Four-stroke manifolds
 

I have a large number of aircraft four-strokes. Most started out with the bent intake manifold and the carb tucked out of reach behind the cylinder. The exception being LASER which has its carb straight on the head.

Now I have turned up new manifolds and have my carb where it should be, just like the Laser, but of varying designs and lengths. All run superbly and with great reliability. Four- strokes in my experience have much better suck than two-strokes, so the need to have the fuel in point low down is not there.

RE: Four-stroke manifolds
 

Hi Engineman,

I read your post several times and don't know exactly why you posted to the "Engine Conversions" forum. I am guessing you are suggesting that four stroke engines don't require a Walbro style pumper carb to meet fuel draw requirements. It appears that you have had some success testing your own machined manifolds that place the carb at cylinder head level.

I have a few questions. First, were these engines that you converted operated on glow or spark ignition? Second, did you notice a drop in RPM with the shorter, straight manifold. The reason that I ask this question is because I wondered if there was a slight tuning effect derived from the long intake pipe found on the Asian four strokes. Third, if you operated the engines on gasoline rather than glow fuel, did you try to insulate the carb from cylinder head heat?

I always liked the direct approach taken by Laser Engines of mounting the carb straight on the head. Perhaps the Laser engines would be a good candidate for conversion to spark ignition, or has Neil already done this?

Bruce