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Post Subject:
carb leaking
carb leaking
I've got a problem with a carb on a '78 SR500 leaking through the
overflow. But it doesn't appear to be the standard ones of the valve not
closing or the floats not floating.
The bike was modified when I bought it (25 years ago!). It has a White Brothers kit in it with
a different piston, cam, and exhaust, and the carb is a Mikuni VM36,
not the original.
There were no changes to the bike prior to the start of the leaking.
It only leaks while running down the road. If I pull over and leave the engine idling it
does not leak, even if I put the petcock on prime. And yes, prime works
- I tested it :-). That would seem to rule out the valve.
When it first occurred, I did the standard things of replacing the valve, twice, and
eventually rebuilt the entire float bowl. Still leaked.
Someone suggested that there might be a crack in the float bowl. I dried out the float bowl
and filled it, first with gasoline and then with alcohol, and left it sit
overnight. No leaks.
Someone else suggested that the overflow hose was siphoning gas due to its placement in the
airstream. I tried moving it to various locations and finally put it in
a bottle through a rubber stopper with a hole in it. Still leaked.
Another suggestion was that the gas tank was pressurizing and forcing the valve open so I
drilled a hole through the gas cap. No effect.
The final suggestion was that somehow vibration was causing the gas in the bowl to cavitate.
I removed the air cleaner and tied the carb to the frame to change any
vibration frequency. That didn't work either.
In desperation, I bought a whole new carb. Guess what? It leaks the same way!
I've just about given up and decided to junk the bike or part it out on Ebay.
But I thought I'd see if anyone on this group has had the same problems or
knows a possible fix I haven't tried yet.
Help! Please!
I've got a problem with a carb on a '78 SR500 leaking through the
overflow. But it doesn't appear to be the standard ones of the valve not
closing or the floats not floating.
The bike was modified when I bought it (25 years ago!). It has a White Brothers kit in it with
a different piston, cam, and exhaust, and the carb is a Mikuni VM36,
not the original.
There were no changes to the bike prior to the start of the leaking.
It only leaks while running down the road. If I pull over and leave the engine idling it
does not leak, even if I put the petcock on prime. And yes, prime works
- I tested it :-). That would seem to rule out the valve.
When it first occurred, I did the standard things of replacing the valve, twice, and
eventually rebuilt the entire float bowl. Still leaked.
Someone suggested that there might be a crack in the float bowl. I dried out the float bowl
and filled it, first with gasoline and then with alcohol, and left it sit
overnight. No leaks.
Someone else suggested that the overflow hose was siphoning gas due to its placement in the
airstream. I tried moving it to various locations and finally put it in
a bottle through a rubber stopper with a hole in it. Still leaked.
Another suggestion was that the gas tank was pressurizing and forcing the valve open so I
drilled a hole through the gas cap. No effect.
The final suggestion was that somehow vibration was causing the gas in the bowl to cavitate.
I removed the air cleaner and tied the carb to the frame to change any
vibration frequency. That didn't work either.
In desperation, I bought a whole new carb. Guess what? It leaks the same way!
I've just about given up and decided to junk the bike or part it out on Ebay.
But I thought I'd see if anyone on this group has had the same problems or
knows a possible fix I haven't tried yet.
Help! Please!
Re: carb leaking
"Larry Blanchard" <lblanch@fastmail.fm> wrote
> It only leaks while running down the road. If I pull over and leave the
> engine idling it
> does not leak, even if I put the petcock on prime. And yes, prime works
> - I tested it :-). That would seem to rule out the valve.
>
Fascinating.
Back to basics.
If the overflow tube has a hose on it (that presumably extends down beyond
the frame) and it does NOT leak when standing at idle then:
1) How do you really KNOW that it leaks going down the road.......I mean
really.
2) Does it exhibit the same behavior with the hose OFF??
3) What happens standing still and revving the engine? Revving in gear with
tire off the ground?
Seems like I remember a case of the leak being at or near the petcock,
running down the hose then around the back of the carb and finally dripping
off the end of the overflow hose.
"Larry Blanchard" <lblanch@fastmail.fm> wrote
> It only leaks while running down the road. If I pull over and leave the
> engine idling it
> does not leak, even if I put the petcock on prime. And yes, prime works
> - I tested it :-). That would seem to rule out the valve.
>
Fascinating.
Back to basics.
If the overflow tube has a hose on it (that presumably extends down beyond
the frame) and it does NOT leak when standing at idle then:
1) How do you really KNOW that it leaks going down the road.......I mean
really.
2) Does it exhibit the same behavior with the hose OFF??
3) What happens standing still and revving the engine? Revving in gear with
tire off the ground?
Seems like I remember a case of the leak being at or near the petcock,
running down the hose then around the back of the carb and finally dripping
off the end of the overflow hose.
Re: carb leaking
On Thu, 13 Mar 2008 18:08:44 -0500, Just Me wrote:
>
> "Larry Blanchard" <lblanch@fastmail.fm> wrote
>
>> It only leaks while running down the road. If I pull over and leave the
>> engine idling it
>> does not leak, even if I put the petcock on prime. And yes, prime works
>> - I tested it :-). That would seem to rule out the valve.
>>
>
> Fascinating.
> Back to basics.
> If the overflow tube has a hose on it (that presumably extends down beyond
> the frame) and it does NOT leak when standing at idle then:
>
> 1) How do you really KNOW that it leaks going down the road.......I mean
> really.
I can look down and see it coming out of the hose. After I
proved that the hose wasn't siphoning, I positioned the hose where I could
see it without being a contortionist.
> 2) Does it exhibit the same behavior with the hose OFF??
I haven't tried that, but what would it prove?
> 3) What happens standing still and revving the engine?
It won't leak.
Revving in gear with
> tire off the ground?
>
I haven't tried that yet but I will. Thanks for the idea. If it leaks
then, what have I proved?
> Seems like I remember a case of the leak being at or near the petcock,
> running down the hose then around the back of the carb and finally dripping
> off the end of the overflow hose.
Unless it's magically penetrating the overflow hose that scenario is not
my problem. The gas is flowing INSIDE the hose.
Thanks for the response.
On Thu, 13 Mar 2008 18:08:44 -0500, Just Me wrote:
>
> "Larry Blanchard" <lblanch@fastmail.fm> wrote
>
>> It only leaks while running down the road. If I pull over and leave the
>> engine idling it
>> does not leak, even if I put the petcock on prime. And yes, prime works
>> - I tested it :-). That would seem to rule out the valve.
>>
>
> Fascinating.
> Back to basics.
> If the overflow tube has a hose on it (that presumably extends down beyond
> the frame) and it does NOT leak when standing at idle then:
>
> 1) How do you really KNOW that it leaks going down the road.......I mean
> really.
I can look down and see it coming out of the hose. After I
proved that the hose wasn't siphoning, I positioned the hose where I could
see it without being a contortionist.
> 2) Does it exhibit the same behavior with the hose OFF??
I haven't tried that, but what would it prove?
> 3) What happens standing still and revving the engine?
It won't leak.
Revving in gear with
> tire off the ground?
>
I haven't tried that yet but I will. Thanks for the idea. If it leaks
then, what have I proved?
> Seems like I remember a case of the leak being at or near the petcock,
> running down the hose then around the back of the carb and finally dripping
> off the end of the overflow hose.
Unless it's magically penetrating the overflow hose that scenario is not
my problem. The gas is flowing INSIDE the hose.
Thanks for the response.
Re: carb leaking
"Larry Blanchard" <lblanch@fastmail.fm> wrote
>> 2) Does it exhibit the same behavior with the hose OFF??
>
> I haven't tried that, but what would it prove?
>
When you are grasping at straws, you don't want to miss ANY, no matter how
small.
Often a tiny piece of the puzzle may reveal the hidden image.
IOW, I don't know; just a wild idea. !!! ;-)
> Unless it's magically penetrating the overflow hose that scenario is not
> my problem. The gas is flowing INSIDE the hose.
>
Well, that's kind of the point. Appearances can be deceiving.
OK, so plug the hose firmly for a while.
Why? I don't know, just another wild idea.
"Larry Blanchard" <lblanch@fastmail.fm> wrote
>> 2) Does it exhibit the same behavior with the hose OFF??
>
> I haven't tried that, but what would it prove?
>
When you are grasping at straws, you don't want to miss ANY, no matter how
small.
Often a tiny piece of the puzzle may reveal the hidden image.
IOW, I don't know; just a wild idea. !!! ;-)
> Unless it's magically penetrating the overflow hose that scenario is not
> my problem. The gas is flowing INSIDE the hose.
>
Well, that's kind of the point. Appearances can be deceiving.
OK, so plug the hose firmly for a while.
Why? I don't know, just another wild idea.
Re: carb leaking
On Mar 13, 11:48 pm, "Just Me" <hitchhi...@dont.panic> wrote:
> "Larry Blanchard" <lbla...@fastmail.fm> wrote
>
> >> 2) Does it exhibit the same behavior with the hose OFF??
>
> > I haven't tried that, but what would it prove?
>
> When you are grasping at straws, you don't want to miss ANY, no matter how
> small.
> Often a tiny piece of the puzzle may reveal the hidden image.
> IOW, I don't know; just a wild idea. !!! ;-)
>
> > Unless it's magically penetrating the overflow hose that scenario is not
> > my problem. The gas is flowing INSIDE the hose.
>
> Well, that's kind of the point. Appearances can be deceiving.
>
> OK, so plug the hose firmly for a while.
> Why? I don't know, just another wild idea.
Maybe the bowl is getting overheated? Maybe air is getting pushed into
the bowl vents? I am curious to know what you find... My 69 CD175 does
a bit of this, I think it is just the float bouncing around. Maybe
your float is too high?
On Mar 13, 11:48 pm, "Just Me" <hitchhi...@dont.panic> wrote:
> "Larry Blanchard" <lbla...@fastmail.fm> wrote
>
> >> 2) Does it exhibit the same behavior with the hose OFF??
>
> > I haven't tried that, but what would it prove?
>
> When you are grasping at straws, you don't want to miss ANY, no matter how
> small.
> Often a tiny piece of the puzzle may reveal the hidden image.
> IOW, I don't know; just a wild idea. !!! ;-)
>
> > Unless it's magically penetrating the overflow hose that scenario is not
> > my problem. The gas is flowing INSIDE the hose.
>
> Well, that's kind of the point. Appearances can be deceiving.
>
> OK, so plug the hose firmly for a while.
> Why? I don't know, just another wild idea.
Maybe the bowl is getting overheated? Maybe air is getting pushed into
the bowl vents? I am curious to know what you find... My 69 CD175 does
a bit of this, I think it is just the float bouncing around. Maybe
your float is too high?
Re: carb leaking
On Mon, 17 Mar 2008 06:35:48 -0700, JS wrote:
>
> Maybe the bowl is getting overheated? Maybe air is getting pushed into
> the bowl vents? I am curious to know what you find... My 69 CD175 does
> a bit of this, I think it is just the float bouncing around. Maybe
> your float is too high?
I have played with the float level to no effect. On the first carb, I
finally got it so low the bike wouldn't hardly run :-). I don't see any
evidence of overheating, but I'll try moving the vent hose around.
Thanks for the response.
What really has me scratching my head is that I know of no change to the
bike that would have started all this.
I've had the bike for 25 years so I've gotten my moneys worth and more out
of it. I just hate to give it up because it fits me so well. I bought
another bike ('83 Suzuki GS450L) so I could keep riding, but it doesn't
fit nearly as well. I like the old standards. Of course, that may be
because I am one - I'm 70 :-).
Maybe I'll try to find a Kawasaki W650. Anyone have good/bad things to
say about that bike?
On Mon, 17 Mar 2008 06:35:48 -0700, JS wrote:
>
> Maybe the bowl is getting overheated? Maybe air is getting pushed into
> the bowl vents? I am curious to know what you find... My 69 CD175 does
> a bit of this, I think it is just the float bouncing around. Maybe
> your float is too high?
I have played with the float level to no effect. On the first carb, I
finally got it so low the bike wouldn't hardly run :-). I don't see any
evidence of overheating, but I'll try moving the vent hose around.
Thanks for the response.
What really has me scratching my head is that I know of no change to the
bike that would have started all this.
I've had the bike for 25 years so I've gotten my moneys worth and more out
of it. I just hate to give it up because it fits me so well. I bought
another bike ('83 Suzuki GS450L) so I could keep riding, but it doesn't
fit nearly as well. I like the old standards. Of course, that may be
because I am one - I'm 70 :-).
Maybe I'll try to find a Kawasaki W650. Anyone have good/bad things to
say about that bike?
Re: carb leaking
On Mon, 17 Mar 2008 09:23:00 -0700, Larry Blanchard <lblanch@fastmail.fm> wrote:
>I have played with the float level to no effect.
Maybe your float doesn't float. Take it out and shake it. If there's gas
inside, you can feel/hear it slosh. Pinholes can be patched with epoxy. Just
be sure to get all the gas out first.
--
Jack
On Mon, 17 Mar 2008 09:23:00 -0700, Larry Blanchard <lblanch@fastmail.fm> wrote:
>I have played with the float level to no effect.
Maybe your float doesn't float. Take it out and shake it. If there's gas
inside, you can feel/hear it slosh. Pinholes can be patched with epoxy. Just
be sure to get all the gas out first.
--
Jack
Re: carb leaking
On Mon, 17 Mar 2008 13:40:07 -0400, Jack Hunt wrote:
> On Mon, 17 Mar 2008 09:23:00 -0700, Larry Blanchard <lblanch@fastmail.fm> wrote:
>
>>I have played with the float level to no effect.
>
> Maybe your float doesn't float. Take it out and shake it. If there's gas
> inside, you can feel/hear it slosh. Pinholes can be patched with epoxy. Just
> be sure to get all the gas out first.
Thanks Jack, but you must have missed my first post. I rebuilt the float
bowl in one carb, including brand new floats, and finally installed a
whole new carb.
It only leaks when moving, not when sitting still. Even revving it to the
same RPM. If it were as simple as a sinking float, I'd have found it long
ago.
On Mon, 17 Mar 2008 13:40:07 -0400, Jack Hunt wrote:
> On Mon, 17 Mar 2008 09:23:00 -0700, Larry Blanchard <lblanch@fastmail.fm> wrote:
>
>>I have played with the float level to no effect.
>
> Maybe your float doesn't float. Take it out and shake it. If there's gas
> inside, you can feel/hear it slosh. Pinholes can be patched with epoxy. Just
> be sure to get all the gas out first.
Thanks Jack, but you must have missed my first post. I rebuilt the float
bowl in one carb, including brand new floats, and finally installed a
whole new carb.
It only leaks when moving, not when sitting still. Even revving it to the
same RPM. If it were as simple as a sinking float, I'd have found it long
ago.
Re: carb leaking
On Mar 17, 3:33 pm, Larry Blanchard <lbla...@fastmail.fm> wrote:
> On Mon, 17 Mar 2008 13:40:07 -0400, Jack Hunt wrote:
> > On Mon, 17 Mar 2008 09:23:00 -0700, Larry Blanchard <lbla...@fastmail.fm> wrote:
>
> >>I have played with the float level to no effect.
>
> > Maybe your float doesn't float. Take it out and shake it. If there's gas
> > inside, you can feel/hear it slosh. Pinholes can be patched with epoxy. Just
> > be sure to get all the gas out first.
>
> Thanks Jack, but you must have missed my first post. I rebuilt the float
> bowl in one carb, including brand new floats, and finally installed a
> whole new carb.
>
> It only leaks when moving, not when sitting still. Even revving it to the
> same RPM. If it were as simple as a sinking float, I'd have found it long
> ago.
So if I read your posts correctlly, you owned the bike for many
years, there was some point where this problem started an
some point earlier when things worked fine ? You also
swapped a whole new carb in and still have a problem.
Can you make it happen by bouncing the suspension hard ?
Bumps and maybe some heat are the only things I can think
of that wouldn't be happening when it's stationary.
Sounds almost like some other component in the fuel delivery
system masquerading as a carb problem, though I can't
imagine what that would be.
On Mar 17, 3:33 pm, Larry Blanchard <lbla...@fastmail.fm> wrote:
> On Mon, 17 Mar 2008 13:40:07 -0400, Jack Hunt wrote:
> > On Mon, 17 Mar 2008 09:23:00 -0700, Larry Blanchard <lbla...@fastmail.fm> wrote:
>
> >>I have played with the float level to no effect.
>
> > Maybe your float doesn't float. Take it out and shake it. If there's gas
> > inside, you can feel/hear it slosh. Pinholes can be patched with epoxy. Just
> > be sure to get all the gas out first.
>
> Thanks Jack, but you must have missed my first post. I rebuilt the float
> bowl in one carb, including brand new floats, and finally installed a
> whole new carb.
>
> It only leaks when moving, not when sitting still. Even revving it to the
> same RPM. If it were as simple as a sinking float, I'd have found it long
> ago.
So if I read your posts correctlly, you owned the bike for many
years, there was some point where this problem started an
some point earlier when things worked fine ? You also
swapped a whole new carb in and still have a problem.
Can you make it happen by bouncing the suspension hard ?
Bumps and maybe some heat are the only things I can think
of that wouldn't be happening when it's stationary.
Sounds almost like some other component in the fuel delivery
system masquerading as a carb problem, though I can't
imagine what that would be.
Re: carb leaking
"Rob Kleinschmidt" <Rkleinsch1216128@aol,com > wrote
> Sounds almost like some other component in the fuel delivery
> system masquerading as a carb problem, though I can't
> imagine what that would be.
>
Like I said: Things may NOT be what they seem.
When you have eliminated all the possible causes, then you must examine the
impossible ones !! ;-)
"Rob Kleinschmidt" <Rkleinsch1216128@aol,com > wrote
> Sounds almost like some other component in the fuel delivery
> system masquerading as a carb problem, though I can't
> imagine what that would be.
>
Like I said: Things may NOT be what they seem.
When you have eliminated all the possible causes, then you must examine the
impossible ones !! ;-)
Re: carb leaking
On Mar 17, 4:19 pm, "Just Me" <hitchhi...@dont.panic> wrote:
> "Rob Kleinschmidt" <Rkleinsch1216...@aol,com > wrote
>
> > Sounds almost like some other component in the fuel delivery
> > system masquerading as a carb problem, though I can't
> > imagine what that would be.
>
> Like I said: Things may NOT be what they seem.
>
> When you have eliminated all the possible causes, then you must examine the
> impossible ones !! ;-)
One other question. Does the behavior change at all with
the tank near empty and on reserve ?
On Mar 17, 4:19 pm, "Just Me" <hitchhi...@dont.panic> wrote:
> "Rob Kleinschmidt" <Rkleinsch1216...@aol,com > wrote
>
> > Sounds almost like some other component in the fuel delivery
> > system masquerading as a carb problem, though I can't
> > imagine what that would be.
>
> Like I said: Things may NOT be what they seem.
>
> When you have eliminated all the possible causes, then you must examine the
> impossible ones !! ;-)
One other question. Does the behavior change at all with
the tank near empty and on reserve ?
Re: carb leaking
On Mon, 17 Mar 2008 17:54:33 -0700, Rob Kleinschmidt wrote:
> One other question. Does the behavior change at all with
> the tank near empty and on reserve ?
I haven't actually tried varying the fuel in the tank other than it's
normal diminishment, but I have tried the petcock on prime, reserve, and
normal - no difference.
On Mon, 17 Mar 2008 17:54:33 -0700, Rob Kleinschmidt wrote:
> One other question. Does the behavior change at all with
> the tank near empty and on reserve ?
I haven't actually tried varying the fuel in the tank other than it's
normal diminishment, but I have tried the petcock on prime, reserve, and
normal - no difference.
Re: carb leaking
On Mar 18, 8:17 am, Larry Blanchard <lbla...@fastmail.fm> wrote:
> On Mon, 17 Mar 2008 17:54:33 -0700, Rob Kleinschmidt wrote:
> > One other question. Does the behavior change at all with
> > the tank near empty and on reserve ?
>
> I haven't actually tried varying the fuel in the tank other than it's
> normal diminishment, but I have tried the petcock on prime, reserve, and
> normal - no difference.
I guess what I'm wondering is whether the tank itself is
fuel tight and not sloshing fuel that might wind up
looking like a carb leak. Wouldn't hurt to run it
near empty on the wild offchance that it might
change the behavior.
It's puzzling that you swapped carbs and got the
same behavior. It's also puzzling that the problem
happens only when riding and not when parked.
On Mar 18, 8:17 am, Larry Blanchard <lbla...@fastmail.fm> wrote:
> On Mon, 17 Mar 2008 17:54:33 -0700, Rob Kleinschmidt wrote:
> > One other question. Does the behavior change at all with
> > the tank near empty and on reserve ?
>
> I haven't actually tried varying the fuel in the tank other than it's
> normal diminishment, but I have tried the petcock on prime, reserve, and
> normal - no difference.
I guess what I'm wondering is whether the tank itself is
fuel tight and not sloshing fuel that might wind up
looking like a carb leak. Wouldn't hurt to run it
near empty on the wild offchance that it might
change the behavior.
It's puzzling that you swapped carbs and got the
same behavior. It's also puzzling that the problem
happens only when riding and not when parked.
Re: carb leaking
On Tue, 18 Mar 2008 11:41:45 -0700, Rob Kleinschmidt wrote:
> I guess what I'm wondering is whether the tank itself is
> fuel tight and not sloshing fuel that might wind up
> looking like a carb leak. Wouldn't hurt to run it
> near empty on the wild offchance that it might
> change the behavior.
>
Someone else asked that. SOmehow or other such a leak would have to get
the gas inside the overflow hose, 'cause that's definitely where it's
coming from :-).
> It's puzzling that you swapped carbs and got the
> same behavior. It's also puzzling that the problem
> happens only when riding and not when parked.
Puzzling is one of the milder words I've used :-).
On Tue, 18 Mar 2008 11:41:45 -0700, Rob Kleinschmidt wrote:
> I guess what I'm wondering is whether the tank itself is
> fuel tight and not sloshing fuel that might wind up
> looking like a carb leak. Wouldn't hurt to run it
> near empty on the wild offchance that it might
> change the behavior.
>
Someone else asked that. SOmehow or other such a leak would have to get
the gas inside the overflow hose, 'cause that's definitely where it's
coming from :-).
> It's puzzling that you swapped carbs and got the
> same behavior. It's also puzzling that the problem
> happens only when riding and not when parked.
Puzzling is one of the milder words I've used :-).
Re: carb leaking
On Mar 18, 7:41 pm, Larry Blanchard <lbla...@fastmail.fm> wrote:
> On Tue, 18 Mar 2008 11:41:45 -0700, Rob Kleinschmidt wrote:
> > I guess what I'm wondering is whether the tank itself is
> > fuel tight and not sloshing fuel that might wind up
> > looking like a carb leak. Wouldn't hurt to run it
> > near empty on the wild offchance that it might
> > change the behavior.
>
> Someone else asked that. SOmehow or other such a leak would have to get
> the gas inside the overflow hose, 'cause that's definitely where it's
> coming from :-).
>
> > It's puzzling that you swapped carbs and got the
> > same behavior. It's also puzzling that the problem
> > happens only when riding and not when parked.
>
> Puzzling is one of the milder words I've used :-).
Did you rebuild the petcock? Maybe it is stuck in free flow and the
slight jiggling of riding lets too much gas pass the needle valve? Is
it a vaccum operated petcock?
On Mar 18, 7:41 pm, Larry Blanchard <lbla...@fastmail.fm> wrote:
> On Tue, 18 Mar 2008 11:41:45 -0700, Rob Kleinschmidt wrote:
> > I guess what I'm wondering is whether the tank itself is
> > fuel tight and not sloshing fuel that might wind up
> > looking like a carb leak. Wouldn't hurt to run it
> > near empty on the wild offchance that it might
> > change the behavior.
>
> Someone else asked that. SOmehow or other such a leak would have to get
> the gas inside the overflow hose, 'cause that's definitely where it's
> coming from :-).
>
> > It's puzzling that you swapped carbs and got the
> > same behavior. It's also puzzling that the problem
> > happens only when riding and not when parked.
>
> Puzzling is one of the milder words I've used :-).
Did you rebuild the petcock? Maybe it is stuck in free flow and the
slight jiggling of riding lets too much gas pass the needle valve? Is
it a vaccum operated petcock?
