SOS.. 911... um... help :)

Black plugs are a sign of incomplete combustion. The mixture is too rich, or oil is bypassing the rings, or there isn't sufficient flame front propagation as the spark ignites the fuel air mixture...sometimes a timing advance issue. An old "shade tree" trick is to hit the anode with a cigar lighter, or small torch, to burn off the excess fuel (gas doesn't burn as a liquid) but if you have new plugs, you are going in the right direction. What did the plugs look like in the other engine? Did you happen to run a compression check on any of the cylinders?
 
From looking at those plugs I would say they look old and worn, but not saturated with fuel.
The item I may have missed is the results of the compression check? You should be getting around 140 PSI on all cylinders. While you have the plugs out doing the compression check look to see if there is any fuel, or large amounts of vapors shooting out of any cylinders. You should see wetness on the plug if there was any flooding with fuel. Do not substitute watching the rotor button spinning for doing a compression check.

The one other question you should start with is "has anything changed since it last ran?" parts replaced or moved, etc..
If the distributor wasn't moved then it more than likely is in the correct location (at least enough for it to run as well as it did) if the plug wires were not removed then they more than likely are oriented correctly.

If there is a fuel problem, with new plugs and a squirt of gum cutter down the throttle plates it should start and run for a few secs, or at the very least pop or spit.

To answer your question, in order to replace the distributor pick-up you must remove the distributor and the drive gear from the bottom of the shaft so that the whole shaft can be pulled up out of the top of the housing. I believe there were some that you were able to remove the rotor button and the metal reluctor wheel was held in place with 3 screws. You would have to check to see if yours is the same. This would avoid having to pull the distributor out.

Another question that may be out of left field, but I have done it.
Does your boat have the fuel shutoff valves/ crossover valve? I have shut mine before during the winter and tried to start the engines in the spring without switching the valve over. Mine would start and run for a minute or so and die, so it may not even be a valid point. Just thought I would mention it.
 
Does your boat have a kill switch or safety lanyard that you might have accidentally hit while cleaing or closing up?
 
Have not done a compression check. I will buy the tool today when I pick up the plugs. The plugs in the WORKING engine look similar, so I will replace them as well.

I do not have a kill switch anywhere that I know of. If there is a secret squirrel switch somewhere let me know! I am thinking that such a switch would not allow the engine to crank at all.

Has anything changed since it last ran... only item was the carb, which I rebuilt. I was thinking great i messed that up, so I swapped the carbs and it didnt help. Also fuel straight down the carb manually does nothing.

I did notice faint smoke puff out of the carb throat. I will put new plugs in, compression check, and probably switch the coil just to make sure there is enough spark.

Thanks for the assistance everyone, its has been very helpful! I REALLY want to splash this weekend (dont we all)

v/r

The distribuitor rotor head was removable. I was able to swap the thunderbolt IV system from the working engine to the non working. No change, but the working engine still works with the other parts. (amen)
 
I agree with others here in that this just doesn't seem right. To fire a gas engine has to have air, spark, fuel and compression. Do a compression check (throttle wide open all plugs removed), change the plugs, inspect the wires, cap and rotor and put fresh gas in the tank. It should fire.......
 
Those plugs do look bad but not bad enough to not let an engine run. As far as the fuel smell it's just due to the amount you have tried turning it over. I may be wrong but I am still sticking with the wireing harness. Completley unplug it and plug it back in and make sure it is tight. I hope that is the problem cause that is a cheap and easy fix with a hose clamp. And yes it is located on top of the engine. Good luck!!!!! looks like there is a lot of support here on this one.
 
Did you really check out the wiring? Wires can corrode inside the insulation and appear ok on the outside but can be totally corroded. I had a similar issue on an outboard where it would spark and had fuel and air. It turned out to be a corroded wire under the flywheel which kept it from firing. Considering the age of your motors, its just a thought. Also if you have a kill switch it is usually on or near the throttle controls.
 
This evening Im buying plugs, and a compression checker. ALSO if the lady allows it, I will totally go over the wire harness. Its kinda ironic that the engine that has less hours, and looks in better condition, is the one giving me grief. I'll update!!
 
One of the easiest ways to really understand what is going on would be to advance the timing. Assuming you are making combustion, the further you advance the timing, the harder it should be for the engine to turn over. If you advance the timing and the engine does not struggle to turn over, and assuming there is fuel in the Carb, I would think you have an ignition issue for sure.
 
RE the gap...

The plugs I removed are all approx 0.35 gap. The gap for the auto version of this engine is 0.35 However... i found a Searay Tech Bulliten that states all carb engines 2002 and older should be 0.45 gap Any thoughts??

(898) v8 305 5.0L
 
I'm sending you this as just an FYI, after going thru the same issue, we rebuilt the carb, put a new fuel pump on, ran new fuel lines, the motor still gave me a starting problem. Today she got fixed, it was a birds nest in the air intake for that engine. It was so far down the line no one could see it. I got word today shes running like she should.
 
chandalen said:
RE the gap...

The plugs I removed are all approx 0.35 gap. The gap for the auto version of this engine is 0.35 However... i found a Searay Tech Bulliten that states all carb engines 2002 and older should be 0.45 gap Any thoughts??

(898) v8 305 5.0L
Click to expand...

Look at your valve cover for the correct information. It will tell you the engine serial #, firing order and spark plug gap along with other items.
 
Ok.. 0.35 gap..

I installed all new plugs. Still nothing.

HOWEVER
I removed 1 (#7 back of engine) plug and attempted to start, and it actually tried to fire.. I removed the plug directly across, (#8) and the engine started. Granted ran like crap, but it ran.
I was thinking yea... just put plugs back in and good to go.. Not so. Put the 2 plugs back in... and back to nothing.

THIS has to mean something... and I hope it isnt bad...
 
Great! You have now determined that its probably not a fuel delivery, harness or safety interlock problem. The fact that the plugs are across from each other also reduces the "cracked head" possibility (they tend to crack in adjacent rather than opposing cylinders). Assuming all your compression checks went fine, the next step I would take is to VERY CAREFULLY pull, check and replace each sparkplug wire, making absolutely sure of integrity and firing order. Use an ohmmeter, and be sure the wires are sound...(hook each end to a lead, resistance should be pretty low, but shouldn't be open). If you have consistent compression, and it runs on six cylinders but on eight-two cylinders seem to be preventing the engine from firing, there is either a crossed wire somewhere, an arc in the cap, an arc in the wire...something.
 
Agreed. I think you have an ignition issue where you are not getting a not enough spark. By removing the 2 spark plugs, the engine is relieved of back pressure and therefore the minimal combustion you get is enough to keep the engine turning over. Has to be ignition not hot enough.
 
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And the one item I have not changed is the coil... SO... thats on the agenda then for tomorrow!

Thanks. HOPEFULLY that's the issue...

To be continued....
 
Make sure that engine is grounded. Is the wire hooked up to the battery? Some are easy to miss.
 
I went to mine today for a test run. The 14 year Merc mechanic was there and he was, like you, completly frustrated with my 350. There is a hose that runs down the front of the block, it runs from the carb down the front. It's just a vacuum line, mine was full of debrie, once replaced the engine fired and ran as if it was brand new. It's stupid but look and see if the line is clogged from fogging the engine. It's a $2 fix and a 5 minute job. Pull the line and blow thru it, no flow or restricted flow, replace.
 
mystic and dwna1a, I will try both of these ideas when I get home. If thoes fail, Im going to swap ignition coils. If that fails Im going to cry.

I am so baffled that the engine will run on 6 but not 8 cylinders.
 
My moms hyundai had a bad coil and was firing on 4 instead of 6. Good luck with your solution.
chandalen said:
mystic and dwna1a, I will try both of these ideas when I get home. If thoes fail, Im going to swap ignition coils. If that fails Im going to cry.

I am so baffled that the engine will run on 6 but not 8 cylinders.
Click to expand...
 
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