boat will not go onto plane

rough rider

Cadet
Joined
Jan 12, 2015
Messages
27
I have a 1978 Galaxy tri hull. It has a mercruiser 898 with a 305 engine. Using a rochester 2gc carb.
My problem is that it runs fine on the trailer but when it is in the water and I try to take off it just bogs down and will not get over about 2,000 rpms. This was a problem a couple years ago and I had the carb rebuilt and it fixed it but could it be anything else? I changed the plugs and wires and the coil. Then installed the old coil back on to see if it made a difference and it did not. I keep playing with the timing but it just never seems to do any good. It also seemed like it used A LOT of fuel for the time I was out tinkering. About 7 gallons for just a couple laps around the ski area. ( Probably about 3 miles total) Could it be something with the float? It has ran great for two seasons with only the basics taken care of. This time I changed the water pump in the stern drive, the coil, the plugs and new wires. Now I have a whole new problem. I should also mention that the idle mixture screws make no difference in how it runs and I have never been able to get it to run good at the suggested 8 degrees BTDC. it has always been more like 15 degrees BTDC and it would ping a little wide open but it would always start reliably and run fine other than slow out of the hole.. Any help would be great.
 

Bondo

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Apr 17, 2002
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Ayuh,.... Welcome Aboard,.... Sounds like the Carb is still the problem,......
 

Tnstratofam

Commander
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Aug 18, 2013
Messages
2,679
Definitely sounds like a fuel problem. Start at the tank and work your way forward. Good fuel in the tank, clean tank, fuel lines, anti siphon valve, fuel filters/water separator, fuel pump, carburetor.
 

alldodge

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I have a 1978 Galaxy tri hull. It has a mercruiser 898 with a 305 engine. Using a rochester 2gc carb.
My problem is that it runs fine on the trailer but when it is in the water and I try to take off it just bogs down and will not get over about 2,000 rpms. This was a problem a couple years ago and I had the carb rebuilt and it fixed it but could it be anything else? I changed the plugs and wires and the coil. Then installed the old coil back on to see if it made a difference and it did not. I keep playing with the timing but it just never seems to do any good. It also seemed like it used A LOT of fuel for the time I was out tinkering. About 7 gallons for just a couple laps around the ski area. ( Probably about 3 miles total) Could it be something with the float? It has ran great for two seasons with only the basics taken care of. This time I changed the water pump in the stern drive, the coil, the plugs and new wires. Now I have a whole new problem. I should also mention that the idle mixture screws make no difference in how it runs and I have never been able to get it to run good at the suggested 8 degrees BTDC. it has always been more like 15 degrees BTDC and it would ping a little wide open but it would always start reliably and run fine other than slow out of the hole.. Any help would be great.

:welcome: to iboats

Agree with Bondo, sounds like your carb and will add your timing should be at 8 BTDC. If you set it to 15 that pinging your hearing is parts of your engine going out the exhaust pipe.
 

Alumarine

Captain
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Feb 22, 2005
Messages
3,684
And after you get the carb right double and triple check that your plug wires are on the correct order.
 

rough rider

Cadet
Joined
Jan 12, 2015
Messages
27
Thanks guys, I have the carb torn down and soaking now. Can someone explain why it wouldn't run right at 8 BTDC? I do not understand this. Could my dist be off a gear or is that obsurd? I had it out when I did all the initial work two years ago.
I did not find anything obvious in the carb but I am still baffled by the fuel consumption! How is it possible to go through that much fuel?
 

alldodge

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Thanks guys, I have the carb torn down and soaking now. Can someone explain why it wouldn't run right at 8 BTDC? I do not understand this. Could my dist be off a gear or is that obsurd? I had it out when I did all the initial work two years ago.
I did not find anything obvious in the carb but I am still baffled by the fuel consumption! How is it possible to go through that much fuel?

If the carb is dumping fuel into the intake, the engine will not want to run, this could be many other things. Suggest running a compression test and leak down test to determine engine health. Thinner spark plugs wire should not be the issue.
 

rough rider

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Jan 12, 2015
Messages
27
I will check the cap and rotor when I get home before it gets dark tonight.
There is no sight tube on this boat from the fuel pump to the carb. Can this be the issue? What purpose does the sight tube serve? There is only the line that carries the fuel from the pump tho the carb. Could this be the problem if it is no0t there?
 

thumpar

Admiral
Joined
Jun 21, 2007
Messages
6,138
You should have a sight tube. It is a safety thing. There should be a solid metal line to feed fuel to the carb and a clear sight tube. The sight tube is there incase the fuel pump diaphragm ruptures.
 

alldodge

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I will check the cap and rotor when I get home before it gets dark tonight.
There is no sight tube on this boat from the fuel pump to the carb. Can this be the issue?
No

What purpose does the sight tube serve?
The tube goes from the diaphragm back side to the carb. It's there so if the diaphragm is ruptured the gas will go into the tube and down the carb. If the tube is not there then the pump has been replaced with an automotive type fuel pump. If the diaphragm ruptures then the fuel goes into the oil pan and the bilge of the boat. The next thing that happens is you blow up and your on the news. :( We REALLY don't want to read about you

There is only the line that carries the fuel from the pump tho the carb. Could this be the problem if it is not there?
No, if it's not leaking then your OK, but need to change the pump to a marine version
 

fishrdan

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Jan 25, 2008
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6,989
Besides what's been mentioned earlier... Have you checked that the distributor is advancing properly, weights sliding free and springs intact.

Also, the harmonic balancer could have slipped, making the timing off. You can check this by bringing the engine up to TDC on spark plug #1 and see if the balancer matches when #1 piston is at TDC. When I do this, I put a spark plug stop into #1 and rotate the engine left and right, then make sure the distance off of 0 on the balancer is equal in both directions.

Once you get your carb back together, look inside it with the engine running (off to the side, not directly over the top) to ensure that fuel is not pouring down the carb throat. It's possible that the fuel pump could push past the carb's float needle/seat, over pressure situation. This could happen with an old internally rusted pump, or even a new defective pump. Carb pressure should be something like 4-6PSI, and I've seen guys here with pumps putting out 9-12PSI, even new!
 

rough rider

Cadet
Joined
Jan 12, 2015
Messages
27
It has an electronic ignition installed so I can rule out the advancing properly issue I think anyways.

I thought about the HB last time I was dealing with this issue and it was good. I will check again though just to rule it out.

I put the carb back together and ran it just for a minute or two because it is dark and I din't want to be to rude to the neighbors. I will check for fuel dumping down the throat tomorrow.

I did check the cap and found a little corrosion and will clean that up as well. I am hopeful to put her in the water tomorrow to test for progress. If all is good I will be taking her out to Laughlin for the weekend for some sightseeing on the lake. If not I guess I will be home working out the problems. I don't know what else it could possibly be. All this advice sure is helpful, Thanks
 

rough rider

Cadet
Joined
Jan 12, 2015
Messages
27
How do I know for sure that I have the right coil for this thunder bolt ignition? It was on there when I got the boat. It doesn't have anything on it that says thunderbolt or anything, just looks like a stock coil.
 

alldodge

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How do I know for sure that I have the right coil for this thunder bolt ignition? It was on there when I got the boat. It doesn't have anything on it that says thunderbolt or anything, just looks like a stock coil.

The TB ignition uses the standard 12V coil. So long as yours doesn't specify use with an external resistor, your fine
 
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