Is it vapor lock?

[mushman]

Oh man, here I go again. Been down this road before. My 821100EZ is back to it's old tricks of surging and dying on me. I hate it when I can't trust my bike and my "solutions" to get me back home again.

Tonight's remedy seems that it will only run without surging and dying when the tank is COMPLETELY FULL. Half a tank and running hot, the sensation of running out of gas and power-- and switching to reserve doesn't help. It shouldn't be on reserve at that point anyway. Sometimes it'll "work through" it, sort of clear it's throat and run clean again. But eventually the motor will die and need a cooling rest before running again, with the petcock on "on". I pulled and checked the petcock earlier this season, replaced the coils, cleaned up a lot of electrical connections including soldering the yellow stator wires where the old (melting) nylon block was. But tonights revelation of a completely full gas tank to insure trouble free riding, at least until it gets down to about 3 gallons, has me scratching my helmet. Vapor lock? Carb trouble? Where do I look first?

Any ideas on what to fix so I can trust this baby to not quit on me miles from home again? Time was when I rode a 6400 mile trip without even a hiccup from this reliable pony. I miss that trust.

Thanks,
Mushman

[chiphead]

Why do you say the bike is "running hot"?
When it dies, how long before it restarts?
When it dies and won't restart, try putting the petcock to Prime and removing the fuel cap for a minute. If it starts, you've got a problem with the vent in the fuel tank cap.

[gustovh]

I am with you on that one Chiphead, Suzie Q does that one to me once and a while. I just pull over ande remove the cap, start her up and am good to go. She usualy does it with about 1/3 tank gone.
V

[Killer2600]

Just keep the tank always full then you won't have to worry about fixing it \\/

But if your like me and don't like the idea of stopping at nearly every gas station then you probably wanna fix that tank vent (in the cap)....or ride with the gas cap off :-D ....no bad idea don't do that.

[Lonthemon]

If your getting vapor lock you need to clean the tank cap vent. Try to breath through the tiny holes.

[mushman]

"Running hot" as in up to normal operating temperature. In the afternoon on the way to work when it happened, I was barely able to keep it running (it felt like it was on only 2 cylinders) before it cleared up and ran fine. Then it was parked for 20 minutes, started and drove away still fine.

On the way home at night when it completely died I had ridden about 25 miles from the day's earlier occurence. I did remove the fuel cap then but did not try the petcock on "prime". Even though the bike was warm, full choke was needed to get it to catch and then lots of revving to keep it running until all four cylinders would fire and run clean and even. This was after a 15 minute rest.

Another 6 miles, then died completely again (fuel cap back on), then pushed in to top off the tank adding 3.75 gallons. Stumbled starting, then caught and ran fine and strong the final 25 miles home.

I disassembled and re-assembled the fuel cap this morning. No noticeable gunk found. Maybe a brand new fuel cap is in order. Seems last winter I ran a wire up the "vent tube" on the bottom of the tank to check for obstructions and made sure the vent hose blew clear.

Now what? Besides keeping it at a full tank at all times? Something's causing this and it's driving me nuts, not to mention preventing me from taking any long rides.

mushman

[chiphead]

Boy, I tell ya, it sure sounds like it's running out of gas.
When it dies next:
Put it on prime. Count to 10 to allow the bowls to fill and fire it up. If that works, it's either a petcock issue or a petcock vacuum line issue.
If that doesn't work and it doesn't immediately fire on four, leave it on prime, pull the cap, count to 10 and try again. If it lights up, replace the cap.

The really scary thing is that there is a slight chance this could be electrical. If it is, just poke yourself in the right eye with a sharp pencil and you'll forget all about it.8-[

[chiphead]

What "vent tube on the bottom of the tank" are you referring to?

[t3rmin]

What "vent tube on the bottom of the tank" are you referring to?

He must be referring to the gauge sender catch drain thingy...

[Calvin Blackmore]

Is this a vacumm actuated petcock?
If so perhaps the vacuum hose is old and collapsing internally

It would likley do so intemittently and expand after the vaccum source i.e the engine was shut off allowinf eule ot flow again.

I have ssen this happen on radiator\heater hoses


just a thought may be worthyour while to try a new hose

[mushman]

Yeah, I'm starting to lean toward the petcock theory and/or the petcock vacume line issue. The petcock is new (12 years-30K miles-not the original) and I did pull it this winter for a quick visual check. Are there different pick-up points in that screened tower for "run" and "reserve"?

The vent tube I mentioned is the small hose fitting on the right side of the tank bottom. It bends rearward and connects to a small diameter black hose, about 1.5 ft long, that runs to the bottom of the bike.

I'm not gonna be able to get to this again for a couple of days. I will try running it on "prime" and do a thorough check of all lines and hoses, drain the tank to half full, try things there, ....all that's necessary to track it down and fix it right. Don't even get me thinking electrical. Been there. Me and multi-testers don't play well together. Next winter's project is to be a whole new wiring harness.

Thanks again for your thoughts and suggestions. I'll re-post with my follow-up efforts and what I find (works). Think I'll take the Triumph to work tonight.

Mushman

[nabrams]

A simple sanity check test scenario should reveal a lot.
Test Scenario:
1. With petcock on prime and a third of a tank of gas, visually verify that fuel flows freely (remove fuel hose from carb).
2. Be SURE that your cap vent is clear.
3. Now, fill the tank to full and leave the petcock on prime and go for a long ride (enough to drain the tank down to a third). If there's no problem in this scenario then your vacuum action is almost certainly the problem. At a full tank the vacuum will not have to work as hard as when the tank is at a third. If there's still a probelm even in this scenario, then you may have a problem with ignition components (ignitor, signal generator, coil) failing when they heat up - somewhat common, especially if they are the originals.

Now, poor vacuum action can be due to several things:
1. Imperfect seal between carb and vacuum hose or between vacuum hose and petcock.
2. Defective petcock.
3. Defective vacuum hose.

[Lonthemon]

Place the tank on a "workbench" with the petcock hanging over the edge. With the pet cock "on" apply suction to the diaphragm. Take notice if gas pours into your mouth or out onto linoleum and into the carpet. Then, with the petcock on "Prime" see if gas soaks the carpet just as fast.:-|

[Guest]

It sounds petcock related to me also.

[mushman]

Well I burned through a full tank of gas yesterday with outside temps at 95 and no surging, no power loss, no cutting out of the motor. In my repairs the petcock checked out okay, ditto the gas cap vents and a multi-tested cold and oven-heated ignitor. I did replace the fuel line and it looks like the culprit was the little bast**d in-line fuel filter. Funny though that it had been on the bike for almost 20K miles before it started the vapor-lock symptoms. It wasn't visibly clogged and gas flowed freely when bench mounted. So far so good. I really hope that was the actual problem as I'm riding the 80 mile round-trip to work tonight. Yesterday's ride with no stumbles was a confidence builder. Time will tell.

mushman