Offshoreonly.com - Excessive fuel usage?

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Quote:

Originally Posted by endeavour32 (Post 3480674)

OK, tested my boat to get some real numbers. I went 7 miles and used around 8 gallons of gas. I cruised 85% of that at 2800 rpms, (max speed of primarys). A short WTO burst and 1/2 mile idling. Either way fuel consumption seems way excessive. Does anyone have any concrete numbers with carb engines on a similar sized boat?

Yes, did it this year. I cruise between 3000-3400 rpm, running mid 33-38 mph at those revs. 26' Powerquest Legend BR with carbed 7.4 Bravo III drive. My measured use was 2.3 mpg. I used an outboard tank filled with 6 gals and measured distance travelled by gps. Was trying to get a good idea of range on one tank.

Quote:

Originally Posted by Dennis Moore (Post 3481445)

If you think the carburetor is running rich you should shut down the engine after a long drive at 3000 rpm. Pull the spark plugs and check the color. Down/inside at the very base of the plug you should have a nice brown color (like a paper bag). This won't work with new plugs.
I suggest replacing the spark plugs with RV15YC4 Champions, gapped at .045 inches (after the plug check).
Check the height of the flame arrestor. If you have a tight engine hatch the boat builder may have installed a low profile flame arrestor that is very restrictive. Install a free flowing K+N marine flame arrestor. Buy the tallest K+N arrestor that will fit. Also make sure that the engine compartment is capable of flowing all of the cool fresh air the engine needs. If nothing else, the addition of the K+N and the Champion RV15YC4 plugs will increase performance!
Dennis

Dennis-
I've got a pair of HP 500 flame arrestors. They are not on the engine yet but it would be a easy swap. Are the K&N's much better than the HP 500 flame arrestors?

I am sure the HP 500 flame arrestors will flow very well and you should use them. I should also suggest that you make sure your chokes are operating fine.

With the flame arrestor change my fuel usage just jumped substantialy! I checked my fuel consumption using a 5 gallon gas can and going about 5 miles I used about 2 gallons per engine, which puts me around the 1.3 mpg range. It seems now that I have a problem with my fuel pickups. I think there cracked. My tank had 4 but two have broke off, I have a feeling the other two are cracked because when I open it up when hooked to the tank the engines surge, when running from the gas can they run great?