new 4.3 vortec stalls out when coming off of plane

S

stang32

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Joined
Jul 17, 2004
RO Number
14425
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i just installed a 2000 4.3 vortec engine with thunderbolt V ignition system. set the timing to spec 10 deg BTDC by grounding the purple wire according to the manual.
the engine runs smooth, idles nicely & gets up with ease.
the main issue is when slowing down to or near idle, the engine stalls. when restarting it, the engine cranks as if the timing is off, cr,cr,crank,cr, cr, crank, etc...but does restart.

i thought the stalling issue was bad gas, I drained it this weekend & installed fresh gas but the problem remains.. I know that bad gas will not make it crank like this so I think the issue is something else.
 
What outdrive is this engine attached to? You might want to look at the shift interrupt adjustment.
 
its not the shift interrupt, i an not taking it out of drive,I am only slowing down to idle speed
its an alpha 1 gen II,
 
Not sure if they ever fixed it, but the 4.3 had a bad habit of running hot. Slowing down slowly allowed the engine to cool down. See if that helps.
 
Is this a carb or fuel injected? It could be a clogged vent or a vapor lock.
 
Is idle in N set to 650 RPM? Carb idle mixture a scosh too rich?
Is alternator output voltage low (below Thunderbolt requirements) prior to stall and are there other substantial current draws when it does stall?
Temps remaining normal and attainable WOT well into the 4400-4800 spec range so it's not loading up from excessive prop pitch?
Low oil pressure at warm/hot idle or possible failing oil pressure alarm sensor?
Are the plugs oily or fouled with fuel or steam-cleaned? Any steam in the exhaust, or fuel sheen in the wake?
Not sure , but I believe a sufficiently maladjusted Alpha shift interrupter switch can cut ignition out when reducing throttle to idle without attempting to reach neutral. But if that was the case shifting would likely be noticeably harder.
 
Might have to set idle to 750 or even 800. What's the RPM when in gear and idleing.
 
As Sandy said, it could still be the shift interrupter if it is far enough out of adjustment.
 
just a little follow up, I rebuilt the carb with excellent results.
no more stalling on deceleration,.
thanks to all who posted
 
Great News and Thanks for posting your results. Too often, we're left wondering!
 
Pretty sure the earlier 4.3 mercs shipped with a Webber carb. That's what I had on my old Bayliner anyway...

Adam
 
its is a mercarb. the donor engine was a 2000 mercruiser, genII w/ thunderbolt V ignition
 
Speaking of MerCarb's, http://www.boatered.com/forum/topic.asp?TOPIC_ID=165822 indicates that a MerCarb may be a Rochester, or a NIKKI, or maybe something else. The OP on the thread is still searching for a Power Piston (pix included) for his MerCarb/NIKKI if anybody can help. We had a Pacific Rim carburetor on a Mitsubishi pickup truck. It was a MIKUNI, which I believe is Japanese for Nightmare.
 
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