Tuning a 4 barrel carb

[69clone]

Hey guys I cleaned my carb the other day and since then it's ran like crap. I'm sure it's because the old tune was for a dirty carb and now that it's clean it needs tuned again. I've never tuned a carb besides adjusting mine a tad here and there, So I was wondering if anyone could give me any advice? I have an edelbrock 4bbl it has two screws in the lower front for adjusting. So my question is when tuning it where should the screws be? What about the idle does it need to be at a curtain rpm before adjusting the screws?

 

[MarPar]

Check this one out...you may have to pick through it a little bit, but good info there!

http://www.forbbodiesonly.com/moparforum/showthread.php?t=10369

 

[Meep-Meep]

What did you change? Go back and retrace your steps. Maybe you dislodged a piece of crud somewhere or have a vacuum leak. Yeah, lots of good info on Mar's thread.

For a basic adjustment the two screws you speak of are idle mixture and they should be 1.5 - 2 turns from lightly seated. The throttle stop screw (idle) should be about 1 - 1.5 turns in from the blades being lightly seated or about 1/3 to 1/2 of the transfer slot showing. Timing should be advanced enough that it will run at around 900 RPM at those carb settings, or 12-15 deg BTC with vac advance disconnected. Total timing shouldn't exceed 38 deg.

 

[69clone]

Thanks marpar i'll check it out.

What did you change? Go back and retrace your steps. Maybe you dislodged a piece of crud somewhere or have a vacuum leak. Yeah, lots of good info on Mar's thread.

For a basic adjustment the two screws you speak of are idle mixture and they should be 1.5 - 2 turns from lightly seated. The throttle stop screw (idle) should be about 1 - 1.5 turns in from the blades being lightly seated or about 1/3 to 1/2 of the transfer slot showing. Timing should be advanced enough that it will run at around 900 RPM at those carb settings, or 12-15 deg BTC with vac advance disconnected. Total timing shouldn't exceed 38 deg.

Nothing changed besides using a can of carb cleaner. It was alittle dirty inside which is why i wanted to clean it. Afterwards the idle went up so i had to adjust the idle screw i then turned both fuel mixture screws down. Figured it was already running rich and now that it was clean it would be worst.
You mention the idle should be around 900rpm? I ask because the guy i bought my car from built race motors and built this one, it idled around 600rpm then and so i've always kept it between 550-650rpm is that bad?

 

[Meep-Meep]

600 RPM is typical for a bone stock engine but I wouldn't necessarily say it's bad, however, you should avoid extensive idling. I like to idle on the high side to keep more oil flying around. On my 440 900 in gear feels about right and in neutral it goes to about 1000 - 1100.

What indication did you have to determine it was running rich? The sudden high idle after cleaning is curious.

 

[69clone]

600 RPM is typical for a bone stock engine but I wouldn't necessarily say it's bad, however, you should avoid extensive idling. I like to idle on the high side to keep more oil flying around. On my 440 900 in gear feels about right and in neutral it goes to about 1000 - 1100.

What indication did you have to determine it was running rich? The sudden high idle after cleaning is curious.

Well it took 4-5 tries to pass our emission test. First idled to low mine was 672, min to pass was 750... and the rest were to rich. Also there is always gas (could be condensation) On the ground behind the exhaust tips.

 

[Satellite65]

Did you unload a whole can of Gumout down the throat? If that's the case you may have fouled your plugs with all that carb cleaner. It doesn't burn very well.

 

[Meep-Meep]

The numbers you posted sound like hydrocarbon readings and a fouled plug will contribute to that. Also vacuum leaks, missfire, too much cam overlap and too lean will do it too. Before going to an emissions test make sure the oil is clean and the plugs are sharp as well as general tune up stuff being in order.

CO is in percent and is an indication of mixture, with a high CO reading being rich. O2 and CO2 (Al Gore's favorite!) are also good indicators of mixture. Proper combustion should be about 14.7% CO2 and O2 should be 1-2% . Too high O2 is lean and too low is rich. Study your printout and try to determine what's going on.

Retarding the timing and bumping up the idle usually helps bring down the hydrocarbons. I had my smog license many moons ago and I got some stuff to pass that way but it barely ran.

 

[69clone]

Did you unload a whole can of Gumout down the throat? If that's the case you may have fouled your plugs with all that carb cleaner. It doesn't burn very well.

I don't think so, Not alot went down the carb maybe a 1/4-1/3 the can. I will add the plugs to the list though.

The numbers you posted sound like hydrocarbon readings and a fouled plug will contribute to that. Also vacuum leaks, missfire, too much cam overlap and too lean will do it too. Before going to an emissions test make sure the oil is clean and the plugs are sharp as well as general tune up stuff being in order.

CO is in percent and is an indication of mixture, with a high CO reading being rich. O2 and CO2 (Al Gore's favorite!) are also good indicators of mixture. Proper combustion should be about 14.7% CO2 and O2 should be 1-2% . Too high O2 is lean and too low is rich. Study your printout and try to determine what's going on.

Retarding the timing and bumping up the idle usually helps bring down the hydrocarbons. I had my smog license many moons ago and I got some stuff to pass that way but it barely ran.

I think you may be right, This was back in May... Hoping for the weather to get better so i can get back out there...