I have been looking around this forum and others and parts diagrams for differnt year and hp outboards. I have not found the complete information anywhere where someone have upgraded a 30hp to a 40hp with full success.
Note: Only regarding 2 cyl, 2 stroke, Mercury/Mariner approximately MY 1995-2005 (please answer with exactly concerned MY if known and I'll edit). I believe this is the same for motor types hand start/electric/control/tiller etc. with only difference in carb type for manual/electric and some difference in carb p/n for some years.
Through forums, parts diagram and service manual the conclusion is that the 30 hp is a "down-tuned" 40 hp. The down-tuning seem to be:
1. Different reed valve assembly
The reed valve main plate itself seem to be the same for 30/40 hp. What differs in part number is the reed valve and the reed stops (and for some MY retaining washer).
2. Different carburetor
The 30hp Electric has the Walbro WME64 (with .054 jet) and for the 40hp electric has the Walbro WME67 (with .066 jet). Later MY seem to have 30hp=WME97 and 40hp=WME99 (same jet sizes).
3. No other difference found in ignition, spark plug, displacement, gear ratio etc.
Could anyone (preferably someone with a successful upgrade) confirm if the WME64 and the WME67 carb is the same with only difference in main jet configuration? Or is there a difference in throat diameter of the carbs. I don't believe there should be any difference in the idle or low rpm between the carbs since the extra 10 hp would be available on top RPM.
Reason for asking is that used WME67/99 (for 40 hp) are scarce on the market and a new one is expensive. The jet on the other hand is next to free. The same goes for a complete reed assemby compared to just the reeds and stoppers.
Note: Only regarding 2 cyl, 2 stroke, Mercury/Mariner approximately MY 1995-2005 (please answer with exactly concerned MY if known and I'll edit). I believe this is the same for motor types hand start/electric/control/tiller etc. with only difference in carb type for manual/electric and some difference in carb p/n for some years.
Through forums, parts diagram and service manual the conclusion is that the 30 hp is a "down-tuned" 40 hp. The down-tuning seem to be:
1. Different reed valve assembly
The reed valve main plate itself seem to be the same for 30/40 hp. What differs in part number is the reed valve and the reed stops (and for some MY retaining washer).
2. Different carburetor
The 30hp Electric has the Walbro WME64 (with .054 jet) and for the 40hp electric has the Walbro WME67 (with .066 jet). Later MY seem to have 30hp=WME97 and 40hp=WME99 (same jet sizes).
3. No other difference found in ignition, spark plug, displacement, gear ratio etc.
Could anyone (preferably someone with a successful upgrade) confirm if the WME64 and the WME67 carb is the same with only difference in main jet configuration? Or is there a difference in throat diameter of the carbs. I don't believe there should be any difference in the idle or low rpm between the carbs since the extra 10 hp would be available on top RPM.
Reason for asking is that used WME67/99 (for 40 hp) are scarce on the market and a new one is expensive. The jet on the other hand is next to free. The same goes for a complete reed assemby compared to just the reeds and stoppers.
