inlet manifold

[Fred]

Yes thats right an inlet manifold. Some of you may member me trying to make a 1400 run on 1 single carb. I have made 3 manifolds of different types all of which did not work satisfactory. The problem being that it would not idle on both cylinders but would immediately burst into life with a bit of throttle. All kinds of adjustments made no difference.

I have just completed a very difficult and complicated manifold with trumpeted runners fed from a Plenum chamber that sits under the tank, unlike the other manifolds this is not an updraft but a side draft having the carb sat as high as could be possible on the right. This meant it was less work for heavy gasses to be pulled 'up' into the manifold reducing depression even more and having fuel that was suspended in the air drop out of the very cold manifold walls and condense. The meant that the engine was running on droplet and not atomized fuel. Numerous times have i increased and decrease the idle jet size along with altering induction signal with the air jet,--- no difference what so ever apart from altering the needle response position. Obviously something else.

The 4th manifold that I have just completed is made of perspex on the top so I can see what is going on when the engine is running, something I have never seen before. It is extraordinary sight to see at each pull of the intake stroke dart like a white ghost from runner to runner.

However I got to see what I suspected and that there was infact nothing wrong with the carb or manifold but the exhaust system. At just over idle it could be seen that the fog of atomized fuel was coming out of the rear runner as well as going in leaving droplets of fuel like rain on the car windscreen at speed. This proved my constant suspicion of reversion in the exhaust.

I have had many pipes and shot gun straights don't work. many modifications have been made including baffles and loli pops all of which change, increase or reduce the reversion affect. I shall now remove my rear cylinder pipe and try to re design a reversion free pipe. The clue being that the front which is shorter does not seem to suffer the same problem.

[hillsy]

Post some pics Fred - sounds interesting [emoji106]

You could put some LED's in the air box to light up the vapour

[WintrSol]

Interesting science project!

[Rick]

So happy to read a motorcycle related topic here.

Sounds like the carburetor is too far from the piston making it difficult for the inlet signal to draw fuel from the float bowl at low rpm. I'd love to see a few pictures of what you're building here too.