RPM / MPH / Prop on a 1986 268 w/ 5.7 omc

[stevea661]

TC
You are going to have the best boat ever:smt038. 145 gallons of fuel, economical (for a boat) fuel use wise. You'll have some good range. The place where you're putting the belly tank is where the shower sump is on my boat. who needs a shower any way. I yanked my water heater and looped the hot into the cold, and also looped the coolant line. I don't think hot water is that important:huh:. The water heater was trash anyway. Your stringers are set up different than mine, mine are about 2.5" across and about 3" high, outboard of the keel. The front motor mounts are fastened to the stingers. It looks like you cut the shelfs open on the port and starboard where you added the eight lateral braces. Are you going to foam and glass the shelfs back in? It should make it way more stout. How long before you're ready to kill fish? The fishing is getting good:thumbsup:.

 

[BillyT0020]

TC,
Looks like you missed the 4th of July Deadline! :smt021 Oh well your doing it right. I don't have those extra stringers either, I just have motor mounts like steve, which had to be replaced last season. Question, are the motor mounts for the 496 going to be in the same position as the 350? Im just wondering when I drop in my 454 on roids, if there will be enough room on the stringers in the case that the motor needs to be moved forward at all. How does the cooling system on the Bravo work? Are you going with a water pump that mounts on the harmonic balancer with a thru hull pick up or a belt driven pump that pulls water through the bravo? Are you going to do thru hull? I think I have my heart set on those oval corsa tips that are mounted on the side with no mufflers :thumbsup:Of course all of this will happen when I repower.

Looking good man, Now get that bildge painted and lets see what that BB looks like in her!

 

[Tail Chaser 661]

TC
You are going to have the best boat ever:smt038. 145 gallons of fuel, economical (for a boat) fuel use wise. You'll have some good range. The place where you're putting the belly tank is where the shower sump is on my boat. who needs a shower any way. I yanked my water heater and looped the hot into the cold, and also looped the coolant line. I don't think hot water is that important:huh:. The water heater was trash anyway. Your stringers are set up different than mine, mine are about 2.5" across and about 3" high, outboard of the keel. The front motor mounts are fastened to the stingers. It looks like you cut the shelfs open on the port and starboard where you added the eight lateral braces. Are you going to foam and glass the shelfs back in? It should make it way more stout. How long before you're ready to kill fish? The fishing is getting good:thumbsup:.

My stringers were only one pcs 3/4 ply. I 'm running 2pcs of 3/4" now. With the glass its 2" thick by 5" high. The 8 braces are on 9" spans. Where it only had one before. forward of the engine mounts going into the aftcabin will be glassing in four more 3/4" marine ply stringers. Everything in the ER room is being coated and glassed in with epoxy resin. Don't think foam would add much more strength there now? Its a total of 8' from the transom forward where everything is getting beefed up. The belly tank sits right at the hatch for my shower sump. Then 60" forward going 15" into the bilge. The tank will be inclosed on the top with bulkheads on each end making the boat stronger. I need the range, Most of my trips are three days. Sucks being out there being in fuel savings mode all the time having only a 120 mile range. the tank builder was suppose to get measurements on tues. Didnt happen. He is based out of San Diego. I just removed my seats and need to take apart the side of the boat in the AM.Looking for a good place to run my filler hose.
Thought to myself.:smt115 Why not paint the decking with some non skid paint while its apart :huh: :lol: Hot water is not that important. I installed a hot/cold water washdown thats in the way of a place to run a tank fill. :smt013 I'm not running my engine coolent through my old water heater either. Atleast im having fun doing this upgrade. I am keeping my time wasting to a min.

 

[Tail Chaser 661]

TC,
Looks like you missed the 4th of July Deadline! :smt021 Oh well your doing it right. I don't have those extra stringers either, I just have motor mounts like steve, which had to be replaced last season. Question, are the motor mounts for the 496 going to be in the same position as the 350? Im just wondering when I drop in my 454 on roids, if there will be enough room on the stringers in the case that the motor needs to be moved forward at all. How does the cooling system on the Bravo work? Are you going with a water pump that mounts on the harmonic balancer with a thru hull pick up or a belt driven pump that pulls water through the bravo? Are you going to do thru hull? I think I have my heart set on those oval corsa tips that are mounted on the side with no mufflers :thumbsup:Of course all of this will happen when I repower.

Looking good man, Now get that bildge painted and lets see what that BB looks like in her!

I kind of hated posting such ugly pics. Couldnt resist posting wondering why my boat is slow:smt018 :smt101

All the engines mounts are in the same location. 454,496,502, etc Give GM a nod for that one :thumbsup:
The 454 and 502 are tight but fit with the stock tank. (I was told) my 496 is 3" longer then the Merc smallblock. it would have hit my tank by 1/4" The serpentine belt on the 496 must be the lenght issue over the V belts on the other two BB.
The 8.1 is its own animal. It has it own impeller, fuel pumps, fuel cooler,and filter tucked mostly in one housing on the front starboard side of engine. You will probably only have room for the side mounted impeller. Henry Boyd had mentioned the 8.1 only uses a thru hull water PU. Ive also read some post of the bravo water intake being restrictive and some other really bad problems.
I hate to glass my stringer shelves back in. Would like to maybe mount a water PU thru hull and trandsducer in a slick configuration under them. I cant be screwing around with everything. I need to get back to work. I ran out of money about 16k ago :wow: Probably another 3k to finish the project. At least I save gas money hanging out in the bilge :grin:

 

[stevea661]

I took the distributer down to the distributer guy today. The problem with it was that the springs were not under enough tension and it was sticking some. So when I set the inital timing the weights were out about 25%, the weights have stops on top so they can only go so far and advance so far from the inital timing. So thats why total advance was low. He bent the ears that the springs are attached to, to put the springs under tension, put the distributer back on the machine, took it up to 3000 rpm and got 22 degrees centrifical advance, just where it needs to be. He also told me to set my inital at 10. He said the 5 degrees that the manual specifies was a little low. I just got done reinstalling it and the timing mark is about 2" past where it was yesterday at 3000. So it's time to take it out and see what it does off the trailer :smt038

 

[Tail Chaser 661]

My 260hp 5.7 timing was 8 BTDC. Did the distributor guy give you any indication how bad your advance problems may have been hurting performance?
Have fun out there :thumbsup:
I just picked up a very detailed 3-Dimensional fishing chart of SM Bay. Has 64 fishing Waypoints. Theres like 6 square miles of reefs 8 miles offshore I didnt know about. Good place to go if I just want to rinse the dust off the boat for the day.

 

[stevea661]

My 260hp 5.7 timing was 8 BTDC. Did the distributor guy give you any indication how bad your advance problems may have been hurting performance?
Have fun out there :thumbsup:
I just picked up a very detailed 3-Dimensional fishing chart of SM Bay. Has 64 fishing Waypoints. Theres like 6 square miles of reefs 8 miles offshore I didnt know about. Good place to go if I just want to rinse the dust off the boat for the day.

I'm just going to run to pyramid, drop it in for about an hour and see what it does if that turns out ok this will be the last time the boat sees fresh water. Where did you get the chart from, I'd like to try some close spots the first time out in the ocean. The fishing down south this time if year is normally better than out of ventura. The distributer guy said that was probably the problem. Won't know for sure even if all goes well tomarrow because since last time out I have a new carb and the pertronix ignition has replaced the points. I did seem hard to keep the revs down today, they really took off after about 2500 rpm. It didn't do that yesterday.

 

[stevea661]

No change. 3400 rpm and 30 mph. I did have to back off the timing because it started to ping. timing is set back at 5btc inital. I had my wife run the boat while I was in the engine room. I did get it to crap out twice and I ran it with the spark arester off. That thing sucks the gas down. You can see the gas spraying down the barrels. When it crapped out there didn't seem to be as much fuel spraying into the barrels so I guess I'll change the seperator and check the fuel filter at the carb although they are both new. The only things left to change are the wires and the fuel pump. Reguardless next week it goes to the ocean, but with a new prop because I had a little accident with the one on there as I was dropping my wife off at the dock to get the truck, a little shallow and rocks sure can mess up a prop:huh:. Anyway it will give me a chance to get a smaller diameter prop that one was (past tense) real close to the cavitation plate on the drive, probably about 1/4". It was 15.8, I'm going to look for a 15.5 or 15 inch diameter by 15 or 14 pitch.

 

[Tail Chaser 661]

No change. 3400 rpm and 30 mph. I did have to back off the timing because it started to ping. timing is set back at 5btc inital. I had my wife run the boat while I was in the engine room. I did get it to crap out twice and I ran it with the spark arester off. That thing sucks the gas down. You can see the gas spraying down the barrels. When it crapped out there didn't seem to be as much fuel spraying into the barrels so I guess I'll change the seperator and check the fuel filter at the carb although they are both new. The only things left to change are the wires and the fuel pump. Reguardless next week it goes to the ocean, but with a new prop because I had a little accident with the one on there as I was dropping my wife off at the dock to get the truck, a little shallow and rocks sure can mess up a prop:huh:. Anyway it will give me a chance to get a smaller diameter prop that one was (past tense) real close to the cavitation plate on the drive, probably about 1/4". It was 15.8, I'm going to look for a 15.5 or 15 inch diameter by 15 or 14 pitch.

Were you ever able to check how accurate your tach is?
I bet its a little off along with you being a little overproped.
If you want, you can try out my 16 x14 alum and my 17" stainless. The PU tube in my tank was very small. Surprised theres not more fuel starvation problems out there. Also the anti syphon valve is that fitting on the tank your 3/8" fuel outlet hose is attached.
Maybe check your plugs, See if you were lean or rich out there today. Bummer dinging your prop. Freshwater sucks, Even though I scratched mine at Santa Rosa island. tucking it in a cove a little tight for an overnighter. Guess the tide went down overnight :huh::lol:
Same trip I was stuck at Skunk Point at Rosa with a 1/2 tank of fuel on a three day. Didnt have the range to go anywhere but back to the ramp:smt013
I learned what I need in a boat, I'm handling that now :grin:
Also... Your mechanical fuel pump has a clear tube going to the carb. Marine pumps have two diaphragms in them. If theres gas in that tube, One of the diaphragms is blown. That may cause low fuel pressure.

 

[stevea661]

Were you ever able to check how accurate your tach is?
I bet its a little off along with you being a little overproped.
If you want, you can try out my 16 x14 alum and my 17" stainless. The PU tube in my tank was very small. Surprised theres not more fuel starvation problems out there. Also the anti syphon valve is that fitting on the tank your 3/8" fuel outlet hose is attached.
Maybe check your plugs, See if you were lean or rich out there today. Bummer dinging your prop. Freshwater sucks, Even though I scratched mine at Santa Rosa island. tucking it in a cove a little tight for an overnighter. Guess the tide went down overnight :huh::lol:
Same trip I was stuck at Skunk Point at Rosa with a 1/2 tank of fuel on a three day. Didnt have the range to go anywhere but back to the ramp:smt013
I learned what I need in a boat, I'm handling that now :grin:
Also... Your mechanical fuel pump has a clear tube going to the carb. Marine pumps have two diaphragms in them. If theres gas in that tube, One of the diaphragms is blown. That may cause low fuel pressure.

I checked the tac against an old sun tester that I have and up to 2500 on the trailer and it was right on. I pulled the plugs this morning and found cyl 1,3,2 rich, cyl 5,7, 4,6,8 good I dont think the 3 rich ones really mean anything. the plugs were gapped at 32, figured with the pertronix I could go a little more and went to 37. Did a compression check on the cold engine ( not so cold temp on the black risers in the sun was 113 and engine was not started since yesterday, just heat from the sun) all cylinders were about 175 except 6, that was at 155, I added oil to the cylinder at it went to 170, but the engine only has like 7 hours on it so it mite not be broke in yet, it could have been as low as 132 and that is within 10% but would have had me concerned. I just figured I should check the compression so that I could cross that off the list. I checked the resistance on the wires all are within 4000 ohms per foot. I need to check the esa system but I think it's working ok because when I unpluged it at wot yesterday nothing changed, if it was causing loss of power unpluging it would have caused it to come up. Looking in the book the spec for the engine compression is between 150 and 160, mine is about 15 lbs more and I'm running regular, I don't know if that would cause me to have to run premium, or if I ran premium I could advance the timing enough to get me the extra rpms I need to be in range. Another thing is my book calls for a 15.5 diameter prop by 15 pitch . The prop I was running was 15.8 diameter x 15 pitch. The other thing is that I only have 8" from the center of my prop shaft to the bottom of the cavitation plate on the outdrive, that left .2 inches space between the prop blade and the cavitation plate. The other thing I don't know is if thats too close and if .5 inches spacing would fix the rpm problem. when I talked to valley prop I talked to the girl and she talked to the guy who knows stuff and relayed the message back, if she left out the part about my drive being an omc and he assumed that like every one else I had a merc I could have got bad info. You said I could barrow your 16x14 but I don't have room for a 16" diameter prop. How much room did you have between the prop and the cav plate with the 16? How much room did you have from the center of the prop shaft to the bottom of the cavitation plate? I will give valley prop a call tomarrow and try to talk to the guy as opposed to the girl. thanks for all the help.

 

[stevea661]

I had the boat out again today. It seems to be pretty well sorted out. My motor guy said to try some octane boost, I had the tank filled with 87 octane. He said I shouldn't need to run premium, It has 167cc heads and about 9.2 to 1 compression but it would be worth a shot. I probably had 50 gallons of regular in the tank and put in 2 quarts of boost 108. Thats suposed to treat up to 64 gallons. Then I added about 28 gallons of 91 to that. I Also have a new prop, an aluminum hustler 15.5 x 15, the old one was a solas 15.8x15. So when I got it out to the lake It would run up to 3600 rpm, but this time it would start to crap out at wot. So I called the mechanic, Less (thats for you TC) and told him what was going on and he said to remove the flame arestor and start to close the chokes down some restricting air flow when it started to crap out. If that didn't make a differance it would probably be electrical. So my brother in law ran the boat I was down with the engine and my son was holding the lid open so it wouldn't slam on my head when we hit a bump. With restricting the air flow on the secondarys only, with my hand, we were able to get it up to 32 mph at 4200 rpm and then it started to cavitate. So I'm thinking it must be running lean. Prior to that I also bumped the timing up to about 8btdc. This is a brand new rebuilt ebay quadrajet carb. So as I am not a quadrajet kind if guy, I'm a holley kind of guy, The boat is going to go to the mechanic on tuesday and get dialed in. Either jets or metering rods or what ever you do on a q jet. It will cruise at about 27 at 3800 rpm as long as you have someone driving and someone regulating the air flow into the carb. Once it gets dialed in with some more gas and I can use all that air, I think I should get a few more mph out of her:thumbsup:

 

[Tail Chaser 661]

Very cool steve :thumbsup:
I'm curious what color your plugs are burning.
Are you sure you just didn't tap your tach with a hammer :grin: WOW!... just got 4200rpm out of her :lol:
Running lean at Pyramid. You will be way to lean at sea level.
May need to go two steps bigger/richer on the secondaries.
Ive mentioned the Edelbrock before. Whats so cool about that carb is.... There is metering rods that go through the jets and they have a spring keeping them seated.Keeping a leaner condition with light loads. When the engines vacuum drops as power is increased the rod will pull out of the jet for a richer condition. If your rich/lean at WOT you can put in a different size metering rod. Only remove one screw for the change out. A thinner Dia rod is as if you took the carb apart to change jets to a bigger size. But its only one torx screw for the adjustment :thumbsup:
Anyhow....You know your stuff. Instead of letting Less rejet your carb you may want to do it yourself. Two jet sizes bigger if your plugs are white. One size bigger if there a light tan color.
I had my tanks measured and ordered today. 154 gals :thumbsup:
That should make 280 miles a max safe range trip. I can see tuna on the horizon :grin:

 

[stevea661]

Very cool steve :thumbsup:
I'm curious what color your plugs are burning.
Are you sure you just didn't tap your tach with a hammer :grin: WOW!... just got 4200rpm out of her :lol:
Running lean at Pyramid. You will be way to lean at sea level.
May need to go two steps bigger/richer on the secondaries.
Ive mentioned the Edelbrock before. Whats so cool about that carb is.... There is metering rods that go through the jets and they have a spring keeping them seated.Keeping a leaner condition with light loads. When the engines vacuum drops as power is increased the rod will pull out of the jet for a richer condition. If your rich/lean at WOT you can put in a different size metering rod. Only remove one screw for the change out. A thinner Dia rod is as if you took the carb apart to change jets to a bigger size. But its only one torx screw for the adjustment :thumbsup:
Anyhow....You know your stuff. Instead of letting Less rejet your carb you may want to do it yourself. Two jet sizes bigger if your plugs are white. One size bigger if there a light tan color.
I had my tanks measured and ordered today. 154 gals :thumbsup:
That should make 280 miles a max safe range trip. I can see tuna on the horizon :grin:

After doing a little looking on the internet, gotta love this thing, it appears the secondary metering rods on the q jet is what you need to change for top end. It looks like they pull out through the top, without having to pull the whole carb apart. So I'll mess with the old carb and see. That way I won't screw up the new one, that still doesn't work right .
The next deal, with the cavitation. When it was at 4200 rpm and about 32mph on the gps the engine rpm quickly went up to about 4600 rpm and the speed dropped down to 29 mph. Is cavitation what happened? It was like the prop lost traction for a second and backing down on the throttle allowed it to grab again and we were able to accelerate back up. I checked the plugs before this test and they all looked pretty good, brownish, 1, 3, and 2 looked a little fat. When is the tank guy going to have your stuff done?

 

[Tail Chaser 661]

After doing a little looking on the internet, gotta love this thing, it appears the secondary metering rods on the q jet is what you need to change for top end. It looks like they pull out through the top, without having to pull the whole carb apart. So I'll mess with the old carb and see. That way I won't screw up the new one, that still doesn't work right .
The next deal, with the cavitation. When it was at 4200 rpm and about 32mph on the gps the engine rpm quickly went up to about 4600 rpm and the speed dropped down to 29 mph. Is cavitation what happened? It was like the prop lost traction for a second and backing down on the throttle allowed it to grab again and we were able to accelerate back up. I checked the plugs before this test and they all looked pretty good, brownish, 1, 3, and 2 looked a little fat. When is the tank guy going to have your stuff done?

Very cool steve :thumbsup:
I thought Edelbrock was the only carb with the metering rods. I assumed Q jet was the same old carbs used back in the 60's :smt101 Daaaa:lol: Tank should be ready in two weeks. I need to clean up the wiring, Paint, Might as well build my storage insulated fish box for my new helm chairs to mount on. And paint the decking and add some none slip walnut shell additive to it since the seating is out. I'm sure I need a 8.1 exhaust Y pipe before I can drop the engine back in.
I may want to install the Airmar B164 thru hull transducer while the engines out also.
Sounds like you got some big time cavitation at WOT. Maybe the engine crapping out or miss firing somehow allowed air to be pulled in front of the prop or you crossed somebody wake. Probably a fluke thing. Get your carb dialed in first. Then you can fine tune the prop. Maybe a little cup to get a better bite/hold on the water. Next concern... How are you going to buddy boat the 200 mile trip to Cortez bank :lol::smt009

 

[stevea661]

I can pull the water tank, not reinstall the water heater, install two 40 gallon fuel tanks and have 180 gallons of capacity. Ok proabably not, I'll meet you out there on the first string and buy you a burger:thumbsup:

 

[sprink56]

I have fooled around with Q-Jets over the years. They were introduced in the early '70s as an emission carb for larger small blocks and big blocks and innovated the "spread bore" concept.

One of the things that gets the air valve opening point messed up is a faulty vacuum "dash pot" diaphragm that actually operates the linkage that opens the air valve. If there is a leak in any part of that assembly including the hose that feeds it, the secondary air valve will not open and all of the metering signals in the secondary circuit will be out of whack. This might be your problem. You can have another problem if the air valve opens too quickly. There is a coil spring on the left side rear (looking from the front) that has a set screw underneath the air horn. You loosen the set screw and tighten or loosen the spring tension to regulate the resistance of the spring on the air valve. If the air valve opens too soon the engine will "bog" down because of too much air and not enough fuel. Remember there is no accelerator pump on the secondary side of these carbs like on a double pumper Holley. On a heavy boat with a small block the air valve needs too have a heavy restriction on it so it doesn't open too soon. The settings for a car will not be accurate due to the difference in load. You mention that the carb came from e-bay and I wonder if it was originally an automotive carb.:wow:

Hope you solve your problem...I know it can be frustrating.

 

[Tail Chaser 661]

I can pull the water tank, not reinstall the water heater, install two 40 gallon fuel tanks and have 180 gallons of capacity. Ok proabably not, I'll meet you out there on the first string and buy you a burger:thumbsup:

I was going to mount a 25 gal on the upper port side ER room shelf. 130 gals or 150 mile range will cover fishing the offshore banks out of SD/Dana Point, Catalina, and San Clemente islands. You can cover Anacapa, Santa Cruz, And most of Santa Rosa at the Channel islands with that range.
After your boats dialed in you may want to add a small thru hull water PU for the engine. Lots of kelp stringers that wrap themselves around the outdrive water pu. Takes about 1 min to pin the gauge on hot.:wow: I met a diver at MDR with a classic 26'DA. He cooked two engines due to this :wow: He had a very small stainless thru hull water pu mounted. He cruises right over kelp stringers now with no problems.

sprink56
Them Q jets are some fairly high tech carbs. I figured they had the nickname QuadraJunk due to very poor metering capabilities. steve should be able to buy a metering kit for for the Q jet. The Edelbrock kit comes with jets,springs,and rods

 

[stevea661]

I have fooled around with Q-Jets over the years. They were introduced in the early '70s as an emission carb for larger small blocks and big blocks and innovated the "spread bore" concept.

One of the things that gets the air valve opening point messed up is a faulty vacuum "dash pot" diaphragm that actually operates the linkage that opens the air valve. If there is a leak in any part of that assembly including the hose that feeds it, the secondary air valve will not open and all of the metering signals in the secondary circuit will be out of whack. This might be your problem. You can have another problem if the air valve opens too quickly. There is a coil spring on the left side rear (looking from the front) that has a set screw underneath the air horn. You loosen the set screw and tighten or loosen the spring tension to regulate the resistance of the spring on the air valve. If the air valve opens too soon the engine will "bog" down because of too much air and not enough fuel. Remember there is no accelerator pump on the secondary side of these carbs like on a double pumper Holley. On a heavy boat with a small block the air valve needs too have a heavy restriction on it so it doesn't open too soon. The settings for a car will not be accurate due to the difference in load. You mention that the carb came from e-bay and I wonder if it was originally an automotive carb.:wow:

Hope you solve your problem...I know it can be frustrating.

Sprink
The carb was sold as a marine carb, It is one, but I don't know is it was one originaly. The Company that did the carb is called I-5 components. They are a rebuild shop. The dash pot appears to be working ok as it allows the air valve to open and the motor runs ok as it's opening. I saw the adjustment on the secondary air valve and if I tightend it up enough so that it would not open all the way it would run ok. It ran ok. When I started to lean out I would cup my hand around the top of the secondary barrels and it would smooth out. When I would remove my hand it would start to pop and miss a little. This leeds me to belive if I go down in size on the metering rods allowing more fuel in it would not pop and lean out. The main thing I was worried about was over working the engine or drive, causing too much strain and breaking something. Thanks for the input. I'll get it sorted out sooner or later.

 

[stevea661]

I was going to mount a 25 gal on the upper port side ER room shelf. 130 gals or 150 mile range will cover fishing the offshore banks out of SD/Dana Point, Catalina, and San Clemente islands. You can cover Anacapa, Santa Cruz, And most of Santa Rosa at the Channel islands with that range.
After your boats dialed in you may want to add a small thru hull water PU for the engine. Lots of kelp stringers that wrap themselves around the outdrive water pu. Takes about 1 min to pin the gauge on hot.:wow: I met a diver at MDR with a classic 26'DA. He cooked two engines due to this :wow: He had a very small stainless thru hull water pu mounted. He cruises right over kelp stringers now with no problems.

sprink56
Them Q jets are some fairly high tech carbs. I figured they had the nickname QuadraJunk due to very poor metering capabilities. steve should be able to buy a metering kit for for the Q jet. The Edelbrock kit comes with jets,springs,and rods

I might add extra fuel capacity in the future. I will need to add a fuel flow gauge with a total fuel used reading. That way I can figure out whats going on as far as fuel use and where I'm going and how much fuel I need to get there and whats left. How would I plumb an extra water pickup. My raw water pump is in the drive. I would think I would need a seperate engine driven pump to a through hull and some check valves to keep the cooling water flowing in the right direction? I know my buddy sucked a plastic bag around his outboard and cooked it. It kind of sucks. I could put adjustable snap disk limits on the exhaust wye pipes that would close at about 150ish and run those up to 12 volt buzzers at the dash. If the exhaust temp would go over 150 the circut would close and the buzzers would go off, You can't always watch you gauges, but you can here a buzzer. With the way my cooling is set up I belive I would start to melt rubber couplers on the exhaust before the engine would over heat if I has a raw water restriction. The last boat had a merc and the gimble housing where the hose connected between the gimble housing and the transome assembly got a hole at the gimble housing causing the motor to heat up at low rpms. That in turn did not hurt the motor but started to melt the rubber exhaust couplings. That boat was raw water cooled.

 

[Tail Chaser 661]

I might add extra fuel capacity in the future. I will need to add a fuel flow gauge with a total fuel used reading. That way I can figure out whats going on as far as fuel use and where I'm going and how much fuel I need to get there and whats left. How would I plumb an extra water pickup. My raw water pump is in the drive. I would think I would need a seperate engine driven pump to a through hull and some check valves to keep the cooling water flowing in the right direction? I know my buddy sucked a plastic bag around his outboard and cooked it. It kind of sucks. I could put adjustable snap disk limits on the exhaust wye pipes that would close at about 150ish and run those up to 12 volt buzzers at the dash. If the exhaust temp would go over 150 the circut would close and the buzzers would go off, You can't always watch you gauges, but you can here a buzzer. With the way my cooling is set up I belive I would start to melt rubber couplers on the exhaust before the engine would over heat if I has a raw water restriction. The last boat had a merc and the gimble housing where the hose connected between the gimble housing and the transome assembly got a hole at the gimble housing causing the motor to heat up at low rpms. That in turn did not hurt the motor but started to melt the rubber exhaust couplings. That boat was raw water cooled.

Good point steve. I was mtn biking at MDR when I talked to the guy with the added through hull. Thats what im suppose to be doing now. But I turned the computer on :smt013 I only took a peek at his thru hull. He used a Tee fitting to the main water inlet. I could only guess if he went to a engine impeller setup:huh: There is a scooper/strainer thru hull designed for engine water intake. A search may reveal if it scoops enough water at slow speed to cool the engine with a clogged or burnt out impeller. I hadnt heard of anyone using a check valve. of my google searches have been useless lately.