Post by 57pan on Apr 10, 2006, 7:01pm
It will be running strong and then all of a sudden it will sputter and die. Pull to the side of the road and put the kickstand down, wait a couple of minutes and it will start right up again. It happened four more times before I got it home.
I am pretty certain that it's a fuel problem (as opposed to electrical) because when it dies I can get a few more bursts out of the motor when I twist the throttle. So it's acting like the intermediate circuit and also the idle circuit are not getting any fuel (like the bowl is empty), but there is still some fuel in the accelerator pump. (It's a Keihin butterfly carb).
I thought maybe something was obstructing the pickup tube in the tank so this past Sat. I drained the tank. Fuel flowed out of the hose at a pretty constant rate with no blockage. I pulled the petcock out and it seems OK (I can blow thru it freely). Checked the fuel filter (sintered metal style) - no blockage. I removed the carb twice and disassembled it, sprayed brake cleaner thru the passages and reassembled it. With the carb assembled I can hear the float go to the open or closed position when I rock it back and forth, and if I blow in the inlet while rocking it back and forth it will open and close properly. I've got the fuel line routed all the way around the back of the motor, not between the cylinders, and it doesn't have any sharp bends or kinks in it. I also have the insulator spacer between the carb and manifold.
Now when I think back I believe that I may have been having this problem very intermitantly in the past. A couple of times I thought I ran out of gas even though by my trip odometer I still had maybe twenty miles before I should have needed gas. On those two other occasions I managed to coast into a station and fill it up and it never did it again. There have also been times when I first started it up and after idling for a few minutes it would just die like I had forgotten to open the petcock. I'll admit that I have occasionally forgotten to open the petcock but that was not the case in these instances.
So, I'm looking for some more ideas. I'm willing to consider just about any possibility. Maybe even a different carb??? There is another thread on the board here about putting a CV40 carb on the panhead. If someone has one that is properly set up for a panhead (S&S 2-bolt manifold) that they would consider selling please PM me.
Post by 51Hog on Apr 10, 2006, 6:42pm
Are your caps vented?
Are the vents in the caps plugged?
When the bike dies, and you remove the cap to check to see that you actually have fuel, do you hear air enter the tank?
Post by 57pan on Apr 10, 2006, 7:22pm
Thanks for the reply. I forgot to mention that when this was happening to me I did try loosening the caps while riding it but it did not help.''51Hog wrote:
Are your caps vented?
Are the vents in the caps plugged?
When the bike dies, and you remove the cap to check to see that you actually have fuel, do you hear air enter the tank?''
Post by fourthgear on Apr 10, 2006, 7:54pm
I would check to see if the bowl vent on carb is partly blocked, I know ya said you blew the thing out but its easy to miss that vent and it may vent into the throttle body area and not out side the carb like a Linkert. You can also look at how much fuel comes out of the fuel line at carb , is it a good steady flow for a time?
Post by Fixman on Apr 10, 2006, 8:37pm
Might be vapor lock. Try routing the fuel line through the cylinders even though that would seem to be hotter.
Post by 57pan on Apr 11, 2006, 3:10am
The Keihin carb has a hollow tube that sticks up from the bottom of the bowl. This hollow tube acts as both a vent and an overflow. The vent/overflow tube is free and clear. When I drained the tank I was getting a good steady flow of gas out of the fuel line. Although, admittedly, the opening of the fuel line was much lower than when it is connected to the carb inlet.''fourthgear wrote:
I would check to see if the bowl vent on carb is partly blocked, I know ya said you blew the thing out but its easy to miss that vent and it may vent into the throttle body area and not out side the carb like a Linkert. You can also look at how much fuel comes out of the fuel line at carb , is it a good steady flow for a time?''
It's worth a try I guess. Maybe the back of the motor is actually hotter than between the cylinders... who knows? And maybe the longer fuel line required to route around the back motor has something to do with it.''Fixman wrote:
Might be vapor lock. Try routing the fuel line through the cylinders even though that would seem to be hotter.''
Thanks for the suggestions.
Post by fourthgear on Apr 11, 2006, 12:38pm
I think you should keep fuel line routing as short as possible , but you seem to be getting fuel as you said when you drained the tank. Heat can be a problem and may be there is too much in the back or the motor. Mine is run between the cyl. and I have a piece of wire loom over the hose from the fuel valve all the up to the carb inlet. Its the heavy duty plastic type thats split all along the length of it , so it is easy to put around the fuel line, you can get it at NAPA or other auto parts stores. You say it starts right up after sitting for a while, that does sound like fuel but , I had a loose condenser wire the just about acted the same way for a while then when it came completely loose (off ) she started back firing and just plain running shitty, just a thought.
Post by Red55FL on Apr 11, 2006, 1:28pm
A bad coil can act this way also.
Start and run fine till the coil gets hot, then shut down.
After the coil cools down, the engine will start and run fine till it gets hot again.
Just a thought.
Post by King on Apr 11, 2006, 7:43pm
I'm voting for a vapor lock. Especially since you loosened the caps when the problem occurred and there was no improvement.
The next time it happens get the air cleaner off as quick as you can and squirt the accel. pump to see if it has gas. Then you can be a bit more sure it is fuel.
I've had the same symptoms but it was venting for sure. Even with caps that tested for open vents on the right tank it would starve out. It only happened when the tanks were less than half full but it was persistent. My cure is to use a cap on the left tank that has holes drilled through it. I keep it in my pocket till the tanks go down and then switch it out. Not elegant but it works.
As others have noted when you suspect a lock: shorten the fuel line as much as possible, use rubber instead of copper, and mount your fuel filter in a vertical position.
Post by JRB on Apr 13, 2006, 12:26pm
External inline filter?
Post by kell on Apr 13, 2006, 3:03pm
And use a clear filter so you can see what's going on in the fuel line.
Post by 57pan on Apr 13, 2006, 5:16pm
Thanks for the suggestions everyone.
Here's what I did:
1) Removed and dissassembled the carb again. Removed all the jets and needle valves. Sprayed brake cleaner thru all the passages and then blew compressed air thru them. Put it all back together again.
2) Removed the intake manifold and found that BOTH O-rings were split. (I have ordered a set of band-style clamps to replace the split clamps I am currently using.) I don't really think that this was causing my problem since I can usually tell that my O-rings are bad because it gets harder to start and runs rough at slow speed and I was not experiencing those symptoms. But who knows... the evil manifold leak can manifest itself in some pretty weird ways.
3) Rerouted the fuel line between the cylinders. The fuel line is now about one foot shorter than it was when I had it going around the back of the motor.
I took it out for a ride last nite and put about 40 miles on it and did not have any problems. I'm not saying it's cured yet - I'll have to burn thru a couple tanks of gas before the final verdict is in.
But, thanks again for your help.