vapour lock in linkert

[chopperzz]

1965 FL-vapour lock allows me to run with moderate loss of power. I re&re line at carb (on side of road) When I remove it takes a gasp of air, then the filter glass fills up. Run it for awhile then it may, or not, empty again.
sometimes it remains OK if the ambient temp is a little cooler (night)
OR if I turn off the petcock and run it down the road until it starves for fuel, then open the petcock, it'll temp fix.

[john HD]

what are you running for gas caps?

john

[FlatHeadSix]

I'll restate John's question; sounds like an unvented gas cap to me.

A lot of riders put an unvented cap on the left side to keep it from leaking fuel while on the kickstand. But, if both the caps are airtight it will pull a vacuum and starve for fuel. The right cap, at least, should be a vented cap. (as long as the crossover is working properly)

learned from experience,


mike

[chopperzz]

left side is solid cap. right side is no-name aftermarket. but it seems to vent if i test it (suck on cap) geeez it hurt to say that.

before i noticed the problem I ran it for a while, is it possible that running it lean could've made any problems by overheating the combustion chamber?

[john HD]

if you are sure your tanks are venting i would suspect crud in the tanks themselves. flakes of paint or a failed tank coating floating around could cause the problem.

perhaps a good cleaning of your entire fuel system is in order.

one of my buddies had a knuck that always ran crappy until i used a pressure washer to completely blow all the crud out.

ran perfect after that!

john

[chopperzz]

I'll triple check, but i'm sure their clean. No tank coating (seen that nightmare before!)
it looks like good gas transfer between tanks, as i looked during a fill-up today. i even ran it with the right side cap off for a while.

do you think I should wrap the gasline in an insulation? ( plastic loom)
what do you think about me running it lean before catching the problem? could i have cooked it?

i'll take off the whole line and see if it's plugged up.

thanks for helping out dude.

[chopperzz]

nice ride you sport, as well. I'll get my photos on here soon.

[fourthgear]

You can cover your fuel line with some thing that will keep the heat away from it as a precaution if you think its getting vapor loc from heat . The stuff in the photo is from NAPA for spark plug wires and such.

http://www.hydra-glide.com/coppermine/d ... p?pos=-890

[Fixman]

You said you tried running with the right side tank cap off with no improvement. I would try running with the left side cap off.

Kent

[King]

It sure sounds like a venting problem. Next time you are running and it starts to starve out twist off the left cap like Kent said and see if that fixes it. I had that problem for years especially when the fuel level was low in the tanks. Now I run vented caps on both tanks which make fueling-up a bit dicey but no more problems with fuel flow.
King

[Cotten]

My money is on the gascaps as well, especially if any are repops like shown on the right. (Note vent locations; The gasket swells to cover them.)



"Vapor lock" should apply to overheated motors where extreme pressures have bound valves shut. (I have only encountered it with a Ford.)
An air lock of any kind is impossible on a HD gasline, as they were all gravity fed: bubbles rise back to the tank.

To get an air lock, you would have to re-route and bend the gasline into a "gooseneck" like the trap under a sink drain.

....Cotten

[65 Eric]

Gentlemen,
I was on a long ride with a friend in July (100deg.) when he "ran outta' gas" every 100 mi. or so. His glass filter was hanging down between the jugs and almost resting on the case at the bottom of the "V". I suspect the problem was as Cotten suggested that the fuel line was forming a trap like a drain. At the time I thought the heat from the jugs and cylinders was causing it. My friend shortened up his fuel line to get it up in the air and the problem was solved. We rode on thinking we solved his "vapor lock" problem.

my .02
Eric

[fourthgear]

Do you have the OEM type tanks on there with fuel shut off through tank or do you have later with the fuel shut off @ mid tank ?

"sometimes it remains OK if the ambient temp is a little cooler (night)"

That could be a clue ! I'm not sure .

[Cotten]

65Eric!

You describe your friend's air-locked assembly as "His glass filter was hanging down between the jugs and almost resting on the case at the bottom of the "V"."

So it dipped well below the carb, and then bent upward.
The filter chamber compounded the obstacles to bubbles, plus allowing surface tension to block the filter mesh.

Shortening it allowed the bubbles to purge. Getting it 'into the air' had nothing to do with it.

No doubt this was not a full gooseneck of the feed line,..
but it reassures us that the Factory design has its advantage!

....Cotten

[chopperzz]

I will say that I'm very impressed by the helpful response from this forum group.
As a result I will try the following, in order; Shorten fuel line, wrap line with an insulator, change gas caps and report back.

Thanks.