Vaporlock revisited

[BobRip]

Has anybody checked for dirt behind the fuel solenoid? This has been mentioned several times and I don't remember a reply. Maybe I missed it. Clint Blake had an identical problem and cleaning out some trash solved it.

Bob Rip

 

[Phils]

Gravy,

I was thinking that moving the fuel hose and pump just became easier than moving the muffler. The stock pump is out of the loop altogether and that will be my next experiment. Of course, as it is now, I've run the PT long and hard and it hasn't quit so the insulation and electric fuel pump have helped. It was only after shutting down AFTER running long and hard that I saw the bubbles coming up into the fuel tank and know that there is still work to be done. I'll relocate the electric pump to the right side and run the fuel hose on that side of the engine.

BobRip,

I haven't checked the solonoid seat but since it's far away in the carb and the vaporization is happening in the hose near the exhaust, I can't see where it could have an effect on the VL problem. I DID have some of the whilte sealing crud that PT uses lodge in the needle valve seat last weekend: PT wouldn't run and temp made no difference. I pulled the air cleaner off and when the ignition (electric pump) was turned on, fuel would start to come out of the bowl vents. It was easy to disassemble and fix and good excercise too, as it happened about 500 feet downhill from the house and tools and it took me at least 4 trips to get tools and complete the job.

I don't know why I didn't think of relocating the fuel hoses earlier other than I was hoping for an exhaust solution that would still allow the stock fuel pump to be used, should I want to revert to it at some future time.

Phil

 

[BobRip]

Phil, given all that you have done and are still having problems, it still strikes me as reasonable to check the solenoid. This may not be vaporization! Yes, you are getting some bubbles, but they may not be the issue.
I will say no more on this subject as I am probably being too pushy.
Good luck.

Bob Rip

 

[BillCroasmun]

Phil,
Something to think about...
The bubbling your seeing lets you know that the gas is heated to at least the minimal boiling point but there are multiple ways to get there. Three ways I can think of are the ambient temperature around the line can be at the boiling point for the normal atmosphere in your area, something in line (even far down the line like Bob is mentioning) can lower the pressure in the line causing a lower boiling point and third remember that gas is a mixture of multiple compunds each with varying boiling points (this page says it better than I can) so different types of gas can contain different compounds that may start to boil at a lower temp than others brands/octanes/etc.

I guess in short I am thinking that since other PT owners with the same design are not having this problem I do not think it is design alone causing your problem. I think the design may be borderline so a small problem (like blockages/fuel pump malfunctions/etc.) is enough to push it to a vaporizing point. But this means if you get rid of the problem by say putting on a stronger fuel pump you might be just treating the symptom and not finding the problem since the base design works in other scenarios.

I know in the real world sometimes all we care about is just plain getting the thing to work. But if your experiencing vapor issues with a normaling functioning OEM fuel pump and uncovered lines there still must be some unknown "problem" outside of the factory design. Not to say the changes you made didn't improve upon the design, just that there is still a problem there that now might be harder to find. /forums/images/graemlins/frown.gif Don't have an answer for you but I wish I lived closer to help look at it.

Also, the thought of rerunning your fuel lines is a double edge sword. You'll be moving further from the hottest heat source but you'll have more line running through a still very hot area. Generally shorter is better with keeping the lines cool.

 

[Gravy]

Bill,

Rerouting the fuel line to the other side, in conjunction with bypassing the mechanical fuel pump, actually reduced the total length of fuel hose on my PT-425. The stock configuration requires looping the hose from the fuel pump on the valve cover, over the fan end of the engine, and in an s-curve around and under the throttle bellcrank to get to the carb inlet. Using an inline electric pump allows running the hose pretty directly from the tank, up next to the dipstick, and over the flywheel end of the engine to the carb.

I agree that it's probably not purely a PT design problem. My understanding is that fuel formulations can vary quite wildly depending on region, supplier, season, and even advertising campaigns. (I was told in the 90's by somebody who should know that "Chevron with Techron" actually had Techron only while the ads were running or the pumps were labled "With Techron".)

In any case, all we can do is to keep trying things until the problem stops...

 

[BillCroasmun]

Gravy, thanks for correcting me on the fuel line length. I guess that's another difference in models. The 180 line is pretty direct as is other than having an excess length dangling down into the tub.

Since we don't have the support of a dealer network hopefully these MUTs of ours will keep spreading across the countyside so we can at least have nearby neighbors to help compare/problem solve with. TBN is a great virtual meeting place for 98% of our issues but for the odd problem there's nothing like sitting down together to brainstorm and fiddle with the problem.

(Is that the first use of the new acronym outside of the proposal thread? /forums/images/graemlins/grin.gif)

 

[Gravy]

I sure wouldn't get near as much out of my PT MUT without all the support from this forum. It would really be great to have some other local owners so we could kick tires and tell lies in person... /forums/images/graemlins/grin.gif

 

[PABenz]

After dealing with stalling from vapor lock for some time now, I believe I have finally got mine to stop. I purchased a new OEM fuel pump for my Robin 422. (I think the heat may cause the internal parts to wear out before their time.)

If I can buy a new pump every few years, I am not happy about it, but I feel it's worth the $41 to stop the problem. Some part dealers sell the internal parts to rebuild the pump, but those parts added up to over $25 so I just bought the complete assembly from Jacks.

Replacement Parts for Robin Model EH63, EH64 & EH65

Just to let you all know, I tried many things such as moving the gas lines, insulating the lines, insulating the muffler and even moving the original fuel pump. None of the options helped and the PT would sputter and die after an hour of mowing or other uses. I decided to buy the new fuel pump this mowing season and have not had a problem yet this summer.

Good luck.
Joe

 

[Phils]

Since this thread surfaced again, I'll update that the side cooling fan I put on the engine cover has elimated my vaporlock problems entirely. It would have been better if I'd tied the power source directly to the hot lead for the hyd cooling fan and someday I'll rewire, for now I just have to flip the switch every time I expect to be operating the PT for very long if it's hot outside.

Phil

 

[Marks481]

I decided to buy the new fuel pump this mowing season and have not had a problem yet this summer.

I suspect that this means that that the problem was not (completely) caused by vapor lock, but possibly due to a faulty fuel pump. Worked fine when cold, but when it got hot, it wouldn't function anymore?