283 SBC suddenly running rich and sputterin - Hot Rod Forum : Hotrodders Bulletin Board
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Old 09-19-2008, 03:29 PM
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283 SBC suddenly running rich and sputterin

Hey guys my old work truck has been actin strange the past couple weeks. It is a 283 SBC in a 1980 C30 pick-up. The motor was built in 1996 but has relitively low miles on it, I think its around 45,000. I can't remember what all they did it when it was built, but i know they put an aftermarket cam in it. Have no idea what size though.

Anyway, its a 283 bolted to a SM465 tranny, and i think the truck has 456 gears, but thats just a guess. I know they're really low for towing. The past couple weeks It has started smelling of gas really bad at idle, and when i come to a stop at operating temp it sounds like the choke is staying on. The carb is a holley 600cfm 80457 electric choke.

I can deal with the smell and high idle but when i get on it at all, like take off up a hill for example it really goes to sputterin and almost "belching" back through the carb in second gear. First gear i can get on it as much as i want and it's fine. but second I hafta just barely give it any gas or it does this. Third is fine as well. Also there are times that when i get on the brakes hard to turn or stop suddenly the truck will just die completely. It wierd cuz I thought it was just the choke causing this stuff from being stuck on, but sometimes the choke doesn't stick on and it still does it. Does this sound like a vac. leak or running to rich or what. thanks
Danny

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Old 09-19-2008, 03:36 PM
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Sounds like the float level is too high when you say hitting the brakes can kill the engine.

That would explain the rich fuel smell. Take a peek at the float levels and ensure you've got no junk in the needle & seat, maybe it's pouring fuel down into the engine.
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Old 09-19-2008, 03:56 PM
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If the carb checks out okay check the ignition for weak spark.
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Old 09-19-2008, 05:23 PM
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Float level

Don't most holley's have a sight glass to set the floats?? This one doesn't have one, It has the adjustment opening with a either 9/16 or 1/2 inch nut (not sure unless i go look) with a flathead screwdriver slit in the top, but no sight glass. Its on the top of the carb though. I thought most holleys were on the side. My double pumper is on the side, and i always set the float to where gas just quits running out of the hole onto the intake, and it runs fine but i'm not sure how to set this one.
Got any ideas?? This truck also has hydraboost brakes too, but i dunno if that will affect anything or not. I'm not to familiar witht hydroboost brake systems and how the pull on the engine. Is it similar to a regular vacuum brake system??
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Old 09-19-2008, 07:32 PM
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Most holley`s have it on the side of the float bowl, you remove the screw and set it at the low side, pretty simple.
I mentioned ignition issues in my before post, and why is due to many carb problems can be ignition problems that diagnose the same as carb problems.
Is there a fuel pressure gauge present? if so what is the fuel pressure?
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Old 09-20-2008, 05:15 AM
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Ignition and fuel pressure

Yea, the fuel pressure is steady at 5 PSI. Spark is very strong and i have no reason to believe the timing has changed. The motor idles great and will rev just fine with no load, and even in first gear i can hammer it and it doesn't miss a lick or sputter at all, its only under hard acceleration in 2nd and 3rd gear.
I double checked the location of the hole for the float and it is in the top of my carb. Mine has no holes or screws in the sides of the float bowls. Is adjustment still the same on these? It really smells and acts like its getting to much fuel, i just don't understand why it just now started this outta the blue. Then theres the issue about the dying under hard braking that. You say you think these are both from the same root cause?? the float level??

what about the choke? I know this truck, and it has never ran like this before. It has always been a little cold natured but not this bad. Like i said previously, the choke is staying on even when the engine is at operating temp. It will actually be on when I leave the house, kick off in town when i'm driving slow and sitting at stop lights, then I have a 4 mile stretch of open highway to work and by the time i get there its back on again. It almost seems like the choke thinks the engine is cooling off so much at hwy speed with all that air circulation that it needs to choke it. I was just gonna unplug the electric choke but its really hard to start with it like that. Have you ever seen an electric choke do this before?
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Old 09-20-2008, 06:59 AM
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bad power valve.

get a 6.5
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Old 09-20-2008, 07:23 AM
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Quote:
Originally Posted by 454C10
bad power valve.

get a 6.5
X2 !!

tom
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