Vaporlock revisited

Gravy · Mar 1, 2006

Phil,

I finally actually LOOKED at mine and realized that the muffler is only
about 2" from the fuel pump, and both extend well above the side rail. This
leaves a good bit of the fuel pump directly exposed to heat from the muffler
at close range. I've seen the muffler glow a dull red when working full
throttle at night. The fuel pump must get a good bit hotter than Robin
designed for.

I plan to try a heat shield between the muffler and the body next. It may be
as simple as a couple of layers of aluminum foil wired to the engine cover
and overlapping the side rail. If that works, I'll make up something
permanent. I hope to try it tomorrow. I'll post the results as soon as I
can.

Dave

SnowRidge · Mar 1, 2006

Soooooo, have any of you PT-422 folk contacted Power-Trac about the vapor lock problem?

Which of the following standard answers did they provide?

1. We never heard of that problem before.

2. Contact the engine manufacturer, not us.

3. You people on TBN are nuts. You obsess over minor problems.

4. Ship it to Tazewell. Standard hourly rates and return shipping apply.

/forums/images/graemlins/laugh.gif /forums/images/graemlins/shocked.gif /forums/images/graemlins/grin.gif

Just kidding............sort of..... /forums/images/graemlins/smirk.gif

MuncyBob · Mar 1, 2006

Why is it that SOME are experiencing this problem while others are not?? I've worked my 422 with the Robin engine fairly hard in some warm to hot weather and have not had any problems... /forums/images/graemlins/confused.gif confused again!

MossRoad · Mar 1, 2006

Good question. I was wondering the same thing. Could it be one of those mid-run design changes that didn't work out? Maybe a carb-to-engine gasket that is made of some heat conducting material(as suggested by others) that no one else has on theirs. Maybe a missing heat shield? I'd just bend up a small plate of thin steel and slip it in there with a tie wrap or two to see if it helps. Does anyone else have the same model year as his? If so, can you post a good picture of your carb and the area around it. Maybe by comparing it, he can find something different or missing?

Phils · Mar 1, 2006

Dave, Yep that exhaust configuration puts the hottest parts just inches from fuel lines. I hope your idea works. I'm not taking the electric pump out now that it's installed. I put it on spacers under the exhaust heat shield (behind the tank).

BobRip, I wondered about heat on the tank and did some careful scientific hand-holding in and around the area and found that gas tank relatively cool to the touch. I expected it to be hot since that whole end of the engine tub has no ventilation. I had wondered if the problem was starting there and considered a cooling fan, but I don't think it'd help in that area. Aslo, since adding the 3A fuel pump, I'd rather not add any more electrical loads unless absolutely necessary.

If aiming the exhaust slightly away from the tub doesn't fix the problem, I think the next thing I'll try is some insulation on the inside wall of the exhaust side of the tub. Gravy's shielding experiment may validate that approach.

Phil

MuncyBob · Mar 1, 2006

( Does anyone else have the same model year as his? If so, can you post a good picture of your carb and the area around it. Maybe by comparing it, he can find something different or missing? )

I would be happy to take some pics and post them if we indeed have the same 422. Mine was obtained May 2004. May be a day or two since we are actually going to have winter here the next 48 hours or so! /forums/images/graemlins/crazy.gif

BobRip · Mar 1, 2006

(
BobRip, I wondered about heat on the tank and did some careful scientific hand-holding in and around the area and found that gas tank relatively cool to the touch. I expected it to be hot since that whole end of the engine tub has no ventilation. I had wondered if the problem was starting there and considered a cooling fan, but I don't think it'd help in that area. Aslo, since adding the 3A fuel pump, I'd rather not add any more electrical loads unless absolutely necessary.

Phil )

I think you are getting close to the problem. If the fuel pump is that close to the exhaust, that sounds like an issue. A heat shield might help. Painting the outside around the exhaust silver might help.

If you need a fan, a small (3 to 4 inch) computer fan would probably do the trick. I could not find the current, but it is probably so low that it would not be a concern.
Your 422 layout is very different from mine.
Take care,

Bob Rip

BillCroasmun · Mar 1, 2006

My 180 was bought about 5 to 6 months after your 422. Not sure if you read about my earlier VL problems with it but it took me three times of cleaning my tank before I got all the crud out of there. The last time consisted of me running pipe cleaners through the elbow, using a bent up coat hanger to pop off pieces of stuck crud around the inside walls of the tank and spraying it repeatedly with a pressure washer to flush it all out.

After that last cleaning it has run problem free. Before that I had the same symptoms as you, didn't seem like throttle or workload effected it as much as the amount of time it ran before stalling and that was pretty consistent.

One thing I did to "test" that it was a blockage was directly after the stalling started I disconnect the line after the filter and let it drain some in a can. Doing this while it was cold always had a clean flow and after it started stalling it would be a sporadic flow. I assumed the vibration of running caused loose pieces to partially clog the line causing a drop in pressure making it overheat at a lower temp but it's just a guess.

Good luck!

Keoke · Mar 2, 2006

Hi Guys, vapor lock usually occures when engine is idling becaues the carb is using very little fuel and thus the fuel stays static in the fuel line allowing engine heat to boil it.
The most sure way to take of this is to allow the fuel to keep moving in the line while engine is idling or going slow. The idea is to keep the fuel moving so will not heat up and boil.
You can do this by putting a tee as close to the carb as possible. Shut off the third tee leg of the with soder or a plug screw. Drill a small hole (start with a 1/32" hole) slip a return to tank hose to tee. The hard part is now to solder a male hose fitting to the top of fuel tank or fill neck for the return to tank fuel.
Depending on fuel pump capacity, your pump should be able at high speed to feed carb and also return to tank a portion of the fuel it pumps. If carb starves for fuel at high speed then the back to tank orfice will have to be reduced in size.
Also, if you go to a NAPA store and look at the in line filter pics you can find filters with one inlet and two outs. The second outlet is the restricted return to tank line. These filters should be mounted with the return line facing up.
This setup was used on some vehicles with A/C to prevent vapor lock before fuel injection took care of the problem with a return to tank system of their own.
Another point, vapor lock sometimes occures more in the spring then
in the summer if there is still a lot of the more volatile winter gas still being sold. This gas has a lower boiling point then the heavier summer gas and thus is more prone to vapor lock.

lots of luck,

Phils · Mar 2, 2006

Bill,

I remember your posts about the tank crud and double-check the elbow for it when I have the lines disconnected for the other mods. No surprise when I found it the first time, but the elbow has been clear since (unless it's clogged again now, but I gotta have the tank low in order to pull it easily).

Phil

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.