Thorp Air Command - T18.net

Guys, here's more questions:

I read all of Bingelis' books cover to cover (great stuff) and get instruction on IF you want to install a fuel primer... But I have no idea if I HAVE to install a primer. The Air Force trainer I used had it, and so does the 150 my friend owns, but like many others they're fuel injected.

I'm still in the construction phase and still learning. How about my T-18 with a simple gravity flow O-320? I rebuilt the carburetor; it has an accelerator pump - would a few strokes on the throttle work? Where does a primer go? into a single cylinder, or the manifold?

Thanks for the help,
Les.

While the accelerator pump on the carb usually works, this method can be a fire hazard and is not recommended in current teachings. You will need to prime on cold days. Primer lines go to the cylinder heads through fittings at the lower side of the intake valves. Usually, you have primers on three of the cylinders with your manifold pressure tap taking up the fourth. The primer gets its fuel from the top of the gascolator.

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Bob Highley
N711SH
SN 835
KLAL

I use the Vans electric primer and it goes to cylinders 2 & 4. I went with the Vans unit as it eliminates another source of "fluids" in the cockpit vs. the "manual turkey baster" unit. I have only used it a couple of times, even then not really sure I needed it ? The few days in KSAN when the temp gets down to about 40, I may need it more often. I know a buddy that had an engine fire on the ground from "pumping" the throttle during start.

RB

444DD has a O-320 with a carb and no primer/electric fuel pump. A couple of observations on starting a 'primerless" non-boost pump T-18 derived from my experience (the teacher of fools!):
Normal Starts-three pumps on the throttle-throttle cracked-starter engaged and it starts.
Cold Weather Starts-three pumps on the throttle-hand prop the engine for 4 blades-three pumps on the throttle-throttle cracked-engage the starter and it starts.
In very hot South Carolina Weather (>100 degrees) make sure you do a complete run-up before each take off because in my airplane, if you don't, you will likely have a momentary power loss just about rotation due to a vapor in the fuel line. This is especially so if you are using non-ethanol auto gas. A full run-up seem to magically cure that quirk of 444DD and save me from soiling my britches and biting holes in the seat cushion!
Cheers,
Graham Kerr

*** admin posted for Graham Kerr ***

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Forum Administrator

N71JE also has an O-320 with carburetor. I live & fly in Colorado, where we have temperature extremes from Summer to Winter not experienced in many parts of the U.S.- minus 30 to 100+ is possible. I normally don't fly it when the temp. is below around 20 deg., but I can honestly say that I have NEVER (knock on wood) had a problem starting with no primer in 21 years of flying this bird. That includes a few times when a hand prop was necessary because of a dead battery. 2 full pumps of the throttle when it's cold, and one when it's hot or for restart after a short stop (when killed with mixture), followed by immediate application of starter.

John Evens N71JE
Arvada, CO

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John Evens
Arvada, Colorado
T-18 N71JE (sold)
Kitfox 7 SS N27JE

N99KK - No primer, gravity pump, O-320. I don't start pumping the throttle until prop is turning. This sucks fuel up into engine. When not cranking, fuel pools in bottom of airbox. That could make for a loud POP if it backfires.

MLM has an o360 and no primer. No problems starting the times I tried it. Fraser, what was your procedure?

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In theory, theory and practice are the same. In practice, they are not.

I have had two T-18's without primers. Both are 0-360's. When I was building my first one, I talked to John Thorp about fuel pumps and also primers. He advised eliminating both. I have nearly 3000 hrs total between the two planes and have never wanted for a pump or primer. I do just as John Evens. Two strokes of throttle when cold then hit the starter. When hot, barely give the trottle a quarter or third of a shot. The new plane with dual E-mags starts instantly every time. The old one with a Shower of Sparks mag started on the second or third blade and when I put the E-mag on it, it also started instantly every time.

I fought the problem of the engine trying to quit right after liftoff for a year or so, wrapping the fuel lines with fiberglass tape and then wrapping aluminum foil over that and installing a blast tube to the gascolater and finally installing an electric fuel pump for takeoffs and landings that resolved the problem untill somebody on this list mentioned that the fuel surge rearward on takeoff, of a full tank and REAR MOUNTED TANK VENT, would momentarily plug the vent enough to starve the carburetor.