Evinrude 3 vs 4 cylinder mpg?

[mfgniagara]

Let me start by saying I own a 1965 MFG Edinboro and a buddy has an MFG Westfield. I run a 1990 110 HP Evinrude V4, he runs a 1974 65hp 3 cylinder.
We run the same water and the same route, sometimes we take my boat, sometimes his. He had some issues with his motor and recently just did a complete top to bottom overhaul, (Done by a pro outboard rebuilding service).
Both our motors are in tip top shape as are the boats.
My question is, did those three cylinder engines burn a lot of gas compared to a V4? My V4 will make one particular 11 mile run down the river and back on less than 6 gallons, his 65hp three cylinder burns nearly double. Both motors are propped to run within a few hundred RPM of their max rpm, and I carry more weight and have a slightly larger boat.
Were those three cylinder engines known to be hard on gas?
When I noticed how hard it was on gas, he said this motor, and two prior to it all got about the same mileage, and that this one was a bit easier on gas than the last two. He has three tanks onboard and needs to fill all three, he's got a fixed 20 gallon under the bow, and two portable six gallon tanks. I made the mistake of only running his with a single 6 gallon on a shorter run the other day, and nearly ran out of gas, while my boat would have had fuel to spare on the same run. His boat runs about 28 MPH, mine at about 32 at max RPM. Mine has a bimini top that sits pretty high, his has the factory top that stretches from the windshield frame back.

This concerns me since I am considering powering another boat I have with a 70hp three cylinder Johnson, vs a 55hp twin cylinder Johnson. I was leaning towards the 70HP but if they are that hard on fuel, I'd have to carry too much fuel to make the swap worth while. I'd be adding more weight to feed the larger motor.

Any ideas as to the mileage of a Crossflow V4 vs the inline three looper?

 

[Chris1956]

Re: Evinrude 3 vs 4 cylinder mpg?

Something is wrong with the scenerio. His looper should be better on fuel than your crossflow. A three cylinder motor should be better on fuel than your V4.

Perhaps his prop stinks? Perhaps the boat is too heavy for the motor, and he needs to run at near WOT to get a comfortable cruise? You need further analysis.

 

[Silvertip]

Re: Evinrude 3 vs 4 cylinder mpg?

I agree that you are not comparing apples to apples. Lots of things affect fuel consumption and hull design, engine setup (mounting height, prop, load) are just few key items. Check the capacity plate for both boats. Boats that are powered at or above the 75% maximum HP capacity should provide adequate performance with the selected motor when properly set up. So in that case, the 65 would burn approximately 6.5 gallons of fuel per hour at wide open throttle. Your 115 under the same parameters would burn 11.5 gallons per hour. However, you didn't mention the size of each of the two boats. If your boat is smallish for a 115 it would stand to reason it would get better fuel economy since you probably run at far less throttle. On the other hand, if the other boat is on the large side for a 65 he would have to run with much higher throttle settings.

Now then, something is dreadfully wrong with the numbers. If the 65 runs at 28 MPH, that 22 mile trip (11 miles each way) "should" consume a approximately 6 gallons of fuel (at WOT). Since you say it burns double that, then something is drastically wrong with the engine. On yours, a 22 mile run at 32 mph would take just shy of 45 minutes (7/10 of an hour). 11.5 x .7 = 8.0 gallons of fuel (at wide open throttle). Now then, going back to the boat size/weight issue, if you run at something less than WOT and he runs at or near WOT the two engines would possibly burn about the same amount of fuel. I simply do not buy the double unless there is a serious carburetion issue. We also don't have the full story on the two boats so again -- make sure you are comparing apples to apples. I'm not sure you could "pour" 12 gallons fuel through a three cylinder if it was tied to a post. I've published fuel economy data on a number of engines including my own 75 HP Merc triple on a 17 foot walleye boat. It burned 7.5 gph as measured with a flow meter. Two aboard, full fuel and live wells and gear.

 

[SC's Forever!]

Re: Evinrude 3 vs 4 cylinder mpg?

I totally agree!!! Something is definitely wrong with that 70-3cylinder~!!! Have had several of these 65-70-75 HP 3 cyl. engines and think, as well as many other people, that they are/were probably one of if not the best engines OMC has produced!!!!!
????? ......Jim

 

[mfgniagara]

Re: Evinrude 3 vs 4 cylinder mpg?

I never did anything very scientific to test either boat, but the fuel usage difference is super obvious. Both boats are identical, same year, make, model, etc. His is a bit lighter since he's got only a pair of pedestal seats while I have Wise back to back deluxe seats. I have only a pair of 6 gallon tanks, he has the same two tanks plus the 12 and 30 gallon tanks. His boat is lighter and rides higher in the water both due to the lower weight and smaller motor. The max hp rating is 100hp. Both boats top out within a few hundred rpm of the max rpm. Both boats feel very comfortable power wise. Mine is a bit slower out of the hull but I have more weight on the stern and less in the bow, he's got that 30 gallon tank up front, and a lighter motor. His boat easily burns three times the gas as mine. The plugs aren't fouled, it don't smoke, and the compression on the 65hp is 140 across all three. My V4 reads about the same compression.
Everything about the two boats should mean that mine would get worse fuel economy but its the exact opposite. If the hulls were very different or if it were only a gallon or two difference then I'd say it could be due to loading or a motor issue but his runs fine, has good response and does nothing wrong. Mine is fine as well. I've owned other V4 OMC motors and the mileage I get on this one seemed about par for the course. But I did have a 70hp on an older boat once and certainly don't remember that being such a pig on fuel.
I'm sure the fact that carrying all that fuel is also a factor in that it adds a lot of weight but I ran it with only the one 6 gallon tank full, the 12 and 30 were empty and I had only a few spare gallons in the other 6 gallon tank that day. He warned me that the thing drinks gas, when I all but laughed it off and said if that's the case, there's a problem, he insisted that the original motor and the last motor were also the same. Other than the weight of the fuel, my boat is probably 300lbs heavier than his, and loaded a bit more in the stern. Mine lags a bit getting up on plane, his pops right up and goes. Mine tops out faster but not by much. The boat he has was also mine before I found this one, my motor was on that boat at one time and I never had a fuel usage issue. The front tank was added when I got it, he added the other three. The foam is dry and in the gunwales, its an all glass hull, both with new poured transoms. His has the off the window frame bimini top which I would think would make it more aero dynamic versus my 6' 3" self standing behind the windshield catching wind. (I sold that hull to him after finding mine since mine now has no snap holes drilled and needed no cosmetic help, his had been bottom painted and had hundreds of snaps all over from past canvas tops and covers, there was no issues with the hull or anything).
At rest, mine sits about 2" lower in the stern and about the same at the bow. The comparison I made was with me driving both boats, in basically the same conditions during the same tide conditions give or take a few minutes. Both days had about 5 knot winds blowing out of the east on shore. Both days were in the mid 60 degree range and overcast.

The first thing I noticed was that the fuel in the portable tank was dropping fast, I was at a point where I probably wouldn't have used any noticeable amount of fuel in my boat, yet his had burned a third of a tank. He's got no gauge, just visual checks through the sides of the three tanks and the front has an on tank gauge. I ran mine today, I did the whole run, basically the same trip again on about 6 gallons, I only switched tanks just so I wouldn't have to deal with it along the way home. On his, I had to stop and switch over fearing I'd run dry on the one tank before making it onto the trailer.
Since mine is over hp by 10hp, plus I have a minty clean 70hp here with power tilt, I was thinking of making the swap thinking I'd save gas and lighten up the stern a bit. But after seeing his boat, I have my doubts.
My 70hp is a lot newer, with VRO and a later style motor bracket.
Both boats run good at wot, I ran both at about 3/4 throttle or so, mostly due to the fact is was a bit overcast with some fog in areas. Being rated at 100hp, it would have been sold with a V4, or an Inline 6 if the motor were black. Out of the hole, his actually jumps up on plane faster, it's lighter in the stern and sits higher in the water. Mine sort of digs in at first then climbs on plane. If I didn't see it run down gas so fast in several tanks, I'd suspect a leak but that's not the case.
He's tried other props, the result has either been over revving the motor or no enough RPM at cruise. My boat originally had a 55hp twin cylinder on it, it planed out just fine and did only a few mph slower. I didn't notice too big of a fuel usage after the new motor on mine, but it did use more fuel. I just added a second tank when I hung the 110.

If his motor ran bad or had some sort of issue other than the fuel usage, I'd say there's a motor problem, but it sounds comfortable pulling that boat. My motor lugs or strains more than his does, but the V4 has more torque by nature of design and a larger displacement I assume.

His motor runs better at low RPM than mine does, mine tends to load up a bit at low speeds, while his will chug along all day at near crawling speeds if needed. Mine will load up and stall if I try to troll with it too slow. I'm sure that's a product of the VRO to some extent, his is an old premix motor.
His motor runs at about 130 degrees, mine at about 140 or so, both have the same temp gauge kits which I installed.

 

[Chris1956]

Re: Evinrude 3 vs 4 cylinder mpg?

OK, His prop stinks, something is dragging on the boat, his motor is not running on all three cylinders, the fuel tank, lines, fuel pump or carbs leak, something is wrong.

The performance parameters you describe do not add up.

 

[JB]

Re: Evinrude 3 vs 4 cylinder mpg?

My 1979 Johnny 70 triple used about exactly half what my 1966 Johnny 100 V4 did. . .on the same boat taking the same trip.

 

[trendsetter240]

Re: Evinrude 3 vs 4 cylinder mpg?

My 1993 evinrude 3cyl 70hp on a 17ft boat gets around 5mpg at high cruise. (4800 RPM) with a 15p prop.

Your buddy's 1974 65hp is rated at the crank so is likely only 55hp at the prop.

JohnnyRude triples are known for great fuel economy. Something is wrong with this picture...

 

[Chinewalker]

Re: Evinrude 3 vs 4 cylinder mpg?

I concur with the above - an OMC triple is VERY good on gas for a carbureted 2-stroke. MUCH better than a crossflow V4 on an even playing field. At cruising speed, my 1980 Johnson 75hp triple can get better than 6mpg. At cruising speed I'm lucky to get 3 with my 1983 90hp 4-holer.

 

[mfgniagara]

Re: Evinrude 3 vs 4 cylinder mpg?

I ran his boat again today, this time we made a concious effort to conserve fuel and save weight. I took along only the two portable 6 gallon tanks, both full, one 56 qt cooler, and left the larger tanks in the truck. His prop is a 13.25 x 17P, the boat weighs in at 1658lbs with fuel, cooler, gear, both of us, and the motor. (I weighed the boat at the Cat Scales and subtracted the advertised weight of the new trailer from the total).
Mine weighs in at nearly 300lbs more.

The prop is a brand new from the dealer a month ago. The prop is the largest diameter that the motor will take, and the pitch seems correct in that the top RPM is right around 5700 RPM, give or take some depending on the current and wind. It revs higher running with the current by about 150 RPM.
Speed varies greatly by the wind and current in his boat, its far more affected by a light headwind than my boat is when it comes to GPS speed.
I run his boat at around 4800 RPM tops, it just sounds better there, pushing it harder just burns more fuel and doesn't gain much speed.
Mine is the same way, once on plane, any extra throttle just burns more fuel. Mine gains speed faster once on plane though, his doesn't. His is on plane at about 14 mph, and runs comfortable around 22 to 25 mph, but can push to 31 mph. Mine would probably go well over 35 mph but I've never pushed it since the boat don't feel comfortable at that speed to me.

We started out today with two 6 gallon tanks, I logged one mile on the GPS and rechecked the first tank, and I could at that point already see it was down over an inch from the full mark I made when we left. At three miles it was down to about the 2/3rds mark on the side of the tank, at 5 miles, it was at half tank. We were running with the current. I turned back to the dock, ran at 4400 RPM upstream doing about 21 mph against the outgoing current and against about a 5 knot wind. I just got back to the dock where we launched the boat and the tank had about an inch of gas left in it.
I know none of this is scientific, but I know my boat with the V4 would run all day, taking us way further, on that amount of gas.
Either my V4 is super great on gas or this 65hp is a pig. The part I don't get is that he swears his last two motors were the same way, both were 65hp triples of roughly the same age.

Keep in mind that both boats are the same model and year, both are 16' 6" long with a 77" beam width. (http://forums.fiberglassics.com/mfg/mfgb65009.jpg).
Both have Nida Core poured transoms, and no wet foam. Mine is heavier due to the larger motor, power tilt/trim, heavier seats, and more electronics. His is pretty much stripped down for fishing to conserve weight and fuel. When I owned his boat I had a 55hp electric shift triple on it but never ran it far enough or long enough to even think about fuel usage.

His motor is 100%, the entire motor was reconditioned by a reputable dealer, it was over bored, new pistons and rings, has 155 psi of compression on all three, has new coils and all new wiring, new cables, new prop, rebuilt lower unit, etc. It runs like a clock, it idles well, accelerates smoothly, no issues whatsoever. I was actually very impressed with what it looked like and how it ran when he got it back. It was a running motor but had overall low compression and had been sitting for a long time but it did run.
My V4 is just a super low hour motor that came from a buddy of mine who hung up his boat keys due to old age. Mine has never had any major work, just a new water pump, carb overhaul, and a tune up when I hung it on this boat.

The 65hp used so much fuel the first time we ran it that I actually did look for a leaky fuel tank or something. I couldn't believe a motor could burn that kind of fuel that fast. I had a 175hp V6 on an old 24' cabin boat that didn't burn this kind of fuel. This motor burns so much fuel that I am leery about how far I'd take it knowing that its range is so limited. Also keep in mind that we are using several different tanks, he's got a handful of 6 gallon tanks that get swapped around, only the 30 gallon steel tank is mounted in the bow. The others are portables that get removed to be filled. Also, he runs a single Group 24 battery, while mine runs two group 27 batteries, one to start the motor, another up front to run all the electronics off of that I mounted under the passenger seat.

I'm at a loss as to why it uses so much gas then, it runs too good to have a motor issue, and it's not overweight by any means. The only thing I could do to lessen the weight is to lose weight, and that's not going to happen anytime soon. At 6' 4" tall/300lbs, I do add a good bit of weight to a small boat but three hundred pounds of weight sure won't make the difference of about 6 gallons per run. It sure doesn't in my boat. I've had my boat loaded down almost to the rub rail after a day of pulling crab pots and it didn't burn that much fuel.

 

[DJ]

Re: Evinrude 3 vs 4 cylinder mpg?

The "65" is dumping fuel somewhere. On a two stroke, an overabundance of fuel doesn't, necessarily, make them run bad.

I would be looking at carburetor; floats, needle/seats, and possibly a loose high speed jet.

As JB eluded to, my 1994 70 (looper) uses about 1/2 the fuel that any crossflow 90 I ever owned. It actually uses less than the 1975-50 (looper-2-cy'l) it replaced.

 

[mfgniagara]

Re: Evinrude 3 vs 4 cylinder mpg?

We took his boat for another run yesterday, about 4 miles downstream with the outgoing current, and back the same distance with the incoming current.
The 65 burned 13 gallons at nearly WOT the whole trip.
He's had two others that he says burned the same amount of fuel.

If it were mine, I'd be going further into it, but when I buy the gas, we run my boat. It's just a pain to have to carry all that gas in such a small boat to go such a short way.

 

[Chinewalker]

Re: Evinrude 3 vs 4 cylinder mpg?

13 gallons to cover 8 miles, WITH the current?? Something is VERY wrong with that motor, or maybe the set-up. Whatever shop has checked it out is missing something. Might be time for a second opinion.

 

[mfgniagara]

Re: Evinrude 3 vs 4 cylinder mpg?

I mentioned the same things to several local dealers, one which I deal with regularly, and was told that there must be something odd about my V4. I was told by several that the normal fuel usage for my boat and motor would be about 2.3 gal. miles per gallon. I get more than triple that or better in most cases. My buddy had another dealer check the set up on the boat, the motor passes all checks, and the boat isn't overweight or water logged. (No wood in the hull.
We did experiment with the motor position yesterday and this morning a bit, it gets far better mileage with the motor in the third hole from the transom, but in that position it rides bow in the air and so rough it feels like it's going to break in two. These are flat bottom V hull boats, mine has power tilt/trim, which lets me optimize the ride position a bit, but his, even though generally carrying more weight, planes out faster since he's lighter in the stern with the smaller motor.
As long as he buys the fuel for his boat, I buy the fuel for my boat, it all doesn't matter much to me I guess but I'd sure like to know why his is so bad on fuel just for future reference. If it were covered in bottom growth or had a damaged prop, or had any defect I'd half understand it, but it runs A++.

 

[109jb]

Re: Evinrude 3 vs 4 cylinder mpg?

We took his boat for another run yesterday, about 4 miles downstream with the outgoing current, and back the same distance with the incoming current.
The 65 burned 13 gallons at nearly WOT the whole trip.
He's had two others that he says burned the same amount of fuel.

If it were mine, I'd be going further into it, but when I buy the gas, we run my boat. It's just a pain to have to carry all that gas in such a small boat to go such a short way.

8 miles and 13 gallons burned?? That is 0.6 miles per gallon. You can talk up your engine all you want but there is something wrong with the buddies engine or he has a barge for a boat. I had a 1976 70 hp Johnson triple and I could run that darn thing about an hour darn near wide open on one 6 gallon tank of premix. The boat it was on would get 30 mph so that gives about 5 mpg. Did that many times in the 10 years I owned that boat.

edit: By the way, you said they are "flat bottom V hull boats". Well which is it. It is either V-hull, or flat bottom, or possibly a "mod-V", but it can't be flat bottom AND v-hull.

 

[mfgniagara]

Re: Evinrude 3 vs 4 cylinder mpg?

8 miles and 13 gallons burned?? That is 0.6 miles per gallon. You can talk up your engine all you want but there is something wrong with the buddies engine or he has a barge for a boat. I had a 1976 70 hp Johnson triple and I could run that darn thing about an hour darn near wide open on one 6 gallon tank of premix. The boat it was on would get 30 mph so that gives about 5 mpg. Did that many times in the 10 years I owned that boat.

edit: By the way, you said they are "flat bottom V hull boats". Well which is it. It is either V-hull, or flat bottom, or possibly a "mod-V", but it can't be flat bottom AND v-hull.

I thought a modified V hull was an aluminum bass boat? A jon boat with a point up front.
These are flat bottom boats, with a V bow. The stern is flat with only a slight curve. The bow is V shaped. A flat bottom boat would be a jon boat in my book. dead flat with no keel or V shape.

I don't doubt what others get in mileage, but the one my buddy has burns fuel like it's going out of style. .6 gal per mile is about right. We're still withing sight of the dock when the first 6 gallon tank is empty on most days. Especially if going against the tide and wind. My point is that I can't fathom how such a small motor can burn that much fuel so fast. It's not leaking it, it don't smoke, and runs good. I'd figure the thing to nearly be hydro locked with fuel at that rate.

Something I did notice about his 65hp is a sticker on the one side of the motor pan which reads, "Modified for use in the State of California".
Other than what appears to be double head gaskets and the carbs have no adjustments on them whatsoever, the motor looks normal.
There is also a recall completed sticker on the side of the hood stating that the compression was reduced as per recall number something or other. I suppose that's the double head gasket reason.

I guess the only real comparison would be to hang my motor on his boat and check the mileage but it's not worth all that to me. I'm not messing with my boat, it works fine, I'm not screwing that up.

The one thing that I have noticed is that weight don't seem to affect his much, it planes out well with even three guys and gear onboard where as my V4 slows noticeably with a third passenger or even an extra 100 lbs or so. On mine, I drop a prop pitch if I'm carrying more weight that day. On the 65hp, it don't make much difference, changing the prop up or down drastically hurts the boat's ability to get on plane or max RPM.

Other than being a bit more used looking, his hull and mine are the same, neither one is water logged or overweight, and like I said, both have new poured transoms. These are all glass hulls with the foam being in the upper hull, not in the floor. His is my old boat, I just found a cleaner hull. I ran an old 55 hp electric shift motor on his boat when it was mine, it did fine on gas then, I'd run all day on a 12 gallon tank, with fuel to spare. He busted up the lower unit on that motor and hung a 65 hp soon after buying it, it's been a fuel pig ever since, on this and the last two motors, all 65hp three cylinder Evinrudes.

This is the first non electric shift motor he's had.

He carries less weight than me, the motor is lighter, and isn't much slower than me. Both are propped to within a few hundred RPM of max RPM, so it's not a case of a wrong prop, and neither boat is overweight. Mine is probably a good 400 lbs heavier on the water between the larger motor and more gear onboard, and better seats. He's got cheap plastic seats, a smaller motor but that weight is probably offset by the extra fuel carried. I also carry a 140 qt cooler full of ice on the bow, and a tool box full of tools and have a windlass installed, fish finder, GPS Plotter, and wood framed back to back seats.
Mine should by all means burn more fuel than his. Maybe even more than it does but I'm sure a lot of that is driver habit.
There is no way a motor that size should dump 50 gallons of fuel in the time I burn maybe 8 or so gallons.
This isn't a new situation, he's been running the boat like that for several years, nothing has changed other then me switching up to the larger motor with the idea in mind that I'd be in for similar fuel results going from a 55 twin to a 110 V4 but what I got was nearly no real fuel use change in my boat. I burn maybe three more gallons per day on a hard running day, and I gained some MPH. I had thought about hanging a mid 80's 70hp to save some fuel, it was after I ran his boat a few times that I had second thoughts.

I bought the 70hp last week, it's got an OEM reman power head on it, new coils, fresh reman carbs and ran like a top on the skiff it was on. Now I just have to convince myself to make the change and hope I improve my fuel usage over what the V4 gives me, and above all hope like hell it's not like his 65hp.

 

[Chinewalker]

Re: Evinrude 3 vs 4 cylinder mpg?

I think you will see a nice improvement in mileage with the 70. Do NOT use your buddy's boat as a gauge as something is not just wrong, but VERY wrong with it...

 

[mfgniagara]

Re: Evinrude 3 vs 4 cylinder mpg?

The 70hp isn't for my MFG, it's going on a 16 1/2' aluminum boat which weighs in at about 700lbs. Its a V hull that morphs into a round bottom hull at the stern with four or five fairly deep strakes. It had a 35hp and did about 18mph and would burn through about 10 gallons in a month of use. It was just too slow. I'm hoping by getting closer to the 75hp max rating I'll get better performance from it.
I hope to only have to carry 12 gallons tops. There's just no room to put a tank any larger in an open boat without tripping over it.

 

[jay_merrill]

Re: Evinrude 3 vs 4 cylinder mpg?

If your friend's motor is a 65hp Erude, its either a 1972 or 1973 engine. The 1974 "triple" is a 70hp motor.

I have a 17.5 foot fiberglass boat with a '72 Johnson 65hp engine. My boat is rated for 130 hp, so I am at 50% of maximum capacity. According to my GPS, my boat goes 29 mph at WOT, with a 15" pitch, cupped SS prop. This is with my bimini top down.

I have checked my consumption on a mileage basis a number of times, by comparing fuel consumption (full tank to full tank, noting gallons to top off again) to a known course measured with Goggle Earth's ruler function. I do this at my typical cruise speed, which is at about 4,200 - 4,300 rpm and about 25 mph. My mileage in this configuration is consistently about 3.5 miles per gallon. That would result in about 6.3 gallons for your 22 mile trip.

I'm not personally familiar with an MFG Westfield boat, but I found info about them in the net. What I saw was a 16 foot boat with generally flat bottom, flaring into a traditional V type bow. This makes me wonder about getting only 28 mph with a 65 Hp engine. My boat is a foot and a half longer and should weigh more, but I get greater speed with essentially the same engine as your friend. This makes me wonder about things like wet foam under the floor, proper engine mounting, engine health, etc.

Something is wrong with the situation that you are describing. Given similar speeds achieved at similar rpms, your motor should be burning more fuel than his, not half as much. Time for you friend to start looking at a few things on his boat.



???

 

[mfgniagara]

Re: Evinrude 3 vs 4 cylinder mpg?

If your friend's motor is a 65hp Erude, its either a 1972 or 1973 engine. The 1974 "triple" is a 70hp motor.

I have a 17.5 foot fiberglass boat with a '72 Johnson 65hp engine. My boat is rated for 130 hp, so I am at 50% of maximum capacity. According to my GPS, my boat goes 29 mph at WOT, with a 15" pitch, cupped SS prop. This is with my bimini top down.

I have checked my consumption on a mileage basis a number of times, by comparing fuel consumption (full tank to full tank, noting gallons to top off again) to a known course measured with Goggle Earth's ruler function. I do this at my typical cruise speed, which is at about 4,200 - 4,300 rpm and about 25 mph. My mileage in this configuration is consistently about 3.5 miles per gallon. That would result in about 6.3 gallons for your 22 mile trip.

I'm not personally familiar with an MFG Westfield boat, but I found info about them in the net. What I saw was a 16 foot boat with generally flat bottom, flaring into a traditional V type bow. This makes me wonder about getting only 28 mph with a 65 Hp engine. My boat is a foot and a half longer and should weigh more, but I get greater speed with essentially the same engine as your friend. This makes me wonder about things like wet foam under the floor, proper engine mounting, engine health, etc.

Something is wrong with the situation that you are describing. Given similar speeds achieved at similar rpms, your motor should be burning more fuel than his, not half as much. Time for you friend to start looking at a few things on his boat.



???

The MFG hulls in those years don't use foam in the floor, they use a trapped air compartment with foam in the gunwales and under the bow deck.
His boat weighs less than mine, both were pretty clean boats when they were found, but I kept mine, the second one I found since the first one, now his, was full of unused snaps from previous mooring covers, tops, etc. Both were in mint condition otherwise.
I carry far more gear and junk than he does, he's the type that takes only what he needs, and not a thing more. My boat is packed with extra lifevests, several cans of lead sinkers, two types of anchors, extra rope, safety gear, fishing rods, spare line, several extra rods and reels, etc. He had an empty boat with four fuel tanks.
The only thing I noticed about his boat the other day is that it has a definite sweet spot at idle, below that it loads up and it don't like to idle for long periods. If we launch his boat, fire up the engine and let it warm up while parking the truck, the motor will sometimes sputter and stall before we get back to the boat. On the water its fine. My V4 will idle all day long and never load up. Mine is a VRO motor if that makes any difference. His smokes a lot at idle while warming up, mine not so much.
We both run the same fuel, same oil, same mix.

I don't doubt his has issues, I'm just wandering when the real problem will rear its head since all normal checks show nothing really wrong. That boat, having been mine just two years ago, I know the hull is sound and not wet, besides, he keeps his beside mine in the same barn, out of the weather.