2.2 hp Mercury Tohatsu to 3.5 hp

[VicS1950]

This is for the older 2 stroke engine, but there are still quite a few of them around.

I picked up a 1986 2.2 hp Mercury outboard skeleton. I was able to put it back together and got it running great. I read about modifying the carb slide to get to 3.5 hp, but my slide was opening fully. I looked for some time for a cheap 3.5 hp carburetor and finally found one on a scrap 1998. Woo-hoo. 3.5 hp here we come.

I pulled the 2.2 hp carb to compare it to the 3.5 hp. Checked 13 mm throat. Both the same (embossed 13 on the throat). Checked the jet. Both were #66 drill bit. Checked lever throw on throttle plastic plate slot. Both had 65 mm throw. I was stumped and thought that maybe the 2.2 hp was already upgraded?

Then I noticed a difference in the front carb plastic plate that holds the kill switch. The 2.2 hp plate has a complete fit to carburetor face. The 3.5 plate has a 13 mm x 12 mm cutout. The air to the 2.2 hp is limited by the face plate. The cutout on the 3.5 hp allows more air to the engine.

Whether right or wrong about this, I'm going to cut a notch out of the 2.2 hp face plate and see if it breathes better.

Any comments? vic

 

[raczekp1]

i saw small restrictor at carb at the back of the carb. removing this restrictor just increase hp

 

[VicS1950]

i saw small restrictor at carb at the back of the carb. removing this restrictor just increase hp

Thanks for the reply.

Because I was concerned about that possibility I used a caliper to measure both the 2.2 and 3.5 carb inlets and outlets for comparison. Both were 13 mm diameter in and out. There is also no difference looking into the carb mount/inlet port of the 2.2 vs 3.5 hp.

Maybe it is a Mercury vs Tohatsu/Nissan brand thing. There are differences with Merc. The Mercury models have USA SAE threads on the clamp screws as opposed to metric on the Nissan. The cowls and tank/fill cap are also different. It appears that Mercury did request some specials in their contracts.

As I stated in my original post, a possibility is that the 2.2 already has a 3,5 hp carburetor or a removed restrictor? As it was acquired used/somewhat stripped, that's an unknown for me. From the performance I would say "no", but I've not done a side by side comparison 2.2 vs 3.5.

I also have access to a 1991 Mercury 3.3 (Tohatsu/Nissan). It will be interesting to pop the cover and see whether that one has a notch in the plate baffle for better air flow. If it has the notch, the actual dimensions 3.3 vs 3.5 hp will be interesting.

vic