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Old 05-23-2011, 11:15 AM
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Carb tuning tips?

Hey guys, I have a 67 El Camino with a sbc 350, headers, edelbrock performer rpm, hei dist, turbo 350 with 3000 stall and comp cam 286h and Holley 670 with electric choke. The elky runs really good and idles great. I checked the spark plugs and they are very white looking on the electrodes. I know this is a sign of a lean condition.

Should I be concerned? Should I fine tune the carb? I am currently using AC plug, (#MR43LTS), gapped at .040. The stock set up on the carb is; main jets-65, secondary jets-68 and the primary power valve is 6.5, I have 10" of vacuum at idle. I have power disc brakes and they work fine. I was thinking of moving up a couple of sizes on the primary jets. What about the power valve? What about E3 spark plugs, are they any good? Sorry for all the noob questions... I don't want to burn a valve....

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Old 05-23-2011, 04:23 PM
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Quote:
Originally Posted by Madmax305
Hey guys, I have a 67 El Camino with a sbc 350, headers, edelbrock performer rpm, hei dist, turbo 350 with 3000 stall and comp cam 286h and Holley 670 with electric choke. The elky runs really good and idles great. I checked the spark plugs and they are very white looking on the electrodes. I know this is a sign of a lean condition.

Should I be concerned? Should I fine tune the carb? I am currently using AC plug, (#MR43LTS), gapped at .040. The stock set up on the carb is; main jets-65, secondary jets-68 and the primary power valve is 6.5, I have 10" of vacuum at idle. I have power disc brakes and they work fine. I was thinking of moving up a couple of sizes on the primary jets. What about the power valve? What about E3 spark plugs, are they any good? Sorry for all the noob questions... I don't want to burn a valve....
I don't know much about Chevy small blocks but I have run and tuned a Holley 670SA. They are calibrated lean IMHO. Definitely go up on jetting until you get some color on the plugs. The power valve is fine for now. Save your money on the E3 plugs.

I am sure others more knowledgeable will be along shortly to help guide you.

In the mean time, this may help:

http://www.nastyz28.com/~ericf/tech/htune.pdf
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Old 05-24-2011, 07:12 AM
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I think 10" of vacuum at idle is a bit low, in fact you should be more at 20". You can play with your timing a little and then reset the carb. So if you are idleing at about 1k rpm try advancing or retarding the timing, that will change your rpm. Then adjust your fast idle screw till you get to 1k rpm again, then adjust your idle mixture screws, the two in the front of the carb. Turn the drivers side all the way in till you here the engine bog down, then turn it out 1.5-2 turns, do the same for the pass side screw. It helps to look at your vaccum while doing so. Also check your timing with a gun at idle and at 2500 rpm. Make sure your choke is working properly. Should be all the way open when warmed up.

I am going through issues with my carb as well and mine likes to run about 1200 rpm to have a perfect 20" vacuum. I then run it at 1k and am getting about 17-18".

Make sure you don't have any intake leaks before you start putting money into the carb. I feel you can adjust the carb and check your timing before you just swap out the jets or metering rods.
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Old 05-24-2011, 08:29 AM
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Quote:
Originally Posted by 99 to Life
I think 10" of vacuum at idle is a bit low, in fact you should be more at 20". You can play with your timing a little and then reset the carb. So if you are idleing at about 1k rpm try advancing or retarding the timing, that will change your rpm. Then adjust your fast idle screw till you get to 1k rpm again, then adjust your idle mixture screws, the two in the front of the carb. Turn the drivers side all the way in till you here the engine bog down, then turn it out 1.5-2 turns, do the same for the pass side screw. It helps to look at your vaccum while doing so. Also check your timing with a gun at idle and at 2500 rpm. Make sure your choke is working properly. Should be all the way open when warmed up.

I am going through issues with my carb as well and mine likes to run about 1200 rpm to have a perfect 20" vacuum. I then run it at 1k and am getting about 17-18".

Make sure you don't have any intake leaks before you start putting money into the carb. I feel you can adjust the carb and check your timing before you just swap out the jets or metering rods.
Comp 286 cam is fairly aggressive so I don't think 10 inches of vacuum is outrageous but your suggestion to optimize timing before getting to deep into the carb is valid. I would just be careful because he has a lean condition and any more timing might result in damage to the engine.
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Old 05-24-2011, 10:27 AM
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Quote:
Originally Posted by Madmax305
Hey guys, I have a 67 El Camino with a sbc 350, headers, edelbrock performer rpm, hei dist, turbo 350 with 3000 stall and comp cam 286h and Holley 670 with electric choke. The elky runs really good and idles great. I checked the spark plugs and they are very white looking on the electrodes. I know this is a sign of a lean condition.

Should I be concerned? Should I fine tune the carb? I am currently using AC plug, (#MR43LTS), gapped at .040. The stock set up on the carb is; main jets-65, secondary jets-68 and the primary power valve is 6.5, I have 10" of vacuum at idle. I have power disc brakes and they work fine. I was thinking of moving up a couple of sizes on the primary jets. What about the power valve? What about E3 spark plugs, are they any good? Sorry for all the noob questions... I don't want to burn a valve....
You said "286" but what I'm hearing is "268". Am I right?
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Old 05-24-2011, 10:32 AM
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Quote:
Originally Posted by cobalt327
You said "286" but what I'm hearing is "268". Am I right?
No, the cam is a comp 286h flat tappet....The car runs great, it is running very lean right now, based on the condition of the plugs...
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Old 05-24-2011, 10:49 AM
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Get a afr gauge. It will tell you a lot and make dialing in the carb easy.
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Old 05-24-2011, 11:55 AM
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Thanks for the replies guys, If I change the front jets from 65 to 67 would that help with the lean condition? Also, what about changing the power valve to a 5 or 5.5?
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Old 05-24-2011, 01:10 PM
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Quote:
Originally Posted by Madmax305
Hey guys, I have a 67 El Camino with a sbc 350, headers, edelbrock performer rpm, hei dist, turbo 350 with 3000 stall and comp cam 286h and Holley 670 with electric choke. The elky runs really good and idles great. I checked the spark plugs and they are very white looking on the electrodes. I know this is a sign of a lean condition.

Should I be concerned? Should I fine tune the carb? I am currently using AC plug, (#MR43LTS), gapped at .040. The stock set up on the carb is; main jets-65, secondary jets-68 and the primary power valve is 6.5, I have 10" of vacuum at idle. I have power disc brakes and they work fine. I was thinking of moving up a couple of sizes on the primary jets. What about the power valve? What about E3 spark plugs, are they any good? Sorry for all the noob questions... I don't want to burn a valve....
If the plugs don't have silvery spots on the insulators, your not on the point of melting anything. The best power comes right on the detonation edge, if you were crossing that place the plugs would show some metal deposition.

Plug color is place where more is going on than mixture ratio, you are, also, seeing the plug's heat range and the engine's timing advance effects. Lacking that appreciation will usually lead you down the road of mixture issues which may, or not, actually be there.

Before you peel the carb apart, I'd recommend dropping a heat range on the plug and watching it for color changes. You can ,also, back off the timing a couple, three degrees and watch the plugs. And or get an AFR meter and keep track of the mixture ratio. Messing with the carb is a much more complicated affair, so do the simple things first.

Bogie
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Old 05-24-2011, 01:13 PM
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Quote:
Originally Posted by Madmax305
Thanks for the replies guys, If I change the front jets from 65 to 67 would that help with the lean condition? Also, what about changing the power valve to a 5 or 5.5?
if you have an auto trans, put car in gear while another person reads a vacume gauge.. if the reading is 7 or so then 5.5 to 6.5 power valve will work but if it reads lower then you will need a smaller valve like a 3.5 or 4.5 just depends on your vacume reading at idle with car in gear.. always go two points lower than your reading
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Old 05-24-2011, 01:27 PM
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Here's a couple pics of #1 plug What do you guys think?
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Old 05-24-2011, 01:37 PM
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Here is a close up.
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Old 05-25-2011, 10:40 AM
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Quote:
Originally Posted by oldbogie
If the plugs don't have silvery spots on the insulators, your not on the point of melting anything. The best power comes right on the detonation edge, if you were crossing that place the plugs would show some metal deposition.

Plug color is place where more is going on than mixture ratio, you are, also, seeing the plug's heat range and the engine's timing advance effects. Lacking that appreciation will usually lead you down the road of mixture issues which may, or not, actually be there.

Before you peel the carb apart, I'd recommend dropping a heat range on the plug and watching it for color changes. You can ,also, back off the timing a couple, three degrees and watch the plugs. And or get an AFR meter and keep track of the mixture ratio. Messing with the carb is a much more complicated affair, so do the simple things first.

Bogie
Thanks for the input. I will back off the timing a few degrees and and drop down a heat range on the plugs...So any idea what the next lower heat range will be on an AC MR43LTS plug would be?
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