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02-10-2011, 06:34 PM

#38

roger damore

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Join Date: Apr 2010

Location: bradenton, FL

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RE: Newbie to Gas General Information

The following was posted in the gas engines thread on 7-1-12

Quote:

Original:Av8tor1977

I've been contemplating lately how much help the use of a primer bulb on our planes could be, and how many problems it could solve, especially for newbies. I know, I don't really want one on my plane(s) either, but it does have some logic. When someone says "firing up your (weedeater, leaf blower, chainsaw)??" when you are using one on your plane, just tell them "Hey, at least my plane always runs!"

Here's the "argument". Most people don't have a clue about how a primer bulb system works, but it is pretty ingenious actually. It does not "push" fuel to the carb, and it does not "inject" fuel into the engine. What it does is draw fuel from the tank all the way into the regulator fuel chamber. It creates a suction that moves the regulator diaphragm open, which opens the inlet needle valve, which allows fuel to be drawn from the tank, through any filter you might have in the tank, through the inlet fuel tubing, through the fuel pump, through the inlet screen in the carb, past the regulator needle valve, and finally into the fuel chamber. The excess is then expelled through the other line in the primer bulb system, and dumped back into the tank.

So think of what all this accomplishes:

1. Flushes old fuel out of the carb and replaces it with fresh drawn from the tank.
2. Proves that the filter in your fuel tank is flowing.
3. Proves that there is probably no kink nor obstruction in your fuel feed line to the engine.
4. Proves that fuel can flow through the fuel pump, indicating that the check valves in the fuel pump are wet and probably functioning. (At least the inlet flapper valve is not stuck.)
5. Proves that the inlet screen in the carb itself can flow fuel.
6. Proves that the inlet needle is not stuck shut. (I have had this happen.)
7. Proves that the regulator diaphragm is not stuck in the closed position. (It still could be too stiff to operate correctly but at least it is opening the needle valve.)
8. Proves that there probably not an air leak at the fuel pump nor diaphragm cover gaskets.
9. Prevents the "dry carb won't draw fuel" syndrome.

Interesting heh?? I fix a lot of yard equipment, and the first thing I do after checking compression and spark is to put fresh fuel in and pump that primer bulb. If it doesn't pump fuel and fill up, the very first trouble shooting step is to find out why not.

AV8TOR

Quote:

Originally Posted by Antique

Ignition systems 101...My carb rotator block is made from 3/8" epoxy board material...the carb is now closer to the cylinder...The throttle connection is at the end of the carb closest to the crank...The throttle servo connects directly to the new brass arm on the throttle shaft...It makes no difference which timing method is used, the connection remains the same...The mechanical advance has a 4/40 threaded rod link between the carb shaft and advance mechanism, a 6202 ball bearing on the back side of the prop hub...The hall sensor is mounted in a ring pressed on to the ball bearing...There is a magnet in the hub that triggers the advance when it passes the hall sensor...With mechanical advance the ring is rotated by opening the throttle..The spark timing is set for 28 degrees before top dead center for either method...The difference is that full advance is reached at 4000 rpm with electronic advance, and at Wide open throttle with mechanical advance..Contrary to popular opinion, I can find very little difference either way...I don't think the engine can tell the difference where the spark occurs after 4000 rpm, and very little if any before that..
To further complicate this, the electronic advance can be made to delay full advance until 6000 rpm..Again, no difference noticeable in performance..
The difference between my mechanical advance and the Brison pictured is the material on the Brison is Delrin or nylon with no ball bearing, and mine is aluminum with a 6202 sealed ball beaing..My hall sensor is epoxied into the aluminum, the C&H ignition setup on the Brison uses the exact same Sony DN6952 hall sensor in a removeable round piece held in by a setscrew...Since hall sensors rarely go bad I use epoxy...
The sensor on the DA is a small transformer using only 2 wires...The electronic advance on the DA works just like the electronic advance on all other engines...
The electronic advance chip on mine and C&H ignitions is the same part...
Static timing on mine and C&H electronic ignitions is set at 28 or 30 degrees BTDC...The first flip of the prop retards the ignition to 4 degrees BTDC, then follows the rpm of the crank.
Static timing on most other electronic advance ignitions is set at about 4 degrees BTDC and advances to 28 or 30 from there..
Hall sensor electronic ignitions with fire at 1 rpm, the other systems must be flipped a little faster for the transformer sensor to make enough voltage to fire the circuit....
Mechanical advance ignitions MUST be started with just a few clicks of throttle because the engine will kick back if the throttle is opened too far...Other systems always start retarded regardless of throttle position...
Spark timing can be changed on either system, by moving the sensor on the other systems or changing the length of the link on the mechanical...
Older engines with fixed EI can be changed to electronic advance by pluggin in a syncro spark module between the sensor and circuit board and locking the timing ring at 28 degrees BTDC..
Syncro spark modules are available from C&H...
Most engines with magneto and source coil ignition are set by the factory at 28 degrees BTDC....It can be changed by removing the mag rotor or flywheel and leaving the key out, then rotating the flywheel or rotor to whatever point is wanted..The key does nothin to keep the flywheel or rotor from slipping, it's only function it correctly place the rotor or flywheel on the shaft during assembly...The key on a tapered shaft crank is so soft it will shear if the retaining bolt comes loose....
Did I miss anything ?

Last edited by w8ye; 11-03-2014 at 09:37 AM.

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