86 gs650 High Idle after throttle up

[Anonymous]

Hi, I hope someone can give me a direction to go here, I'm trying to get my brother in laws '82 gs650 up and running after sitting outside for a year, I disassembled and cleaned the carbs and it starts but after I throttle up to 3 or 4k it continues to idle at that speed. if you shut the bike down and restart, it idles properly around 1500rpm, cv type mikuni carbs, the other thing is sometimes after shutting the bike off i get fuel drain out of the airbox which would normally indicate to me leaking float needle valves if it weren't for the fact that they are brand new and i checked float level settings as well, it almost seems as if vacuum is holding the main jet needles open, is that possible? and if so, how is it supposed to vent that vacuum? any info would be a help.

[vstan905]

First, check for a leak at the intake boots, that can screw up the idle. As far as the gas leak, sounds like a stuck float

[Anonymous]

sticking float seems possible, i'll have to drop the bowls and check that out. As far as the idle issue, i did check all the airbox to carb and carb to engine connections with spray carburetor cleaner while running but didn't notice any change in idle, if it were an air leak why would it only KEEP the idle high after i open the throttle instead of just raising on it's own, i'm an auto mechanic and if a car has a vacuum leak it raises the idle from the start, does a bike work differently ?

[earlfor]

You cant have a gas leak unless the petcock diaphram has taken a dump. If the petcock works properly, gas couldnt leak if you removed the float bowls and float needle valves when the bike is shut down. Since intake air pulls gas into the carbs, gas cannot leak upstream into the airbox when the bike is running.

You cannot set an idle speed correctly without first doing a vacuum synch on the carbs.

Earl

[KEITH KRAUSE]

The sticking throttle is either the piston/diapragm/spring assy' or the throttle plates not operating smoothly. As long as the motor's running, the vacuum will not allow the sticking part to return to "idle". Once the motor's off, vacuum's off, and the problem part returns to closed position.
If it was an intake leak, it would do this all the time once warmed up, not just after blipping the throttle.
Could be just one carb hanging it all up.

[Anonymous]

thanks!

All three answers helped me out, I realized that the fuel tank petcock was set on primary so it was freeflowing, I think the diaphram/piston assembly in carb 3 is hanging up a little bit due to some corrosion inside the cylinder, which i'm planning on trying to clean out with some emery cloth, and I also had not synced the carbs yet, both carbs 3 and 4 were a little more open to vacuum at idle than the others, that combined with the sticky cylinder wall was holding the idle up after acceleration. It does still hang up around 3k for just a second, but i think it's just because of the sticky cylinder, now I'm trying to figure out why the idle is so erratic when first started, idle jumps around in the high range no matter where i set the choke, unless it's about 2/3 of the way to off then the idle drops too low and it dies, that is until it warms up then it runs fine.
thanks again for the help, by the way my brother in law who owns this bike found this forum before me, you'll probably be hearing from him too.

[KEITH KRAUSE]

Hi. DON"T clean the carb body corrosion with emery cloth. In most cases, you should be able to get the body nice and slick by using Blue Magic, Semi-chrome polish, Mothers aluminum polish, etc. Rub that in there and you should see it get slick without too much effort.
The cold start problem sounds like a dirty choke starter jet tube in 1 or more carbs and/or dirty pilot circuit, and/or mixture screws not adjusted correctly. I assume the carbs are synched well, which would also cause this problem.
Also, you can have gas leaking from the carbs or airbox, even if the petcock is fine.
After shut down, there's enough fuel in the fuel line and passage to the bowls to drain past a slightly unseated float valve(s) and cause an overflow. With time, you can accumulate quite a bit into the airbox and crankcase. I've seen bikes leak a little like this while on the side stand, but not leak while on the centerstand. I've seen leaks with perfect looking float valves, even new float valves if they're the cheaper made ones. You can test for this by using a clear fuel line and monitoring the fuel level in the line.

[gspaul]

Also a little synthetic 2 stroke wiped aroud the carb piston prevents it sticking and slightly improves responce( old honda trick.......oops suzuki!)

[Anonymous]

Thanks, I'll give that a try.

I'll also try using the center stand for a bit and see if the problem reoccurs.
I'll let you know how it turns out.