Mid bores VS big bore carbs.

[neveredge]

Can someone please educate me on the pros and cons of each.

My application is an 85 Evinrude 3.6XP. It has the med bores. The 86 and 87 3.6XP used big bores. I assume it would give me a good HP boost. I know small bore carbs to med bore carbs on a V6 are worth about 25hp. Can I expect the same going from meds to bigs??

My bottom end is slow but not horrible. Will big bores really affect the hole shot to much on a 1200 lbs. boat?

I have heard that there is a mid range lean also that can destroy a motor????

Really need some advice.

[TomAprilsswitzers]

We blocked off the mid range jets with number 0's. This will turn a 3 stage carb into a 2 stage and prevent mid range lean out.....We also did a bunch of other stuff too...where are you located? And what kind of boat are you running on your v8?....Tom

[neveredge]

The boat is an 18 foot Champion bass boat that was made for the V8. Boat runs low 80s bone stock with out a LWP.

I just added a 6" Bobs extreme jack, turn signal trim for the jack and trim and a hot foot. Also went with Sea Star pro Allison cylinder steering..

Motor is getting a good tune up this week and hard upper and lower mounts. The stock gearcase is going to Bobs for a LWP also.

[powerabout]

If omc swapped engines from big to medium under warranty that tells you at fishing rev range they dont make much difference.

[neveredge]

I have never heard of big bores being switched out under warranty but can understand why on a heavy boat. My boat is light and the 3.6 revs much higher than other loopers do.

[powerabout]

I have never heard of big bores being switched out under warranty but can understand why on a heavy boat. My boat is light and the 3.6 revs much higher than other loopers do.
heavy boats were the issue

[Jim_Pat]

We blocked off the mid range jets with number 0's. This will turn a 3 stage carb into a 2 stage and prevent mid range lean out.....We also did a bunch of other stuff too...where are you located? And what kind of boat are you running on your v8?....Tom

How can you tell if you have mid or large bore carbs? I have a pair of 89/90 225hp Johnsons and I believe to still have the stock carbs on them.

[powerabout]

venturi id over 1.6"

[Mr. Action]

Last digits on the side is 340 for big borea

[neveredge]

So what kind of hp gain over med bores can I expect?

[racer]

The 85 engine also has 5 pedal reed blocks compared to 6 on the newer engines. The crab exchange under warranty was on the big bore V6 engines. The med bores will be better on take off with the big bores gaining a bit on top end, the dyno shows no HP gain until well over 6000 RPM. Plugging of the mid range air jet does not turn them into a 2 stage carb, if you eliminate the mid range fuel they would be even leaner. The mid range air jet changes the amount of pull the engine has on the mid range pick up tube, by going to smaller or plugging them off the engine pulls harder on the mid range pick up tube thus suppling more fuel. Adding or going to a smaller pull over tube brings the main in sooner. Hope this helps.

[neveredge]

What difference will switching to the 6 petal reeds have as I have already intended to do this.

Is the porting on the later 3.6XP's the same as the 85?