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.

 

[BobRip]

Would a couple of layers of aluminum foil around the fuel line help. It would be reflective and give some thermal mass. Pretty cheap too.

Bob Rip

 

[Phils]

Ok, got the pump... $39 total. Hope to take off early today and install it. But I won't know if it solved the problem until I have enough work to do that'll take over an hour of full-speed PT effort. Since this weekend is s'posed to be rainy, it could be weeks until I'll know! Dang.

Phil

 

[Phils]

OK. Fuel pump installed. Now I just need a hot day and lotsa work to do to see if the problem is solved. So far it works great, but I only was running it for less than 1/2 hour.

I mounted the pump (sized and shaped like a 3" x 3" transformer) under the muffler heat shield. If this is successful I'll take and post photos.

Phil

 

[Phils]

Ok. THAT didn't work! After an hour of stumpgrinding, vaporlock again.

Analyzing the situation:

Had vaporlock (VL) from the start.

Added Supertrap muffler (and another poster said that doing that caused his to start VL). I assumed the Supertrap didn't make a difference since I had VL before installing it.

Wrapped the stock fuel tubing with larger split hose. VL seemed to go away but maybe I never ran it hot/long enough.

Replaced the stock fuel hose with better. Also removed the tank junk clogging the elbow. VL back.

Found gas cap holding pressure, bypassed relief spring. Still got VL.

Added electric fuel pump. Still got VL.

Re-routed and somewhat shielded the fuel hoses. Still VL.

PABenz mentioned that the Supertrap seemed to heat his PT up faster. So I cut a 'V' in the pipe between the stock and Supertrap, bent the Supertrap away from the machine maybe 15 degrees and welded the pipe. I installed the original PT exhaust deflector to the rear of the Supertrap to prevent brush from hitting it.

So now the Supertrap exhausts about two inches away from the PT tub, instead of the one inch it was before. It's TWICE as far away from the tub. Because this is an exponential thing, it should reduce the heat transfer to the tub by 75% (somebody here can check my math).

I have enough stumps that I'll be able to tell in an hour or two if the VL problem is fixed or not. Of course, rain is in our forecast for the next week so it may be awhile until I can test it.

Photos coming if if works, no point if it doesn't. And before I can take photos I'd have to do some serious cleaning.... if MossRoad saw how dirty my PT is he'd be beating me bodily about the head and shoulders with a hydraulic hose.

Gravy -- I'd hold off on the electric pump for now. I've been thinking of putting a panel of heat insulation inside the muffler side of the tub (like auto underhood insulation with the foil-colored backing). I may still do that if moving the angle doesn't stop the VL. I'd try more than one thing at a time, but then I'd never know exactly WHAT fixed the problem.

An on it goes..... as it is now, I have to take a long break after doing an hour or two of hard PT work. So far, that hasn't been a bad thing as I've been thirsty by then too.

Phil

 

[BobRip]

Phil, even with the electric pump, if your fuel going into the pump gets hot, it may vaporize at the pump inlet (which is still low pressure) and not pump. Try teeing off the outlet of the pump and return a small flow back to the tank. These means you will constantly be getting cool fuel into the pump inlet.
This is what all modern automotive systems do. They found a solution to vapor lock 20 years ago, why not use that. Sorry to sound like a broken record.

Edit - As I understand vapor lock, it usually occurs at idle where there is little flow (and consequently little cooling). Is this where you are seeing the problem? If it occurs after long hard use followed by idle, then it is probably vapor lock. If not it might be something else. Hard use pulls over a gallon an hour, which should keep the pump inlet pretty cool. Idle has little flow and will not cool as much. Have you check fuel pressure when this happens? Have you checked for oil in the vacuum line inlet? Clean this out if it is there.

I am not an expert in this area, so please take my comments as theoretical.

Good Luck

Bob Rip

 

[Phils]

BobRip,

Your suggestion on the fuel bypass hose may be a solution, but I'd need to plumb the return back to the tank through another fitting. Tee-ing to the one line coming from the tank would only recirculate hot fuel. I'm not sure of the best way to add a fitting to the poly gas tank.

This VL occurs more a function of time rather than engine speed or anything else. I can be grinding at full speed and it'll start sputtering and die. I can look and see bubbles rising up the fuel line and into the tank elbow. I can be driving up my driveway and it'll sputter and die, again bubbles. In all cases I must have been running the machine for at least an hour or more. Idle or full speed makes no difference that I can see.

I'm going to try and cool the engine tub more if this last thing doesn't fix it. Hopin' for good weather this weekend.... I have enough stumps to continue testing.

Phil

 

[SnowRidge]

OK, heat seems to be transferring to your carb from the engine proper, thence to the fuel line in the immediate vicinity of the inlet. I would suggest doing what the racers sometimes do. Put a heat isolator between the carb and the engine. If a commercial unit is not available, make one out of some sort of material that doesn't transmit heat very well. It is really nothing more than a thick gasket made out the right material.

I have read of people doing it just by stacking non-metallic gaskets together. If there is room to do it on the Robin, it might be worth a try.

 

[Phils]

Thanks, Snowridge!

It seems that the heat/VL problem is occurring in the fuel hose as it transits through the engine bay, not in the carb. Having a clear fuel filter and the semi-transparent elbow into the gas tank allows me to monitor where the "vapor" is, and it's in the lines. If it were starting in the carb, it would kill the engine before filling the lines.

Dang good thought tho.

Phil

 

[BobRip]

</font><font color="blue" class="small">( BobRip,

Your suggestion on the fuel bypass hose may be a solution, but I'd need to plumb the return back to the tank through another fitting. Tee-ing to the one line coming from the tank would only recirculate hot fuel. I'm not sure of the best way to add a fitting to the poly gas tank.


)</font>

Maybe someone else can suggest a good tee in method. I just wonder if you could have a tank outlet blockage again. If the line were bigger would that help? It's easy to make suggestions, and I know it is harder to implement them. Especially since the problem is hard to create.

Bob Rip

 

[BobRip]

Phils, just some other suggestions. The goal I believe is to cool the gas line.

If you could put a small fan on the sides to blow outside cool air onto the fuel line it might cool the line enough.
Blowing cold air onto the fuel tank might help a little bit.

Use the engine coolant fan to pull air away though a jacket that is around the fuel line, with the other end of the jacket running outside the engine compartment to cool air.
Put some ice cubes in a jacket around the line after the problem starts to verify that cooling helps.
Put a heat shield on the gas tank between it and the heat source (I am not sure of the 425 configuration)

Put a small fan in the front of the engine compartment blowing outside air directly on the tank. Maybe the tank is getting hot. Measure the gasoline temperature before and after running. Insulating the lines does not help if the gasoline coming in is hot.
In cars the gas tank is not in the engine compartment.

Just some more crazy ideas. Maybe they will trigger some better ideas from you or others.

Bob Rip