l have a 2 stroke2 H.P 1000 watt generator (genmate).
l wan to operate it in the engine compartment of my 26 ft boat.
The exhaust port is a small diamter maybe 3/4 ''.
If l connect a metal flex pipe with pipe strap and increase the diameter directly behind that connection my thought is to connect it to the bilge vent pipe while I am stationary and using the generator. Does anyone see this as a problem with carbon monoxide or any other potential issues.
The other option is to just run it on the swim platform but I am trying to avoid the noise.

Its a bad idea. besides the heat it makes since it is air cooled, the gas tank is vented directly into the bilge if you do this. That is a danderous situation. Metal flex pipe is not marine rated and also poses a high risk. Do not do it.

l would sell it and get a 4 stroke model first.. The flex pipe leaks CO like crazy. That is why they are outlawed on cars.

Agree 100% with mark-really bad idea. When in flordia- all the sailboats waiting in the marina for the weather ran their generators up the main mast with a long extension cord. This solved the cooling/exhaust problems & u can not hear them up there. Do u think a $700,000 sail boat could afford to hide a gen in the motor compartment safely but decided to run it up the mast instead? If all u want to do is charge the battery-go solar or wind. PS- about shore powered little chargers? l have had 2 catch fire after years of hard service.

Ditch the genmate and look at a marine generator.

The news ones are compact and enclosed, easy to install, and will meet the safety needs.

Found a great article on them here:
http://saltwatersportsman.com/article.jsp?ID=21012042

l like the Westerbeke models.
Westerbeke
(508) 823-7677
westerbeke.com

Good Luck and Safe Boating ! !

All none marine gen must be on deck where there is plent of air flow> Not below deck> Or you will risk your life> The heat from the exhaust will melt or cause a fire>