5.7 Mercruiser(thunderbolt iv)/Alfa 1 out drive intermittent issue

[BattenDownTheSnatches]

Hello, I'm new to the forums so please let me know if I do something out of line and sorry in advance for the long post. I just want to give all the details. Lol

I purchased a non running boat this spring with the 5.7 Mercruiser/Alfa 1 outdrive and thunderbolt iv ignition. Cranked fine, good compression, but had no spark..

After doing some basic trouble shooting and following the thunderbolt IV flowchart I found on this forum, disconnecting the tach and shift interrupt switch, I decided to replace the ignition amplifier with a "known good" one from ebay. Then I had spark from the coil to the distributor but it was only intermittent and i would get spark at random post on the distributor and it kinda wanted to run but wouldn't.

At this point I was stumped so I went to replace the pick up in the distributor. When I popped the cap off I noticed the rotor wasn't pushed all the way down onto the distributor shaft. I tapped it down so the pick up could see it, bolted the cap back down, cranked the engine and it fired right up.

I tuned the carb, set timing, took it out 3 or four times and it ran flawlessly.

Two weeks ago I backed it in the water, it fired right up and let it idle until the choke was open. Unhooked it from the trailer, put it in reverse and it died. It cranks fine but wont run. It has spark on all 8 distributor post( I keep a spark tester in the glove box).

I pull it home and go try to do some trouble shooting the following morning. I hook the muffs up, bump the key and it fired right up. Let it run for a few mins and figure that's good enough so I headed to the lake again a few days later. Back it in, fires right up, dies when trying to go in gear and won't start again but yet still has spark..

Today I went out to look at in the driveway and the same thing happened.. hooked muffs up, bump the key and it fired right up. This time I let it run for 40 mins, went from forward to reverse several times, free revved it in neutral many times. I'm just at a loss at this point.

Has anyone had similar issues and figured it out or see anything I'm missing?

Thanks

 

[poconojoe]

Here's a long shot idea...
Have you checked to see if it's getting fuel?
Any chance the boat is sitting at different angles at the two different locations and the fuel tank is close to empty? Maybe at the lake, the boat is at a certain angle and there's no fuel near the fuel pickup.
Long shot idea!....

 

[alldodge]

I'm thinking a carb issue. Starts when its cold and on trailer (no load). In the water it needs a different fuel mix, bit more. Unless spark is stopping, then its fuel.

Boat being on the trailer and after its warmed up. If the motor is shut off will it restart?

 

[BattenDownTheSnatches]

Poconojoe- I had the same thought, so after I pulled it out of the water last time i jacked the trailer tongue up as high as I could with a floor jack (it was a steeper angle than when the boat is in the water) and it still wouldn't fire.

Alldodge - I agree it's a fuel issue, Im just not convinced it's a carb tunning issue though since it ran great on the lake for a total of 15ish hours, then boom.. more problems.. also like I told poconojoe, it doesn't restart on the trailer after putting it in the lake. (But it does after being run on the trailer)

I have pulled the fuel filter and dumped it and nothing seems a miss. No junk came out or water in it and it was plum full.

I just spoke with a friend who was a boat mechanic for many years and he suggested I pull the sending unit and make sure the pick up isn't cracked or any thing. But that wouldn't explain why the fuel filter was fuel..

Does anyone see a problem with blocking off the mechanical fuel pump and putting and electric one in place? I'm not very familiar with this old school stuff with mechanical fuel pumps distributor, and carborators. Lol

Keep the great ideas up and if I find the cause I'll share it with everyone.

 

[BattenDownTheSnatches]

Also something to add is the fuel tank is completely full..

 

[alldodge]

(But it does after being run on the trailer)

. It has spark on all 8 distributor post( I keep a spark tester in the glove box).

Need fuel, air,spark, compression to run

Putting in reverse "should not" use the interrupt switch. You said have spark on all 8. Compression does not just disappear, and its not being started in a vacuum, so it has to be fuel

That is unless this might be the twilight zone and Rod Sterling is narrating

 

[dubs283]

Putting in reverse "should not" use the interrupt switch.

unless the lower shift cable is worn, binding or misadjusted

a faulty lower shift cable can and probably will shift properly with no load, i.e. boat on trailer running on muffs. put the boat in the water with a load, cable binds, etc, and engages shift interrupt prematurely/improperly

 

[BattenDownTheSnatches]

Update. It was a combination of me being an idiot and not tighting the dist. hold down tight enough, and my choke not working properly. I ended up tying the choke fully open and setting the timing correctly. I took it out yesterday and it ran flawlessly for the 3 hours we were on the water. The wife and kids even got to go tubing! Lol.

When I checked the timing it was 6 deg AFTER TDC around 650 rpm.. I think a combination of an incomplete burn and the choke not opening all the time was causing it to flood under load and fowl the plugs.

Thanks for the help everyone!