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Discussion Starter #1
OK next question, at 4,400 RPM's my engine bogs down then I let go of the gas and the motor climbs to 4,500 RPM. problem just started and the carb is 670 CFM so the flow should be good
 

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My Engine Bogs At 4400 RPM

OK next question, at 4,400 RPM's my engine bogs down then I let go of the gas and the motor climbs to 4,500 RPM. problem just started and the carb is 670 CFM so the flow should be good
It sounds like your engine is getting too much air. What kind of carburetor are you running? It sounds like the secondaries are opening way too soon.
 

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A friend of mine had a similar problem turned out his exhaust became plugged with rust. You could also have a fuel delivery problem. Check your fuel flow rate and for a restricted exhaust. :food-smiley-019:
 

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Bad Bog At 4400 RPM

A friend of mine had a similar problem turned out his exhaust became plugged with rust. You could also have a fuel delivery problem. Check your fuel flow rate and for a restricted exhaust. :food-smiley-019:

He claimed the problem just started so I'm wondering what he did to cause it. If the problem started the moment he bolted on his new carb then it is most likely carb related.
 

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Discussion Starter #7
sorry I didn't explain my situation, the carb. has been on the car for 5-6 years (I rebuilt it a year ago) and the problem just started after it was parked 2-3 weeks because of the fuel tank leak and everything in the tank is new.
 

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sorry I didn't explain my situation, the carb. has been on the car for 5-6 years (I rebuilt it a year ago) and the problem just started after it was parked 2-3 weeks because of the fuel tank leak and everything in the tank is new.
If that's the case then start back at the tank just cause it's new doesn't mean it's right. It could be as simple as a clogged filter, a pinched hose, missing vent, etc.... You may have contaminated the fuel system downstream of the tank. If the tank was leaking , it was probably badly rusted.
 

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Discussion Starter #12
OK X3 makes me want to change the filter
but still could the carb be to big for the engine at full throttle the engine bogs down but at 3/4 throttle the engine works fine @ max RPM's
The easy fix would be don't step on it so hard but I want to know why
 

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more power at less throttle opening usually means fuel delivery problems-i agree, check the filter first, as well as the fuel pump,lines,etc....or you could have an internal carb problem too. good luck, i know its frustrating when it takes awhile to figure something out.
 

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Loses Power At 4400 RPM

It's very possible you have a spark escaping from one of your wires at that particular load. Do you have hedders? Are any of the wires real close to one of the tubes?
 

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Discussion Starter #15 (Edited)
It's very possible you have a spark escaping from one of your wires at that particular load. Do you have hedders? Are any of the wires real close to one of the tubes?
no headers and the spark plug wires are new, last time I checked they only had oil stains
I will check the fuel pressure at high RPM's how many pounds should it have? around 14psi
 

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sorry I didn't explain my situation, the carb. has been on the car for 5-6 years (I rebuilt it a year ago) and the problem just started after it was parked 2-3 weeks because of the fuel tank leak and everything in the tank is new.
If the carb wasn't to big before wouldn't figure it's to big now still sounds like a filter, or maybe a malfunction in the carb.
 

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is it bogging , too much gas , or leaning out ?
there is a huge difference
what do the plugs look like ?
post a good pic of a couple and I can read them for you
 

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If it is a 350 then a 670cfm should not be too big. You might want to have an old drag racer check the cams and springs that control the opening of the secondaries. Small changes in spring rate or cam lobe can make drastic differences in the way that the flow of the air and fuel will mix.
 

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Checking Your Fuel Pressure

Put a tee into your pressure line and then run a hose and gauge up to your windshield. Then duct tape the gauge to your windshield and then take it out for a drive. The gauge should show 4-1/2 to 5 psi under all throttle conditions. If it doesn't show that much you have a fuel delivery problem of some kind. Old hoses sometimes will suck shut so check out your hoses (or simply change them). Also there is the possibility your nylon sock filter in the tank is plugged.

By the way, the only thing that happens when a carburetor is too large is you lose some of the "driveability" of the car because of the larger primaries. A 350" engine that has 100% volumetric efficiency can only swallow 608 cfm at 6000 rpm. But a stock engine is usually is about 75-80% volumetric efficient which means it can only swallow 460-490 cfm at 6000 rpm. And only 370-390 cfm at 5000 rpm. That's why the Rochester Quadrajet was so outstanding. It would flow up to 780 cfm but ONLY if the engine needed that much as it had an "air valve" secondary (like the Carter AVS series). So it could be used on anything from a little 6-cylinder all the way up to a 454".
 
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