BobRip
Elite Member
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
Bob Rip
Vaporlock revisited
- Thread starter Phils
- Start date
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OP
Phils
Platinum Member
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
Phil
OP
Phils
Platinum Member
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
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
OP
Phils
Platinum Member
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
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
Elite Member
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
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
OP
Phils
Platinum Member
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
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
Elite Member
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.
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.
OP
Phils
Platinum Member
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
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
Elite Member
</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
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
Elite Member
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
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