Carb question Options

[last337]

Hello everyone! I got my new EMPI 40s on yesterday and I have been going through the adjustment all day today. It has been a long time since I have messed with carbs and Im not sure if I am doing this correct.

Initially I got my linkages all set up and correct with the speed screw at about 1 turn in. I have all the air bleed screws all lightly seated and mixture screws about 1 1/2 turns out.

At this point it is very rich but runs well at an idle of about 900 and actually comes up really nice but is smoking and even spitting out fuel from exhaust. I figured at this point I could begin going in 1/4 turn at a time on each mixture screw to the point the engine starts to run rough then back a 1/4 turn. I did this on all and it was still smoking badly. I havent set timing or anything like that but I would assume the only electrical issue (am I wrong?) that could cause rich conditions at idle would be a fouled plug but it is running smooth and not as if it is missing with a fouled plug.

I am wondering if maybe I should go another half turn on the speed screw then see if I can go in further with the mixture screws. Is there anything I can do with the air bleed to adjust this? I thought they were only adjusted for syncing and not for a rich condition.

The vendor I got them from claims they have the following jets:
52 idle jets
115 main jets
200 air jets
28mm venturi
550 EX. pump jets
50 accelpump jets
F11 emulsion tubes

Am I oversized with that I have in there now? I have been reading the following link to troubleshoot and it says if I am over 1 1/2 turns in on mixture then my jets are too big. The problem is that I cant get it to run at under 1 1/2 turns on mixture. However, maybe I should try another half turn on speed screws?

Any help is greatly appreciated (IMG:style_emoticons/default/biggrin.gif)

[rhodyguy]

thomlinson (cb perform book) suggests setting the by-pass at 1/2 turn off closed for the initial setup. a 40 i'm looking has 50s for the idle jets. 52 might be a tad fat and you cut some air off the idle mixture when you closed the by-pass. open all 4 up 1/2 a turn and see what happens. if the idle circuit is rich to begin with and the engine is idling a lot when you're adj the carbs you'll be loading the plugs up with carbon. if your unregulated facet is over driving the fuel float needle valve you''ll in a rich condition all the time.

[last337]

thomlinson (cb perform book) suggests setting the by-pass at 1/2 turn off closed for the initial setup. a 40 i'm looking has 50s for the idle jets. 52 might be a tad fat and you cut some air off the idle mixture when you closed the by-pass. open all 4 up 1/2 a turn and see what happens. if the idle circuit is rich to begin with and the engine is idling a lot when you're adj the carbs you'll be loading the plugs up with carbon. if your unregulated facet is over driving the fuel float needle valve you''ll in a rich condition all the time.

Thanks for the help! I realized two things. By backing out the air bleeds I was definitely able to lean things out a bit although at this point they are almost seating completely again. Secondly, I was trying to do my adjustments with the engine way too cold.

At this point I have a 'somewhat' smooth idle but I hear a popping/sucking sound from the carbs at times. Under the load there is a bad hesitation coming off idle and you can hear the carbs almost start to whistle as if they are starving for air after the hesitation goes away. Any ideas?

[ThePaintedMan]

thomlinson (cb perform book) suggests setting the by-pass at 1/2 turn off closed for the initial setup. a 40 i'm looking has 50s for the idle jets. 52 might be a tad fat and you cut some air off the idle mixture when you closed the by-pass. open all 4 up 1/2 a turn and see what happens. if the idle circuit is rich to begin with and the engine is idling a lot when you're adj the carbs you'll be loading the plugs up with carbon. if your unregulated facet is over driving the fuel float needle valve you''ll in a rich condition all the time.

Thanks for the help! I realized two things. By backing out the air bleeds I was definitely able to lean things out a bit although at this point they are almost seating completely again. Secondly, I was trying to do my adjustments with the engine way too cold.

At this point I have a 'somewhat' smooth idle but I hear a popping/sucking sound from the carbs at times. Under the load there is a bad hesitation coming off idle and you can hear the carbs almost start to whistle as if they are starving for air after the hesitation goes away. Any ideas?

Kevin (rhodyguy) and John (FourBlades) have both been through this with me and I trust them implicitly. I'm still learning of course, but I also would suggest a few things. We don't know - did you do a good valve adjustment first before doing any of this? This can have a big impact. Make sure you do it with the engine dead cold. I was having issues with the carbs "coughing" the way you describe, but a lot of it went away once I did a good, honest valve lash adjustment.

Then I would ensure your timing is as good as you can get it. Depending on the distributor, you want it around 27 degrees before top dead center around 3,200-3,400 RPMs (again this varies with engine and distributor). Again, this seemed to help me get rid of some of the coughing.

Then, you can move back to the carbs to fine tune the idle. The stumble off idle probably has a lot to do with a lean condition, but can also be due to a crappy distributor (the Bosch 009 is often installed on these cars and is notorious for having a big "flat spot") or more often, not having the carbs synched left to right. Are you using the "hex bar" linkage or some version of it?

[last337]

Thanks for all the input. I am on Pelicanparts today ordering everything I need to do a full and proper tune-up of the ignition system. I also need to do a good valve adjustment. I did read somewhere that not having the air filters on could also cause backfiring in the carbs because of the lack of flow restrictions. I guess for the time being I will just cough up the tuning I have done thus far to a learning curve (IMG:style_emoticons/default/sunglasses.gif)

I did find the following link last night which was really good info.

http://racetep.com/webjettune.html

Oh, and he mentions two books there for tuning but I have seen you guys mention other 'bibles' for tuning. I dont recall which they were. Which should I buy?