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convert 20hp evinrude to a 25 hp?.....

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cjbrill715

Regular Contributor
Hi everyone, I have a 1992 e20crend Evinrude 20 hp....I have the a 25 hp carb off a 1993 j25rwete, and a intake manifold off a 96 25 hp. I also have the proper 25 hp throttle cam...My question is, on the timing, does the stopper screw have a ratio of turns per degrees of timing adjustment??...Someone told me that for every turn of the screw, you get a (1) degree of timing adjustment on this era of motor...The timing needs to be adjusted from 34 degrees BTC to 30 degrees BTC, but I want to be sure that I know what I'm doing, any help would be greatly appreciated.
 
Sounds right to me. Do you have to change the intake too on these? Don't think you have a 1996 intake, must be a '95. The 96 is a new generation......isn't it?
 
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Not sure, it fits the carburetor, and has the 1.375" (slightly over, like 1 and 7 sixteenths) intake hole...It was labeled as a 96 on ebay, but who knows
 
Okay, then it should be an easy job. When you have the manifold off it is a good time to check those crankcase bolts for tight, I have found them loose before, but that was on a motor that had been overhauled.
 
cjbrill715 said:
Hi everyone, I have a 1992 e20crend Evinrude 20 hp....I have the a 25 hp carb off a 1993 j25rwete, and a intake manifold off a 96 25 hp. I also have the proper 25 hp throttle cam...My question is, on the timing, does the stopper screw have a ratio of turns per degrees of timing adjustment??...Someone told me that for every turn of the screw, you get a (1) degree of timing adjustment on this era of motor...The timing needs to be adjusted from 34 degrees BTC to 30 degrees BTC, but I want to be sure that I know what I'm doing, any help would be greatly appreciated.
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I was told the 20hp carb and the 25 are the same by a marine mechanic.Just swapped the intake on my 1985 20hp.Never read anything about changing timing?This conversion has been discussed before.
 
Really? Maybe the same carb but certainly not the same main jet. The timing limit might have to be retarded by that 3 or 4 degrees.
 
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newyota said:
I was told the 20hp carb and the 25 are the same by a marine mechanic.Just swapped the intake on my 1985 20hp.Never read anything about changing timing?This conversion has been discussed before.
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Don't quote me on this, but pre 87 era were as you are describing....They just had a restricted intake from what i have gathered. But my era (early 90's) the 25 hp carb has a significantly bigger venturi that matches the intake hole size. The timing according to the manual is different between the 20 and 25 in my era by 4 degrees....But the throttle cam may have some extra plastic molded on the side of it to offset/retard the timing somewhat without even having to mess with the timing screw....I'll have to measure it to verify. The 25hp and 30 were both set at 30 degrees BTC from my era,(could possibly explain why they share a throttle cam??) the 20's, atleast mine was set at 34 degrees BTC
 
timguy said:
Really? Maybe the same carb but certainly not the same main jet. The timing limit might have to be retarded by that 3 or 4 degrees.
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I just measured the two throttle cam pieces. The 20 hp one had noticeably less plastic molded to the side of the cam that makes contact with the spark advance/retard stopper screw, so it appears that my era of motor they didn't monkey with the timing screw, but more probably just put on a different throttle cam to retard the timing several degrees between the 20 and 25/30 hp models.....I guess the only way to know for sure is to put the 25 hp parts on it, as well as the throttle cam piece, take it to the lake, and do a WOT timing test on it with a timing light, and a buddy to steer the boat, and use the screw to make fine adjustments if need be.
 
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cjbrill715 said:
Don't quote me on this, but pre 87 era were as you are describing....They just had a restricted intake from what i have gathered. But my era (early 90's) the 25 hp carb has a significantly bigger venturi that matches the intake hole size. The timing according to the manual is different between the 20 and 25 in my era by 4 degrees....But the throttle cam may have some extra plastic molded on the side of it to offset/retard the timing somewhat without even having to mess with the timing screw....I'll have to measure it to verify. The 25hp and 30 were both set at 30 degrees BTC from my era,(could possibly explain why they share a throttle cam??) the 20's, atleast mine was set at 34 degrees BTC
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I had bought a carb and intake that came as a set from a 25hp.Mine is an 1985 and I do not remember the year of the 25hp or the seller did not know.The venturi was the same as mine.Just swapped the intake and sold the carb.According to the parts the main in the bowl is a 47D for both models.
 
newyota said:
I had bought a carb and intake that came as a set from a 25hp.Mine is an 1985 and I do not remember the year of the 25hp or the seller did not know.The venturi was the same as mine.Just swapped the intake and sold the carb.According to the parts the main in the bowl is a 47D for both models.
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Could very well be. Some of the 80's 20hp outboards may have had a 25 hp carb with just the intake restricted, therefore drawing less fuel/air. Mine I know for sure has both a different carb and intake needed to hit 25 hp, the venturi in my 20hp carb isn't much bigger than a quarter. The intake hole wasn't either. The 25hp intake hole is over 1 3/8", and the venturi in the carb is the same. The carb came off a 93 Johnson 25hp
 
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