Hi, I've got a 460 in my 76 F250. Last year it passed emissions testing easily with the stock manifold and motorcraft carb. Since then, I've swapped out to a new Weiand stealth and edelbrock 1405. I can't pass emissions !!

Have high HC and CO readings, under load and idle.

1 I've gone through igntion system 3x, timed it dead on at 12btc with vacum advance plugged. Hook vacum up to ported vacuum (its the right one for this year- if I use manifold vacum, timing jumps to 28btc when reconnecting advance). plugs, wires, cap & such are all new. Have rebuilt stock dist on it

2. adjusted carb using vacuum guage. warm up engine, turn in one side fully lean, back out to max vacuum. same thing other side.

3. compression is good, consistent within 6 pounds +/- per cylinder. I'm not blowing or burning oil.

still fails emissions. high HC at idle and load High CO at load. I can add that it really doesn't have much power either, seems to shake a bit on initial acceleration, and gas pedal seems a bit "fluffy" when crusing (as in no real throttle response, considering its a 460 trailer special and I need it to PULL)

Any ideas? I do have some ratty old 1" open aluminum spacer between the carb and manifold - could that be it? I've read alot about open vs 4 hole spacers- no idea which one to go with

 

With HC high at idle and CO high at load it sounds rich. The open spacer makes the dual plane intake act more like like a single plane. Less idle and mid-range performance, maybe more top end and pulls more fuel through the carb. A 4 hole spacer adds volume but does not defeat the purpose of the 2 plane manifold (low/mid range torque).

I'd start by removing the spacer... and idle may need to be adjusted leaner than what you get with the vacuum gauge method. If CO is still high at speed, you may need to jet down.

Also a PS... Is that Ed carb the 750? I've never run one but hear they are hard to get right.

 

for passing the test when we still had that here lowering the timing 6-8 degrees would would lower the hc a deacnt amount
and the eddy carbs tend to be jetted rich out of the box

 

You and Blue and White are talking waaaay too technical for me, but, on my Motorcraft stock carb, i had to jet down to size #54(stock is #56) to pass smog.

I have a 400, btw

 

Another trick is to throw in a couple bottles of heet fuel dryer in the tank with less than 1/2 a tank. It's methanol and will burn cleaner then gasoline. It helped my 90 Acura pass with no issues with over 200 k on the clock.

Rice racers with big turbos, cams, timing, big injectors etc pass by running almost all methanol in the tank. They run poorly that way but they smog then immediately fill up with gas to dilute the stuff.

Also don't forget a new air filter as well.

 

Thanks. I,ve got the 1705 600cfm on it. I have a 750 also, but will wait till i rebuild with hottrt cam before i try that again. Will pull that spacer & try it. Also ordered a 4 hole phenolic 1\2 inch and will test that also.




QUOTE=Blue and White;14467851]With HC high at idle and CO high at load it sounds rich. The open spacer makes the dual plane intake act more like like a single plane. Less idle and mid-range performance, maybe more top end and pulls more fuel through the carb. A 4 hole spacer adds volume but does not defeat the purpose of the 2 plane manifold (low/mid range torque).

I'd start by removing the spacer... and idle may need to be adjusted leaner than what you get with the vacuum gauge method. If CO is still high at speed, you may need to jet down.

Also a PS... Is that Ed carb the 750? I've never run one but hear they are hard to get right.[/QUOTE]

 

Update- I pulled the spacer as blue & white suggested, instant better throttle response. Put a jegs 4 hole phenolic 1" spacer on it to test, pretty much the same. That Weiand is already pretty tall, probably don't need one. Redid my carb settings- vacuum was lower than with open spacer. Right now its around 16hg. Dialed the mixture screws in all the way, then backed them out to max vacuum. its at around 2.5 right now, which is 1.5 less turns than with open spacer. Had to adjust idle speed down a bit to get 0 vacuum at ported vacuum on carb, then reset timing to 12btdc.

Still runs rich, but not as much, but still can smell it and see a bit of smoke coming out the breather on valve cover.

so- what next- I have a hard time thinking i need to rejet a stock 1705 in phx area, but mabye:

1. fuel pressure too high- getting too much fuel in carb?
2. float need to be reset (again, its a new carb with less than 8 hours driving time on it)?
3. bad compression? havent done a comp test yet, but engine seems to be smooth. I'd expect - been avoiding this, as bad results will mean time for a new short block - and while i'm in there..........
3.

 

On the fuel pressure... a stock type fuel pump will typically put out 7-9 psi. Ed carbs like 5 psi max. Easy to check with a "T" fitting on the fuel line to the carb and an inexpensive gauge. You probably need a regulator. Holley regulators are generally considered the best.

 

Coming from a non-smog state, this may or may not be helpful.

Why not put the factory equipment back on the truck for the smog test? You already know that the factory setup will pass. After the test is done you can go back to power parts.