its thing, the increased firing rate on the coils draws a little more, which brings the voltage down a bit.

Let us know what you find.

.

[maro]

then I guess I'll pull the carbs (again) and adjust the floats in #s 1 and 2 to lean them out a bit.

I had to pull my carbs yesterday to diaganose and clean my pilot jet in carb 4 and I was dreading it. I am happy to report that this being the 3rd time pulling my carbs in less than 4 months, I managed to due it with ease (grain of salt) . All in all, the whole procedure took me about 2.5 hours. The wrestle of getting the carbs in and out is becoming less and less and I spent more time, taking my time, opening up the bowls and cleaning the jet. That said, I'll be quite happy not having to pull the carbs for a while, but it's night and day from when I first pulled them.:-D