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Old 06-23-2015, 02:18 PM   #1
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Default 1995 Maxum 2100 SRB

Hello all,
I just purchased a 2100 SRB in great shape here in central NC. Not new to boating but it's been awhile. The boat has a 5.0L Alpha motor....whatever that means. The engine is original and it only has 216 hours on it.

We took it out last weekend and had a great time with the 4 kiddies and 4 adults on board.

Two problems surfaced. The trim up wouldn't work but we did have a jumper wire on board that we used to bypass the solenoid for an on-water fix. Where can I purchase a replacement solenoid?

The major problem, however, was the engine would not rev past 3400 rpm and sucked up 19 gals of fuel in a couple hours! It sounds like the exhaust is restricted in some way and the engine can't breath. So at partial throttle the four barrel is cutting in passing lotsa of gas!!!!

I've not located a cutaway of the exhaust yet so that I can determine if there is an obstruction somewhere. I'm making a wild guess that due to the low engine hours something weird could have occurred to block the exhaust. The boat has never been in salt water. I would appreciate any pointers to quickly fix this....summer's here.

Thanks, Bill
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Old 06-23-2015, 04:19 PM   #2
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Bill welcome aboard.

5.0 is a maximized GM 5.0 (305 Cubic Inch) inboard engine.
Alpha is the mercruiser drive that is mounted on the back of the boat. This is the entry level drive for basic applications. They also offer a Bravo drive for high HP applications.

Regarding the trim solenoid any boating store will have it such as West Marine, or online stores. These are available in aftermarket from many suppliers such as Sierra.

An exhaust flapper may be stuck closed. This is located in the Y-Pipe where the lower rubber exhaust hose is. The flapper is there to prevent any water from flowing back up the exhaust from entering the engine thru its exhaust port.
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Old 06-23-2015, 06:02 PM   #3
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I once had a Y pipe on a car that collapsed inward showing no damage on the outside but the inside, once hack sawed open, had a 440 cu in engine trying to exhaust out through a pencil sized hole. So this seemed like a similar problem.

Is the exhaust flapper only on one side? How would you suggest freeing it up? WD40 or similar? Or a really big hammer?

Thanks.
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Old 06-23-2015, 09:03 PM   #4
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There are two flappers one on each side.

First verify its stuck closed. If it is I would replace them as they do break and fall down to the bottom of the pipe and are then a real PIA to remove.
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Old 06-24-2015, 03:13 AM   #5
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I don't believe the 5.0l was ever offered with a 4 barrel. Only 2 barrel and efi/mpi.



Could it be a carb problem running the engine so rich that it can't rev?



Those flappers are just rubber or plastic. Can't imagine they would stick hard enough that exhaust pressure couldn't force them open.
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Old 06-24-2015, 11:28 AM   #6
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Not thinking the boat is running rich as a 5.0 turning 3400 rpm is going to burn 8 - 10 gph so in the couple of hours the OP ran the boat he burned 19 gallons which is in check with what I would expect.

Another potential source of not achieving WOT is the boat is over propped.

Also you had 8 people onboard which depending on the kids weight a good load for your set up.

What rpm can you achieve with 2 adults?

What prop is on the boat?
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Old 06-24-2015, 11:45 AM   #7
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That's a good point Mike. My old boat was a 21' cuddy with a 5.7. I could plane with 4 adults, they had to walk up to the front untill I was on plane, then they could go sit down.
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Old 06-24-2015, 12:38 PM   #8
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Moved to the GENERAL sub-forum. Not sure why so many new threads are starting in the 'New Member Introductions' section lately.
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Old 06-24-2015, 12:57 PM   #9
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Haven't yet taken the air intake cover off to verify 2bl/4bl. Will do that Friday to see what we have.

Does anyone have a good diagram or part # for the exhaust flapper? From a drawing I saw earlier I'm not certain of the flapper location.

Thanks for your input.
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Old 06-24-2015, 01:25 PM   #10
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Go to www.mercruiserparts.com they have all the exploded diagrams.



If you follow your exhaust, it goes header, possibly a spacer, riser elbow, then a rubber coupler, a piece of hard pipe, another rubber coupler, and then the y pipe. The flappers sit at the entrance to the y pipe, under the second rubber coupler.
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Old 06-24-2015, 04:19 PM   #11
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Here you go

Click image for larger version

Name:	exhaust.JPG
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ID:	4211
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Old 06-26-2015, 04:51 PM   #12
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Alright. Got an early start on it...last night we got down to the exhaust flappers on both sides. No problems noted. Ran water both ways and also did not discover any problems.

The boat is a 1995 Maxum 2100 SRB. It does have a 4bbl. Since it's a chevy 5.0L, I assume it's a Rochester carb with vacuum operated secondaries.

Putting it all back together and running it with the muffs on, it backfired through the intake on quick throttle jabs. Unable to check engine timing as I have not had a timing light in years. Will buy one and see what we have.

Is the idle engine timing 8 degrees BTDC for this engine? Is there any special procedure to properly check the timing?

It looks like the carb accelerator pump squirts ok.

We checked that all plug wires went to the right plugs and distributor cap placement.

With 4 adults (550 lbs) and 4 kids (200 lbs) the boat had extreme difficulty getting up on plane and the engine would not go over 3400 rpm (30 mph) once on plane. Naturally, even once on plane with WOT the 4bbl was open and sucking lotsa gas.

Does the distributor have old fashioned weights inside? Or vacuum advance like a car?

Unless the engine timing is way off, anyone have any other suggestions?
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Old 06-26-2015, 04:57 PM   #13
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Does that carb have a marine certification on it? Someone might have tossed an automotive carb on there, which is VERY unsafe. Particularly if it is a mechanical fuel pump. I don't believe 4bbl was an original option in that motor.



What prop is on the boat?
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Old 06-26-2015, 05:00 PM   #14
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Whoops, I take that back, 1988-1995 they did offer a Rochester 4bbl.



http://www.mercruiserparts.com/Show_...2D+4+BARREL%29
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Old 06-26-2015, 05:13 PM   #15
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What ignition system do you have Thunderbolt IV or V? If V there is a procedure to set base timing that requires to ground a wire (do not recall right now).
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Old 06-29-2015, 04:56 PM   #16
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Replaced both trim solenoids as the 'up' one was acting up. Figured both solenoids were the same age so went ahead and replaced both.

'ear' timed the engine to eliminate back firing through the intake with no load (muffs on). Took the boat out yesterday and it ran much better. rpm's went from 3100 to 3500 with no 4bbl cut in. boat cruised much nicer. I've heard (and experienced) chevy crankshaft marks being way off. I'll verify #1 TDC with a screw driver and get basic timing correct.

Does the distributor have mechanical and vacuum advance?

The springs for the mechanical advance have been know to malfunction.

Once I'm convinced the plugs/wires/cap are ok, that leaves carb & fuel.

Should the fuel filter be changed out?

Thanks for the help.
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Old 06-29-2015, 04:59 PM   #17
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Nothing is vacuum operated on a boat engine (save maybe secondaries). Distributor is mechanical advance in older system, I believe it is electronic advance in thunderbolt V and up.
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Old 06-29-2015, 10:00 PM   #18
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Quote:
Originally Posted by Kevlar7r View Post
Nothing is vacuum operated on a boat engine (save maybe secondaries). Distributor is mechanical advance in older system, I believe it is electronic advance in thunderbolt V and up.

+1 TBV has electronic advance. No vacuum advance on boats, would not work due to high steady operating rpm.
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Old 06-29-2015, 10:13 PM   #19
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Quote:
Originally Posted by mmwjr View Post
+1 TBV has electronic advance. No vacuum advance on boats, would not work due to high steady operating rpm.


Not to nit-pick, but it's the open throttle, not the rpm that leads to lack of vacuum.
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Old 06-29-2015, 10:16 PM   #20
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Quote:
Originally Posted by Kevlar7r View Post
Not to nit-pick, but it's the open throttle, not the rpm that leads to lack of vacuum.

Correct nit-pick.

Thought you were out of town this week.
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