Newbie question -- throttle stuck open?

[JShapiro]

Howdy.

Just picked up my first motorcycle, a 1978 GS400, about a week ago. Today I had my first problem with it -- the throttle got stuck open about two miles from my house. The throttle grip snaps back in place nicely so I guess it's stuck open at the other end of the cable.

I'm pretty green w/mechanic work and would love some tips on how to fix this. Thanks!

 

[tkent02]

Take it apart. See whats wrong. Fix it. Put it back together. Ride it!

 

[tom203]

Howdy.

Just picked up my first motorcycle, a 1978 GS400, about a week ago. Today I had my first problem with it -- the throttle got stuck open about two miles from my house. The throttle grip snaps back in place nicely so I guess it's stuck open at the other end of the cable.

I'm pretty green w/mechanic work and would love some tips on how to fix this. Thanks!

That always makes for an exciting ride! Does this bike still have two cables coming out of throttle grip- one pulls one way (opens throttle), the other pulls back (hopefully closes throttle) ? Best to remove gas tank and follow cables to carbs to make sure everything is still attached.

 

[JShapiro]

That always makes for an exciting ride! Does this bike still have two cables coming out of throttle grip- one pulls one way (opens throttle), the other pulls back (hopefully closes throttle) ? Best to remove gas tank and follow cables to carbs to make sure everything is still attached.

Yep, it's got two cables. It's a bit hard to see under the tank, but it looks as if everything is still attached.

The throttle got stuck open as I was approaching a stop sign. I came to a stop w/the clutch in and it was still revving at 4k. I pulled off the road, killed the engine, turned it back on, and it steadily climbed from about 1k to 4k rpms. Then I poked at the throttle cables where they attach to whatever pivoting part is it that they attach to.

That seemed to fix it, although nothing visibly came un-stuck. I was able to ride home fine but don't know if I should ride it again as is. Do y'all think this could happen again?

 

[JEEPRUSTY]

Yep, it's got two cables. It's a bit hard to see under the tank, but it looks as if everything is still attached.

The throttle got stuck open as I was approaching a stop sign. I came to a stop w/the clutch in and it was still revving at 4k. I pulled off the road, killed the engine, turned it back on, and it steadily climbed from about 1k to 4k rpms. Then I poked at the throttle cables where they attach to whatever pivoting part is it that they attach to.

That seemed to fix it, although nothing visibly came un-stuck. I was able to ride home fine but don't know if I should ride it again as is. Do y'all think this could happen again?

Yes it will happen again.
Disassemble and lube the cable.
It may be worn and chafing in the tube.
It may be that your routing is causing or at least contributing to the issue.

My bet its bone dry and mucky inside.

 

[Agemax]

Take it apart. See whats wrong. Fix it. Put it back together. Ride it!

helpful as usual to a newbie

 

[mike_of_bbg]

Search the forum for "hanging idle"; could be caused by air leaks that are intermittent or heat related. But you definitely need to take a look at the mechanism and make sure it moves smoothly and is not binding. Check your cable routing vs. the manual.

Once I tightened up one of my intake boots and the screw stuck out just enough to occasionally hit the throttle mech until I moved it.

 

[Nessism]

My thought was air leak too. Very common problem.

What we have here is a 33 year old motorcycle desperately in need of maintenance. A hanging idle, or binding throttle cable are just the tip of the iceberg. Makes me wonder when was the last time the valves were adjusted, carbs cleaned and synced, etc.

The only way to assure the bike is going to be reliable, and not destroy itself though neglect, is to go though the service manual maintenance schedule and take care of everything. A lot of work, but necessary.

 

[JShapiro]

My thought was air leak too. Very common problem.

What we have here is a 33 year old motorcycle desperately in need of maintenance. A hanging idle, or binding throttle cable are just the tip of the iceberg. Makes me wonder when was the last time the valves were adjusted, carbs cleaned and synced, etc.

The only way to assure the bike is going to be reliable, and not destroy itself though neglect, is to go though the service manual maintenance schedule and take care of everything. A lot of work, but necessary.

I bought the bike from a mechanic and he said that very recently (i.e. this year) he'd cleaned and sync'ed the carbs and checked valve clearance and found it to be good. In fact, he did a lot of work to it and told me all maintenance was up to date.

I'll work on cleaning the cables for the throttle. Also I'll check the forum for hanging idle threads.

And thank you all for your prompt and helpful responses.

 

[JEEPRUSTY]

I bought the bike from a mechanic and he said that very recently (i.e. this year) he'd cleaned and sync'ed the carbs and checked valve clearance and found it to be good. In fact, he did a lot of work to it and told me all maintenance was up to date.

I'll work on cleaning the cables for the throttle. Also I'll check the forum for hanging idle threads.

And thank you all for your prompt and helpful responses.

People lie. I am nto saying this fellow did but...........
People lie. Or sometime labour under mis-aprehensions.

The only way you can no for sure is to run throught the magic list ont he mega welcome.

My money is on stuck gummed up cable. Esp if it has only done it once.

 

[JShapiro]

Read a few 'hanging idle' threads and saw someone mention that the old GS bikes will idle really high if the choke is left on. I've been leaving the choke on for a good while after starting the bike up since it has a really hard time not dying when I come to a stop. Could this have something to do with it?

I can't remember 100% but I'm fairly certain the choke was on. This happened about 2 miles from my house, so about 5 minutes of riding give or take.

 

[mike_of_bbg]

Yes!

The "choke" on the GSes is actually a "fuel enrichment circuit". Turning it on feeds the bike an enrichened fuel/air mixture. Yes, it can idle VERY high with the choke full on. The choke is not a "on or off" device, you can turn it down. When I first start my bike in hot weather the choke will be 1/2 to 3/4, and as it warms up and starts revving I'll turn it down to keep it around 1500-2000 RPM. Usually it's just a sliver left when I pull away, and I turn that off after a minute or so.

 

[mike_of_bbg]

If your bike can't idle when warm without the choke, you're running lean and need to get to the bottom of that.

 

[JShapiro]

My choke lever is all or nothing -- all it has are 2 positions, on or off.

How long after I get the bike started should I be able to turn off the choke and have it idle on it's own w/out dying?

 

[tthayer]

If you watch the choke rail on top of the carbs when you actuate the lever, you should see it slide the chokes in and out of the carbs. It says ON and OFF on the top but there is some variability to it. You should be able to push the rail with your finger to get a feel for how much spring is there.

How long to leave the choke on is entirely dependent on temperature, humidity, etc... I generally turn mine down or off when the revs start to climb, but I'm a bad GS owner and haven't done my valve adjust yet so that could be part of it.

 

[JShapiro]

If you watch the choke rail on top of the carbs when you actuate the lever, you should see it slide the chokes in and out of the carbs. It says ON and OFF on the top but there is some variability to it. You should be able to push the rail with your finger to get a feel for how much spring is there.

How long to leave the choke on is entirely dependent on temperature, humidity, etc... I generally turn mine down or off when the revs start to climb, but I'm a bad GS owner and haven't done my valve adjust yet so that could be part of it.

I just checked and although it's designed to be either on or off, you're right, there does seem to be some adjustability -- good to know.

So just to be clear, you're saying I should leave the choke on until the engine revs up like it did this afternoon, then turn it down or off?

 

[tthayer]

Right. The choke is just to get the bike warmed up. If it won't run without the choke then you have other issues (air leaks). Have you replaced your air filter yet?

 

[JShapiro]

Right. The choke is just to get the bike warmed up. If it won't run without the choke then you have other issues (air leaks). Have you replaced your air filter yet?

I haven't changed it -- I don't know when it was last replaced.

It runs fine w/out the choke, but is very prone to conking out at stop signs so I've been keeping the choke on in an effort to keep it from dying.

 

[Steve]

. I've been leaving the choke on for a good while after starting the bike up since it has a really hard time not dying when I come to a stop. Could this have something to do with it?

So just to be clear, you're saying I should leave the choke on until the engine revs up like it did this afternoon, then turn it down or off?

Sounds like it's past time for a GOOD carb cleaning and re-o-ringing.

When the carbs are properly adjusted (along with the valves), you should not need the "choke" for more than 30-60 seconds, then you can pull away. By the time you get into second gear, you should be able to turn it completely OFF.

.

 

[Guest]

Mate I'm gonna pop in and say welcome to the forums, but not a lot I can add to the already excellent advice on the posts here

It does sounds suspiciously like either a hanging idle problem (unsealed air intake somewhere), excess choke, idle set to low (conking out), and/or an old throttle cable that needs lube.