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1980's Johnson/Evinrude 20/25hp conversion to 30hp with pics
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<blockquote data-quote="Edstrossner" data-source="post: 372210" data-attributes="member: 15774"><p>Great info!</p><p></p><p>But I am looking to go farther in the 25 to 30 hp mod.</p><p>I recently bought a 16 foot Lowe with a 2000 25 hp Johnson, 2 cylinder cross flow.</p><p>The stock carb has a .875 Venturi with a 1.250 throttle bore. Wot is 5500rpm at 24mph gps.</p><p>I had an old 70 hp carb with a 1.187 Venturi and a 1.375 throttle bore. It bolted up to the intake although the linkage was slightly out of line. The 70 hp carb has a longer throttle shaft. The motor fired up easily with the big carb and idled a bit better than the stock carb. At wot there was only a slight increase, 5800rpm at 25 mph gps. It appears that the motor cannot take advantage of the bigger carb.</p><p>I have modified many larger omc crossflows in the past with good success but I need some measurements from a 30hp block If anyone has one. </p><p>I seen one post than indicated that the 30 hp ports are oval. How many ports on the intake side? How many on the exhaust side? What is the deck to the top of the ports measurement? What is the size of the passage way from the crankcase to the transfer ports?</p><p>Any info would be greatly appreciated!</p></blockquote><p></p>
[QUOTE="Edstrossner, post: 372210, member: 15774"] Great info! But I am looking to go farther in the 25 to 30 hp mod. I recently bought a 16 foot Lowe with a 2000 25 hp Johnson, 2 cylinder cross flow. The stock carb has a .875 Venturi with a 1.250 throttle bore. Wot is 5500rpm at 24mph gps. I had an old 70 hp carb with a 1.187 Venturi and a 1.375 throttle bore. It bolted up to the intake although the linkage was slightly out of line. The 70 hp carb has a longer throttle shaft. The motor fired up easily with the big carb and idled a bit better than the stock carb. At wot there was only a slight increase, 5800rpm at 25 mph gps. It appears that the motor cannot take advantage of the bigger carb. I have modified many larger omc crossflows in the past with good success but I need some measurements from a 30hp block If anyone has one. I seen one post than indicated that the 30 hp ports are oval. How many ports on the intake side? How many on the exhaust side? What is the deck to the top of the ports measurement? What is the size of the passage way from the crankcase to the transfer ports? Any info would be greatly appreciated! [/QUOTE]
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1980's Johnson/Evinrude 20/25hp conversion to 30hp with pics
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