92' Mercruiser 7.4L Won't Idle
 

Hello, me and my dad are in the process of restoring a 1992 Wellcraft Corsair 35'. We are in the process of trying to get the engines to run, but have had minor success these past few months. They have run before, but stalled often and backfired a lot. We put new carbs, fuel filters, new plugs, new rotor and caps, new ignition sensors for both engines. The carbs are Rochester 4BBL Quadrajet w/ electric choke just installed lady week. Since then, the boat has barely been able to idle, unlike the last carburators. We would have kept the last ones, but they were leaking fuel everywhere. Anyways, today I tried tuning the choke and preliminary idle air/fuel screws. I first did the choke by loosening it, turning it counter-clockwise until the secondary choke was barely closed with some spring, on both engines. I also did the idle screws by lightly seating them, then loosening 2 turns. As of now, the port engine will start if it is given some throttle and idled at 1500. And the port is not starting at all. I'm not even slightly familiar on how to tune carburators, but I have followed the matienence manual to a tee with no luck. I have no clue where to go from here. Any help is greatly appreciated!

You didn’t hook the power wire of electric choke to the ignition coil, did you ? Is anything else hooked to coil ? Is there 12volts at ignition coil + ? Is there 2 purple wires there or ?

How long did this boat sit ? Did you do a fuel sample ?

If timing or something else in ignition is off, tuning a carb is meaningless.

I did hook the electric choke to the ignition coil, on the positive terminal. I see one purple wire, so the terminal on the ignition coil now has a purple wire, the electric choke, and one other wire I can't remember where it goes. All fuel was drained when we got it. It was used 2-3 years without any matientence done to it, and then 6 months sitting. It has a new fuel pump, fuel filter, most ignition components have been replaced, and batteries are good. I need to check for 12v, I'll be at the boat later today, so I'll check that first. I have a timing light, but obviously I cannot get it to idle properly, so checking it is tough. My father worked on the ignition stuff, is there any way I can check if any timing was thrown off there? Thanks for your help so far!

what ignitions are you running, tb ? what gen

Thunderbolt IV

Look for an ‘S’ terminal on back of alternator. If it has one, use that for the electric choke. Note: alt needs to see engine rpm over 800 to energize this circuit. Once this happens, idling under thisrpm’s, it stays energized. So, each time engine is started do a quick rev to over 800 rpm.

Also ck grounds to ign module/amplifier and also the one to the distributor. Very important they are hooked up and in good condition !


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Gotcha, I'll be heading up to the boat in minute so I'll keep in touch. Does the electric choke need to be grounded?

Thpically grounds thru carb which should ground thru intake which shoukd ground thru heads……etc,etc.

Shoukd is a big assumed word. Lol.

Easy enough to check with a $7 test light

Good point, I'll bring some electrical tools down there and start probing around and see what's up.

It won't let be send pictures, but there is no s terminal on the back of the alternator, just a wire for the starter, a blue wire that goes to purple, a red/purple wire, and a few black wires. Just checked and carb is grounded.