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'79 MAKO INBOARD
06-22-2010, 05:24 PM
I've got a '79 23' Mako with a '99 Marine Power 350 Vortec. It's new to me, and runs great except I can't hit max RPMs, supposed to be 4400-4600. Max right now is 26kt @ 3500. That's with me and my 160lb 17 year old son, half tanks of fuel, say 40 gallons total. I'm only a few pounds heavier than my son.

I'm guessing the motor should be putting out 320HP at 4600, but since I'm 1000 RPM down from that there's no way to know for sure. This is under load I should add. In neutral I can hit the mark easy. I'm playing with props, but it's not as easy as it used to be to find samples to try. Right now I'm spinning a 3 blade 13 X 12, bronze Federal. One other thing is that if I advance the throttle beyond 3500 I the engine starts bogging slightly and RPMs drop slightly. There's a good inch and a half of room in the throttle play still to go, but with no response.

Any ideas? I'm new to this forum so any help is much appreciated!

makomark
06-22-2010, 10:02 PM
You need to find out why that last 1.5" of throttle have no response. Is this one injected or carb'ed?

If carb'ed, make sure ALL the throttle blades open to vertical at max throttle. MP used a lot of Holleys in the 90's and, going on memory, they were all vacuum operated secondaries. Quite possible the secondaries just aren't opening.

'79 MAKO INBOARD
06-23-2010, 09:33 AM
Thanks Mako Mark. The engine has an Edelbrock carb, and I'll check the blades for sure. I can hear the secondaries kick in (and also see the evidence on my fuel flow meter...). In fact I was thinking about the fuel flow situation, and I'm going to double check that the meter I'm using (I reinstalled the one my buddy had -- Standard Horizon -- after re-wiring the entire boat) is rated for max throttle with a 350. I'm also going to double check the timing and advance on my electronic distributer. Lastly, I'll check the carb filter -- you never know, right?

Thanks!

makomark
06-23-2010, 06:32 PM
If you can hear and see the secondaries open, the carb is probably ok. Since it is new to you, you really don't know if the current prop is 'optimal', as far as the load the engine sees. Since MAKO is still making boats, I'd call them and see what the original wheel size was. Since the engine has been upgraded, you may need a little bit larger wheel. A good prop-scan shop should be able to "dial it in".

Many owners repitch their props to achieve a higher cruise speed at the expensive of WOT rpm. Personally, I don't recommend that approach as a heavy load and some bad weather will put a lot of extra load on the engine.

Making those checks would still be prudent before any wheel change.

RicardoMarine
06-23-2010, 11:23 PM
............. I'm also going to double check the timing and advance on my electronic distributer.
Thanks!
Now you're heading in the right direction!
Always always always check your ignition curve and TA.
Don't take it for granted that your ignition system is doing what it's suppose to be doing. Particularly any of the EST systems.
Check this for yourself!
See your OEM specs for this.

FYI, the common misnomer about the 5.7L marine Vortec is the horse power rating. They are rated at/near 5,200 or 5,400 rpm. An rpm that we just don't operate at.
Rest assured that you still have a good 280/290 horse power in the range that you need it to be in. That's plenty of horse power!


................
Many owners repitch their props to achieve a higher cruise speed at the expensive of WOT rpm. Personally, I don't recommend that approach as a heavy load and some bad weather will put a lot of extra load on the engine.

Making those checks would still be prudent before any wheel change. Ditto and Ditto!
Your OEM designated WOT RPM must be achieved, but the double edge sword here is.... the engine must First be in absolute full tune in order to do this. (and of course the prop must be in tune, and the hull must be clean also)

I'm with Mark! Do Not risk over-burdening your engine if your system is over-propped.
That is what the WOT RPM TEST if for! :)

.

'79 MAKO INBOARD
06-25-2010, 05:04 PM
Thanks for the comments, guys -- really appreciate the advice. Will post again after some further work this weekend.

'79 MAKO INBOARD
07-07-2010, 11:04 AM
Well, a new prop solved just about everything. WOT is now 4500 with no lag, and top speed is 30kts. That's with only me onboard, full tanks -- 82gal total -- and a bit of a chop. I repropped with an Acme 13X10.5 cupped at 80/1000. I still wish I could squeeze another 5 or 6 knots out of the engine, and am looking for a much taller flame arrestor to see if some more air might help.

Thanks for the suggestions!

makomark
07-07-2010, 05:06 PM
That was a relatively easy fix.

what does "cupped at 80/1000" mean....never seen that kind of descriptor.

I doubt the taller flame arrester will yield what you are looking for. As long as there is adequate flow into the engine box, engine accessories won't help much. Make sure the bottom is clean and any paint is smooth and in good shape.

if you really want that much increase in speed, better start saving for a big block.