1996 4.3 lx thunderbolt iv ignition problems.

[Scottcanser]

Hi guys, I'm new to this forum and new to boating. I purchased a 1996 Chaparral 1930ss. 4.3lx with thunderbolt iv ignition. The first few times out had no problems. The last time out, after about 20 minutes of running at about half throttle, the engine started running rough. Could only run at about 1000 rpm. Any more and the engine would die. It would start right back up and idle fine but under load it would try to shut off. Any ideas as to where to start looking? I changed the fuel filter, no joy.

 

[Chris51280]

there is possibly another filter inside the carb where the line comes in. my 2 barrel carb is build like that. check that too. sounds like fuel starvation. clogged jets. Clean your carb out possibly.

 

[achris]

That sounds like a carb problem. Pull the carb, strip and clean it, see how you go.

(Me being me, I'd run a compression test, check the timing and spark plugs, and all that sort of thing too).

Also worth checking the coil for a corrosion hole on the bottom. The coil is in a bad spot, and any moisture can drip to the bottom and corrode a hole. All the oil leaks out, the coil overheats, and you have exactly the problem you have. That said, coil problems are VERY rare. But it is worth a quick check. Put your hand on the bottom of the coil. If it comes back oily, or you feel a corroded hole.....

Chris.....

 

[Scottcanser]

Thanks for the information gentlemen. It gives me a starting point.

 

[JoLin]

If your distributor cap is OEM Mercruiser, pop it and take a look at the contacts. Merc stopped brass-plating them and I had one cap corrode after a single season. Sierra still coats them and that's all I use now.

My.02

 

[Scottcanser]

It's weird. If it sits for an hour or so it will run fine for about 20 to 30 minutes. Then it acts as if it's fuel starved. Shutting of under load etc. When it shuts off it will start right back up. But if you put a load on the engine it will shut off. I can limp back to port at a little above idle.

 

[bman440440]

check your fuel tank vent line.... all you have to do for that is once it shuts down under load open the fuel fill cap and restart the engine... if it runs fine then all you have to do is fix the clog in the vent line