Did you remove the tube and replace the other o-ring too?

The dual stage power valve isn't making it run overly rich, something isn't right. The PV doesn't flow any fuel at idle, only from the boosters off-idle.

 

Thanks for the suggestion of a new carb Franklin2, but if I had the $300 for one I wouldn't be here asking how to fix the old one. Also my diagram doesn't show where the check ***** go.

 

Yes Sw1tchfoot; I pulled it out with pliers and put a new o-ring on. I followed the instructions and replaced everything that my kit had the parts for. This kit, being cheap, didn't have new jets or anything that might need replacing in the throttle body itself, just parts for the bowls and new gaskets. Cleaned all I could with carb cleaner. The accel pump passages were clear through the metering block. The accel pump is looseded up now and working well. I basically went from what I was told here was a lean condition, backfiring when punched but with the truck starting and idling well, to a rich condition where it won't hardly run at all just by replacing the PV and secondary diaphram.

 

I would just put the old power valve back in it I guess since I can't think of anything else to check, the new accelerator pump diaphragm may have fixed the lean backfire condition.

 

Can you put the old PV back and see if the black smoke goes away?

 

I guess that's all I can do. Think I can reuse the bowl gaskets; they weren't on very long. Question: Does the accel pump tube split in the throttle body and deliver fuel to both primary "barrels"? When Franklin2 said to look down and check to see two fuel streams I couldn't figure out why two when there is only one mechanical fuel source, right?

 

Also, where is the fuel supposed to come out? From the primary bowl side of carb, or from what I suppose are jets that spray down the middle of the barrels?

 

Yes, Dave meant one squirt in each of the two front barrels.

In the middle of the barrels are the annular boosters.
Those deliver the regularly metered fuel.
The accelerator pump just squirts fuel from the forward side of the barrels.

 

Sorry to keep updating this thread, but I still have issues with my 4180. However, I am learning a lot about this carb.
I pulled the carb again and reinspected everything. Then started browsing this site and others to figure out why I have too much fuel now. Somewhere I read that this engine (351HO) runs from 10-18 in of vacuum at idle. That two-stage power valve is rated 2-12, which means that if I have 10 in of vacuum at idle, the power valve will open and dump fuel in at idle when it is not needed. Went to Advance and ordered a 125-75 Holley single stage power valve (7.5 in) and installed, then had to buy another base gasket as the one I just put on tore when removing the carb. Just put the carb back on, fired right up and idled perfect, punched the throttle and NO BACKFIRE!
Great except for one thing. I again have fuel running out the tube in the middle of the air horn. The last time that happened, I had the float too high. Now I have the float valve down as deep as possible, and I still have fuel running out that tube. I put new o-ring on the exposed end of the accel tube, but left the old one on the end in the metering plate as it seemed tight.
During my research I ran across some rebuild instructions that said to drop the large BB in the kit down that tube. I did't do this the first time I had the primary bowl and metering plate off and my only problem was the backfire. Idle was fine. Should I do this?

 

I wouldn't block the vent tube with anything.
It is there to equalize bowl pressure to atmospheric.
Carburetors work on differential pressure drawing fuel from the bowl into the venturi.
Your float must be hanging up (down) on something.
Check that all the clutch screws in the rear metering block are tight.

 

Isn't that BB an important part?

 

In the secondary vacuum circuit....

Never in the vent tube sticking straight up at the front of the carb.

 

I'm also thinking the float may be sticking. Does the fuel go straight from the bowl into the vent without a valve somewhere? It is already vented out the front into the vacuum system.
Is there a valve in the middle post where the air cleaner wing nut goes? Maybe this is where that BB goes? I know about the small one in the secondary diaphram, it's still in there. If I can find that rebuild step again I'll post it.

 

Yes, the float bowl is directly connected to that vent.
The vent hose coming off the bowl has a check valve, but not the tube intended to vent into the air cleaner housing.

 

The power valve enriches the primary circuit. Not the idle or transition circuit. You can wire a power valve open and the engine will still idle fine if everything else is okay. If the power valve is blown, that fuel travels through it and causes problems even at idle.