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Old 06-24-2015, 05:19 PM   #11
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Here you go

exhaust.JPG
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Old 06-26-2015, 05:51 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, 05:57 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, 06:00 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, 06:13 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, 05:56 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, 05:59 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, 11:00 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, 11:13 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, 11:16 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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