engine will not rev past idle

[thestigmach1]

I recently built a 350 for my boat with agressive cam and intake. Ive done similar builds many times before. Intermittently it will not rev past idle. It just sits and makes a chugging sound. The tach drops to very low rpm even though I can hear the engine is not that low. Sometimes it runs great sometimes it does this. I cannot find any air leaks in the intake or carb. Seems to be worse when engine gets hot. I triple checked that all the wires are in the correct order. Im using a high energy msd coil. Had it running on muffs earlier and ran fine for nearly 30min at 2k rpm then took it to the lake finally for the first time this year and it pulled this mess again.

 

[Bondo]

Ayuh,...... Are ya sure it's gettin' a good solid fuel supply,..??

On the muffs means little,..... No load on it,.....

 

[thestigmach1]

Ayuh,...... Are ya sure it's gettin' a good solid fuel supply,..??

On the muffs means little,..... No load on it,.....

Sorry I thought I posted a reply but apparently it didn't go.. I didnt even get so far as to have a load on it in the water. Didnt even leave the trailer that go. Took it out again last night ran good for about 10 min then stopped to make an adjustment to timing, left motor running it just felt a bit off under load, and when I tried to go again it would not rev past idle. I put the dizzy back where it was no change. When its doing this the tach drops to very low rpm and the voltmeter is showing less than normal voltage like theres a heavy load somewhere.

 

[Camaro4life18]

Voltage drop is probably from alternator at low RPMs, more of a symptom than the problem. I'm having a similar issue with my 4.3L TKS, and it seems like fuel starvation. In all my troubleshooting I found a loose connection on the gas tank hose causing the pump to suck air. Didn't completely fix my problem, but something for you to check.

 

[thestigmach1]

Tried dumping small amounts of fuel down the carb when its having its issue and no change. It should come out of its issue at least momentarily by adding fuel if its a lack of fuel. Replaced coil with new coil thinking it went bad and starts to overheat. As long as I dont let off the throttle itll stay running with rpm but lack of power once hot.

 

[thestigmach1]

I'm getting 7v at the coil when motor is hot. Could a bad ignitin module, thunderbolt iv, cause this? Or do I need to look at the sensor inside the cap