tpabayflyer

Getting my new 509 installed this week in the Donzi and working on the little details now...... Should be around 550HP and 600 torque..... I have the stock fuel pump/ sea water pump combo and it uses a 3/8 line to feed the carb...... This seems to be a little small but might work. It will be feeding a mighty demon 850... I am not sure how much rpm I will get with the 26P prop so I will guess 5,300rpm........ What has worked for your similar combo? I am planning on installing an electric fuel pump with a regulator as a backup in case of mechanical pump failure. Should I just plan on a full time electric setup? I like the idea of having a backup fuel source just in case. -6 lines adequate? -8? Ok? I was unable to get the motor dyno tuned so I will not be exceeding 3,000 rpm for a while until I can get a proper tune. I will be installing a wide band A/F gauge for monitoring so if it started to lean out on the top end I would be right on it........ TIA.... TBF

mike tkach

iTrader: (3)

the stock pump ia sufficant for 600 hp with -6 line,my buddy has run this way for 2 years with no problem.his engine is 516 cu in and also has a demon 850 carb.

MILD THUNDER

iTrader: (3)

Ive really never understood the whole "install a electric fuel pump as a backup in case one fails".

I mean, its not like the mechanical pumps $hit out all the time. I think you have just as good as odds at losing a ignition coil, module, starter, alternator, etc. Not looking to stock my cabin with all those parts "just in case".

IMO, the whole electric pump into the mechanical is BS. Pick a quality pump, whether it be electric or mechanical, and run it. I don't have a backup fuel pump in my car, and when its -20 degrees at 2am when im in the middle of nowhere, I don't think to myself, "Geez, I hope my fuel pump don't crap out right now".

tpabayflyer

OK thanks Mike..... I will use the stock pump with a -6 line...... As far as the backup goes, I already have a carter and a Holley blue pump and there is plenty of room to mount one of those right next to the fuel hose inlet from the tank. I can wire in some spring loaded clips for quick and easy clip on to one of the batteries and have a simple hook up to the fuel hose inlet. I figure I can keep the pump and clips sealed up in a Baggy to minimize corrosion problems........having the ability to switch to a backup fuel delivery system in a couple minutes is worth it's weight in gold if you crap out on the water.... I boat in the Tampa area and frequently cross the bay which is 12 miles wide...... my wellcraft cruiser has a gen 6 7.4 with the cool fuel setup... I have had 2 electric, high presure pumps fail and on the 3rd now and each time it failed it was a tow in..... I Have the parts on hand to this
So it is a no cost, piece of mind backup! TBF

MILD THUNDER

iTrader: (3)

How about a spare mechanical pump. I can probably swap one of those sea pump mechanicals in minutes.

Mercury ran those pumps on lots of engines that went many many hours on stock pumps.

I boat in big water myself, and the idea of having to get towed in sucks. Our lake is 80 miles wide , several hundred long . Free Unlimited towing from boat us for a Hundo a year is my piece of mind! Most guys have a better chanc at blowing a bravo than losing a mechanical pump lol

tpabayflyer

Yeah, having an extra mech pump is a good idea but I have some good used parts on hand now so I will use them..... I also keep a few plugs,extra coil, etc.. Boat US has been very good to me as well! Waiting a few hours and then towing at 6 knots is not my idea of fun. I was at the local island a few months back and there was a guy next to me with a Baja hammer or something like that and when he left he nailed it and everybody watched him go... About 1 mile and he stopped... I was leaving as well as it was getting dark and pulled up next t him and asked if he needed a hand and he said he has no fuel to the carb and had a full tank.... His buddy was coming to tow him home..... His female crew members were not looking to happy?? Ethanol is bad on rubber components and the fuel pumps use rubber diaphragms? My next boat will have twins for sure! TBF