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

Sundancer said:
I think most of the 268's with the 350 ran a top speed between 30 and 34. It's a heavy, deep V hull that is a little under powered. I had the same vintage 250 with a 454 Magnum and the top speed was BARELY 40 mph. With a heavier boat and smaller motor, I'd say anything over 30 mph is gravy. Unfortunately to get on a clean plane you need to be doing around 25 or so. There just isn't a lot of extra oomph in that combination. Someone else might chime in here, but it does appear that you have some issues in the carb/jets/prop combo.
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The more I've been thinking about it the more I'm leaning to the secondarys not kicking in. If it was jetted wrong the engine would be crapping out, Too much fuel, too much air, pick one. But It's real smooth so I think the air fuel mix is right. Just not enough fuel and air mixed together. If the jetting is right and the secondarys open there should be plenty of air / fuel mix. If the jetting is right and the secondarys don't open it would be smooth but lack power. If the secondary jets are lean and the secondarys open the motor would crap out, too much air, same if they were clogged, too much air, or rich too much fuel. If it's the carb, It's got to be the secondarys failing to open right.
 
Sundancer said:
I think most of the 268's with the 350 ran a top speed between 30 and 34. It's a heavy, deep V hull that is a little under powered. I had the same vintage 250 with a 454 Magnum and the top speed was BARELY 40 mph. With a heavier boat and smaller motor, There just isn't a lot of extra oomph in that combination. Someone else might chime in here,
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Sorry steve and Billy,
I couldn't resist.:grin:
The engine on the left goes in the lawn mower.
The engine on the right, Is for the boat.:lol::lol::lol:

steve,
I concur.
If the secondaries are not kicking in completely. Your fuel/air mixture is correct. But running only off the primaries is like having a 300 CFM carb. I did that on purpose with a RV camed ford 302ci before. Truck still ran very good. But it did not weigh over 7000 lbs
 
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Orderd a new carb today. Might as well throw some more parts at it. I know I'll never get my money back out of it:smt101.
That engine on the left looks like it came from a marine lawn mower. Like something you might mow your kelp with.:smt043
 
The 26'Sea Ray is a good platform to work with.
Just keep the boat a very long time.
That's how I justify the cost.
There is a resent thread on this topic.

Off to MDR for more boat stuff :lol:
 
stevea661 said:
Orderd a new carb today. Might as well throw some more parts at it. I know I'll never get my money back out of it:smt101.
That engine on the left looks like it came from a marine lawn mower. Like something you might mow your kelp with.:smt043
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Did you stay with the quadrajet? I'm going to probably need to get one soon as well. Did you find a good deal?

Maybe Tail will let me have his Holley since its sitting in his garage un-used! :grin:
 
BillyT0020 said:
Did you stay with the quadrajet? I'm going to probably need to get one soon as well. Did you find a good deal?

Maybe Tail will let me have his Holley since its sitting in his garage un-used! :grin:
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Yea I stayed with the quadrajet. I got it off or ebay from a store called I-5 components. The cost was 280. It's a rebuilt and has a one year warante. The guys here in ca so the shipping should be quick. Hope between the carb and the ei I'm done fixing stuff for a while. You've got a point about TCs edelbrock though ,maybe holley, I'm real good about blowing up power valves on holleys.
 
Billy
Don't get a Holley.
Look at the float bowls on them things. If bowl gasket would leak. Gas is going all over your engine. Maybe they use an O Ring. But still.:wow:
I like the metering rods on the Edelbrock.
You can really fine tune the idle circuit.
But like anything aftermarket. Need to do some mods.
An intake spacer, fuel inlets on the back of carb. And a different throttle pin hole size. I picked the Carb up for 300.00 5 yrs ago.
Picked up a Gal of epoxy resin today. Now I can do more unnecessary work :smt021 :lol:
Going to install a 40 gal belly fuel tank under the bunk.
It will go through the aft cabin bulkhead and stop approx 4" before the engine.
Losing 20 gals by trimming the stock tank down 4" for the 8.1:smt013
My boat headaches are different then steve's

Billy,
I don't need a pic of your charger setup.
I hadn't realized how flat and roomy the sides were.
Thanks for the offer:thumbsup:
My Bravo and transom should arrive on the 26th. That should help put a fire under my rear.
 
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Tail Chaser 661 said:
Billy
Don't get a Holley.
Look at the float bowls on them things. If bowl gasket would leak. Gas is going all over your engine. Maybe they use an O Ring. But still.:wow:
I like the metering rods on the Edelbrock.
You can really fine tune the idle circuit.
But like anything aftermarket. Need to do some mods.
An intake spacer, fuel inlets on the back of carb. And a different throttle pin hole size. I picked the Carb up for 300.00 5 yrs ago.
Picked up a Gal of epoxy resin today. Now I can do more unnecessary work :smt021 :lol:
Going to install a 40 gal belly fuel tank under the bunk.
It will go through the aft cabin bulkhead and stop approx 4" before the engine.
Losing 20 gals by trimming the stock tank down 4" for the 8.1:smt013
My boat headaches are different then steve's

Billy,
I don't need a pic of your charger setup.
I hadn't realized how flat and roomy the sides were.
Thanks for the offer:thumbsup:
My Bravo and transom should arrive on the 26th. That should help put a fire under my rear.
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TC
I hope you are moving right along. I finally got everything and got everything installed. It runs great on the trailer. Yea I know it did that before:huh:. Can't check it like a car. It's like 3 hours round trip to the water. Tomarrow starts the long weekend and it will probably be a zoo so I'll pass. Then next week is also out, But I have the whole week off after that. so it will have to wait till the 13'th. I just don't know where to look next if this don't get it.
 
stevea661 said:
TC
I hope you are moving right along. I finally got everything and got everything installed. It runs great on the trailer. Yea I know it did that before:huh:. Can't check it like a car. It's like 3 hours round trip to the water. Tomarrow starts the long weekend and it will probably be a zoo so I'll pass. Then next week is also out, But I have the whole week off after that. so it will have to wait till the 13'th. I just don't know where to look next if this don't get it.
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The 13th? Ouch
MDR ramp always has tons of room. Even on a big weekend.
You don't head up swell and into the wind like CIH either.
I would baby the boat, then do a prop test later.
I think your boat is fixed. lime4x4 said he could not spin a 15.75 x 15 prop. Try calling Valley props in Ventura. If need be, Maybe remove some blade area or trim it down to like 15.25 The prop guy will know.

Im adding and beefing up stringers on my boat. They are glassed on one side only. Not even sealed on the bottom. Only 3/4" ply also.
Going over the boat with epoxy/glass adding 3/4 marine ply to the transom. The aft cabin bulkhead is only glassed on the bottom. 1/4" gap on the sides and upper deck. Completely glassing in the bulkhead. Building this boat very solid for offshore use.
I just got my B3 in on the 2nd. Things a beast :grin:
 
Tail Chaser 661 said:
The 13th? Ouch
MDR ramp always has tons of room. Even on a big weekend.
You don't head up swell and into the wind like CIH either.
I would baby the boat, then do a prop test later.
I think your boat is fixed. lime4x4 said he could not spin a 15.75 x 15 prop. Try calling Valley props in Ventura. If need be, Maybe remove some blade area or trim it down to like 15.25 The prop guy will know.

Im adding and beefing up stringers on my boat. They are glassed on one side only. Not even sealed on the bottom. Only 3/4" ply also.
Going over the boat with epoxy/glass adding 3/4 marine ply to the transom. The aft cabin bulkhead is only glassed on the bottom. 1/4" gap on the sides and upper deck. Completely glassing in the bulkhead. Building this boat very solid for offshore use.
I just got my B3 in on the 2nd. Things a beast :grin:
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Wow you're doing a bunch of stuff. Even sprung for the high dollar epoxy resin, I would have cheaped out and done polyester. My stringers are completly encapsulated in some pretty heavy roving. I don't remember anything odd about the bulkhead. No one is answering the phone today, so I can't get any stupid prop questions answered. You should have some real good range with all that fuel capacity. I'm going to have to wait till the 13'th too much stuff to do. but after that I'm off again from the 27'th of july till the 17'th of augest. If I don't get it sorted out by then I could always blow it up or use it for lawn art:thumbsup:
 
I have a Gal of poly resin. Then reading about how it will delam off of wood. Decided to go epoxy. Fith the fillers. The epoxy can be very thin for soaking into wood, Or make it thick for filling voids and it will not run. Also with the pump. Its a 1 to 1 ratio. I bought the slow hardner. I should have like 100 mins working time in 70/80 degree heat. Stuff should be a breeze to use after fooling with a couple of gals of poly in the past. In the ER room. You can't see how SR cheaped out on the bulkhead till the engine/tank is out.
From what you said about your stringers. Everything else may be glassed in pretty good also.

You can cross reference prop mods with www.propmd.com
See if both prop shops give you the same info.

I never plan on selling my boat. I can visualize heading 100 miles offshore to the Cortez Bank in my over built/overpowered SR converted offshore fishing boat. Having over 50 days at the islands with this boat. I know it suites my needs.
Steve,
You should splash yours soon, It will help make all the work youve done worth while. Fishings getting good also.
 
stevea661 said:
TC
I hope you are moving right along. I finally got everything and got everything installed. It runs great on the trailer. Yea I know it did that before:huh:.
Click to expand...
Mine ran pretty darn good on the trl also, Even with a rocker arm laying on its side :grin::lol::lol::lol:
You have a 30 mph boat now. Hopefully your old carb was screwed up. With the new carb hopefully you can pull some higher rpms. If not, I'm sure a little prop tuning will fix you up. Comforting having lots of new parts on the boat.
 
Tail Chaser 661 said:
I have a Gal of poly resin. Then reading about how it will delam off of wood. Decided to go epoxy. Fith the fillers. The epoxy can be very thin for soaking into wood, Or make it thick for filling voids and it will not run. Also with the pump. Its a 1 to 1 ratio. I bought the slow hardner. I should have like 100 mins working time in 70/80 degree heat. Stuff should be a breeze to use after fooling with a couple of gals of poly in the past. In the ER room. You can't see how SR cheaped out on the bulkhead till the engine/tank is out.
From what you said about your stringers. Everything else may be glassed in pretty good also.

You can cross reference prop mods with www.propmd.com
See if both prop shops give you the same info.

I never plan on selling my boat. I can visualize heading 100 miles offshore to the Cortez Bank in my over built/overpowered SR converted offshore fishing boat. Having over 50 days at the islands with this boat. I know it suites my needs.
Steve,
You should splash yours soon, It will help make all the work youve done worth while. Fishings getting good also.
Click to expand...

Polyester isn't so bad, you just have to measure your hardner accurate. I've done a lot of work with polyester in hot weather and direct sunlight, I used 16 oz soft drink cups from costco, the ones that are like wax coated paper. Mix about 4 to 5 cc of mek to 16 oz, wet out whatever I was going to glass with a chip brush, lay out the mat, cloth or woven roven over it dry, role it, then wet out on top of that and role again. You get about 10 minutes before the stuff starts to gell. about 1/2 hour before you can sand. You should definitly use a resperator through the whole deal. Two problems I had were the fiberglass makes me itch and I can't smoke through a resperator. I've seen the fishing getting good and my boat in the desert at 4400' above sea level. I'm leaving for fla tonight, to visit my dad for a week so the boat has to wait. I hope to have it squared away the week of the 13'th. I'll probably kill some fish in fla. Good luck on yours:thumbsup:
 
David Morgan said:
A little off topic but why do most power boaters seem to use MPH and not knots?
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Good question. The prop chart in my omc manual reads in miles per hour as does my gps. I think knots is like the metric system. We kind of go with what we know:grin:
 
This is interesting. I bought a 1985 26' Weekender w/260 last year. I have no idea what I should get out of her. She'll rev up past 4k in neutral, but won't go over about 3400 in fwd at about 18kn. I'm used to heavy twin inboards, so what do I know? I figured this is just a heavy smaller boat. It has a SS prop which I assume was bought with the correct pitch for this boat. It hasn't been out of the water for a couple of years, but it's kept in freshwater and doesn't seem to have much of a beard. Most of my boating is in no wake zones, but last weekend we went about 40 miles down river. I'm glad I didn't know these boats are that fast, I'd have been po'd.
So, what can I can I reasonably expect from this rig? What should her cruising rpm and speed be? We are about 300# of people, and maybe 50# of personal gear. Two #27 batteries and half load of water. We are interested in going farther down river, so a little more speed would be nice.
Thanks
 
partgypsy said:
This is interesting. I bought a 1985 26' Weekender w/260 last year. I have no idea what I should get out of her. She'll rev up past 4k in neutral, but won't go over about 3400 in fwd at about 18kn. I'm used to heavy twin inboards, so what do I know? I figured this is just a heavy smaller boat. It has a SS prop which I assume was bought with the correct pitch for this boat. It hasn't been out of the water for a couple of years, but it's kept in freshwater and doesn't seem to have much of a beard. Most of my boating is in no wake zones, but last weekend we went about 40 miles down river. I'm glad I didn't know these boats are that fast, I'd have been po'd.
So, what can I can I reasonably expect from this rig? What should her cruising rpm and speed be? We are about 300# of people, and maybe 50# of personal gear. Two #27 batteries and half load of water. We are interested in going farther down river, so a little more speed would be nice.
Thanks
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Well something is def setup wrong. First indication is the RPM's being that low. I have my boat over propped with a 14.5 x 17P SS prop and I can still get it to about 4100 RPM's at WOT with the top end speed around 36 to 37 mph I cruise around 3500 RPM's right around 30 mph. This is usually with just me and the girl onboard. The more people on the boat the slower she gets in a hurry.

At 3400 RPM's you may not even be cleanly on a plane with these boats. I usually have to take it up to 3500 RPM's to get up and then I can trim the drive out and back off to around 3200 or 3300 and stay up but anything less then that and she falls right off.

I would raise your outdrive and pull your prop to see what pitch you have on there now or atleast throw on a set of googles on a clear day and get it that way. Unless you have like a 21P on there now the prop may not be your only problem. Each inch of prop pitch will drop your WOT RPM's by 200.

Prob a good idea to see what compression you have in your cylinders and check to see if the carb is opening fully but getting the current prop size and pitch is the first step to getting you set up right.

Good Luck!
 
Talked to valley prop last week. They said retest it with the new stuff I put on and that my drive / motor combo should have no problem spinning the 15.8 x 15 prop. They also said the speed sounded good and I should check the tac. I need a day to rest but tuesday It goes to the lake and we will see what happens.
 
I'm pretty sure I've got this thing figured out. Initial timing advance is 5 degrees. At 3000 I should have around 33 degrees total, I have about 14. This would really bring down the power on the top end which is where the problem is. It runs real smooth but does not go over 3400 rpm. I'm taking the distributer to a shop tomarrow to be recurved. I hope thats the end of this trouble shooting session. I will let you all know how this turns out.
 
Very good :thumbsup: You had a top speed of 30mph? Fixing the advance issues hopefully gets you at least top speed of another 6 mph.
I'm looking all over for the reason my boats so slow:smt101:smt043
Looks like my belly tanks going to hold a good 45 gals.Taking up all the space under the aft cabin bunk. From the cabin sump pump extending 15" into the bilge going below the main tank.
Losing 15 gals on the main 100gal tank. Giving myself 3" of room in front of the 8.1 and 4" room on the front/sides for servicing the filters/impeller assemblies. The orig stringers were only 1 pc 3/4" ply on edge. I added a bit more. Adding at least 3 pcs 3/4 marine ply from the front motor mounts going into the aft cabin. Need to go buy another gal of epoxy resin. Used a little of the poly resin. Stuff sucks. Gels to fast, then too slow to cure :smt013
 
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