Rough idle and occasional hesitation and misfire

If I remember right, this also happens to Paul
Evaporation in the fuel line when hot and sitting. He vented it and it cranked right up?

Zach, didn't you tell Paul to do that?

Come on Pete, get with it!

Gt40= multi port efi, not sure what you're thinking with the ei conversion and ballast resistor talk.

Heat soak/vapor lock is largely overstated on carb'd engines, but it IS a problem on early multi port marine engines- such as this first-year, pre-FCC Gt40. Paul has had the same issue, and I've experienced it on an early multi port Mercruiser. I suspect that is what is going on here. I believe adding the FCC is the fix, there may be more info in the GT40 troubleshooting thread.

I have never experienced this problem with mine, I wonder if it's because my engine sits in a much larger vented compartment compared to a DD? I also wonder if the engine has a low pressure pump? It was my understanding when talking to a PCM rep that they added them to address that issue. Might be worth the effort to raise the engine cover when parked to see if it helps.

phatsat67 wrote: Toertel wrote: If I remember right, this also happens to Paul Evaporation in the fuel line when hot and sitting. He vented it and it cranked right up? Zach, didn't you tell Paul to do that? I think that's how we got it started fast Seb. I was probably several beers deep by then ha. I let Paul get gas all over his hands while I cranked it ha.

So there ya have it, it's either beer and gas on the hand or buy and add the FCC (500USD cost for the FCC buys a ton of beer...just saying)

No I am not. I was told the low pressure pump was not originally in the system. It was added when PCM started having vapor lock problems. This was from the PCM rep I met last year at the Miami boat show. He said it was tough adding the pumps when in the engine was in the boat already. I wonder if there was a recall and some boats might not have a LP pump. My boat does not have a plug on the LP pump like many I have seen, it is hard wired. Wonder if it was added later?

All of the early stuff was hard wired gt-40 or not. The plugs were on the carter pump. The new pumps have non removable wires in place of the old style plugs hense the deutsch connector you see now days. Every pump I've seen on older boats is the plug on pump style even in carb boats.

Gary, if yours has butt connectors and the pump shiny gold instead of black it's probably been replaced with a newer unit. If it looks hard wired and original it probably has 90 degree booted connectors on the bottom they push on to electrical nipple connectors. If not I'm lost

absolutely

BUT, there's other things you need to check first

fuel pump relays are good
that tube inside the FCC is not cracked

^common GT-40 problems

Yep looks as if. They always painted them in the motor even back in the carb days. It's sort of a pain to hard wire them rather than use the plug.

I went through this methodically last year right after getting my 96 SS. I started by venting the fuel line at the Shrader valve (relays were both good) letting air out. I replaced the LPP and the problem went away. When they start to go, they act up by losing pressure when they get warm.

There are other potential causes, but this solved the problem for me.

Yes it is a shi7 job to switch them to the Deutsch
Connector. I was happy when finished.