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