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Old 06-19-2012, 03:50 AM   #1
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Default 1994 Maxum 2700 SCR - Bravo 2 Prop Size?

Hey guys!
I have a 1994 Maxum 2700 SCR with a 7.4L merc bravo 2, I just purchased it a few days ago and I know something is wrong with it (I assume the prop pitch is wrong)
I'm topped out at about 3200 RPM and am barely pushing 20mph (and it is sucking gas like no other).
I'm not sure what size prop is on it now (i think the previous owner said 21" pitch but i could be wrong - haven't had the chance to pull it out of the water).
(The previous owner also blew the old lower unit because he forgot the thrust washer and it ate the prop, he gave me the old lower unit and old prop, the old prop has a 19" pitch.)
There is a brand new lower unit on the maxum now and what i believe to be a 21" prop. do you have any insight for what could be the correct prop size? or perhaps the solution to this low rpm, gas guzzling, sluggish problem? These props cost like $400 - $600 so I'm trying to get the right size once lol.
To top it all off, i blew the starter today and i realized its not a high torque starter so that was on its way out anyway i researched online and think i need an ARCO 30470 starter but I'm not 100% on anything, if someone could double check that also for me it'd be greatly appreciated.

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Thanks for your help,
- Joe
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Old 06-19-2012, 04:40 AM   #2
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welcome to the zoo joe.....I answered your im too me....as for the starter parts no....I'd get the hin # and the engine # and call your local bayliner dealer and he can get you a marine grade starter...be sure it's marine grade ........


SP
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Old 06-19-2012, 01:55 PM   #3
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I have a 1990 SCR-2700 with a 7.4L Bravo engine. It also has a Bravo 2 stern drive with a 2.00:1 gear ratio.

My current prop is about a 18x23 3 blade aluminum (i'm not sure if it's an 18.5x23 or 18.75x23).

If you want to check your gear ratio, call Mercruiser with the serial numbers of your engine and outdrive. They can look up what the gear ratio is/was.

I say is/was, because if your lower unit was replaced, perhaps they put in a different gear ratio? This will affect what prop to use.
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Old 06-20-2012, 11:26 PM   #4
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Hey guys, I just wanted to keep everyone updated in case they have the same problem. I spoke to a propeller expert and they assured me that my low wot problem is due to the wrong prop pitch.
I ordered a 18 3/4" x 17" pitch Stainless steel prop (rated for boats 27' - 34' long and 5900-8700 lbs). Since the boat's dry weight is about 6,500 lbs, it seems fitting. The propeller people also said that if i went from the 21" pitch (currently on boat) to a 19" pitch that it would be much better but i would still not be reaching the rated rpms. for every 1 inch pitch, they said is equivalent to about 300 RPMs. so with the 17" pitch i should be gaining about 1,200 RPMs which should put me at about 4,400 RPM. The boat is rated for 4,200 - 4,800 RPM. The prop is being ordered and I will install as soon as i get it. I will keep everyone posted if interested.
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Old 06-21-2012, 03:11 AM   #5
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I know I'm new here and to the Maxum, but I would be sure to check that your engine is working properly before trying a 19 inch pitch prop.

Why? See this previous thread of mine: http://www.maxumownersclub.com/forum...rive-questions

When I had my first test ride of my SCR-2700, with the 7.4L, Bravo 2 with 2.00:1 gear ratio, I couldn't get over 11 MPH (measured by GPS) and the WOT was low!

Later tests and the engine started running better. The dealer rebuilt the carburator and found that the timing of the distributor was off a couple of degrees. Now I get good speed and WOT with the 23inch pich prop. Before this, I was about to try to purchase a 19 inch pitch prop myself.

Be sure to let us know what you find in the end!
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Old 06-21-2012, 03:32 AM   #6
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Hey Rich,
I really hope its just my timing. I have a quick question for you. when you had a low WOT and were going 11mph, were you also burning up a ton of gas? right now i'm literally burning like 70 gallons in about an hour at full speed and im probably moving about 20mph (rough estimate, no gps yet and speedo is broken at the moment). Engine seems to be running strong. I read your forum post a while ago and saw that you said you were hitting 4,000 rpm at wot and going 11mph, im only hitting 3200 rpm at wot. that's why im leaning more towards the prop as the culprit. im gonna take your advise though and check the carbs/timing tomorrow morning and see what im working with. worst case scenario, i'll have an extra prop. the 17" pitch may not get me up to 40mph but it should put me to plane really fast since its a wider diameter (fingers crossed).
I hope i get this problem licked soon, kinda just wana get out and enjoy the season.
the boat's name fits haha,
We'll Sea...

-Joe
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Old 06-21-2012, 11:55 AM   #7
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I don't know the fuel consumption as this was during the first check out ride. But I would guess that the fuel consumption was high. I noticed at the time that I went from 3000 to 4000 RPM and it only changed the speed by 1 mph! (from 10 to 11 MPH). I also couldn't get the boat on plane at the time.
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Old 06-22-2012, 06:13 PM   #8
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Installed the new starter yesterday, engine was still having trouble starting. I checked the plugs, gas in all cylinders. the #4 cylinder also had some water in it (uh oh). I checked compression in all the cylinders (1 plug at a time at cold engine) and found that my compression for all cylinders was pretty consistent at around 120psi. However, the #4 cylinder only had compression at 90psi (it was also having trouble holding the compression as the meter slowly dipped down during the test). There was no spark coming from 1 plug that i tested (possibly more than 1), so I replaced all of the spark plugs. cranked the engine and noticed that my carburetor is dumping a ton of gas in it. disconnected the fuel line and manually got it started finally. took the boat for a test spin with the new plugs. at wot i was hitting only 2600 rpm, at 3/4 throttle it jumped back up to 3000 rpm, at 1/2 throttle it brought me to idle at about 1000 rpm. im not sure if it was because the fuel filter was affected from when i disconnected the fuel lines but i was in a hurry to go to work so i couldnt risk getting stuck on the water. I ordered a reman carb from a reliable place and will be installing that this week along with the 17pitch prop. I am pretty certain that there is an underlying problem at play here, but i dont want to be pulling the engine at the beginning of the season unless absolutely necessary.

Here's a little history on this boat, the guy i bought it from got it after it had been sitting for 2 years. he put New plugs, wires, cap rotor, alternator, propeller 21pitch ,risers, belts, zinks, boots and hydraulic lines,The bravo 2 unit is new with receeipt '04-30-12', 3 new batteries, Trim tabs work.

when i picked up the boat i drove it for a 5 hour transport on the water and it performed pretty well with no sputtering, just rpms never passed 3200 and i was topping out at about 15-20mph.
I also touched the risers yesterday when we had it running, the port side was cool as a cucumber but the starboard side was much warmer.
From my experience, the manifolds should probably be changed. i hope the block isnt cracked, and im hoping the heads arent cracked either.
water is not spitting out of any spark plug ports, just enough is noticed when pulling the plugs out.
When i checked the oil, there was a small amount of water in there as well (condensation?) or leak?

any help is greatly appreciated, slowly losing my sanity lol

- Joe
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Old 06-22-2012, 07:00 PM   #9
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Seems like you have some work to do:

Rebuild carb
find out why #4 cylinder has water and lower compression (probably one and the same reason, if your lucky, it's just a head gasket).
Get it running properly.

After the above is fixed, then check your WOT and prop size.
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Old 06-26-2012, 04:39 AM   #10
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Hey guys, I finally found time to mess with the engine. I've decided I'm going to get the carbs rebuilt, heads redone, and new manifolds (risers also if bad - previous owner said risers were new, we'll see).
pulling boat out of the water in 2 days hopefully and gonna have in back in the water within 2 weeks. I'll let you know if we get the problems licked. I wish I hadn't put down a deposit on the 17" pitch prop because im starting to think the rpm problem is compression related and not prop related.

We'll Sea...
-Joe

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