Backfire thru carb
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Junior User
Joined: Nov 2011
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Okay, I pulled the front bowl off again, and everything seems to be fine. the float is not stuck, and the valve seems to be working. So where is the excess fuel coming from? Even if fuel was filling the secondary bowl and passing down the transfer tube to the front it still has to go through the primary valve. I'm at a loss. The only thing I can think of is the float itself is bad as is not rising to shut the fuel off. I am checking to see if the float can be purchased separately.
Also checked the o-ring on the valve, looks a little flat. Am installing a new one with a fresh o-ring.
Is it possible that the float is working but the fuel is just finding a way through the metering block and coming out the vent? The mystery continues.....
Also checked the o-ring on the valve, looks a little flat. Am installing a new one with a fresh o-ring.
Is it possible that the float is working but the fuel is just finding a way through the metering block and coming out the vent? The mystery continues.....
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Sw1chfoot, I'm confused. You said that with a wired open PV the engine will still idle fine if everything else is okay. Then you said a blown PV will let fuel travel through it and affect the idle. Isn't a blown PV "open"? therefore in both cases fuel is passing through the PV? How can one case affect the idle and the other won't?
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Just noticed something else. The bowl inlet valve has an open slot below the threads, then the o-ring, then another open slot where the needle tip is. If the upper slot is below the threads in the bowl casing, won't fuel be admitted into the bowl regardless of where the float is set?
pedant
Joined: Jan 2008
Posts: 23,576
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From: EXTREME southwest CT
It's always a good idea to change out both the needle and seat when you have flooding problems.
Both are included in the 3-1346 rebuild kit I suggested.
Floats are available separately.
In the MTBE days I shied away from nitrophyl floats. P/N 116-1
The brass ones don't like methanol, but seem to be okay with ethanol. P/N 216-1
Here are the adjustment instructions.
http://www.holley.com/data/TechServi...Carburetor.pdf
Here is a pdf from Holley describing the powervalve system.
http://www.holley.com/data/TechServi...wer_valves.pdf
Both are included in the 3-1346 rebuild kit I suggested.
Floats are available separately.
In the MTBE days I shied away from nitrophyl floats. P/N 116-1
The brass ones don't like methanol, but seem to be okay with ethanol. P/N 216-1
Here are the adjustment instructions.
http://www.holley.com/data/TechServi...Carburetor.pdf
Here is a pdf from Holley describing the powervalve system.
http://www.holley.com/data/TechServi...wer_valves.pdf
Old School Hot Rodder
Joined: Feb 2006
Posts: 6,472
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From: Exmore, VA
Backfire thru carb
Just noticed something else. The bowl inlet valve has an open slot below the threads, then the o-ring, then another open slot where the needle tip is. If the upper slot is below the threads in the bowl casing, won't fuel be admitted into the bowl regardless of where the float is set?
pedant
Joined: Jan 2008
Posts: 23,576
Likes: 38
From: EXTREME southwest CT
Sw1chfoot, I'm confused. You said that with a wired open PV the engine will still idle fine if everything else is okay. Then you said a blown PV will let fuel travel through it and affect the idle. Isn't a blown PV "open"? therefore in both cases fuel is passing through the PV? How can one case affect the idle and the other won't?
In fact one test is to turn the idle mixture screws in all the way, if it still runs the powervalve is likely blown.
Properly functioning, the powervalve should never open with that much vacuum present.
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I don't think the PV is affecting my idle. I put in that new 7.5 and the running rich issues went away (stumbling, black smoke, etc.). It was definitely the two-stage PV that my truck just doesn't like. Now, it starts and idles fine, I just have a gusher out that vent tube with it running fine, albeit a little rich. The two-stage PV may work but I would have to make lots of adjustments to the idle and main mixture screws that I don't want to do. Going back in with the same PV meant that I shouldn't have to touch those screws at all since they were preset for my truck. And from the way it's cranking, idling, and revving, I believe I'm right. The two-stage valve I put in was new in the kit, and I believe it was functioning properly. I think that my vacuum at idle was below 12", thus opening the valve prematurely and dumping too much fuel. Don't have that issue any more.
pedant
Joined: Jan 2008
Posts: 23,576
Likes: 38
From: EXTREME southwest CT
If you have only 12" at idle you have much deeper issues than a powervalve.
My truck pulls 20.
My truck pulls 20.
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Yes, I may have. It's got 50k on a rebuild. 85Lebaront2 you gave me a thought. Maybe all I have to do is make sure the valve is up enough, then BEND the float to set the approx. level. Is this ok to try?
pedant
Joined: Jan 2008
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From: EXTREME southwest CT
These Holley's adjust backwards from what you might expect.
The 'locknut' is your float setting, the screw locks it in place.
Always set the dry height parallel to the top of the bowl as LeBaron explained, before installing the float bowl.
The 'locknut' is your float setting, the screw locks it in place.
Always set the dry height parallel to the top of the bowl as LeBaron explained, before installing the float bowl.
Old School Hot Rodder
Joined: Feb 2006
Posts: 6,472
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From: Exmore, VA
I'm going to ask the burning question. Do you really understand how a carburetor works? ArdWrknTrk is correct, on a Holley, with the proper needles and seats, the screw locks the setting, the nut is for adjusting the level. On the primary (front) barrels, after making an adjustment, particularly to lower the level, I usually run the engine up about 1500-2000 rpm for a bit to consume some fuel. On the secondary side, I usually loosen one of the two bottom screws and let it dribble onto a rag after making an adjustment down. Only go a little at a time, as you lower the level, the float pushes the fuel out of the way raising the apparent level DO NOT BEND THE FLOAT!!!!! If you don't know what you're doing, find someone who does. Unfortunately, most "mechanics" today aren't old enough to understand carburetors. God help you if you have something with breaker points.
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When I first started this troubleshooting, I knew nothing about carbs at all, except how to adjust the choke. After removing carb and tinkering I have learned a lot. My main problem was that there are few moving parts but many fuel passages that I only recently found a schematic for, all vacuum operated which takes me some time to digest. Thanks to many of you I have solved my initial problem (no fuel to carb) and the backfire problem (blown PV), and now am close to getting it right. Truck is cranking, idleing, and revving, so I'm almost there.
I understood how the adjusting nut and tightening screw work the first time I had the bowl off. I have done the dry setting again and will reinstall and let you know how it goes. Thanks.
I understood how the adjusting nut and tightening screw work the first time I had the bowl off. I have done the dry setting again and will reinstall and let you know how it goes. Thanks.
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