GS650 won't Launch in 1st at less than 3K RPM

[WingMan71]

So,

My just restored '83 GS650GL has a strange clutch issue.

Valves have been adjusted and are in spec. Carbs were completely rebuilt according to this site's carb rebuild instructions. 20 hours in the carb rebuild effort and I know that all circuits are open and clean.

The bike will not launch in 1st gear at anything less than 3,000 RPM. If I try to ease the clutch slowly through the friction zone at less than 3K the engine just dies (stop running all together if I don't pull the clutch back in). I know that the red line on this engine is 9,500 RPM, but 3K RPM to launch in first seems way too high to me.

(That said, it's been a while since I've ridden a bike with this small an engine, so maybe that's normal, but I don't think so.)

The clutch is adjusted to spec. Clutch lever pull effort is about right for a mechanical clutch. The bike has only 25,000 original miles on it.

I actually finished the mechanical restoration back in late summer/early fall, and I don't remember the clutch having this issue back then when I rode it. But now it does. Strange!

Bike runs very strong at speed and engine is smooth, but starting out in first is an issue.

Any suggestions on what to do/check would be appreciated.

Thanks.

 

[tom203]

".....and I know that all circuits are open and clean."

Not a chance, your pilot circuits ain't delivering, so it starves coming off idle under load .How much out are those mixture screws?try another half turn . This thing should pull away in first at 1000 rpm no problem/no protest!

 

[WingMan71]

Pilot screws are all set at 2 full turns out. I can certainly turn them out more and see what happens.

And, yes, I'm absolutely certain that the pilot circuits were cleaned and open during the carb rebuild. I couldn't have been more careful or more deliberate with the carb rebuild. Even took pictures all the way through. Also did the "spray carb cleaner in the appropriate orifices" test to check to see if the circuits were clean as directed in the rebuild instructions. Everything was open.

The mystery is that the bike did NOT do this immediately after the mechanical rebuild process (tank, carbs, brakes). It only started doing it now since it's been sitting in the garage for a couple of months. Gas tank is nearly full and has plenty of Stabil in it. Can't believe something could have gotten plugged up in that short amount of time.

Makes ya want to say "Hmmmmmmm?"

 

[Nessism]

Sounds like the bike isn't running on four cylinders. With the next cold start very carefully monitor the header temperature to see if any cylinders are not firing.

BTW, open the pilot screws to 3 full turns too. I've never seen a GS that ran properly on 2 turns open.

 

[blowerbike]

all good suggestions.
did you have the cams out?
if so could they they have been re-installed maybe a tooth out of time?
just a thought...

 

[WingMan71]

Thanks everyone for the troubleshooting tips.

I will definitely turn the pilot screws out to 3 turns. Easy to do.

I have checked the headers on warm up and they all seem to be firing at idle. I know they're all firing at speed because the engine pulls amazingly strong for its size when you get on it. I had my doubts about idle though at one point. The vacuum sync solved that issue.

I did not take the cams out when I checked the valves, so that should be good.

Supposed to be nice weather for most of the day today in Atlanta, so I'll turn out the pilot screws and see if that does it.

Thanks!!!

 

[Steve]

Although there might be the rare carb that runs correctly at 2 turns out, most of the ones that I have seen run best in the 2 1/4 to 2 3/4 range. When starting up a set of freshly-rebuilt carbs, I always set tham a bit rich at 3 turns, then tune from there.

By the way, not all the carbs in the rack will necessarily need the same adjustment, so don't just set them all to one setting and leave them. Tune each one individually. On my son's 650, one of the carbs does not 'come alive' until the pilot screw is out almost 4 turns.

.

 

[WingMan71]

... By the way, not all the carbs in the rack will necessarily need the same adjustment, so don't just set them all to one setting and leave them. Tune each one individually. On my son's 650, one of the carbs does not 'come alive' until the pilot screw is out almost 4 turns.

Steve,

What's the proper way to tune the pilot circuits individually?

Do you adjust the pilot screw for fastest idle speed as indicated on the tach, or what?

Thanks much!

 

[Nessism]

Steve,

What's the proper way to tune the pilot circuits individually?

Do you adjust the pilot screw for fastest idle speed as indicated on the tach, or what?

Thanks much!

Koolaid Kid made a tutorial on how to tweak the pilot screws. You may want to search out the link.

 

[WingMan71]

Koolaid Kid made a tutorial on how to tweak the pilot screws. You may want to search out the link.

Found it! THANKS!

Update:

Sun came out this afternoon so I put the bike on the center stand in the driveway and ran through Koolaid Kid's adjustment procedure.

My pilot screws were originally all set to 2 turns out. (I was able to adjust them today by just lifting up the back of the tank about four inches with everything still hooked up, so that helped.)

I made adjustments to them in 1/4 turn increments on the center stand with the bike running, and then put the seat back on and did a road test up and down the street a bit.

I tried 2-1/4, 2-1/2, 2-3/4 and 3 turns out. The magic number on my bike was 2-3/4 turns out.

BIKE RUNS BETTER THAN EVER!

The idle settles right down quickly when the throttle is let off and sits there nice and steady. No more problems starting off in 1st. Pulls hard from right off idle. Very strong little motor... it surprises me.

Thanks all for taking time over the holidays to post up answers and help me out! :applouse:

 

[Steve]

Steve,

What's the proper way to tune the pilot circuits individually?

Do you adjust the pilot screw for fastest idle speed as indicated on the tach, or what?

Thanks much!

There are several ways to tune them, most of which can be called "proper". Koolaid Kid's version is one way. I tend to use that more as a diagnostic tool, rather than a tuning method, though.

Personally, I will adjust the mixture screws while the vacuum gauges are connected for a carb sync. Do the vacuum sync first, to assure that all the carbs are at least providing the same amount of air. Next, turn the mixture (pilot) screw slowly, watching for a change in vacuum. As the mixture gets close to the best-possible ratio, the engine speed will increase. Might not be quite enough to see on a tach, especially if the needle bounces a bit, though. Lean the mixture a bit until the vacuum starts to drop, then richen it back up about 1/8 turn. Repeat on the other carbs. After doing all four carbs, I usually go back and verify that a 1/4 turn in on each screw definitly drops the engine speed (and vacuum), then turn it back to where it was.

.