Why am i so disappointed in merc 1500

[monk-monk]

As thread title states, im very disappointed in overall performance of mid '70's merc 1500. Maybe im expecting too much..i got this thing tweaked to the nth degree, but just seems to be lacking something. As stated in my other Thread, i can move the timing one tooth and its like its on steroids, but when set to factory specs it just doesn't seem to "have it"...all i've heard is how fast these motors are and how "bad" (great) they was compared to other motors. From my perspective, im not getting any of that...I know these motors from top to bottom, inside and out...nobody can "talk above my head" when it comes to these motors, so if anyone would like to give it a shot and tell me something i don't know and why i might be so disappointed, please give it a try....

 

[Faztbullet]

Re: Why am i so disappointed in merc 1500

all i've heard is how fast these motors are and how "bad" (great) they was compared to other motors.

Its only going to have the performance of a strong 115 as thats all you got at prop. Does it still have the high dome pistons? If its been apart it may have been built with low domes which dont perform as good as high dome but you can run a dash more timing. Whats the compression? What type hull?

 

[monk-monk]

Re: Why am i so disappointed in merc 1500

Hey Fazt...I completely rebuilt this motor, it does have high dome pistons...it did have low domes from factory..i mean i have meticulously payed attention to every little detail, right down to new restrictor bleeds and all, carbs are perfect, timing done "by the book" with dial indicator etc...it starts great, idles great, purrs like a kitten...will run right up to 5500 RPM without really dogging it to wide open throttle...the motor is on a 1975 Glastron V-178 bowrider...the only thing i can think of to question is why it will not idle with carbs fully closed and timing retarded...it idles at 3 degree advance and i have to have carb butterflies very slightly open...i have 2 of these 1500's and my other one idles and timing point is exactly like this one..

 

[wired247]

Re: Why am i so disappointed in merc 1500

I think a lot of the love for those things are from when they were one of the only choices in outboards and boats were a lot smaller and lighter. There were a couple of low points in that model lineup too. Some of the '73's were total dogs on the bottom end with ports that were really too high to be useful for a production motor. Pretty good on the top end but absolute dogs out of the hole. In any case if you are running too much prop for a unresponsive 99 inch motor it will make you miserable no matter how much timing you run. I wouldnt go over a 17 pitch prop with any boat that weighs more than 900 lbs and even that is pushing it. Don't put in too much timing no matter what as you WILL burn those pistons up doing so.

Pay no attention to what your idle timing number is. Make it idle with the idle screws and enough timing to keep it running in gear at 700 to 800 rpm in the water. The number of degrees advanced doesnt matter one bit.

 

[monk-monk]

Re: Why am i so disappointed in merc 1500

Wired, i do believe my prop is a tad big and i planned on reducing that...plus, since the time of rebuild, i have learned to use a 10X lighted magnifyer to inspect the veins on the reed blocks...though i did carefully inspect the blocks by naked eye, a magnifyer is priceless when it comes to verifying just how good the blocks are...pertaining to my idle timing and carb butterfly settings, the reed block veins might explain that, but as far as overall strength, speed etc, i doubt the reed block veins are the reason for my disappointment (BTW, i rebuilt reed blocks with mercury OEM leafs) inspected the contact points of the leafs to reed block etc...no leafs were seated to block, none were open more than factory specs...

 

[Bob_VT]

Re: Why am i so disappointed in merc 1500

The older inlines like to wind up....... many people run them at 5800-6000 (which can shorten their life) and run the WOT normally with a 17 or even a 15" prop.

Your motor needs to be adjusted at the right height, thr prop needs to be right and the hull needs to be good......not overweight from too much garbage or even water-logged foam.

Follow this procedure to the letter for timing http://forums.iboats.com/engine-fre...q/timing-sync-merc-inlines-1988-a-168855.html

 

[monk-monk]

Re: Why am i so disappointed in merc 1500

Thanks for that addendum to your reply Wired (about timing number etc)...the last time i had boat out, i opened the idle screws about 1/4 turn and it was a noticable difference coming out of the hole..might open them a bit more...Now, from what im being told, the reason for the 21 max advance is because of octane rating of fuel (from yesteryear compared to todays octane rating)..SO why can't i add octane boost to fuel and add alittle timing?

 

[wired247]

Re: Why am i so disappointed in merc 1500

Thanks for that addendum to your reply Wired (about timing number etc)...the last time i had boat out, i opened the idle screws about 1/4 turn and it was a noticable difference coming out of the hole..might open them a bit more...Now, from what im being told, the reason for the 21 max advance is because of octane rating of fuel (from yesteryear compared to todays octane rating)..SO why can't i add octane boost to fuel and add alittle timing?

Octane booster is almost completely worthless. If you can find 9 gallons of good 92 non ethanol gas and add a full gallon of toluene ( the active ingredient in most octane boosters ) you end up with about 93.5 octane gas. It works. Imagine what 12 ounces will do for the octane number. Not much.

Mercury dropped the recommended timing number from 23 to 21 degrees way back when they started getting engine damage warranty claims

 

[monk-monk]

Re: Why am i so disappointed in merc 1500

Bob, like i told Wired..i do think my prop is a tad big and im going to reduce that (i think that will be a big help)...as for my hull, it is waxed and slick as ice, my motor heigth is correct as the planing fin on lower unit is level with bottom (keel) of hull...i have learned quickly that these motors are very sensitive to the weight of boat, gear and passengers (simply pulling a tube can require a prop change)...and, not to "discount" any of your advice, but i won't even click on the link for the timing proceedure as i could recite that to you word for word, LOL...again, i appreciate all thoughts/input and i thank everyone for trying to help! I think a prop change will be a step in the right direction as it is lazy out of the hole. I have .080 jets in it now, think it will help to go to .082's?

 

[monk-monk]

Re: Why am i so disappointed in merc 1500

I think 2 things have to change: first is my expectations of a 99 ci motor and secondly reduce the prop size...i mean, this motor runs great...i guess thats all i can ask for from it...

 

[wired247]

Re: Why am i so disappointed in merc 1500

Making it richer will make it lazier out of the hole.

Get that motor out of the water. I have no idea why people sink those things so low. It totally tanks the high speed performance. The anti-ventilation plate is only there to keep the prop from ventilating off idle. Jack that sucker up. 4-5 inches from prop centerline to the bottom of the hull is more than adequate for best high and low speed performance while retaining adequate cooling. Any deeper than that, you might as well just drag the anchor behind the boat.

 

[monk-monk]

Re: Why am i so disappointed in merc 1500

OK, let me make sure i understand you correctly...first, the mercury manual says that ventilation plate should be on plane with bottom of hull...SO, you're saying raise the motor up to a point where from prop shaft to bottom of boat is about 4 to 5 inches?

 

[wired247]

Re: Why am i so disappointed in merc 1500

Absolutely. That ventialtion plate even with the bottom of the hull crap is for displacement hulls where you dont want to go over 30 MPH. You can certainly go higher but with most through hub exhaust props and with the stock cooling intakes 4-5 inches at the most is ideal for those motors if you want to get up on plane fast and get up to decent speeds. The lowers on those "20 inch" long motors are so damn long it puts the bottom of the skeg a good foot and a half under the boat and kills speed and handling.

Here is a previous incarnation of my boat which would handily run 60 MPH at 6200 RPM although to be honest it took a while to get there. Note the jackplate . Prop center is 4 inches from the bottom of the hull.

 

[monk-monk]

Re: Why am i so disappointed in merc 1500

Got it!! Now that explains alot...see, last time i had boat out, i noticed that the more i trimmed motor up, the faster it would run, plus the more air i got under boat from the wake made it increase speed too...thats kind of an obvious scenerio, but it still highlights the point of what you're saying...as i trimmed motor up, it was running better, but i also realized the ventilation plate was dragging water because of the angle it was on..so now, if i get that motor up, get the ventilation plate level, it will do even better!!...Mr, your info is key to what im missing...Bob_VT statement about motor position was correct, but you elaborated on that...Im enthused, im not giving up on my mercs!!

 

[monk-monk]

Re: Why am i so disappointed in merc 1500

I've been wondering what "jack plates" purpose was, now i know...tell me more about that plate you have...is it hydraulic adjustable or just nut and bolt adjust, i imagine hydraulic would simply add more weight...tell me more about jack plates...educate me!!

 

[wired247]

Re: Why am i so disappointed in merc 1500

Jackplates raise the motor to get it closer to the surface. Makes it steer easier and go faster. They also push the motor back farther which is important if you are really going to raise it up high and use a surface piercing prop so that the prop gets into less turbulent water. Jackplates do essentially the same thing as trimming the motor up but they allow you yo keep the prop pointed perpendicular to the surface instead of angled up so you spend your motors energy going forward instead of pushing the rear of the boat down.

Hydraulic jackplates are great for racing and other go fast stuff where you want to make an on the fly adjustment but to be honest a good setting of the plate on a manual jackplate is going to stay about where you want it for most purposes.

The one I had in that pic is a Vance Mfg unit. They make a good strong reasonably priced jackplate but so do half a dozen other manufacturers.

 

[monk-monk]

Re: Why am i so disappointed in merc 1500

Thank you so much for your time and sharing your knowledge!! I won't waste your time, i am very mechanically inclined and "catch on quick"....how do i determine optimum setback...obviously, the higher i raise motor the more setback i need, what is a good starting point on the setback, and educate me about a "surface piercing" prop...never heard of that....

 

[wired247]

Re: Why am i so disappointed in merc 1500

Surface piercing props are props like choppers and cleavers that are positioned so that the props blades come out of the water. To run one that surfaces you need to be able to raise the motor very high which puts the water intake holes out of the water so you need to install something called a low water pickup lower end that pulls water from the lower part of the nose cone of the lower unit. Setback is going to be 6-12 or more inches and only really matters when you have a surface piercing prop.

This is a semi cleaver Yamaha Drag Prop and is the sort of prop you'd want to surface for maximum speed.

 

[Faztbullet]

Re: Why am i so disappointed in merc 1500

as for my hull, it is waxed and slick as ice,

This can actually slow a hull down !!! Google it......

 

[monk-monk]

Re: Why am i so disappointed in merc 1500

Fatz, what are you saying will slow a hull down..waxing it?...raising the motor?....please elaborate!! You quoted me so im assuming you mean waxing it...