Vaporlock revisited

Phils · Mar 2, 2006

Bob,

I've ordered some insulating material (fiberglass with the foil backing) from eBay. It was only about $12 for a roll. It won't be here before this weekend and I have some storm damage to repair so I'll give the PT a decent workout. If I still have VL, I'll put the insulation in. Heck, if I DON'T have VL, I'll still probably put it in.

If it's necessary to install another cooling fan I'll do it. But I was surprised that the tank and front tub area was as cool as it was... which reinforces the theory that it's those areas adjacent to the exhaust that are the problem.

Phil

Phils · Mar 2, 2006

Keoke,

Thanks, I'd forgotten about the fuel filters with the bypass. I'd probably want the bypass at the carb inlet tho, and I'm not sure I could fit a filter in there.

I think the bypass solution will be the next one I'll try if the current "move the muffler away" and the pending "add insulation" don't solve the problem.

Phil

Keoke · Mar 2, 2006

Phil, I hear you on finding a good spot for the three line filter.
These filters are most effective when mounted with the tank return facing up. The return line is tapped into the top of the can to pick up air bubbles for tank return, line to carb comes off the bottom.
Also, insulation on fuel lines works as a double edge sword. Yes, it helps to keep the line from gettin hot but once it gets hot it works to keep it hot as well.
Heat deflector shields to keep radient heat away from fuel lines along with increase air flow are usually a better choices if conditions allow.
On placing the three outlet filter. Consider lengthing pump to carb line and placing the filter vertically just short of the carb if conditions allow.
It goes without saying, but never use a plastic body filter any place where there is a fair amount of engine heat.

Phils · Mar 2, 2006

Thanks, George.

It MAY be possible to install one of the smaller 3-line filters right at the inlet to the carb. Anyplace else after the electric pump and it'd be receiving heat from the exhaust. I spent many years working at an auto parts store and remember some all metal 3-line filters being available. That may be the next "try" if the bent exhaust and fiberglass insulation don't stop the VL.

The clear plastic filter I'm using now is located directly under the tank and seems to stay fairly cool. I noticed when I rerouted things the last time that there were little chunks of the sealer stuff (like clogs the tank outlet) in the filter. There were none in the elbow tho, and I flow tested it with no restriction apparent (I blew through it successfully).

I understand your point on hose shielding, but [?] used it successfully to stop his VL [can't remember for sure who and don't have time to search].

Phil

Gravy · Mar 2, 2006

Phil,

I tried simple heat shielding (a double layer of aluminum foil zip-tied to the engine cover) today. Net effect: zip, zero, nada. 20 minutes of full throttle and heavy load and it sputtered and died. After that point, I couldn't work it hard. I noticed that closing the choke partway and dropping the throttle to idle would sometimes keep it running.

I let it cool over lunch, then pulled the top off of the carburetor. Despite the large metal fuel filter (Fram G-1 equivalent) there was some crud in the float bowl. I cleaned it out and started again, 20 minutes later...well you know what happened.

I started experimenting then, and discovered that once it sputtered, if I shut it off and let it sit for a minute or two, I could restart and get several minutes of full throttle, or I could run at about 1/2 throttle more or less indefinitely, as long as I didn't load it too heavily.

These symptoms do not entirely make sense for a vapor lock problem, at least based on experience with cars. With vapor lock, the fuel boils away in the float bowl or the fuel pump. The engine generally won't restart until it cools down enough for the fuel to stay liquid, which takes more than a minute or two.

My best guess at this point is that there is a restriction somewhere in the fuel supply. It may be that the fuel pump is somehow losing efficiency when it gets hot, and can't keep up with demand. When the engine is shut off, enough fuel gravity flows to the carb to fill the float bowl, allowing a couple of minutes of full throttle.

If I try an electric pump, I plan to bypass the mechanical pump, and run the fuel hose around the right side of the engine to keep it away from the muffler. I also am planning to replace the plastic elbow on the bottom of the tank with a straight brass fitting. That should eliminate the most likely place to trap debris before the fuel filter.

We should keep in mind that we may have two different causes for our similar symptoms. What works for one may not work for the other...

I'll let you know what happens next /forums/images/graemlins/tongue.gif

Gravy

MossRoad · Mar 2, 2006

Can you bypass the fuel pump altogether and just gavity feed the thing with a full tank of gas? If that works and it still locks up after 20 minutes, the problem is probably in your carb, not your fuel line.

Gravy · Mar 2, 2006

Why didn't I think of that? /forums/images/graemlins/blush.gif I'll try it tomorrow and let you know.

Gravy

BobRip · Mar 2, 2006

Have you tried checking the fuel cutoff solenoid. Clint Blake had trash built up in his. He removed it, cleaned out the trash and that fixed it.

Bob Rip

J_J · Mar 2, 2006

I believe I would tee in a pressure gage on the fuel line by the carb to see if you are getting fuel pressure and how much. The pressure should be no more than 5 to 10 psi. Either route the gage where you can see it, or open the hood to observe the gage.