how do i ignite the engine

What do you mean?[sm=confused.gif]

Like i how will it work.

The weight depends apparently on which system you will purchase. The Rcexl system weights 4.4oz, without batteries. The battery pack is a normal 4.8V Rx pack.
I would not recommnend using the receiver's battery pack for the ignition. Noone would recommend it. It can cause neither system to operate adequately. Just use two battery packs, even though as the airplane size decreases, the extra weight becomes an issue. (that's why most people convert engines more than 0.60 cu.in, which are used by big airplanes.)

you use a separate power switch harness for the pwer for the ignition, turn the switch on and the ignition turns on, turn it off and the engine will turn off.

you will probably have better luck putting the ignition on the engine and running it on glow fuel, this can give you better performance than a glow plug with better reliability, if you get the bugs worked out that way change the fuel lines and maybe try gas.

Well thanks for all the help guys.

So it looks like I will be using two battery packs then. And to make things easier I will get it running on glow fuel first. Gotcha
I still have a few litres of glow fuel left over anyway. Better use it before it goes stale [:@]

Just to let you know, I will be buying the parts for it this weekend. I can't wait to start working on this

Some of this has already been covered.

The ignition has a maximum RPM above which it will provide progressively weaker spark or not spark at all. RCEXL doesn't specifically publish this RPM. We do know they run up to 15k just fine. I would bet it can do 18-20k, but haven't tried. As mentioned above fitting the sensor and magnet will take some work and probably a custom sensor mount and smaller than typical magnet. Unless you can get an ignition with a straight plug boot or make one, you won't be able to get the boot onto the plug deep inside the heatsink head.

Gasoline will have much less power than the typical 20-30% nitromethane glow fuel.

The engine will run much hotter on gasoline. What this will do to the ABC piston and liner fit or life is for you to find out. Oil ratio should be similar to the glow fuel being used, or potentially even more. Use a high temp, high viscosity racing oil.

The carb is designed for the above mentioned glow fuel, on gasoline adjustment will be tough. If it has two needles the idle and WOT throttle can be tuned fairly well, but midrange will be rich, probably very rich. A "third" needle is unlikely to help much in this case. It will be very sensitive to needle adjustments. The difference in a car application compared to an airplane for a carb is that the engine will be operating in a wide range of RPM for a given throttle setting such a simple carb has a hard time dealing with that. It works well with glow fuel because it tolerates a very wide range of air fuel mixture. Gasoline is much more critical. The glow carb will likely also be too large for gasoline. With a slide carb it's fairly easy to just limit WOT as long as this doesn't interfere with tuning the needles.

Bear in mind, that using glow fuel might dictate alteration of the static ignition advance (ie the angle you set the spark when you turn by hand). When using gasoline, this angle is usually 28-30 degrees Before TDC.I do not know how much it should be when trying glow fuel, which has different flame propagation speeds. The guys who are trying spark ignition with glow fuel may help you.