4.3 V6 carb help

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Alvarez1112
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4.3 V6 carb help

Postby Alvarez1112 » Sun Nov 27, 2016 4:05 pm

I have a 4.3 vortec motor with a 350 cfm holley 2-barrel carb that I could use some help troubleshooting. I've had a couple different issues. First has been a stumble on the hit of the throttle, both off idle and if stabbed while on cruise. I've checked the float level and tried a larger discharge nozzle (went from a 31 to a 35) that didn't seem to help at all. Then this morning running out it started running rough at low speed and had fuel puddling/leaking from somewhere, but no visual leak anywhere. All I can figure is that it was pushing fuel out of the vent tube because there was fuel on the tipside of the carb. I'm going to pull it apart and see if anything seems wrong. Anyone have any ideas or suggestions? The motor is stock aside from the Edelbrock intake, DUI HEI with timing locked @ 28 degrees, and the holley 350 with the stock 61 jets and 8.5 power valve
~Chris Alvarez

Johnny's Welding & Machine Works

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glades cat
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Re: 4.3 V6 carb help

Postby glades cat » Sun Nov 27, 2016 5:23 pm

You need to go through the Holley and make sure everything is as it should be. The power valve at 8.5 sounds a bit early. It is not an enrichment circuit, it is intended for wot only. Ball park is 1/2 of idle vacuum. Does it have a 50 cc accelerator pump? How do the plugs look? Look at the ground strap for heat marks. Are 61 jets sufficient? It sounds lean and trying to compensate with the power valve.
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John Fenner
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Re: 4.3 V6 carb help

Postby John Fenner » Tue Nov 29, 2016 11:47 am

Assuming this is direct drive, the 350 is too big for it, I built an adapter to put a small dualjet Rochester on the tbi intake with 1-1/4 pipe down each port to build velocity, it worked flawlessly and snapped the prop up quickly.
However if it is reduction drive, the 350 can be tuned, I would consider an air fuel gauge to see what is going on when it is hesitating.
I never finish anyth,,,.

Alvarez1112
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Re: 4.3 V6 carb help

Postby Alvarez1112 » Sat Dec 03, 2016 8:16 am

Finally had a chance to check it out this morning. I checked the float level once again and no change there. Pulled the plugs and took some photos. This is a DD boat and these plugs have approximately 7 hours of mixed use. Sorry for the size I don't know how to resize in photobucket. Cylinders 1,3,5
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Last edited by Alvarez1112 on Sat Dec 03, 2016 10:08 am, edited 1 time in total.
~Chris Alvarez

Johnny's Welding & Machine Works

Alvarez1112
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Re: 4.3 V6 carb help

Postby Alvarez1112 » Sat Dec 03, 2016 8:19 am

2,4,6
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~Chris Alvarez

Johnny's Welding & Machine Works


hdsadey
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Re: 4.3 V6 carb help

Postby hdsadey » Sat Dec 03, 2016 2:04 pm

Looks lean. The white porcelain should be the color of a brown paper bag if the fuel mixture is correct. What temp is the engine running? A lean engine will run hotter.
02 Predator 12' 0320 Lycoming
92 Big O 12' 302 Ford DD
99 Donzi 16 Classic 350 Vortec

Alvarez1112
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Re: 4.3 V6 carb help

Postby Alvarez1112 » Sat Dec 03, 2016 2:11 pm

Engine has never run over 180* . Usually sits at about 175*
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Johnny's Welding & Machine Works

hdsadey
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Re: 4.3 V6 carb help

Postby hdsadey » Sat Dec 03, 2016 7:24 pm

I just reread your first post. Question, when you say you have the timing locked at 28 degrees, what are you referring too? Do you mean you have it set with zero vacuum advance and zero mechanical advance? I have a stock 302 DD Ford running a HEI distributor and a Holley 500 2 barrel. I have the vacuum locked out and run 16 degrees of mechanical, for a full total of 32 degrees advance at 2800 rpm. I also have my power valve blocked off. I've always understood power valves to be more for cruising down the highway under a load to provide extra fuel. Might have too much power valve under a load and when you stab the throttle the accel pump is flooding the intake choking down the engine.
02 Predator 12' 0320 Lycoming
92 Big O 12' 302 Ford DD
99 Donzi 16 Classic 350 Vortec

Alvarez1112
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Re: 4.3 V6 carb help

Postby Alvarez1112 » Sat Dec 03, 2016 7:48 pm

The timing is locked out as in no vacuum advance and no mechanical advance. The ignition is at 28 degrees from idle to 3000 rpm.
I'm not too keen on reading plugs at this point, but to me the mark on the ground strap seems like it's a little cold, and the mixture looks a little lean, but the carbon on the base ring throws me off a little. Again I'm still learning the whole plug reading thing
~Chris Alvarez

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hdsadey
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Re: 4.3 V6 carb help

Postby hdsadey » Sat Dec 03, 2016 8:51 pm

28 degrees at and idle is way too much initial timing. That will clean the plugs when idling. My suggestion is to unlock the mechanical advance. Idle timing at 12-16 degrees and all in at 3000 ending somewhere between 32-34. The carbon ring is most likely too much fuel at 3000.
02 Predator 12' 0320 Lycoming
92 Big O 12' 302 Ford DD
99 Donzi 16 Classic 350 Vortec


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