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Dadamsnv 08-02-2012 05:19 PM

Searching for the golden tuning
I am beginning the saga of fine tuning my amc 304 for best performance. I will be working on both the carb and timing to make my tired old motor perform to its fullest.

As for equipment, I have a freshly rebuilt holley 2300 2bbl carb (similar in tuning to a motorcraft carb), an unknown brand HEI, an edelbrock performer intake, and unknown brand tube headers.

I will be using JeepHammer's "tuning amc v8s" instruction thread as my guide. I will list part numbers of all my tools, parts, and kits as I use them. I will post everything I do, even the embarrassing srew-ups.

This thread is for people who are interested in tuning their motors at home using good, old fashioned elbow grease, and for those looking for a laugh I'm sure.

Wish me luck, here I go! :2thumbsup:

Dadamsnv 08-02-2012 05:34 PM

4 Attachment(s)
The first step I'd recommend to anyone looking to REALLY dial in their carbs, is to at least take the thing apart and clean/inspect everything. Ideally, one would simply rebuild the carb whether it needed it or not, but the wallet is a different story. Mine was terribly sooty (pic 1), so I went ahead and rebuilt it. Also, my baseplate was leaking, so I bought a new baseplate assembly from ebay for $100.

Besides making sure the carb is in good working order, pulling the carb off of the manifold may expose a potential problem you didn't know you had (pic 2). Not only did I have a vacuum leak from this square bore to motorcraft spreadbore setup, but there was so much gasket and manifold interference that I figured I'd need either a motorcraft spreadbore carb, or a new manifold. I chose an edelbrock performer manifold (pic 3 and 4).

1SASjeepster 08-02-2012 05:50 PM

I am interested in seeing how this develops THE OLD SCHOOL WAY. I also am surprised you didn't go with a small Holley four barrel. I think you would get better gas mileage and much more power.

Take care,

Dadamsnv 08-02-2012 06:10 PM


Originally Posted by 1SASjeepster (Post 13961832)
I am interested in seeing how this develops THE OLD SCHOOL WAY. I also am surprised you didn't go with a small Holley four barrel. I think you would get better gas mileage and much more power.

Take care,

I hope you enjoy the read. :thumbsup:

Who knows, this exercise may eventually lead to a new carb by the time I'm done. In a perfect world, I'd dyno the jeep now, then after I get a full holley 2300 tune, and finally after I add a small, 4 bbl carb, but money is also a factor.

I may have to resort to girlfriend calculated 0-60 times :rofl:

Oxmarqt 08-02-2012 08:02 PM

Good luck and I hope to keep track of your progress.


Originally Posted by Dadamsnv (Post 13961925)
I may have to resort to girlfriend calculated 0-60 times :rofl:

Hopefully(for her sake), the Jeep is the only thing your girlfriend will be calculating 0-60 times for.....:laugh:


Dadamsnv 08-03-2012 12:20 AM


Originally Posted by Oxmarqt
Good luck and I hope to keep track of your progress.

Hopefully(for her sake), the Jeep is the only thing your girlfriend will be calculating 0-60 times for.....:laugh:


"those" times would be 60 and on... In minutes ;)

And she'd be too distracted anyway.

Matt1981CJ7 08-03-2012 03:44 AM


Do you plan on messing with your advance curve at all? How about jetting the carb for your specific altitude? I found these two tasks to be key in getting a proper tune.

Here's a video of my 31-year old 258, that's never been torn apart, after I successfully tuned it.


em2mccue 08-03-2012 08:48 AM

This is what I will be doing this weekend. So I guess I hope you have to get everything done on Saturday during the day. That way I can read it Saturday night and do it Sunday. Cause I need as much help as I can get. Good Luck.

Dadamsnv 08-03-2012 10:29 AM


Originally Posted by Matt1981CJ7 (Post 13963695)

Do you plan on messing with your advance curve at all? How about jetting the carb for your specific altitude? I found these two tasks to be key in getting a proper tune.

Here's a video of my 31-year old 258, that's never been torn apart, after I successfully tuned it.


Nice vid Matt :thumbsup:
That thing raps up nice and smooth!

I plan on digging pretty deep into this tune. I will start with a base tune (vacuum tune the idle mix screws, set base timing to 8*, set fuel height, etc). Then I will step it up and chart and tune both the centrifugal advance, and the main jets. Once I nail those, I will chart and tune the vacuum advance.

I probably wont screw around with really fine tuning (with cams and whatnot) the accel pump, or digging into the power valve channel sizes in the carb. Unless I have to that is.

1SASjeepster 08-03-2012 10:35 AM


Your video is awesome! I didn't even see the engine shake. Great job.

Take care,

Matt1981CJ7 08-03-2012 10:51 AM


Thanks, man. The timing light and vac gauge were loosely duct taped to the rail. If you watch closely, there is a slight shimmy at about 3700 RPM, but it goes away quickly above 4000.

The ol' girl actually had a bit more throttle to go, but I didn't want to blow something up with video proof. :laugh:

My 258 has got almost 100K miles on her, and I think she knows she's about ready to get replaced by a 360. So she's trying to prove she's still worthy. ;)


Dadamsnv 08-03-2012 11:11 AM

Tools I will use for this project.

vacuum gauge:

I have two of these: a cheapy for the cab, and a nice one for tuning. Here are their summit part numbers

nice one-

Timing light:

I read a few reviews on these, it seems you either need to buy a simple (on button only) unit or a $150 unit. I heard good things about this one, so I bought it.

Timing tape:

Vacuum pump:

I don't have one yet, but I will get one when I begin the vac advance testing

Dadamsnv 08-03-2012 12:45 PM

9 Attachment(s)
With a fresh new manifold, and a freshly rebuilt carb, I begin the quest. The very first thing I would do, if I hadn't done it already because of a bad missfire, would be pull the plugs and make sure they are in decent condition, and make sure they are meant for your rig, and make sure they are gaped appropriately for your ignition (.035" for stock points, .045" for HEI). My plugs were gaped at .045" on the driver side, and .035" on the passenger side. WTF? I cleaned them with a wire brush and brake cleaner, then gaped them all to .045". Also, now is a good time to replace your old plug wires, cap, and rotor/points if you even think they may need it. I had 8mm summit wire and a brand new cap and rotor on my rig.

These are the steps I followed to prepare for the base tune. I originally tuned the base timing and mix screw with the vacuum gauge just to get her going, but once I bought better tools, I redid all the tuning. I will start from the "redid" part since I don't recommend tuning the base advance with the vac gauge for reasons I will cover later.

before starting the motor.

Step one: set idle mix screws where they were before the manifold and rebuild. If you don't remember set them to 2 turns out. [PIC 1]
Step two: disconnect vac advance and plug it to prevent vacuum leaks [PIC 2 & 3]
Step three: hook up timing light to number one cylinder and battery. Number one is the front most cylinder on the driver side. Make sure to hook the induction clamp away from other wires and metal and as close to the plug as possible [PIC 4 & 5]
Step four: hook up vacuum gauge to manifold vacuum source. [PIC 6]
Step five: put some fuel in the float bowl. [PIC 7 & 8]

You are now ready to start the motor.

These are the events that unfolded when I started/attempted to start the motor.

Event one: "clilck" and nothing happened
Event two: try to crank again, and "click" no crank
Event three: SMOKE from the motor compartment
Event four: PANIC
Event five: notice the smoke came from the manual choke cable
Event six: assume the starter ground was now the choke cable and firewall
Event seven: trace ground lead from block to batter
Event eight: tug on negative lead, and it pops out of the battery terminal.
Event nine: buy new terminal
Event ten: rewire block lead to terminal
Event eleven: start motor, and it runs like crap (what I expected)

The motor started and barely ran, so i kicked up the idle adjust screw to make it idle faster, but the motor was running very badly. My vacuum gauge read a steady 12 in Hg. I thought to myself, "at least its steady, that means the motor is somewhat healthy." A vacuum gauge can tell you all kinds of diagnostic information besides tune. I forget what all the various needle behaviors mean, but look it up some time. Its great info to have.

The following steps are the ones I took to get a rough initial tune. At this point, I do not have a timing tape on the balancer. Aslo, my original screw setting was 3/4 turns out on both sides

Step one: turn passenger side mix screw out half a turn. the motor instantly began to run smoother and vac went up 2 in Hg.
Step two: turn passenger side mix screw out until vac stops climbing. set the screw at the point where vac stops climbing and round it to the nearest 1/4 turn (1/8 turns become hard to remember)
Step three: turn driver side mix screw out until vac stops climbing. This should put the screws at the same setting, BUT MAKE SURE THAT THE SCREWS ARE TUNED OUT THE SAME AMOUNT ON BOTH SIDES. At this point the idle was well over 1400 RMP and very smooth and nice. So I backed the idle adjust screw down to roughly 800 RPM. I had no tach at this point. I now have a sunpro super tach II from autozone mounted on the steering column (I will eventually have a full gauge set mounted indash)
Step four: Adjust base timing to 6*-8* advance using timing light. Originally I used the vac gauge to set base timing. To do this you simply advance the timing until it stops increasing vacuum, then retard timing until you decrease 1 in Hg from max. Upon buying the timing light, I discovered this put me at about 13* base timing (yikes). This is why I amended my steps to include a timing light. [PIC 9]
Step five: allow motor to warm up completely
Step six: Check fuel height in float bowl. I adjusted this height to be about 1/16" below the check hole since I intend the wheel this rig.
Step seven: readjust idle mix screws to max vac.

The base tune is complete!

Dadamsnv 08-03-2012 01:46 PM

I'll admit that I have an advantage over the average joe when it comes to fuel mixture. I've been tuning dirt bike carbs for a while now, and I have developed that special "feel" for when my mixture is off. This Holley carb is WAY simpler than a Keihin FCR on a more modern 450f/250f. For example, the FCR has a pilot jet and mixture screw (idle and barely off idle circuit), jet needle profile and height (mid range circuit), and main jet (top end circuit).

I can give some pointers in detecting the quality of your fuel ratio by "feel". First, the better way to do it is with an O2 sensor and rich/lean meter or multimeter/voltmeter. The next best way to do it is with a plug test. Install new plugs, get up to "haul ***" speed (about 2500 RPM I'd guess) for a short while (1 minute is probably fine), push in clutch and kill motor, stop vehicle in neutral or with clutch in, check plugs, light tan is good, white is too lean, brown is too rich, black is TOO rich. I have no $$ for sensors and bung welding into the exhaust, and I have no long flat "haul ***" stretches where I can get to and perform this test.

Keep in mind this is all about main jet tuning

Pointer 1: Smell. Its easy to smell when a motor is running rich. With the top off, I can smell a small amount of exhaust fumes in the cab, and, if they are rich (smells like fuel), the main jets are too rich. If you don't smell fuel, the jets are either good or too lean. Make sure you don't confuse the rich smell with any fuel leaks you may have in the motor compartment. Non charcoal canister jeeps tend to smell like fuel all the time, so when you smell exhaust smell, pick it apart and determine if there is also a added fuel smell to it. Also, make sure you are only using the smell test at RPMs and loads that don't involve the powervalve, accel pump, or idle screws as these will all mislead you. So basically run this test at part throttle cruise (PTC) in the 2000 and up RPM range.

Pointer 2: Sound (assuming no catalytic converters). A backfire (while driving) usually means you are too lean, as do fluctuations in engine RPM for a steady throttle position. Alternatively, if you have an exhaust system you can hear off idle, you should also be able to hear it on decel and PTC. A quiet or silent exhaust pipe durning PTC or decel usually means too rich.

Pointer 3: Sight. This one is easy, black smoke is a sure sign of way too rich. Be sure that its not your power valve or accel pump making the extra rich smoke, those are separate issues. You want to make sure its not smoking during PTC or decel where there is no influence from other systems.

Pointer 4: Fuel mileage. Unless your power valve is always open (bad), or you are perpetually climbing a hill, or perpetually start-stop-start-stopping, your main jetting and timing curve make the largest impact on fuel economy. Without going into the timing curve yet, the main jetting is rich if you have poor economy. For example, I've been getting 8 MPG before attempting to make changes to the timing curve and main jets.

Pointer 5: Feel. If you have sluggish and smooth performance in RPM ranges from 1300 and up, your motor is likely rich. If you have poor and erratic and noisy performance in the same RPM range, your motor is likely lean.

Pointer 6: Temperature. A hot motor may indicate a lean setting.

The most difficult piece of information to obtain, and the piece I cant give you, is exactly what a great performing motor is like in all these categories. You have to tweak and tune up to and slightly beyond your best tune, to discover exactly where that mark lies.

1SASjeepster 08-03-2012 03:18 PM


I read where you cleaned your spark plugs with brake cleaner. I know it would probably never happen in a spark plug situation at least not enough to get you BUT I will tell you this anyhow. Brake cleaner and high heat create PHOSGENE GAS. It is a very deadly chemical weapon that only one whiff of it is enough to destroy your lungs for life. One whiff, not one full breath, just one whiff. A welder used brake cleaner on some parts because he ran out of degreaser and didn't want to go to the parts store. He was in a greatly ventilated garage. He began and was out. He got to the hospital and he has been going weekly for breathing treatments because his little whiff destroyed most of his lungs. It is something to think about.

I understand the spark plug is in the cylinder and exhaust gases flow out through the exhaust pipes BUT there are instances in a mechanics life when the gas mixture backs up and goes out through the carburetor. Be careful.

Take care,

The time now is 02:46 AM.

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