Hi I just recently got done spending a lot of time rebuilding a 74 F250 "HiBoy" It has the 300 c.i. six in it but I have a clifford header and 4bl. intake manifold w a holley 450cfm square bore carb w vacum secondaries, also a clifford "torque" cam. I just got back from trying to get it emissions tested and it failed. I only have to pass a "tailpipe" test, the HC ppm (hydrocarbons/parts per million) was to high at idle the limit to pass was 1000 and I Failed with 3769 ppm of HC. So what do I have to do to fix this? The engine should be tight, I just rebuilt it; are the idle mixture screws to rich? The idle to high? Or will I ever be able to pass with this setup? The CO% reading (carbon monoxide) @ idle was 0.23 the limit was 4.00 how can the CO be so low and the HC be so high? I can use all the help I can get, snow is coming and I want to use it as my winter driver. Getting too cold and wet for the Harley...

 

It sounds like it's running rich, not enough O2. Adjust the mixture and get the right idle speed and you SHOULD be good to go.

Good Luck!!!

 

I second that thought! Lean her out and try again.

 

Leaning it out may work, but if the cam has too much overlap, you're gettin' a lot of intake going out the exhaust. If leaning doesn't work, swap the cam for the test.

 

Another trick would be to set the idle speed as high as you dare. When you get off the idle circuit it will naturally lean out some if it is jetted right. Also try bumping the timing down a little just for the test. You can set things back afterward. Worked for me.
Just my $.02
macguyver

'77 F-250 Camper Special 400ci
'76 F-250 Supercab 360ci
'71 Mach I 429CJ

huct on foniks wurkt fer me

 

Sounds too rich.

...Here are Harold's helpful hints to pass emmissions.

Lean out the idle. Use a vacuum gauge to get the highest reading and then lean it out slighty more.

Use quality fuel of just enough octane. If alcohol is added to any of your local fuels use it.

Set the timing to minimum to get an acceptable idle.

Set the idel speed up to about 900.

Change the oil just before. Use synthetic if it's burning any.

Take a drive on the highway to blow the cobs out and keep it good and warm untill they test it. 195/205 deg.

Good Luck!

 

Before I was smart enough to drive a Ford I had a Dodge that failed emissions big time. I didn't want to put any money into it so I bought one of those bottles of "guarantee to pass or your money back" junk. I just followed the directions on that and it passed with flying colors. I'd give that a try.

Brendan
1977 Ford F-250 4X4
351M / 4-Speed
33" BFG Tires
www.angelfire.com/ma4/1977fordf250