Vaporlock revisited

[Phils]

Thanks for the feedback!

The muffler situation is indeed needing help and could be contributing to this heat problem. I keep waiting for one of you TBNrs to mention that you build headers for a living/hobby and for fifty bucks you'd build one for the PT.

Heat IS the problem, no doubt about it. When I vaporlocked during the summer while mowing it was almost expected. It was a timed "beer break" kinda thing. That it's happening when the weather is cooler and the work easier is disappointing.

As far as "... if the engine stops, what stops the fuel pump?...": the needle valve in the carb stops the pump. Float goes up, needle valve goes shut. 4psi won't open it.

If it's a more serious problem, like a broken fuel hose, then there'll be gas going all over the place until the key is turned off. However, as it is now, if a fuel line broke there'd be fuel all over the place and it wouldn't stop when the key was turned to off, it'd only stop leaking when the tank was empty. I hope I don't have to deal with problems like that.

If it's even MORE serious: the PT is upside down and the fuel pump is still running. It wouldn't be pumping any gas because the fuel would be all against the top of the tank. I REALLY hope I won't be having that problem.

So as I understand it, the big problem is the heat from the engine intensified by the lousy exhaust design. Fuel under vacuum is travelling through and by the hottest part of the machine and turning to vapor after an hours' use. Better engine bay cooling could help. A better exhaust design might help. I don't see easy fixes for those problems. What I can do is have the gas make that hot trip under a slight pressure and (I hope) not turn to vapor.

There's still time for more thoughts. I won't be buying a pump until the weekend, at the earliest. And before I do, I'll check the tank elbow for debris again. I just want to be the one to pick "break time" this summer.

Phil

 

[KentT]

Owning a Kohler, I "have no dog in this hunt"... but, I have to wonder if at least some of this may be due to the difference in California fuels and a small company like PT hasn't experienced it, because all their testing of engine cooling etc. was done in Virginia....

Based on my experience with air-cooled VWs long ago, if the cooling system is somewhat marginal to start with, the difference in fuel (or fuel mixture, if at altitude) could easily make a difference of 25-50 degrees F in the head temperature...

Just a thought...

 

[Phils]

Yep, Kent, I think CA's gas formulation may be contributing to the problem but I see little change coming, unless it's for the worse. Mebbe I ought to be moving my intentions to the "diesel PT" thread.

As long as I don't work my PT for more than an hour straight I don't have the vaporlock. I just need to work less. And play more.

Phil

 

[BobRip]

They also did this for non fuel injected cars. Standard engine mounted with an extra outlet. Still low pressure. My 1982 S10 had one.

Bob Rip

 

[Gravy]

I don't think it's just a California problem, and not necessarily just a heat problem, either. Mine does it in Virginia while plowing snow. I do suspect fuel formulation as a contributing factor. It might be informative to try different brands and grades of fuel.

Like Phils, I plan to use an electric fuel pump. I'm not worried about the pump running with the engine off. Diaphragm pumps are pressure sensing and only cycle when there is demand, i.e., when the float valve opens. If the engine dies, I'll turn the ignition off anyway, which will cut off power to the pump.

I don't think this is a Robin problem as such. I think it's caused by the very close quarters in the engine compartment, coupled with the mostly unshielded exhaust design that adds more heat to that side of the engine compartment. I suspect that a Kohler or Honda engine would have the same problem if it had the same exhaust layout.

One of these days Real Soon Now I hope to do something about the exhaust. The Robin factory side outlet exhaust system in the back of the engine parts manual looks like it might work with a little adapting. If I can make it work, I think it would probably help with the vapor lock, the backfiring, and the noise.

Gravy

 

[SnowRidge]

Don't you Robin guys have most of the muffler outside the engine compartment? If so, I don't see how it could be as hot in there as with a Kohler powered PT, which has the entire thing inside the engine compartment.

What am I missing? /forums/images/graemlins/confused.gif

 

[tracdoc]

Phils,

Quite the bummer to learn that you are having vaporlock issues still (or again). When we last dialogued about it on the forum {HERE-Post #613229} I mentioned the steps I took for the same problem with my unit. Knock on wood, it has not recurred. Of all the things I did, I think the most helpful was changing the fuel line itself AND sheathing it it the DEI heat shield {HERE}, which will withstand 500 deg direct continuous contact. I used a long segment to sheathe the fuel line from the tank outlet to the fuel pump, and a shorter piece to sheathe the fuel line fom the pump to the carb. The DEI stuff is 2-layer, an insulating inner layer and a metallic reflecting outer layer, and has a velcro closure along the entire length. That way, it will close around the bulk of an in-line fuel filter.

If you haven't as yet tried it, I would heartily suggest it. The over-cover of fuel line with another fuel line (if I understood your description correctly) will not provide a significant barrier to heat transfer. The heat shield type material like DEI is the only type approved for aircraft use where vaporlock is potentially a much more serious event.

As you may recall, I used DEI "Floor & Tunnel Shield" and header wrap to assist with heat containment and removal from the engine bay. I have been pleased with the improvement. I would, however like to have a header with better intrinsic design. I am having our racecar welding guru look at the PT header to see what would be involved in a re-make using larger bore round tubing which I would then connect to one of the Supertrap mufflers. I'll post a thread if it looks promising.

 

[Gravy]

Yes, the muffler is on the outside of the engine compartment - unshielded, parallel to and very close to the sidewall that the fuel line runs next to. I suspect that considerable heat transfers through that sidewall plating and re-radiates to the inside.
Gravy

 

[Phils]

Thanks, Tracdoc. I looked at that heat shield per your link. It wouldn't fit around the inline filter I'm using, but that could be changed. I may have to add that shielding too, even after the electric pump, but maybe not. At $35 for 3 feet it's pretty pricey but so are most things that work.

On hindsight, I think I was lasting longer before vaporlocking when I had the original fuel tubing wrapped in larger hose. Possibly the larger diameter hose I installed allows the gas to stay in the "heat zone" longer, making the problem worse. The hardest thing is that you can't tell if it's fixed without working the machine for better than an hour. And I can't do repairs with the engine hot so each step is far apart.

Maybe wrapping the new hose with something to shield it is the correct solution, but I've ordered a pump and I'm gonna give that a try. At the least it'll be an attack from another direction, and may give this group an answer (one way or the other) as to whether it's a viable solution to this problem.

I was going to get one of the diaphragm pumps but my parts person is recommending the smaller inline electonic pump. I've never used one but it sounds easier to install. I called this morning and it'll be here this afternoon. Supposed to rain this weekend so I should get it installed then.

Phil

 

[tracdoc]

Phils,

Sounds like a good plan. Keep us posted with your progress.

BTW, if you're interested in the Velcro closure heat sheathing, you can get it for sub $30 at Summit Racing on-line. I have a pretty large after-market in-line fuel filter and the sheathing closes over it w/o a problem.