74 460 Emissions tips please

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Jan 13, 2011 | 05:35 PM

fenderjazz

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74 460 Emissions tips please

Hi, I have to run my F-250 with a 460 through emissions in Phoenix,AZ. My first run through almost passed, but the 35mph test failed by about 20%. I passed at idle, but not by a huge margin. I am running an RV cam,headers, Weiand Stealth intake, Edelbrock 750 (electric choke model) and I shaved off the smog bumps on my heads. I shaved the bumps and flowed the heads to get more performance for boat hauling as there were no emission tests for 74 and older in Oregon. Stock vacuum dizzy, MSD-6 ignition box, new plugs and plug wires. If I run the stock ignition timing the motor doesn't idle well. So... my question is, what tricks can I try to drop the hydrocarbons overall in my exhaust. I'll double check but I think I have my max ignition at 38 degrees. Should I tune to smoothest idle with the carb and ignition, ignoring factory recommendations or should I drop my main jets a step or change metering rods in the carb. I have a carb rejet kit, I think the carb is a 1407 model. I can tune my engine to run right, my plugs are all light tan with where its at now but it just barely fails... I could always re-tune after the test if I have to run it too lean for a few miles.... What would be good ideas for me? What ignition advance should I run for the test? Thanks in advance, Roy

Jan 13, 2011 | 07:22 PM

tikkakoski

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From: Tualatin OR

My buddy with a 79 460 same carb and intake had a similar issue passing deq here in oregon. He put in different metering rods and ran the truck til it was good and hot then he also turned his fuel screw all the was in then dropped his idle to like 6 or 700 in the parking lot lol. It worked for him. Then he un did everthing as soon as he passrd and pulled out of the booth. I plan on doing all the same stuff here soon in my 78 with the same set up.

Jan 13, 2011 | 08:03 PM

fenderjazz

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I'll search here for the recommendation on the metering rods. I bought a kit that should include the right ones to try. Man that's rough trying to lean an engine with light tan plugs. Does anyone know if the newish E-3 plugs make any difference at all? In theory they might burn even cleaner.

Jan 14, 2011 | 01:50 PM

mdr617

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From: Maryland

i know this may sound stupid and/or obvious, but what condition is your catalitic converter in? do you have a cat? We had a jeep fail horriablly, but replaced the cat and it passed better than some new cars.

Jan 14, 2011 | 08:19 PM

fenderjazz

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mdr617: The 74 did not have a cat. I think they were in 75 or later, not sure. Just EGR on 74's, perhaps California models had cats sooner. I have full length headers so I think it would be possible to add a cat but I'd rather avoid that. I wish my headers had a bung on them so I could screw in one of those simple oxygen sensing probes there to get the carb adjusted perfectly. I would even consider adding one, a good welder could probably do it on the vehicle at a muffler shop. Other than that I can't think about how I could nail the emissions problem without sending it to a tune up shop and having them charge me a couple hundred bucks or so to do the job. I'm trying to get it done without that expense. I have already run some Sea Foam through it and I don't really believe any of those "majical" products that cost 50 bucks for 12 ounces.

Jan 14, 2011 | 10:21 PM

fenderjazz

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On the fuel issue: will my engine have less emulsification enriching down the throats using premium fuel for the test? Here in AZ winter fuel has lots of volatility which you can sometimes smell under the engine compartment. My thinking is that maybe a couple of gallons of racing fuel set aside in one of my twin tanks might be the ticket for just the emissions test only. Any good thoughts on this? I know that generally speaking increased octane actually means fuel is less likely to burn fully at a given CR. But maybe is the difference between regular and better fuel less than the difference between winter fuel and summer fuel? I am thinking that I want no enriched fuel/air vapor bypassing the primary and secondary circuits and shortcutting down the open carb throats, thus enriching my mixture at low RPM and idle, where the testing is done. Am I over thinking???