Carb help, Holley 390 or 470TA

[drawk]

I have a 74 CJ5 with a AMC 258 i6 / 4.2l running original dizzy with pertronix points conversion and clifford 6=8 intake and herman header. Transmission is a ford top loader. I have a edlebrock 1404 on it now but it has vacuum leaks around the throttle shaft and it runs like . So of the two the holley 390 or the holley truck avenger 470 which one serves the better purpose for a 4bbl. If you run either what setup are you using jet wise and power valve etc… I searched and used google foo but I have a melting pot of awnsers. Im just looking for the facts and to hear from people who have actually used these carbs knowing their pluses and minuses. Thanks Ahead of time.

 

[Old Dog]

I know some people say they have good luck with the TA but I've seen more junk ones than good ones.
IMO with the AMC 258 i6 / 4.2l you would be better served with the MC2100 2bbl.

 

[mtnwhlr]

I think a 4bbl is to much carb for a AMC 258 i6 / 4.2l .

 

[elwood blues]

I'm running a stock out of the box Holley 390, the only thing I've done to it is change the vacuum secondaries spring to a heavier one. Without some internal engine work, I believe a 470 truck avenger will probably be too much carb for you.

 

[drawk]

So I found a deal on the 470 TA I could not turn down. It had a edlebrock 1404 on it which was decent with a metering rod change but it developed a vacuum leak on the throttle shaft. That carb came with the truck so I figure time for something new. I will document the changes I make to the carb and let every one know the progress of each change so hopefully this post helps someone in my same position. I will try the settings that the clifford website has for the holley 390 cfm and work my way from there. If anyone has any info or tips for setting up this holley or timing degrees they find work best. Please let us all know. I will also throw in my vacuum gauge readings as well.

 

[Bent]

I would suggest switching to annular discharge boosters on the primary bores. That type of booster is much better at handling low vacuum levels than the Holey standard down leg booster. This is why the MC 2100 is so good on the AMC 258 i6 / 4.2l . If the 470 TA is a mechanical secondary I wouldn't use it on the AMC 258 i6 / 4.2l .

 

[drawk]

Im waiting for my holley parts to come into NAPA I will be doing a .031 discharge with a 8.5 power valve and my main and secondary jets at .050 to start. It does have annular discharge boosters and vacuum secondaries. I will try my timing at 10* BTDC and the black secondary spring. I will let everyone know how this combo works. Im just outside of Portland Oregon so it will be sea level or close too. I plan on taking it up into the tillamook state forest for a little elevation change and to test it on some angles and heavily washboarded gravel logging roads.

 

[drawk]

So I got everything thing installed with only only hitch and that is the choke linkage keeps binding on me. I can kick it down with my finger but the minute I use the accelerator it kicks itself back on. So I sprayed it with carb cleaner and then some sea foam deep creep. It help a little but sometimes it still has issues. I took it for a drive last night anyway at 11pm. Feels way better than the edlebrock 1404 that was on it. Smells rich so i thinking of jetting down some more. Im thinking .048 or the next step below that. My vacuum is at 17-18"HG at idle at 8*BTDC with 750rpm at idle. Any tips on the choke linkage fix please let me know.

 

[drawk]

So I talked to holley about the choke issue and did some checks on ohms and the carb choke thermostat was out of spec so they are sending me a new one. I will let you know an update as soon as I get it and install it.

 

[gutthans]

Your setup is somewhat similar to mine (which I have been running for 10+ years...so let me share what has worked, but first:

Originally I started life with a CJ258 w/ 4.0 head conversion...I'm now running a Golen prepared 4.7 stroker with Clifford headers, Offenhauser intake (dual-plane), and Holley 390 w/ vac secondaries and HEI ignition. Just transferred the parts over and upped the jets mostly.

My running specs are as follows:

Carburetor:
#51 Primary jets
#52 secondary jets
6.5 power valve
stock pump cam on #1 hole
.025 discharge nozzles
annular venturis
choke set on index


Ignition:
Idle @ 750 rpm
16* static (initial) setting
20 - 21* mechanical advance
15* vacuum advance on FULL MANIFOLD VACUUM

Advance curve begins@ 800 rpm
Full-in @ 2400rpm

Full Mechanical Advance = 36 - 37*
Total Advance at cruise = 52*

Your 470 shouldn't be too far from where mine is, BUT, note that Holley uses poor sealing in the base plate around the throttle shafts. If you have a used carb I would really suggest you get a NEW base plate. Alternatively, have a reputable carb shop REBUSH the two throttle shafts. I first used a used 390 and saw 15-17 inches of vacuum...when I replaced it with a new unit my vacuum went to 21 inches @ idle. Same thing happened after about 24,000 miles on the newer 390...this time I just ordered a new base plate from Holley and Viola! same jump back to 21 inches. The shafts will leak and pull air. That will give you a difficult idle eventually, and affect performance up to about 2400 rpm when you transition to the main carb circuits. Don't bother trying to tune if your vacuum isn't right, you should be pulling at least 18 inches @ idle. Find the leak (spray carb cleaner onto the primary/secondary throttle shaft while idling...see if your idle does a quick change!!!)

BTW...don't try MY ignition settings if you aren't running an HEI and haven't done your homework. No factory (computer control) setup can run this.

 

[drawk]

I'm at 8-10 btdc in timed spark port and my distributor is the original with a petronix point conversion. The carb was brand new so everything seems to be going good except the choke cap was out of spec. I have it set at 17-18" vac at idle at 750rpm right now. I took it for a quick drive but the vac secondaries didn't open "black spring" but also the choke got stuck on it too. Once I get the choke set up right I will retest.

 

[gutthans]

You can use either carb well on the AMC 258 i6 / 4.2l . However, my choice would be the 390cfm. The 470TA is good, but the extra airflow is wasted on the older style AMC 258 i6 / 4.2l head. If you can find the cash, you will be very happy to install the 4.0 head conversion onto your AMC 258 i6 / 4.2l .
It wouldn’t hurt to try a pair of annular venturis in place of the doglegs…you might like the low speed help.
I’d start with #51 jets, a .025 discharge shooter, and the stock pump cam. Tune the shooter first, looking for the crispest throttle response with out any sudden bog from a stopped start. You’ll probably like the .025 or .028 for that.
Next, work on picking a vacuum spring that doesn’t open before 2400 RPM. Probably the plain steel one is my guess. Attach a paper clip to the diaphragm rod just under the housing and go drive. Shift all gears at 2400-2600 rpm and inspect the clip. If the secondaries opened, the clip will be further down on the rod. Go stiffer until you find one that doesn’t open until higher than 2400. That’s the typical cruise range for your jeep and you don’t want them to open there…or mileage will suck.
That done, now you can go find the correct cam setting. The right cam should not have any bog at cruise, so punch the throttle around 1800 – 2200 and if there’s hesitation, try the other hole in the cam , then try a few different cams until the midrange has no bog.
Now you can drive easy for about 2-3 days and check the plugs. Look for a very light gray/brown on the porcelain. If the plugs stay white, it’s too lean… try one to two jet sizes up (52 - 54) depending on how white the porcelain is. Black soot is the reverse, too rich.
If you can, get a GM HEI unit. Hands down it’s the BEST ignition change to make on the jeep. You’ll want a 6cyl unit from the early 250 inline six, like what came on Chevy Nova, Camaro, or S-10. You will also need the Mopar AMV 360 V-8 distributor gear to mate with your cam. It costs more than the Crown part, but the quality control IS worth the extra bucks.
I have links for engineering articles that detail much of the things I mentioned and have done on my own motor, if you’re interested. I've been playing with these settings for about 10 years on the AMC 258 i6 / 4.2l platform and feel really good about where it's at. Oh and yea, I use the old manifold on the newer head...there's a simple mod that let's you install onto the hi-port head with a little bit of Dremel work on the outboard intake runners. Good luck.

 

[drawk]

I got the new choke cap and took it for a drive. Grey spring for the secondaries paper clip didn't move but I put it on funky as well so I will try again. No bog and the throttle response is great. So here's the specs so far.


AMC 258 i6 / 4.2l with clifford 6=8 intake and hedman header with stock dizzy and petronix module holley 470cfm truck avenger
10*btdc


Holley is set as follows

.031 discharge nozzle
.050 jets main and secondaries
8.5 power valve
800rpm idle on manifold vacuum
19.5" hg of vacuum at idle

I will check spark plug color and reply with the results

 

[gutthans]

Mileage or power? That's the tuning question with the Holley setups. Sounds like you might be right where you'll like it, but I'm going to bet you'll want to drop your power valve to a 6.5 or 6.0...if you do a lot of around town driving. I think you'll find that the 8.5 is too close to where the vacuum is while shifting.

If you can get a long (3-4 ft.) piece of vacuum hose and hook up a gauge to the full vacuum manifold port...you can drive around and watch what your vacuum does (tape the gauge to the hood where you can see it of course ). I found that while my sitting idle was 21", and my steady cruise was 13 - 15"...my vacuum dipped to around a 7.0 while I was accelerating and shifting up and down in traffic. At 8.5 you are going to have extra gas from the power valve opening too often and lose mileage.

You'll see soot at the tailpipe exit and may find it on the plugs after a bit, even if your jetting is perfect because of that.

 

[drawk]

Ok I will take a look at the plugs after driving a bit or I just might experiment with the new power valve anyway. I pulled the plugs and all but number 6 and number one are turning the nice brownish color the other two are a little lighter just a little more gray. I have the plain secondary spring in and they haven't opened yet so I'm going to go down another secondary spring to see if that helps. I had it on manifold vacuum but it bogged down twice on me coming from a full stop. So I set it back on ported vacuum and now its gone. Overall this holley truck avenger is a world of difference better than the edlebrock but i have only taken shorter trips. I will let everyone know where this all ends up. Hopefully this thread helps someone out.

 

[gutthans]

Your #1 and #6 plugs will ALWAYS run slightly leaner than the center plugs. You sound very close to just right. I think you'll like them better though with a lower rated power valve.

If you like the timed spark...use that. I find that with correct vacuum can tuning, the full manifold port gets better mileage, but you may not want to do that much experimentation.

The spring issue is a toss-up. If it opens too early, you lose gas mileage. You won't really notice if it's too late, because that really only comes into play on freeway ramps generally above 3000rpm where the motor wants to produce power. DD jeeps around town spend LOTS of time between 1000 - 3000 rpm. That's why I said you probably want to tune it to start opening around 2400+ rpm.

My rear gear is a 4.10. My mph/rpm is as follows: (in 5th gear)
30 mph = 850 rpm
55 mph = 1950 rpm
65 mph = 2250 rpm

As you can see, I don't need an early power valve or a quick secondary, however, I do so appreciate the whole 4 barrel dropping in when it's time to embarrass a Tundra, Explorer, or an unsuspecting F-AMC 150

 

[drawk]

I changed the power valve to a 6.5 and i do notice less of a fuel smell so thank you for the tip. What are your settings for timing on a AMC 258 i6 / 4.2l off manifold vac …. like 10*btdc?

 

[gutthans]

Depends...

1. Warm the motor up
2. Disconnect and plug the vacuum to dizzy line.
3. Start at 10*
4. Run the jeep uphill or accelerate a few times from about 10 MPH on flat
5. No ping???
6. Advance 2*
7. Do it again
8. Stop when you get ping and back off 1- 2*

This sets your mechanical for your altitude/compression/gas quality. You can add 2* in winter...but you may have to subtract 2* or more in summer depending upon the weather. All you need to check is that you can run at 3000 + RPM with no ping or knock with the vacuum hooked up and you can leave it alone.


With your near stock setup you probably will like 12 - 14* initial setting, IF, and I say IF you want more from your motor...you can experiment with vacuum settings you can get way better idle and torque, but it'll take buying about 3 or 4 different 'cans' from Autozone or O'Reillys unless you have a Crane or other adjustable can that will fit your dizzy.

I can find some of the links and layout some instructions you'll need to read IF you really want to consider tuning more, but see if you like it as it is for a few days...

If you want to go there, I'll have to tell you how to find your total built-in advance and the RPM curve, as well as how to identify some guinea pig vacuum cans to try until you get the combination you really like.

http://www.corvetteforum.com/techtips/viewsubtopic.php?SubTopicID=115&TopicID=3
http://www.crankshaftcoalition.com/wiki/How_to_make_a_timing_tape
Use these to start your research into continuing to tune for best performance, if you're motivated...

 

[drawk]

I will give the manifold vac a shot again. I think i might have a small vac leak but i can't seem to find it anywhere. I have checked everyplace possible I even replaced all the gaskets I could and I'm still getting a little fluctuation in my vac reading. Anyway, what RPM are you running off of manifold vac? I have mine on ported vac at 10* at 750rpm right now. Is is possible to just switch to manifold and leave the settings as is? whats the highest idle rpm I should have for a AMC 258 i6 / 4.2l ? Thanks for the help

 

[gutthans]

If you switch to full manifold, your idle will go UP! The dizzy will 'see' more vacuum immediately. You will have to turn the idle speed screw down about 1/8th of a turn to get back to 750 rpm.

The deal with ported has to do with EPA emission regulations and NOX. The delay in vacuum rise on ported makes the idle have less NOX as you sit. On full manifold, the dizzy 'sees' what the carb venturis see for vacuum...which is partly why mileage will be better. Also, with more available vacuum at idle the dizzy is slightly advanced and firing the plugs earlier...more power on the same gas, but more idle emissions

If you bog from manifold vacuum, then it means the vacuum can isn't right for the setting. That's where experimenting comes into play. Also, if you have ANY emissions stuff (like EGR) it will require careful fiddling to get it running as well as just plugging into ported, setting 10* and driving. BUT, if you invest the time it will eventually run MUCH better.

I think 700 -750 is a fine AMC 258 i6 / 4.2l idle...understand that any changes you make will probably alter the idle quality and speed...always go back to the idle speed screw and reset to your 750 after each permanent adjustment. If you drop the dizzy to 8*, you would have to raise the idle speed...if you take it up to 12* you'll probably have to drop it down. Got it?

Get a can of CRC Brakleen or Carb Cleaner...while it's running use the attached red tube thingy to squirt a small blast at the following places:
1. Primary throttle shaft return spring
2. Secondary throttle shaft (at base same side as the primary)
3. Brake power booster hose fittings
4. all along ANY vacuum hose leaving the carb or manifold.

When you hit the leak, the motor will go up about 50 - 75 rpm for a sec or two.