1997 60 vs. 70 hp yamaha 3 cylinder carburetor bore difference?

ttankmoran

Seaman Apprentice
Joined
Mar 22, 2015
Messages
39
Hi guys, long time lurker here.

Have a carburetor question I was hoping someone could confirm for me. Are the carburetor bore diameters different between the 60 and 70 hp engines?

The reason I ask is because I have 97 Pro-60 that I have always been interested in getting a little more performance from. Comparing parts breakdowns the first 3 characters of the part number is different for the carburetors (6H2 vs. 6H3) I just wonder if the part numbers aren't just different because of the different jets that come installed? I know the jetting is different and will be changing those at the very least.

Another difference between the 60 and 70 I have come up with are the reed stops are far more restrictive on the 60 hp, easily bypassed by installing aftermarket boyeson reeds with rev plates and discarding the reed stops. The reed stops appear so much more restrictive when looking up pictures comparing the two that I wouldn't be surprised if all the air flow limiting was accomplished with the reeds rather than both the carbs and reed stops

The other difference I found was the exhaust tuner being different between the two. The 70 hp exhaust is reasonably cheap and I have absolutely zero problems with the work and know-how involved in swapping out the exhaust.

Otherwise I have spent a lot of time comparing parts breakdowns between the two models. The block, head, head gasket, piston and rotating assemblies are identical part number wise between the two.

The end goal in mind is to get a few more MPH out of my combo. Right now I am turning a 17 pitch yamaha K aluminum prop, WOT, trimmed out I am seeing about 33 MPH at about 5300 RPM. With 70 HP I would expect to be in the 5700-5800 rpm range and If I saw 35-36 mph I would be happy.

So can anyone confirm carburetor bore differences between the 60 hp and 70 hp carburetors?
 
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