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Engine primer source

NYTOM

Well Known Member
For those of you with the Vans electric priming system and don?t have a gascolator on the firewall, where did you pipe the feed fuel to the solenoid from ?:confused:
 
I guess I wasn?t very clear in my question. Installing Vans primer on carbureted engine and I don?t have a gascolator. Wondering if I should put it before or after the engine driven fuel pump. Thinking if the solenoid stuck open if installed after the fuel pump, it would make the engine run wild. If the solenoid failed open if installed before the fuel pump, the pump would suck air or at least loose suction. Now I?m thinking I should install before the fuel pump and put a check valve in line at the solonold to prevent engine failure if the solonold should fail open. Just trying to work this out. Not really fond of throttle pumping to prime. Though someone would suggest a solution.:)
 
Why not put a "T" fitting on your firewall such that the fuel to the carb goes through the straight part of the "T" and the primer is fed from the leg of the "T"?

This would put it downstream of the electric pump but upstream of the mechanical pump.

That basically replicates the gascolator install, doesn't it?
 
Kyle that is exactly what I?m planning to do. Found a AN 6 coupling with a 1/8? tap for the primer that Im installing at the suction side of the pump. Thanks for your imput. There?s a lot of guessing going on here and I guess Im looking for some reassurance that Im not screwing up. :rolleyes:
 
Any details of fitting

Hi Tom ... need the same fitting ! Any details . Part # , where you bought it , picture ? Thanks. Stew
 
Tom...
Kyle said at the firewall. You are saying at the fuel pump...if I am reading right. Pretty sure you are mounting the solenoid on the firewall. Remember every time you connect a firewall mounted item to the engine, you use a flex line. so be careful about keeping your system neat and tidy. The TEE at the FW then run to the solenoid then the flex line to the engine, seems to keep it cleaner. Just my .02.
 
Hi Tom ... need the same fitting ! Any details . Part # , where you bought it , picture ? Thanks. Stew

I purchased all the steel fittings from Aircraft Spruce and the flex hoses from TS Flightlines. Had my aircraft inspected by Vic. Systems works great with no problems. Quarantined now and can?t get to the hangar.:mad:
TS Flightlines also sells the fittings . Tom at TS was extremely helpful and his service is about the fastest and highest quality around. Ended up teeing after the engine driven fuel pump and running a SS / Teflon firesleeve hose to FW mounted primer solenoid valve. From there another SS/ Teflon firesleeved flex hose to primer line manifold on engine. Having a flexible connection is very important since the engine physically moves so much. I?ll check it when and if I ever get to it again and get some photos and numbers if you still need them.
 
For those of you with the Vans electric priming system and don?t have a gascolator on the firewall, where did you pipe the feed fuel to the solenoid from ?:confused:
Tom,

Sounds like you're finished and happy with your installation but perhaps this will help someone else in the future.

I removed a 1/8" NPT plug near the fuel inlet on the carburetor and ran a flexible hose (also from TS Flightlines) to the primer soleniod mounted on the firewall. No fittings required outside of a 1/8" NPT-to-flared-tube nipple at the carburetor.

When the solenoid is activated there's good primer fuel pressure from the engine-driven fuel pump while cranking and even better pressure when the boost pump is running.

Your concern about a leaky solenoid is valid because the engine runs very rich (but mine does run) with a solenoid that is not completely closed. I learned this when I installed the fuel solenoid "backwards". The three primered cylinders were excessively rich and the engine would not stop at idle-cutoff. I did not realize that the primer solenoid has "polarity" and it matters which port is input and which is output. It's mentioned in the Overview and the Q&A on the Aircraft Spruce web page.

--
Joe
 
Thank god for you guys !!

Joe and Tom. Thanks so much as your sharing here saved me a whole bunch of rework ! Going to do as Joe did from the pity on the carb that used to be fuel pressure line to gauge ! Saved just a bunch of work and I like the idea of being on the engine side of the fuel pump .... I guess however that if the primer line fails we will be spraying fuel into the cowl ( scary ) at fuel pump pressure ? If primer line same off before pump thinking that since the primer line is very small that pump wouldn't suck too much air ... ok. Now I am not sure which is lesser of two evils ?? Have I got that right ?? Thanks. Stew
 
Joe and Tom. Thanks so much as your sharing here saved me a whole bunch of rework ! Going to do as Joe did from the pity on the carb that used to be fuel pressure line to gauge ! Saved just a bunch of work and I like the idea of being on the engine side of the fuel pump .... I guess however that if the primer line fails we will be spraying fuel into the cowl ( scary ) at fuel pump pressure ? If primer line same off before pump thinking that since the primer line is very small that pump wouldn't suck too much air ... ok. Now I am not sure which is lesser of two evils ?? Have I got that right ?? Thanks. Stew

I tapped my system near the gascolator. I felt it was safer to have an air leak on the suction side vs spraying fuel on the pressure side in the event of failure. primer works off of the boost pump. I can't think of a reason to use the primer in a situation where the engine is spinning and therefore the eng fuel pump is providing pressure.

Larry
 
I originally purchased the primer solenoid kit while building my 7. During the build I purchased a 4 with no primer. Pumping the throttle 2 or 3 times when cold, using the accelerator pump in the carb for priming, worked fine for 4 years and 450 hrs, winter and summer. I removed the primer on the 7, which I had not flown yet, liking the idea of fewer things to go wrong. After 375 hrs in almost 3 yrs on my 7 and in weather down to -10C (using preheat) starting has never been an issue. FWIW.
 
I originally purchased the primer solenoid kit while building my 7. During the build I purchased a 4 with no primer. Pumping the throttle 2 or 3 times when cold, using the accelerator pump in the carb for priming, worked fine for 4 years and 450 hrs, winter and summer. I removed the primer on the 7, which I had not flown yet, liking the idea of fewer things to go wrong. After 375 hrs in almost 3 yrs on my 7 and in weather down to -10C (using preheat) starting has never been an issue. FWIW.

This ^^^^

Save the weight, and risk inducing complexity and don't install it. I bought a -9A that didn't have a primer and was concerned about it for WI weather. Not an issue at all especially with electronic ignitions ability to ignite very lean mixtures.

Here's the logic to this decision...
  1. Carbed vehicles started off accelerator pumps for decades without priming
  2. You should preheat your engine below 32F anyway so the transmitted warmth from engine to carb bowl is actually better because it "warms" the fuel providing greater vaporization. Primer fuel won't be warm.
  3. For fire you need a fuel...that fuel has to vaporize before igniting (even wood or paper doesn't burn, it needs to heat to vaporize first and mix with O2 to produce a combustible flame). Priming is simply dumping enough fuel in the induction system that enough vapor is created to support combustion. The colder the fuel and air the more primer fuel qty to create the vapor to go bang! Therefore the goal to successful starting should be turning fuel into vapor and regulating air to support combustion, not necessarily more fuel.

I did my insurance checkout with rocketbob and he recommended "pumping" the gas a couple times at the start of cranking. This has worked flawlessly this winter...even without my Pmag installed. My start technique cold...crank and pump throttle 2x, then throttle back all the way to idle to choke off air. Fire right up and idles at 600-700 rpm, then I slowly bring to a smooth idle around 900. Hot starts require NO pump/priming. Crack throttle 1/4" and just crank...starts like a car.

I believe primers are only necessary in our lycs when it comes to hand propping to help "precharge" cylinders with vapor. Much like a hybrid engine does for quick restarts.
 
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It is up to the builder. I do recommend as suggested above, if you have no primer, do not pump the throttle until you are cranking the engine.

Some O-320's have carbs ( MA-3A is one ) with out an accelerator pump carburetor. You need a primer system. Just FYI.

Solenoid and some copper tube to one, two or three cylinders is not a huge expense or weight. Put it in if you want. My RV-4 had a primer solenoid. I'd turn boost on, push the button for a second and light the engine. No throttle pumping needed.
 
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