Need Advise Please
 

Have 454 Mag Gen VI in my boat. Need some help to get it running right again.

The back story...

Two summers ago we were cruising down the river and the v-belt on the alternator broke. Naturally the engine started running like crap because it wasn't getting the voltage it needed to keep the spark plugs firing. I looked down at my gauges and saw the temp gauge was at 200 so i shut the engine down immediately. Opened the hatch and some how the broken alternator belt slung off and knocked the raw water pump belt off in the process. This whole situation unfolds in the matter of 20 seconds. A couple of weeks later I get in the boat and replace the belts, got everything back together, go to fire it up and it takes forever to fire up. I get it running and as soon as I try to give it gas it "pops" out of the carb causing it to kill. I decide to play professional mechanic and start digging into the engine. Took the carb, port side exhaust, valve cover, distributor and the intake manifold off to see if anything stands out or looks broken. Everything in there looked to be ok. No push rods were bent, no lifters or rocker arms were broken. At this point I'm at a lose and lose interest in the boat, it sits for 2 years.

Fast forward to 2 weeks ago. Got back in the boat put new intake and exhaust gaskets. Took all the plugs out rotated the engine to TDC put the distributor back in, put new plugs, put the plug wires back on. Quadruple checked that the wires are going from the post on the distributor cap to the correct cylinder. Rebuilt the carb, made sure the floats are set correctly. Squirters are working properly. Got the engine to fire up but it is still very hard to start when cold and it still pops out the carb when trying to accelerate and will not idle.

I know that the popping out of the carb normally indicates a lean condition but after letting it run for a while, I pulled the spark plugs and they were pretty black indicating a rich condition. I personally think it's an ignition problem, but I'm no mechanic.

Any advise or help is appreciated.

Thanks

Start with basics. Change spark plugs, cap and rotor and fuel filter.

Already did the spark plugs and fuel filter, need to do the cap, rotor and plug wires. Any suggestion on where to get them from for a good deal?

Thanks

Sounds familiar. I had msd ignition. Put the old HEI back in place, it worked fine. BOTH ENGINES!

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Did you pop a cap off of a vacuum nipple?

Thanks man. Mine did the running like a tractor sound too. Sounds almost like the exact same issue. Now I have to decide if I should rebuild the thunderbolt or order the HEI. What would you recommend?

Put an HEI in even if it's an automotive cheap one just for starters to see if it's your problem. Or borrow one from a friend etc. If it fixes your problem then go from there for replacement. You don't think it jumped timing do u? Might be a long shot but otherwise your fuel vent. Maybe remove your fuel cap.

No but the vacuum nipple was never plugged and it ran fine before.

EDIT: Sorry read that wrong. The distributor never had the vacuum port plugged. The carb base plate and metering plate have good plugs on them.

Also how did you find TDC? When I bought my formula they found it on the wrong stroke and it was all whacked. Re did TDC and distributor. Ran like a champ

Took all the plugs out. Cranked it by hand with my thumb over the #1 cylinder spark plug hole till the cylinder pushed air out of the hole. I knew it was on the compression stroke by doing that and used the timing mark on the balancer from there.

Might see if I can find one that will work at the local auto parts store. Like I said before I'm not a mechanic but I'm pretty sure it didn't jump timing. Not going to rule that out completely though. Going to run it with the fuel cap off when i get home.

using clean fuel? Not the 2 yr old stuff?

It's the old fuel but it was doing the same thing when the fuel was new. I would like to get the old fuel out though. Can I use the electric fuel pump to get the old fuel out? There's about 30 gallons in the tank. Don't want to burn the pump up.

I would buy a used separate one to do that. Not real difficult.

Get the old fuel out, run it in your lawnmower. Fill with non ethanol 91, new fuel filter and some sea foam. Bet it clears up your problem. 2 year old fuel could have phase separation.

did you roll the engine over while having the valve covers off to confirm consistency of intake and exhaust valves? Is it possible to have a lobe or two or lifter wiped out? Vacuum leak somewhere? Where did you set timing? Distributor gear look good? Last resort pull timing chain cover and make sure your marks line up.

try replacing the coil.

Do a compression test. You probably burnt a fire ring (headgasket) between two cylinders.

Right on. I meant to mention that earlier also. Good call.

Thanks for all the suggestions guys. Got most of the fuel out. Went to the local auto parts store and picked up a hei distributor. Got home to put it in and it wouldn't work without splicing wires so I returned it. Going to order the parts to rebuild the thunderbolt. The sensor in it was rusted and nasty. The coil was the same way. Going to get that and new plug wires to see where that gets me. Hopefully that'll get it running right. If not those parts look worn and rusted and probably will go out soon anyway. Going to order the parts this weekend. I'll get back on when the parts come in.

Thanks

Well guys the new coil, sensor, rotor / wheel, and distributor cap did the trick. Thanks for all the suggestions and support. I appreciate it... now anyone looking for a boat? Got one for sale!

glad to see you got it sorted out.

Glad to see it was relatively inexpensive and you had no internal issues. Process of elimination and begin with the basics. Good call.