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Chasing a sticking idle........Need carb help!
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Chasing a sticking idle........Need carb help!
Just finished ultrasonic cleaning and replacing all the O-rings on the carbs from my 1978 GS750. I set the fuel and air screws back to where they were before the cleaning. (3/4 turn and 1-1/2 turns). Now the bike is very slow to start when cold, and when warmed up it idles around 2,000 rpm unless I "blip" the throttle, then it goes back down to 1200 rpm. Once warmed up, the bike starts fine and the choke will raise the idle to around 3,000 rpm when applied. I have ridden the bike a few miles and it pulls and accelerates well throughout the entire rpm range. Adjusting the pilot air screws do not seem to have any effect on the idle at all??? I have not synced the carbs with a set of gauges yet. My question is, will a carb sync cure this, or do you think that I have other issues? Any idea of where to start???Ron
When I die, just cremate me and put me in my GS tank. That way I can go through these carbs, one more time!https://www.thegsresources.com/_forum/core/images/smilies/cool.png
1978 GS750E - November 2017 BOTM
1978 GS1000C - May 2021 BOTM
1982 GS1100E - April 2024 BOTM
1999 Honda GL1500SETags: None
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Forum LongTimerGSResource Superstar
Past Site Supporter
Super Site Supporter- Mar 2006
- 35549
- Torrance, CA
Sync may cure the idle issue but not the starting issue. Did you clean the float bowl choke passages and make sure they are open? Check the choke pick up tubes to assure they are open? And did you replace the intake boot O-rings or better yet replace the boots entirely?Ed
To measure is to know.
Mikuni O-ring Kits For Sale...https://www.thegsresources.com/_foru...ts#post1703182
Top Newbie Mistakes thread...http://www.thegsresources.com/_forum...d.php?t=171846
Carb rebuild tutorial...https://gsarchive.bwringer.com/mtsac...d_Tutorial.pdf
KZ750E Rebuild Thread...http://www.thegsresources.com/_forum...0-Resurrection
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Replaced the intake boots, all O-rings, even the boots going to the airbox. Checked and cannot find any air leaks. Choke passages are clear. Choke increases the rpms when warmed up so I think the choke is working as it should. Guess that a carb sync is in my future???Ron
When I die, just cremate me and put me in my GS tank. That way I can go through these carbs, one more time!https://www.thegsresources.com/_forum/core/images/smilies/cool.png
1978 GS750E - November 2017 BOTM
1978 GS1000C - May 2021 BOTM
1982 GS1100E - April 2024 BOTM
1999 Honda GL1500SE
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Forum LongTimerGSResource Superstar
Past Site Supporter
Super Site Supporter- Mar 2006
- 35549
- Torrance, CA
Originally posted by 1978GS750E View PostGuess that a carb sync is in my future???Ed
To measure is to know.
Mikuni O-ring Kits For Sale...https://www.thegsresources.com/_foru...ts#post1703182
Top Newbie Mistakes thread...http://www.thegsresources.com/_forum...d.php?t=171846
Carb rebuild tutorial...https://gsarchive.bwringer.com/mtsac...d_Tutorial.pdf
KZ750E Rebuild Thread...http://www.thegsresources.com/_forum...0-Resurrection
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Anytime you rebuild the carbs or do a valve service you HAVE to do a vacuum sync.Rob
1983 1100ES, 98' ST1100, 02' DR-Z400E and a few other 'bits and pieces'
Are you on the GSR Google Earth Map yet? http://www.thegsresources.com/_forum...d.php?t=170533
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A carb sync certainly won't hurt anything, but probably won't cure everything.
If nothing else, it ensures that each carb is pulling the same amount of mixture, so that adjusting the screws will actually make a difference.
How did you decide on your 3/4 turn and 1 1/2 turn settings on the screws?
If your intake and exhaust are stock, the 3/4 turn on the fuel screws is probably close, but the 1 1/2 might be a bit too much, making it run lean. Running lean makes it act a bit like you are describing. 1 1/4 turn should help to get it running better, but that is only to get it to a point where you can do the fine-tuning. It runs better with a too-rich mixture than it does with one that is too lean. Of course, it runs even better with the proper mixture, but take it one step at a time.
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mine: 2000 Honda GoldWing GL1500SE and 1980 GS850G'K' "Junior"
hers: 1982 GS850GL - "Angel" and 1969 Suzuki T250 Scrambler
#1 son: 1986 Yamaha Venture Royale 1300 and 1982 GS650GL "Rat Bagger"
#2 son: 1980 GS1000G
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Hmmm, does he have VM or BS?
I had a sticking idle on my VM's once that was caused mechanically, not by an air-leak.#1: 1979 GS 550 EC "Red" – Very first Bike / Overhaul thread New here? ☛ Read the Top 10 Newbie mistakes thread
#2: 1978 GS 550 EC "Blue" – Can't make it a donor / "Rebuild" thread Manuals (and much more): See Cliff's homepage here
#3: 2014 Moto Guzzi V7 II Racer – One needs a runner while wrenching
#4: 1980 Moto Guzzi V65C – Something to chill
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I set the fuel and air screws back to where they were before the cleaning. (3/4 turn and 1-1/2 turns).
They are VM carbs.
Roeme, what was the mechanical issue that you experienced causing the idle issue? Maybe that is something to look into.
Going to get gauges and do a sync in the next couple of weeks after a valve adjustment.
Thanks for the help!Last edited by 1978GS750E; 12-23-2018, 09:03 AM.Ron
When I die, just cremate me and put me in my GS tank. That way I can go through these carbs, one more time!https://www.thegsresources.com/_forum/core/images/smilies/cool.png
1978 GS750E - November 2017 BOTM
1978 GS1000C - May 2021 BOTM
1982 GS1100E - April 2024 BOTM
1999 Honda GL1500SE
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standswithabeer
all four evenly hot on start-up? i'd do a plug chop, to confirm a lean setting. if adjusting the pilot air screws does nothing (as stated in first post), idle circuit(s) maybe still be plugged. there's info on the web somewhere with a nice pic of where the carb spray should exit, when sprayed into each circuit.Last edited by Guest; 12-23-2018, 04:07 PM.
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Adjusting the pilot air screws do not seem to have any effect on the idle at all???
Plugging very common I found...then broken tips and improper assembly of the tiny spring, oring and washer...
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Originally posted by 1978GS750E View Post(...)
They are VM carbs.
Roeme, what was the mechanical issue that you experienced causing the idle issue? Maybe that is something to look into.
(...)#1: 1979 GS 550 EC "Red" – Very first Bike / Overhaul thread New here? ☛ Read the Top 10 Newbie mistakes thread
#2: 1978 GS 550 EC "Blue" – Can't make it a donor / "Rebuild" thread Manuals (and much more): See Cliff's homepage here
#3: 2014 Moto Guzzi V7 II Racer – One needs a runner while wrenching
#4: 1980 Moto Guzzi V65C – Something to chill
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Back to the original question: Check the routing of your throttle cable for any tight bends, sounds like it's hanging up and not returning all the way to the off position.1980 Yamaha XS1100G (Current bike)
1982 GS450txz (former bike)
LONG list of previous bikes not listed here.
I identify as a man but according to the label on a box of Stauffers Baked Lasagne I'm actually a family of four
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