18hp opposed twin model 422707, older model

That's a lot of wasted fuel vaporization(cant think of the right word) and flow with all those bends and long intake manifold. If you could find an intake manifold for a horizontal opposed twin and just made an adapter plate to mount the slide carb to it'll be a whole lot more efficient. I don't think that little carb will feed the oppy as it is.

RichieRichOverdrive wrote:

That's a lot of wasted fuel vaporization(cant think of the right word) and flow with all those bends and long intake manifold. If you could find an intake manifold for a horizontal opposed twin and just made an adapter plate to mount the slide carb to it'll be a whole lot more efficient. I don't think that little carb will feed the oppy as it is.

thats true...never considered that. thanks for the info.

Not sure about what size carb your planning on but, I think the extra distance might not be a huge problem. I would be careful about having more weight so far out on the manifold though, more stress on the bolts which hold the flanges on the ports. Do opposed's have a brace in the middle of the manifold somewhere? Not sure. But if your carb is too small, the engine would still run, just high rpm power would be restricted somewhat. Low end would be better, probably a more responsive throttle. You might be able to go smaller than you think before you notice anything.

If you did have trouble with running the longer manifold, you could try heating it slightly somehow, maybe with some sort of pipe which directs some heat from the exhaust. Just to warm it somewhat, doesn't need to be super hot. But I don't think you will notice too much difference. The extension piece being down draft should be a help.

(Not to knock what you said richie, as it is a long distance from the carb to the port, just adding my ideas)

I think the bolts would hold it fine. Probably less weight with the smaller carb and filter than stock. You're right, the extra distance probably won't make that much difference, I've seen a carb setup like this on an oppy before that worked fine. Not like you can get these engines more inefficient than they already are. I'm more concerned with the governor gear being oversped, it could fly apart and kill the whole thing.