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Who knows carbs ?

pearljam724

pearljam724

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I have a 650 CFM carb on a 360. My plug readings are a little leaner than I would like and I know the secondary jets are probably a hair too lean as it seams to be starving a little on steep mountain grades once I reach near the top and throttle it to the floor.
Anyhow, I bought a calibration kit and intend to increase the jet sizes, etc. My calibration kit doesn’t have parts labeled. It seem to me that these kits only include the primary jets, does this sound right ? In addition to that, I can’t find any secondary jets listed for Edlebrock Thunderseries carbs separately. Do you actually have to increase the cfm on a carb to increase secondary jets ?
I’m sure, many would say that a 650 cfm carb is plenty for a 360. I found a professional write up that recommended a 750 cfm carb for 340/360’s.
I know I’m leaner than I’d like. So maybe, this holds true. I also have a bigger cam. I just don’t know the duration as I didn’t install it. Aftermarket intake, etc.
My question is, secondary jets aren’t included in calibration kits or can’t be purchased separately ? Or will the same jets work in primary and secondary ?
 
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How's about consulting the manufacturer of the carburetor?
Here, I'll help:
https://edelbrock-instructions-v1.s3.amazonaws.com/edelbrock/carb-tuning-guide.pdf
https://edelbrock-instructions-v1.s3.amazonaws.com/edelbrock/carb-tuning-guide.pdf
Since you didn't mention which Edelbrock Thunder AVS 650 you have, I'll assume it to be the 1825. The appropriate tuning kit for it:
https://www.edelbrock.com/edelbrock...ation-kit-for-1825-1826-carburetors-1842.html
Yes, it has secondary jets in it.

Oh, by the way....Edelbrock also has an entire series of videos on how-to as well. Either go to their website or to YouTube.
 
Get a jewelers loupe or magnifying glass. There are numbers on the rods and jets. For the primary, there are charts available that show whats needed to richen the carb. .098 is the stock secondary jet.
Screenshot_20191030-191125.jpg
Screenshot_20191030-191113.jpg
Screenshot_20191030-190952.jpg
 
moparedtn said:
How's about consulting the manufacturer of the carburetor?
Here, I'll help:
https://edelbrock-instructions-v1.s3.amazonaws.com/edelbrock/carb-tuning-guide.pdf
Since you didn't mention which Edelbrock Thunder AVS 650 you have, I'll assume it to be the 1825. The appropriate tuning kit for it:
https://www.edelbrock.com/edelbrock...ation-kit-for-1825-1826-carburetors-1842.html
Yes, it has secondary jets in it.

Oh, by the way....Edelbrock also has an entire series of videos on how-to as well. Either go to their website or to YouTube.
Click to expand...

I agree. Edelbrock already did all the research. Just email 'em and tell them what you told us. They will respond with all the part numbers you need. Easy.
 
You could always start by hooking a vacuum gauge to full manifold vacuum and see how much vacuum your pulling at idle since your not sure of the cam or duration.
Higher duration will mean lower vacuum which in turn may not be a strong enough signal to pull the gas in to the intake which will cause it to run lean. I would start will 4% richer or just switch to .065x.042 rods and .101 jets in the secondary's and see how it runs after that. That would be 8% I do believe, you could go down if plugs start to look on the rich side after a few days of driving.
 
superbeedave said:
You could always start by hooking a vacuum gauge to full manifold vacuum and see how much vacuum your pulling at idle since your not sure of the cam or duration.
Higher duration will mean lower vacuum which in turn may not be a strong enough signal to pull the gas in to the intake which will cause it to run lean. I would start will 4% richer or just switch to .065x.042 rods and .101 jets in the secondary's and see how it runs after that. That would be 8% I do believe, you could go down if plugs start to look on the rich side after a few days of driving.
Click to expand...
I agree. Good info. That’s where I would start. Kim
 
I understand how to tune the carb. I was just wondering if the primary and secondary jets were the same jets ? I was trying to get a jump on that before I take it apart. I ll just have to wait until then. Yes, my engine pulls about 14.5 to 15 pds of vacuum at idle. A little low compared to some engines probably. But, I believe normal for a LA engine with a larger cam. I think you’re right superbeedave. I have a Edlebrock Thunderseries 1805. Someone installed it before me and let the base components in the carb. The engine runs very well, but could use a tad more gas pulling long mountain inclines once I reach the top of them. Car runs great. Hair too lean. I think I will notice a ton of improvement by just changing the step up springs alone. But, I’m stepping up jets and rods 1 step too.
 
Same Jets with 2-stage rods. The Original AVS with 3-stage rods is the only one I know that uses the longer primary jets.
I found the best tool for reading the jet/rod markings in the magnified lighted inspection light that the Ear/Nose/Throat (ENT) doctors use.
Just use the light without the plastic part that goes in your ear.

I don't know the exact brand I have, but it was like this one:
https://www.amazon.com/Generation-M...ht&qid=1572633498&sprefix=ENT+,aps,207&sr=8-8
 
451Mopar said:
Same Jets with 2-stage rods. The Original AVS with 3-stage rods is the only one I know that uses the longer primary jets.
I found the best tool for reading the jet/rod markings in the magnified lighted inspection light that the Ear/Nose/Throat (ENT) doctors use.
Just use the light without the plastic part that goes in your ear.

I don't know the exact brand I have, but it was like this one:
https://www.amazon.com/Generation-Mom-Stainless-Otoscope-CLAMSHELL/dp/B000J1FT4W/ref=sr_1_8?crid=1G82AGCNPKNU2&keywords=ent+light&qid=1572633498&sprefix=ENT+,aps,207&sr=8-8
Click to expand...
Thank you, yes it’s incredibly hard to read them. But, I think mine are arranged properly now so I can tell them apart. I bought an aftermarket kit by Renegade and their printing is more difficult to read than the original Edlebrock parts. Plus, the case the parts come in isn’t labeled. But, I know what’s, what now.
 
I must be a Mopar nerd I could read these threads all day long. Some great answers .
 
Out on a ride now. Only changed step up springs. A lot more peppy at mid throttle. Gonna add 1 step up on rods here soon. Might have to wait until I get back home to change jets 1 size up.
 
Threw in some jets. Wow, it’s a new car. Upped jets 1 time to 98 primary and 101 secondaries. 87 octane gas. I’m tempted to try 104 secondaries, but this car only averages 9-12 mpg and that’s before I increased them. Maybe, I ll wait to read plugs on a few trips. Step up springs made a huge difference, throttle a lot more snappy and revs higher. I suspected it was a little too lean based on those symptoms. A lot of mid to top end power now for a small block pulling a B body.
The old girl loves cold air, lots and lots of gas.
 
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are you reading plug color or using an a/f meter?
 
ir3333 said:
are you reading plug color or using an a/f meter?
Click to expand...
Plug readings and driving diagnosis. If an engine doesn’t rev as high as it should, that’s one indicator of a lean carb. I have a dash tach. A motor with a slightly lean carb can run fine on flat ground. I live at the bottom of a steep mountain. I’ve learned through carbureted motorcycles. Same deal, when they don’t pull hard enough up that same mountain. It needs more gas (bigger main jets) A air/fuel meter would be best. But, it’s not necessary if someone understands symptoms and reads plugs at different rpms.
 
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oldkimmer said:
So u did all these changes at once. Kim
Click to expand...
No. I changed step u springs only, first.
Changed rods, second. These first two steps resulted in faster mid throttle response. I knew when I was about to change the jets to larger ones, last. It would get me my results. I believe if I up the secondary jets one more time. It will be perfect based on my last plug reading and power at high rpm’s. The plug is just starting to turn a light brown color. Which is what I want, but I’d like slightly more brown. But, gas mileage may prevent me from wanting to go any further. The Edlebrock calibration charts work, but are unnecessary if you take small steps and monitor each result. Basically, that’s what the charts are all about. I knew, based on my vacuum reading the step up springs that were originally in it were too light and that was definitely going to improve mid throttle. The secondary jet sizes effect high rpms or overall power. I knew the engine needed slightly more gas based on a few driving observations. But, if the car stayed on relatively flat ground or under 65 mph, you wouldn’t know any better. Because it ran well. Well, for those conditions.
 
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To my surprise. I’m actually getting slightly better fuel mileage after increasing jet sizes two times. A lot cooler outside though, could be contributing. Regardless, it’s no worst. Big surprise, to me.
 
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