i tried to get my 80 f250 with a 351M to pass inspection the other day, but she was running way too high on the HCs, somewhere in the 650 range where the legal limit is like 250. so i paid the failed inspection so i could get a nice 30 day waiver. the next weekend i drive out on the highway a good 25 miles to the flea market and on my way back i decided to get it tested on the HCs again. this time it was somewhere in like the low 300s for the HCs. the guy at eh inspection said that the carb was a aftermarket one(its a holley 2 barrel 500 cfm) and that could be one of the reasons that its doing that. im fairly automotive able( i replaced the waterpump, alternator and changed al the belts and fluids bu myself). is there a quick fix to this, or is this something seriuse?

 

It could be all kinds of things. I have a pseudo friend that tried to get his car inspected that he hasn't drove in a year without replacing so much as the gas. Guess what, it failed. New gas and it passed. OK, now that we had a laugh.....

Could be a sticking EGR valve which is very common. They can be taken off and cleaned. Just take it off and spray the heck out of it while exercising it up and down to knock off all that nasty carbon build up. YOu can be kind of aggressive if need be on the tapered part that slides in and out of the seat. Just don't ruin the rubber diaphram. You need to be careful with that and not spray it or scrape it, poke it etc. Your just trying to get that tapered metal part clean.

If the mechanic is sure it is the carb, you can try and rebuild it if you know what you are doing as leaky seal and seats will cause it to run rich and lope. Most kits are around $30. Just make sure your work area is clean as a surgery room and you clean the carb really well before opening it up. Cleanliness is everything with these. I usually clean the heck out of it, then let it soak over night and clean it again before starting. You will go through a lot of cleaner before you are done because the insides are going to be all varnished and need cleaning too.

I wrote like I did at the beginning to make a point not to skip he obvious. Out here in California, they are strict on the air standards so I always clean my EGR, put in fresh gas, change my plugs, cap/rotor and oil and it flies through every time even though I replaced my double Cat stock setup with a Magnaflow single high flow one. It isn't even close. I could smog up 2-3 times as much and fly through though I do have EFI which burns a bit cleaner.

If you are in a hurry, you could always just change plugs, cap and rotor then throw on a brand new carb since they are fairly cheap now days. $100 will get you decent small carb that should be good out of the box. A rebuild kit will run you anywhere from $25 to $50 depending on what carb you have now.

As to what could be wrong with the one you have, leaking seats, accelerator pump seal or if it is one of those cursed unbrella float models, those possessed things are always getting dirt stuck in the float which causes it to stick and floods the heck out of them.

Good Luck,

Lee

 

ok... your hc's are high because it's running rich. Figure out what jets are in it, and drop down one size. Also, on a Holley carb there is thins thing called a power valve. to get the correct poer valve, first you have to set your air fuel mixture at idle to the highest vacuume possible... then take that reading and divide it in two (if you have 21 inches at idle, you need a 10.5 power valve) this valve is installed on the back side of the main metering plate. Both the jets and power valve should be available at any reputable speed shop. You might want to get the bowl and metering block gaskets too while your there.. sometimes they do tear when your doing changes. Another possibility is the float height. If it's too high, it will also give you a high reading. to set the float height, you must remove the sight plug on the side of the float bowl. Then with the engine running (unless you have an electric fuel pum where in that case, just energise the pump)you adjust the float to the point where fuel is ALMOST running out of the hole... it may be hard to get this proper if the engine vibrates at all but take your time and you'll get it. To adjust the float height, on the top of the float bowl, there should be a blade screw and a 5/8 nut.... loosen the screw and turn the nut (clockwise lowers and counterclockwise raises) then tighten the screw back up.
In all honesty, there should be no reason why the HC's are beond legal limits if the carb is tuned properly...if anything, you shoule be passing with flying colors. A Holley carb, when set correctly, should pass any smogg testing, less it's not 50 state legal, but I'm guessing you already knew that.
As a last resort, there is a book available on Holley carburetor tuning.
have funs and happy motering!!!

 

My RV fail idle emmisions I put RXP to clean out the HO but the instructions were very poor and it failed. I ran the truck for 40 miles+ on the second tank without the RXP and it still failed.

Previous owner had the carb (holley) rebuilt but could never get it to run right. The rebuilder was not the installer and they blamed each other without any resolution...

Recently I changed the plugs and verified the gap. Now the truck is suffering for power. It runs poorer now than before the changed plugs. The only thing I can think of is that I may have crossed a sparkplug wire. I can't image when I changed them one at a time.

Does anyone know of the firing order for this 460? Do you think new wires would help, I will change out the Rotor and Cap. Any suggestions?
I need this inspected so I can sell it, I am done with carbs and my other 95 RV- 460 EFI runs like a top!

 

I had the same problem with my 351W. I screwed the jets in and then backed them out only 3 turns each. I put a can of that emissions testing fuel treatment you can get at autozone, filled the truck up with good gas and drove about 30 miles. Then it passed just fine. This was all done after three failed attempts. Good luck.

 

Thanks, I'll have to take it to a mach. Is it true too refill using low octane gas to reduce the unburned gas. The testing center told me this.

 

With HC failure,I would look for anything that would cause a misfire.Vac leak,timing,plugs,lean condition,etc.
With CO failure,Rich condition,too much fuel or not enough air.
It doesn,t look like you are that far off.Always make sure the cat is hot.
Also what rpm is it failing at?If it is just at idle,sometimes raising the idle will clean it up.

 

when they test the HCs they test it at idle all they way up to something, i think they go about a grand less than redline, not sure. im thinking about changing all the plugs, then going and getting it tested after i have run it hard for about 30-40 mins, i think the heated up catylitic converter will cut down on the HCs.