30mm intake for 150cc... should I port the head or...?

[jpark1]

I acquired a 30mm CVT carb and shiny aluminum 30mm 'gy6' intake. It's a VERY tight fit with the engine mount being all in the way, but I got it to work... however, I noticed the 'output' hole on the intake is quite a bit larger than the 'intake' hole of the engine, and the rubber spacers I had to use. Runs ok, tremendous midrange pull and great throttle response, bit of a stumble though, some hesitation...Did I get the wrong intake(possibly for 250cc?), or should I tear off the head and take a dremel to it? I would think it's best to get a smooth flow of fuel/air... right? You guys who went up to 30mm carbs... what did you do?

[MEAN_MOTOFINO]

I would just match the ports until you get the head fully ported. Make sure that the head stays equal to or larger than the intake elbow4 and spacer. You dont want any walls for the air to hit(reversion). Same with exhaust. Make sure the exhaust steps up as the goes out of the head.

[jpark1]

Yeah, that's what I thought, it looks like porting is necessary to get any real benefit from the larger carb, otherwise you have the same bottleneck, but with the fuel/air flow disrupted, which is pretty much a downgrade... It shouldn't be TOO hard, maybe I can just stuff a rag down the hole and do it with the engine in place. Dremel with sanding drum should work. I read about so many who upgrade to these larger carbs, yet I don't recall anybody talking about porting... odd... Thanks man!

[bloodymomo]

Also look into getting a performance cam. Will help with oversized carb

[jpark1]

I thought about getting an A9 or maybe A14 cam at some point. Not really sure I'll need it, I can cruise along at 60mph with the old 24mm carb, but just can't get past 7000rpm. The 30mm carb gets it up to 8500rpm, but I haven't really tried for top speed on it yet. It's not tuned in quite right yet, and it's cold as hell out anyway. I suppose I should mention this is one of those Scrappydog oil-also-cooled 161qmk united motors "200cc" (more like 170 or so) engines... just trying to take advantage of the slightly larger displacement, maybe get more hill climbing torque without screaming along on lighter weights, I'm not really trying to get too much faster.

[GypsyKing]

Mind if I ask, whats the gap on your vowels? I just dropped in a 200cc bore kit in my once 150 gy6.

[blueboy5000]

Gap is gonna be the same as stock, even w double cams.