Idle exhaust boot - Mercury V6

[AMD Rules]

In order to ask my question I need to explain what I have for a motor.

Acquired the following:

(1) 1985 Mercury 2.0L 150hp V6 complete (with a blown power head).

2) 1988 Mercury 2.0L 150hp V6 rebuilt power head only

(3) Cowling with lower mounts from what appears to be a 1991 Mercury 135hp motor (shown sitting on the '85 mid-section).

I want to build one motor using all three of the items above in unison. I'm led to believe the 1988 power head should mount on the 1985 mid-section without any major concerns, but I am making an assumption that the upper plate assembly on the 1985 drive shaft housing will mate up with the base gasket from the newer 1988 power head, hope so.

Finally, my question(s):

I see on the pick list for the newer cowling there is a rubber exhaust boot which connects the exhaust holes on the upper mid-section to the exterior hole in the lower skirt of the cowling. I don't have this rubber boot and will be ordering one. I don't understand how or where the boot connects to the mid-section. Does it just rest against it, or on the newer motors is there a round port where that boot would fit into? I'm concerned if I run without this boot the idle exhaust gas will collect in the cowling and starve then engine for fresh air supply. Anyone familiar with that boot?

Let me know if you think I am overlooking something to allow me to mount this power head on the older mid-section.

 

[Chris1956]

My '93 135HPV6 has that hose. The midsection has an exhaust port that the boot slips into. The other end goes into the lower cowling, where the two halves join. I know the V6 motors changed a bit (especially the cowling) from the 80s to the 90s. If the midsection you have doesn't have the port, you will need to try it w/o the hose. How's that for the obvious?

 

[AMD Rules]

Chris, thanks. I appreciate the reply!

I'm not certain what year this cowl is from, its in that range of years based on what I can see from the parts lists diagrams and its appearance.

I figured there must be a different place it slips into. Upon closer inspection, the existing exhaust relief holes in this midsection line up almost flush with the bottom of the newer cowl. Another inch lower and it would have been fine. I'm pretty sure without the boot the cowl will hold too much exhaust gases at idle and starve the motor.

I have two other midsections here, never really inspected them closely. Maybe I'll get lucky and one of them will have that exhaust port for a boot.

 

[Chris1956]

BTW - Your '91 cowling has identical decals to my '93. You might start with that one, and see if you can use it's swivel bracket and midsection. That should give you both ends for that exhaust hose.

 

[AMD Rules]

I'm not sure if it is a '91 135hp cowl or not, could be a '93 or any year for that matter. Interestingly, I feel kinda awkward having asked the question only to go looking afterwards and find out that I DO have an exhaust boot and can clearly see where is attached. I never looked at the spare midsections I acquired before.

Seems I'll have to swap this newer mid-section over to my motor now. FrankenMerc it will be.

I'm always confused about all the difference between base plates and exhaust tubes I have (4 or 5 different flavors, various years and possibly from different HP powerheads). No idea which ones I should use. Onward I go.....

 

[AMD Rules]

Assembled the powerhead onto the mid-section. I had to swap out the mid-section for one of the spares which had the appropriate exhaust boot for the cowling. Ran the motor for the first time on the stand, runs really bad but started right up. I need to review the basics air/fuel/spark because something is not right. It growls, surges, seems to have a misfire and a couple of times it seems to breath fire (literally) out the bottom of the mid-section. I'm thinking the base timing may be off. Only a run at idle, as a test.
I had a few different choices for the exhaust diffusers/tuner, and I chose the longer one. Its much longer than what was on the '85 150hp motor I had. How sensitive is a motor to that exhaust diffuser/tuner? Should I use the shorter one?
This motor sounds like it would eat me for breakfast!