Idle problems

[agh1989]

Hello! I have some problem with my idle.
the bike is an GS750 -82. Original air box and 4 into 1 Delkevic exhaust. Stock jetting.
It will start on choke, revs good, quite high rpm on full choke.
but soon as i let go of the choke it dies.. Even when the engine is hot.
I have cleaned all the jets.
Anyone know where to start?

 

[rphillips]

You didn't say, have you checked the idle adjustment under the carbs?

 

[Rich82GS750TZ]

Depending on model you either have a thumb lever under the left hand control or a pull knob centered under the instrument cluster. Either mechanism provides for holding the cable to the enriching circuit (choke) on the carb rack in the position where you set it. You say “let go of the choke”, so I assume your lever or knob is going back to fully closed when you “let go”. The thumb lever has a screw under it that could be tightened if not holding in position. The pull knob has a knurled collar that can be tightened to allow the shaft under the knob to stay wherever you let go of it.

If not run for a day or more you may have to start at full choke, progressively backing off as rpms increase, possibly for several minutes until the engine settles at idle with the choke completely off.

And as rphillips wrote above. Once you get the engine warm and get it to idle without choke, adjust the knob that pokes out rearward below carbs 2 & 3. You can use a long flat head screwdriver to do this so as not to touch anything hot. Give it a gentle tap to figure out which way raise the rpms and which way lowers it. 1100 rpm would be ideal. Slightly higher won’t hurt anything.

 

[agh1989]

Thanks for the answers!

Yes i have tried to turn on the thumb lever, when the choke was fully on, that made the rpm go up, Still died when i turned the choke back to off tho.
Maybe i wasnt turning it enough? Maybe the engine wasnt hot enough? I can try screw it in a bit more today.
(Dont really know the engine temp because i dont have any temp gauge or rpm on at the moment). But i left it running on choke for about 2min, so you barely could touch the cylinders.

Yes i have a thumb lever for the choke, i Will look if i can tighten it, thanks for the advise, because now it snaps back to off when i let go off it.

 

[rphillips]

Get it started with choke full on, as it warms up, rpm will go up. as it goes up, gradually decrease choke to keep rpm near 12 to 13 hundred & keep going gradually & see what happens.

 

[gustovh]

It’s time to pull and clean/dip the carbs.

V

 

[tom203]

It’s time to pull and clean/dip the carbs.

V

Absolutely, your idle circuit passages are likely clogged, not permitting enough mixture flow as you back off “choke” so bike dies.

 

[agh1989]

Hi, i have allready cleand the carbs and all the jets.
did it by hand and also used a ultrasonic cleaner.

 

[tom203]

So you fully disassembled all the carbs, not just from the rack…before the ultrasonic ?

 

[agh1989]

No i kept all 4 on the rack, but took out all the jets, and needle.
maybe i should have dissamble it more?

 

[tom203]

Sadly yes….then you need to replace o-rings too.
lots of tiny drilled passages to clean out
Hopefully you can see this link

https://gsarchive.bwringer.com/mtsac/~cliff/storage/gs/Mikuni_BS-CV_Carburetor_Rebuild_Tutorial.pdf

 

[agh1989]

Hi again, found another thing now, the Pilot screws was almost to tight i think. 1 was all the way to the bottom and the other 3 was open a half turn. If i read in the manual for the BS32SS it only says ”Pre set” but in the Rebuild guide it says 2 and half turn out.
thing is mine doesnt look the same as in the Guide, the screw on my carbs bottom starts earlier if you know what i mean. It feels like if i screw it up 5 turns it will fall out.
you think 2,5 turn is Pre-set?
it is in bottom in my picture. Thinking i can try this first before tearing down the carbs again.

 

[rphillips]

Not a carb mechanic but what you're say'in seems reasonable. How bou't turn them all in till bottom and write it down. Then back them all back to the recommended 2 1/2 turns out, see what happens. I'd do everything I could think of before the complete tare down. If all the simple, easy stuff fails, it's time for a complete do everything.

 

[tom203]

Those pilot screws are preset at factory at 2.5 turns off bottoming, but they get capped to prevent tampering..at least over here. 2 to 3 turns out is normal for good running. If yours are way off, maybe someone screwed up. But there’s always the chance that the tiny points on these screws are damaged . At the very least, I think you need to remove these pilot screw and inspect ….compare them to each other, in case one or more shows damage.

 

[gustovh]

If you didn’t remove those pilot screws for carb cleaning, you didn’t clean your carbs. Do a full tear down and dip in good carb dip overnight, flush with the hottest water that you can. Then ultrasound them and all parts, and rinse in very hot water again and as soon as you can handle the carb bodies, blow them out with compressed air. Verify that all passages are clear including the hole in the float bowl.

Now you can reassemble. Be sure to check the tips of the pilot screws, they should come almost to a point and all be the same length. After reassembly do a bench sync and set the pilots to the 21/2 turns out from “ lightly” seated, you can adjust them during the tuning session.

have fun.

V

 

[agh1989]

Helloooo guys! A little progress, but apparently solving one problem leads to another..

I backed down the pilot screws then opened them 2 turns, so now the bike idles perfect and revved up perfect BUT…
after a while (5min) it stalled and wouldnt start for a while.

Waited and it started fine again.
road it up and down the street slow in 1st gear, it wouldnt rev up. Almost felt like it was vacuum in the tank so
I took apart the fuel cap and cleaned it thinking it was vacuum problem. Is it anywhere else i should look?
Only have about 3-4 litre fuel, could this couse this?
maybe something electrical?

 

[tom203]

At the very least, you needed to remove all the pilot screws and inspect for damage..broken/blunt tips,etc . Just turning them out like you did, might have found a “sweet spot” on one or more of the carbs and let it idle ..but it falls flat as you feed it throttle….. pilot circuits have to be perfect as you give throttle

 

[rphillips]

Simple and easy, try running it on PRI instead of ON, just to see fuel is flowing properly... Unless the screen in the tank is clogged.

 

[agh1989]

tom203 Yes as you say its probably good just in case to inspect them.

rphillips i didnt think of that, i shall try that tomorrow
by ”screen” du you mean that one on the petcock?

 

[Grand Rouge]

Pilot Screw 'caps' The European spec.....Canadian spec too carbs ..did not have caps over the screws. The screws are longer and the top of the screw is generally flush with the carb body opening

There were (apparently) no published restrictions or government decrees prohibiting adjustment.