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Old 11-11-2014, 09:50 PM   #1
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Default 1999 1900sr 5.0 won't run full throttle

I have had the carb rebuilt, new fuel pump, new filters, new spark plugs, new starter, and it still will not run correctly. It seems to bog at about 3/4 throttle and will not take a rapid acceleration. I am at a loss as to what the problem could be at this point. Is there something simple I am overlooking with this thing? Background is it sat up for a while and upon taking it out the one and only time last summer, it didn't have the power when attempting to plane out. It sputtered when it did finally get on plane and lacked power on top end. It would surge as if it had trash in the fuel etc.. I assumed it was from leaving the fuel in it for so long. So I had the carb rebuilt, changed filters, drained the tank and tried again. It still missed. I did notice the rpm gauge doesn't work now (have no idea why as it did before). As the repair attempt progressed....the plugs and fuel pump were replaced. It still doesn't run right. Its better but not right. Suggestions on what to check? I am tired of throwing money and time at it.
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Old 11-12-2014, 01:28 AM   #2
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How long is it running before you can try to speed up and the condition occurs?

Does it just not have the power, sputters, breaks up? The latter could be a bad ignition coil.

What carb do you have? 2/4 bbl weber/ Rochester ?

Could also be clog in fuel pick up in the gas tank or maybe clog vent. Try running with gas cap off.

Have you have the timing checked? Mechanical weights in the distributor sticking?

Just my initial thoughts

Regarding the tach check the connections on its rear, gray wire is the sense from the coil
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Old 11-13-2014, 12:59 PM   #3
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Thank you for the info. I am going to replace the coil, distributor cap and rotor this week and see if it corrects it. I have removed the fuel lines, and pickup line in the tank. All lines are clear and clean, as is the anti syphon valve. And its a 2bbl carb, although I am not sure which make. Its the stock carb it came with. I am hoping this corrects it, as it got better after the plugs were replaced but still isn't 100% an seems to be getting worse the more its run. it definitely seems worse at high throttle, but may just be more noticeable at those speeds. Yes it surges and the rpms drop off and if throttled back it often corrects and maintains for a bit.
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Old 11-13-2014, 01:07 PM   #4
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I would check the timing as well. Plug wires could also be breaking down.

In my experience surging is typically a fuel issue and not electrical. Let us know what happens after you perform the work you listed.
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Old 11-15-2014, 08:44 PM   #5
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Well, I just got back from the Lake. I changed the cap, rotor and coil but still not running normally. It is fine until about 3/4 throttle and then it just bogs down as if it is running out of fuel. It will sometimes come back, but still will not reach maximum speed. Its doesn't really surge...just acts like its running out of fuel. I guess checking the timing and maybe the fuel pressure is all I know to do at this point. The fuel pump is new so I don't see it lacking pressure and it seems to run and idle fine at lower speeds. I am stumped.
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Old 11-15-2014, 08:50 PM   #6
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Any changes sine it last ran good? Bottom growth, damage to prop, ...

What rpm and speed does it max at?

Is the flame arrestor clean?

Check static timing and timing at speed to see if it is advancing.

Change all fuel filters?
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Old 11-15-2014, 09:58 PM   #7
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the only change since the last time it ran good is the tach was working then and doesn't now. Other than that and the things listed (fuel pump, cap, rotor, plugs etc from trying to correct it). When you say filters ...am I missing one? I changed the fuel water one. I don't see any others as far as fuel related.

I can't tell the rpm at the moment but around 35-40mph it starts the bogging. It normally would run around 52mph (with the speedo) although I no its not accurate, it is good enough to judge for this issue. If I remember correctly, somewhere around 5400rpm (when the tach worked) it would max out.

Yes flame arrestor is clean.
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Old 11-16-2014, 12:38 AM   #8
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Did you try Mike's recommendation of removing the gas cap? Your symptoms sound like a vent problem.
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Old 11-16-2014, 01:44 PM   #9
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There is a fuel filter in the carb when the gas line connects. Disconnect gas line then undo large nut to access filter.

If you stay below 3/4 throttle does the boat run fine all day? If yes then this should eleminate a clogged vent.

Not sure I understand how it would cause the issue but since tach is misbehaving remove the gray wire on the S terminal (wrap it in tape to ensure it does not short to anything) from it and see if the problem goes away.
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Old 11-16-2014, 02:26 PM   #10
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Quote:
Originally Posted by jrsick View Post
Did you try Mike's recommendation of removing the gas cap? Your symptoms sound like a vent problem.
I removed the tank vent line and was able to blow through the vent hose from the tank side, so I believe it is clear.
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Old 11-16-2014, 02:31 PM   #11
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Quote:
Originally Posted by mmwjr View Post
There is a fuel filter in the carb when the gas line connects. Disconnect gas line then undo large nut to access filter.

If you stay below 3/4 throttle does the boat run fine all day? If yes then this should eleminate a clogged vent.

Not sure I understand how it would cause the issue but since tach is misbehaving remove the gray wire on the S terminal (wrap it in tape to ensure it does not short to anything) from it and see if the problem goes away.
That filter was changed when the carb was rebuilt.

I think it is just a bad tach gauge. I pulled the under side cover out and checked the connections, pulled and cleaned the wire connections, and replaced. Still doesn't work at all. I am going to have the timing checked and be sure the fuel pump has adequate pressure at the carb.
Is there any way the oil pressure switch is malfunctioning and causing the pump to shut down at higher rpms?? The gauge reads plenty of pressure but I have heard of those switches being bad. Although it seems they usually wont allow the boat to run at all.
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Old 11-16-2014, 04:07 PM   #12
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The oil pressure switch has two staes open or closed. Since the boat does not die and the fact that it would at lower rpms when the pressure is lower means the switch is not the issue.
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Old 11-19-2014, 08:13 AM   #13
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Not really familiar with Mercruiser motors but I have had the same thing happen on a motorbike
After many hours and plenty of $ I found that the carby float was a little too low causing it to starve at high rpm
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