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RPMs hang, drop slowly 79 GS850

  • Thread starter Thread starter sltstl
  • Start date Start date
S

sltstl

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Just bought a 79 GS850, ran great at first, but the more I ride the more it does this: When you let off the throttle, the RPM's stick for a few seconds and then drop very slowly. If I accelerate and then pull in the clutch, the RPMs race really high before slowly coming back down again. I checked the throttle cable, its not sticking. Is this just due to a leaky intake boot?
 
sltstl said:
Just bought a 79 GS850, ran great at first, but the more I ride the more it does this: When you let off the throttle, the RPM's stick for a few seconds and then drop very slowly. If I accelerate and then pull in the clutch, the RPMs race really high before slowly coming back down again. I checked the throttle cable, its not sticking. Is this just due to a leaky intake boot?
Click to expand...

Check out MisterCinders' help thread. Also, Check out Cliff's help page. Do yourself a favor and read everything on his site a few times before doing anything else. The "hanging" is a classic problem on the forums.

Welcome to the forums :D:D
 
And yes, that is one (but most likely not all) of your problems.
 
koolaid_kid said:
And yes, that is one (but most likely not all) of your problems.
Click to expand...
And the fun begins ;) Hopefully theres not too much else to it, previous owner replaced all the o-rings and cleaned/adjusted the carbs. it idles great and runs good, just started doing this trick. I'll just slap some duct tape on the intake boots and call it a day.......Ha! j/k, I'll order some new ones:D
 
sltstl said:
And the fun begins ;) Hopefully theres not too much else to it, previous owner claims he replaced all the o-rings and cleaned/adjusted the carbs. it idles great and runs good, just started doing this trick. I'll just slap some duct tape on the intake boots and call it a day.......Ha! j/k, I'll order some new ones:D
Click to expand...
Fixed it for you. Trust, but verify.
If he did not replace those intake boot o-rings, question what else he did not do.
Go to cycleorings.com, Bob will help you out.
 
Well...I HAVE replaced the manifold orings twice, checked all the linkage bolts that hold the slides to the throttle linkage, all new Robert Barr orings, 24 hours for each carb body in Berrymans, tons of carb spray and air each way thru the crabs when out of the sauce, poked and primpt out every hole in the jets..etc etc etc and STILL have had that hanging and slow decreasing RPM sybdrom. In fact one bike still has that issue. I even rebuilt a second set from ground up and retriple checked everything 9 times and still have it. Airbox sealed, new paper filter...the whole 100 yards...so what do you all say about that???
 
I would say it's a bit lean. A hanging idle is symptom of running a little lean. Just richen up the idle circuit a bit. If you take it to far and richen it to much, it will bog down after the throttle is blipped. :)
 
chuck, assuming this is a thread jack, I agree with LarryD. Classic symptoms. You mention one bike, do you have this on multiple bikes?
 
I had a similar problem on my old gs500, and it turned out to be the diaphragms. Check those for cracks and pin holes.
 
Not a thread jack at all...it was mentioned the manifold orings and many other possible causes...which I too have addressed on the 1000 and it seems to be a persitant thing with this one bike. None of the others have issues and I set them up all basically the same from the rebuilds. Pilot screws are out 7/8 turn from slightly seated and the mixture screws out 2...which is the same as i started with all the others, but this one isnt right for some reason. I wasnt jacking into his thread..just expounding that even though you do all these obvious things and its still persistent...then what is one to think.
 
I've mentioned this before a number of times, but I haven't seen it mentioned lately, so:

Carbs that need to be synced (balanced) will exhibit this behavior. A bench sync is a reasonable start, but you need to sync the carbs before you pull most of the hair from your head. (OK, that wouldn't be a lot of pulling in my case, but you get the idea).
 
New intake boots are on the way, but some initial poking around revealed a few interesting things.

1. My fuel petcock is only on/off. Looks like a replacement with no hookup for a vacuum line. I wonder if I have a loose vacuum line floating around, anyone know where that comes out?

2. I pulled the airfilter....K&N oil poured out. Previous owner way over-oiled it.

I ran out of light, more poking around tomorrow :D
 
Sooo.... I figured out that the vent hose connected to Carb 3 is actually the Vacuum hose for the fuel tank. When the previous owner swapped the petcock for a on/off version, he just draped that Vacuum hose with the vent hoses, completely open and sucking in air :eek: Now thats a heck of a vacuum leak :D

So I plugged it up, turned the air screws in a 1/4 turn to richen that up, and she is behaving much, much better. Now I'm just waiting for my K&N filter to dry out after washing all that oil off and then I can re-assemble everything and ride!!
 
Bike runs great!! I plugged the loose vacuum line, re-oiled the air filter, cleaned the carbs, and set the mixture screws which were all over the place. Honestly, I'm surprised the bike ran at all before all of this. This forum rocks, answered so manyof my questions just searching around.
 
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