sleeping

Thanks for the explanation.

Of course I believe you as you have run and rebuilt! your motor, mine is still in the box... But it just doesn't sit well for some reason? I'll explain what I think is happening;

I'm cool with how the reg and the pump works ( I hope...) it's easy if I refer to the manual for part numbers just so we avoid mixing words yeah?

The pump is driven by the intake pushrod that runs of the cam, this rod is split into parts 61 & 62 which run the tappet for the intake valve as where the exhaust pushrod is not split. As has been noted the pump and reg are combined. The diaphragm within the pump 48 is deformed by the 'button head plungers' 52 & 53 that move in and out perpendicular to the pushrod. One very clever design move is the fuel line down from the Regulator Body 45 to the crankcase. Remembering that there is no pressure in the crankcase, by inserting this line it ensures that the diaphragm will never have any - air - pressure on it's side facing to the front of the engine. That pressure is determined by the Reg spring only and that is why we are told to adjust the idle mixture via the reg screw ( onto the spring ) my old 160 was very different and the reg was 'not to be touched ' as it was factory set. A completely different system. The same goes for the reg on my us Heli engines. A different system again.

Back on track...

Once the fuel exits the pump via the line that connects to the nipple on top of the carb body 63.

In your post you noted that this line was a high pressure fuel line. I think it would be better to cite that as fuel under standard pressure; After all, that is the whole job of the reg. High pressure fuel coming into the throttle body would give the high speed needle no chance to fine tune the flow of fuel. To that point, if the reg was wound out too far it would render the high speed needle useless.

To cover off the sub-needle valve, straight off the instructions, that simple let's a little bit of fuel into the crankcase to lubricate the bearings and keep things cool.

There are some very complex timing ports 28, 30,31 that double up as the backplate onto the carb body that I have no idea about without pulling apart the engine. I am assuming they are opened and shut by the back of the crankshaft.

From here, things just aren't adding up...

Let's stick with full throttle to keep things simple; it's time for the fuel and air to mix. The correct fuel flow rate has been established by the pump/reg/ high speed needle and the carby is fully open.

In my head, the mix is completed in the carb body and the travels up the intake pipe 79 when the intake valve 7 is opened. The intake valve then closes and that phase of the cycle is complete.

In your post you noted" It all gets squirted in at the intake valve as the valve opens, as below the black check valve there's a small needle that is pointed at the intake valve. "

I cannot see any needle near the top of the cylinder head; physically or in the exploded diagram. The role of the sub-needle we've covered off.

In my mind, it's the intake pipe that delivers the air & fuel mix to the combustion chamber.

It makes no sense to inject the fuel into the chamber at the top of the head via a one-way check / bleed valve.
Unless I am reading your explanation wrong ( Ohms law!!)?


I think the role of the fuel line in question is to allow any fuel below the cylinder head a path of escape. This ensures there is never a residual build up, or pool, of fuel hanging around the carb body which would upset things. Remembering that via the sub-needle we are directing a small amount of fuel into the crankcase. It needs an easy path of escape. That in my mind makes sense. OS use the same method on the OS 200 standard (not f3A). And although that line may always full of fuel the flow rate would be much lower than the flow rate of the fuel coming from the pump. The one thing the instructions don't cover is adjusting the 'bleed' of that valve which has a direct -force - pressure differential on the fuel that us trying to exit the crankcase. The instructions give fair warning about opening the sub needle too far. But if you're engine is running too hot, but if you open the sub-needle it will affect the motor's performance, in theory (if I have got it right) you could open the bleed valve a little and the sub needle a little which, in effect, would see a greater flow of fuel below the cylinder head - in & out - to cool the engine without affecting the overall performance. The answer is in those timing ports....

I-will-fixit, what is the answer????

Cheers to all. Wrong or right I will ultimately know exactly how every bit of this engine works. So come set-up time, it will be easier to diagnose any issues

Thanks to all
I'm asleep