Vaporlock revisited

Gravy · Mar 5, 2006

George,

It wouldn't pump even with the engine running. I suspect the oil prevented the diaphragm from moving properly. It probably would work now that it's cleaned out, but I expect it would eventually fill up again. I feel more comfortable with the electric pump, but will keep the OE in place in case the electric pump dies at an inopportune time.

I used a standard Bosch 5-pin relay to power the pump, using the oil cooler fan power wire to operate the relay coil, and connected the contacts direcly to the battery (with a fuse, of course).

I agree about OE limitations. I kind of doubt that the engineers at Robin expected the engine to be operated at the angles a PT can routinely handle. I believe the lubrication system is rated to 20 or 25 degrees of slope, but they probably didn't test the fuel pump for hours at those angles. It probably works just fine at the angles a conventional tractor can handle.

One other thing I did while making changes to the fuel system was to add a shutoff valve to the tank outlet. I don't like gravity-feed systems that can't be readily shut off in case of a hose leak. You can spill a lot of fuel while you run around looking for a plug.

The QA cylinder leak appears to have been due to the shaft seal coming adrift from it's seat inside the cylinder. When I removed the end cap, the seal ring was moving with the shaft, not staying in the cap. I cleaned and inspected everything under magnification, and saw no damage or any indication of why it came loose /forums/images/graemlins/confused.gif, so I reseated the seal and reassembled. I've operated it several dozen times so far with no leakage, but I'll be watching it closely for a while.

Gravy

SnowRidge · Mar 5, 2006

<font color="blue"> I kind of doubt that the engineers at Robin expected the engine to be operated at the angles a PT can routinely handle. </font>

It would be interesting to find out if that is indeed the case. It is my understanding that small engine manufacturers typically review customer engineering data before approving their engines for sale to OEMs. Supposedly, this is so they don't get stuck covering warranty claims for damages that are caused by improper application of their products. For example, I was told (I forget by whom) that Kohler had to approve the PT 'tank' muffler since it would have a direct bearing on engine life, and thus Kohler's potential liability for warranty claims. I wonder if Robin has similar requirements?

RegL · Mar 5, 2006

"I used a standard Bosch 5-pin relay to power the pump, using the oil cooler fan power wire to operate the relay coil, and connected the contacts direcly to the battery (with a fuse, of course)."

I'm not really up on electric fuel pumps but I have a question. On my tractor the cooling fan has power with the ign. switch in the on position even if the engine is not running, and for some reason my key sometimes ends up in that position after I shut down. Put some extra hours on the clock also. Anyway, if that occurs, is the fuel pump going to keep pumping fuel ?

J_J · Mar 6, 2006

If there is no fuel pressure regulator, it will keep running as long as it has voltage. You should be able to hear or feel it running.

Gravy · Mar 6, 2006

The pump will be powered, and will draw current, but no fuel will actually flow unless the carb float needle leaks. If you leave the key on, and have a leak, the pump could empty the tank pretty quickly. Of course, since the tank is higher than the carb, a leak could empty the tank even without a fuel pump. It would just take longer.The pump I'm using maintains 4psi and shows no signs of flooding the carb. Also, leaving the key on overnight would likely run the battery flat.

The ideal setup for an electric fuel pump would require a relay that senses ignition pulses and only energizes the pump with the engine running. I'm not sure that any such automotive relays I've used would be compatible with the Robin ignition system. I believe Kohler has a line of fuel-injected engines that might use a relay that could be adapted.

Having worked on plenty of cars (from MG's to Nissans & Hondas to hotrods) over the years with exactly the sort of setup that I'm using, I'm comfortable with it as-is. Your results may vary...

Gravy /forums/images/graemlins/tongue.gif

Keoke · Mar 6, 2006

Gravy, if you folks want want fuel pump to run only when engine is running consider the following:

1. Tee off one of your engine oil pressure sender switch. If there is no oil pressure sender tap into a hydraulic pressure line and plumb in a pressure switch that closes when seeing hyd pressure. Engine oil is prefered because of much lower pressure and a cheaper switch to buy. These switches are common to hour meters. Another source is old Chevy Vega oil sender sw that used oil pressure to trigger the elec fuel pump and oil light in one switch. Bottom line, what you want is a switch that closes to gnd (single wire preferred) when it sees engine oil or hyd pressure. Most hyd systems run a pressure between 2,000 & 2,500 psi so you DON"t want use an auto oil sender sw here. Also, most automotive pressure switches go open, (to put out light) and not close when they see pressure. You want just the opposite here.

2. The Bosch relay has two terminals (85&86) for the pull in coil, one for B+ (sw high) and the other for gnd (sw low). Hook the hi one to ign on and the low one to the pressure sending unit. Terminals 85&86 are not polarity sensitive unless a anti-spike diode inside is wired aross these two. If you don't know about diode make 85 B+ & 86 gnd. Number 30 should be B+ in and 87 goes to load (pump).

3. With this setup it will take both ign on and engine running to run fuel pump. The down side of this setup is that the fuel pump will not run until engine oil light goes out. However, this should not be a concern since you have gravity flow to your carb at all times.

hope this helps,

Gravy · Mar 6, 2006

George,

Jeez, I'm embarassed - CRS strikes again! I've done that exact circuit before, AND my engine has an unused oil pressure switch.

A few years away from the auto repair business, and I'm practically a drooling moron. I hate to admit it, but my calibrated eyeball isn't what it used to be, either. I used to be able to grab the right wrench at least 95% of the time without even thinking about it. Somehow, on this project I grabbed the wrong wrench at least 3 times. I'm beginning to feel like a candidate for the Home for Bewildered Old Mechanics.

I will be making that circuit change.

Thanks,

Dave

SnowRidge · Mar 7, 2006

Since there is some interest in installing electric fuel pumps on PTs, I thought I would mention a type I've used a couple times in the past.

Stewart Warner makes them. They are a line of fuel pumps that, as far as I know, do not draw power when they are not delivering fuel. They are piston pumps with built in pressure regulators. In operation, they make a clicking sound (as opposed to the whirring of motor driven pumps). If no fuel is being consumed, the clicking stops as soon as the fuel line is brought up to pressure.

I've used a couple of these pumps in different applications, and if I remember correctly, they are entirely electro mechanical; if the pump isn't clicking, no power is being consumed.

The pumps are in the model number range of 82050 to 82057, and perhaps higher. They are available with 4, 5, and 7 PSI pressure settings, that I know of. They are not adjustable, so you have to buy the right one up front.

I don't think they are cheap, though.

Keoke · Mar 7, 2006

Gravy, there is a good chance that the second oil pressure sending unit was intended for an hour meter.
Let's hope it's a pressure gives gnd switch and not open sending unit.
Hey, I hear you on the fading memory business. I too have trouble coming up with the proper wrench size with each call.
On the plus side, some things are best flushed away ASAP.
It's like clearing up the temporary folder!!

cheers,

Phils · Mar 7, 2006

SnowRidge,

The diaphragm pump that you mention was the one I intended to install but my parts guy recommended the "electronic" pump that I ended up putting on. It's working fine.

Attached is a photo of the angle I am trying on the Supertrap. I worked the PT for a couple of hours Saturday and had no indication of VL. However, an hour or two of stumpgrinding will be a more accurate test. A couple of hours of brushhogging when the temps reach 90 will be the ultimate test.

Please limit comments on my welding ability to "constructive criticism". I did this mod quickly and will grind and fill to make it look nice once I've determined that my VL problem is gone. IF it solves my problem.

And I should be receiving the fiberglass insulation any day now.

Phil