450T Runs well then sputters out after 20 miles

[Phil]

I finally got my license and have been able to try and ride the bike for the first time. I bought it back in the fall and have done some of the maintenance work on it as is always suggested here.

I completely tore down the carbs and dipped them and replaced all the O rings. I also replaced the o-rings on the intake boots. The boots themselves appeared to be in decent shape. I have replaced the air filter, spark plugs and oil. After I rebuilt the carbs it appeared to start and idle well. Though I wasn't able to ride it at the time.

Well I finally have started to ride it. Yesterday it ran pretty well with no real issues for about 40 miles. Today I took it out and it ran ok for maybe 15 minutes or so and then while at speed (around 45 or so mph) it just died out. The speed just dropped and dropped until it stalled out, over maybe a minute or so span.

After that it wouldn't start for around 5 or 10 minutes. It repeated this same pattern a couple times in a row until I could get it home.

Anyone have any ideas what's going on? Could it be a fuel issue? Would a poorly performing petcock cause this, or possible something in the gas that may have found its way to the carbs?

[tkent02]

Check for a clogged fuel tank vent... It will run until a vacuum forms in the tank, then quits. See if it runs fine if you crack the gas cap open so it's not air tight.

[airbornespud]

this may sound dumb, but check the gas. even if you filled it a while ago before you stored it, check it again. i've had a lot of older bikes and they seem to have a tendency to lose gas mysteriously. one i had was actually leaking thru the intake into the cylinder and then into the crank case. after several weeks there was a case full of gas / oil mixture that almost killed my bike. once i figured it out it was a simple fix. shut the fuel off right before i got to where i was going so that the carbs weren't empty, but they weren't full either. i had another that had a slow leak on the stand side that i didn't detect for a while because it dripped right on the ground and left no sign on the bike. so the moral of this story? you may just be out of gas. i've done it more than once.

[Big Rich]

What about aging coils? I know it's not a common problem, but when they start to go bad they overheat and shut down until they cool off.

[Phil]

I did check the gas. There certainly was enough in the tank, I would guess about half full, and there didn't appear to be any in the crankcase.

this may sound dumb, but check the gas. even if you filled it a while ago before you stored it, check it again. i've had a lot of older bikes and they seem to have a tendency to lose gas mysteriously. one i had was actually leaking thru the intake into the cylinder and then into the crank case. after several weeks there was a case full of gas / oil mixture that almost killed my bike. once i figured it out it was a simple fix. shut the fuel off right before i got to where i was going so that the carbs weren't empty, but they weren't full either. i had another that had a slow leak on the stand side that i didn't detect for a while because it dripped right on the ground and left no sign on the bike. so the moral of this story? you may just be out of gas. i've done it more than once.

[cowboyup3371]

Do the rest of the maintenance as well like adjusting your valves, carb synch, etc.

[Phil]

The first time it died out like that and wouldn't start I checked the gas. It didn't start right up after. I am guessing that would rule out this possibility. Am I wrong?

Check for a clogged fuel tank vent... It will run until a vacuum forms in the tank, then quits. See if it runs fine if you crack the gas cap open so it's not air tight.

[Phil]

I was wondering if it could be an electrical issue. I really hope this isn't what's wrong as the coils are a bit expensive. Is there any way to test for this?

What about aging coils? I know it's not a common problem, but when they start to go bad they overheat and shut down until they cool off.

[cowboyup3371]

Do you have a multimeter? Have you done any testing of anything yet? Replacing parts before knowing the problem through testing can get very expensive for little gain.

[Phil]

I am not sure if it's related or not, but what is the small hose that comes from the petcock to the side of the carb? The fitting that the hose attaches to that slides into the carb does not fit well and easily falls out. I put a small amount of tape around that fitting and now it fits more snuggly. What is that connection for?

[cowboyup3371]

The smaller hose is your vacuum line.

[tkent02]

You know, the vacuum line that turns on the gas.

[Phil]

I thought maybe that's what it was (I was checking the Clymer manual online when you replied). It has always been fairly loose since I have had the bike. Is that abnormal? I thought it being loose seemed odd because its a metal fitting that pushes into a metal hole. I put a small amount of tape around the outer part of the fitting and it pressed it and seems to hold ok. The issue with it dying still happened after this.

You know, the vacuum line that turns on the gas.

[tom203]

Might be best to just replace vacuum hose. In any event,check for correct petcock operation- very common problem. Put 1/4 inch clear vinyl tubing on petcock vac fitting, with lever in "on" or "res" spot, suck on it, fuel show flow copiously down gas line.

[pete]

Today I took it out and it ran ok for maybe 15 minutes or so and then while at speed (around 45 or so mph) it just died out. The speed just dropped and dropped until it stalled out, over maybe a minute or so span.

After that it wouldn't start for around 5 or 10 minutes. It repeated this same pattern a couple times in a row until I could get it home.

Just looking at that statement about dropping and dropping until it stalls over a minute or so says to me fuel starvation, but of course I've been wrong before...

Did you check the fuel tank for rust? Just wondering if there's a layer of rust covering the fuel tap filter in the tank that is able to float away a bit when stopped but gets sucked back against the filter when the fuel starts flowing.

Do you have a fuel filter inline at all?

That symptom reminds me of when I (stupidly) used a plastic bag over the fuel filler on a car when I lost the cap. The bag got sucked into the tank and would gradually get sucked over the tank outlet and cause the car to stall after a while, then would start and run for a bit after the bag floated away...