422 vaporlock

Phils · Mar 22, 2005

I've got the Robin engine but I s'pose it could have a fuel shutoff solenoid. I'll look closer this weekend. I didn't notice any wire to that area as I was inspecting the fuel flow path while waiting for it to cool off. That's when I noticed the clear filter had no fuel in it until about 20 minutes later. After starting it back up, I watched bubbles form at the low point of the hose, and gradually displace all the gas in the filter again.

Adding a shutoff solenoid woudn't be too difficult though and may be the eventual answer since high octane didn't help (dusting off the brain cobwebs revealed that I originally ran 87 octane and switched to 91 hoping to stop the run-on and backfires).

Maybe when I solve the vaporlock problem entirely, getting cooler fuel to the engine might solve the run-on and backfire too. I imagine that feeding the machine fuel with vapor could make it run leaner, thus hotter, and cause the backfire/run-on.

Since it only happens when I've been working the PT for a half hour or better in warm weather, I don't think there's a problem with restricted flow from the tank.

Rerouting the fuel hose away from all heat sources could fix all three problems.

Phil

J_J · Mar 22, 2005

One more trick you might try, and that is to run your fuel hose through another hose with ample air space. Maybe a 5/8 or 3/4 heater hose . It will also give more protection from abrasion.

pairodime · Mar 23, 2005

Phils,
I too, had very similar problems with all the symptoms pointing to vapor lock. My fuel hose dipped under and was in contact with some of the hydraulic hoses. I rerouted the hose, change gas grades, used fuel additives, replaced the fuel pump, insulated the exhaust manifold and the fuel hose. It kept happening until I found a blockage way down in the elbow off the fuel tank. It was not readily visible. I say check that first before going through any other elaborate steps.

Since you have a 422, you can also upgrade your fuel pump to the one for the 425. They look exactly alike. Make sure you confirm part numbers.

I also recommend against insulating the exhaust header or muffler. It retained so much heat, the header sagged and twisted. Power-Trac has replaced it.

Here's the thread that discussed this problem Need help with Robin Engine

Good luck.

Schultz · Mar 23, 2005

If you continue to have problems with vapor lock, try wrapping the fuel line with aluminum tape or something reflective. This worked on an old Craftsman tractor we had. On that one the muffler was directly below the carb.

Phils · Mar 23, 2005

Thanks for all the great suggestions.

We are in a rainy spell like we haven't seen in a very long time. Been rainy the last week, and the 7 day forecast is of the same. So when weather permits (on a weekend) I'll check for a blockage or restriction in the fuel line and at the tank, and if I find nothing will re-route the fuel line probably through a larger hose. I'll post on the results or lack thereof.

Phil

newyorktrac · Mar 23, 2005

I also have been using high octane fuel in my 422; if I use 87, the engine will run on when hot.

Phils · Mar 23, 2005

Yah... and I bet you have REAL hi-octane still in NY. Here in CA it's 91 for the highest, also "specially formulated" to reduce smog. Krappy at best.

Ahhh - I remember the good ol' days of Sunoco or Norwalk or ? (when I lived on the East Coast) and you could set the dial to whatever octane you wanted. Seems like 104 or 106 might've been the highest, but that's been a long time ago. Like the late sixties. And people have told me I had a great time in the sixties. Yeah... like I could remember.

Phil

MossRoad · Mar 24, 2005

When I worked at the airport out of high school one of my duties was to sump all the trucks to check for water. The fuel was then dumped into a waste tank. I had an agreement with the boss to use the sumped 100/130 octane in my motorcycle. It was a Yamaha RD400 two stroke twin. Mix in a little oil and ZZZOOOoooooom! One of my co-workers ran it in his '66 Vette with the 327/350HP. Smelled kind of dry at the exhaust. A very unique smell. Car ran fine.

The mechanic said his brother built up a real nice car for the round-e-round track and they ran a tank of 115/145 octane in it. He said is was the fastest car on the track... for about 4 laps, when the pistons melted through. /forums/images/graemlins/tongue.gif

landscapercarl · Mar 24, 2005

You might try a larger fuel pump we had this same problem the heat can be areal problem it may completely melt out the muffler innards and make more problems. Get a hold of robin and see what they can do for you. This solved all running problems for the machine, but we spent a fortune fixing the problems it caused.

Phils · Mar 24, 2005

Thanks, Carl. A 425 fuel pump is now added to the list of potential fixes. I'm not sure it would really help this situation tho as the fuel pump is presently being fed vapor when the problem occurs.

Maybe a sunny day Saturday (then back to rain) so I'll do the reroute inside some other larger hose, during which I'll check for any restriction in the tank outlet.

I should clarify that when it backfires, it's ONE 'pop' only and when it runs on, it's probably only for one second. Never both. And neither unless I've been using the PTO while stump grinding or mowing for a half-hour or better. The hydraulics are all pretty hot, the cooler fan is running, and even the hydraulic tank is very warm to the touch. Insulating the fuel line from the hydraulic heat will be the next step.

Phil