Slant Six Forum
https://mail.slantsix.org/forum/

holley 390 (0-8007) tuning
https://mail.slantsix.org/forum/viewtopic.php?t=4581		 Page 1 of 1
Author:  Pierre [ Tue Dec 03, 2002 2:10 pm ]
Post subject:  holley 390 (0-8007) tuning
Hey Guys -

I got a 225 in a 71 plymouth duster that just got recently rebuilt. Decided to put on new headers/intake/carb while I was at it. I chose the clifford 2/4 barrel intake with a holley 390cfm and the dual outlet headers.

I can't find the book that came with the carb, so I got no clue what screw does what ;) This is my first time working with a 4 barrel. Anyone know where I can find pictures that point out what is what? (Hose diagrams would be awsome, too!). Any tuning tips/instructions? It runs somewhat ok out of the box, but the problems Im having with it now - dies at stopsign (maybe 25-50% of the time?), bogs upon inital acceleration, and seemingly low power out of the engine as a whole compared to the original 1920. Im pretty sure its the carb because I ran the rebuilt engine with the original carb setup and it worked fine.

Carbs are so frustrating.. starting to research some efi possibilities ... ;)
Author:  Philip Cook [ Tue Dec 03, 2002 3:38 pm ]
Post subject: 
You need to change the Main jets to abour .48, Chnage the power valve to a 7.5 if you have an aftermarket cam or 8.5 if using the stock cam, and change the dischrge nozzles to .31

That is what I used to recomend when I worked for CLiffords. That is what Jack taught me years ago. That combination cures about 85% of the carb problems.
Author:  Trysix [ Tue Dec 03, 2002 7:10 pm ]
Post subject:  Trysix
Haynes Publishing makes a good Holley carb book that may be available at the large chain Auto parts stores....of from JEGS OR SUMMIT RACING. Also you may check out the Holley website.

Trysix
Author:  Doctor Dodge [ Tue Dec 03, 2002 9:57 pm ]
Post subject:  390 Holley Tune
Phil has a good combo outlined, basically a SL6 needs more accelerator pump shot and likes to have the power valve "tip-in" sooner. In some cases, the power valve restrictor holes need to be opened-up. (last resort, this is tricky) Power valves are best tuned-in with a vacuum gauge and a good carb book will walk you through the process.

One other thing to check is for the correct ported vacuum signal to the distributor's vacuum advance. The hose should come off the bib midway up the front metering block. If this line is plugged into direct manifold vacuum, a big bog off idle and "flat" acceleration is what you get. Check this with a timing light, your t.mark should jump into advance as soon as you crack the throttle open.
DD
Author:  Pierre [ Tue Dec 03, 2002 10:10 pm ]
Post subject:  holly 390 carb
I poked around holley's website and couldn't find the manual that came in the box, and haven't seen a response via email I sent them. Maybe I'll give them a call. I did go to a bookstore here in town to see if I could find some holley books.. I came across three or four, and I do believe one of them was the Haynes manual. Oddly enough none of the books came with a simple diagram that says air/fuel screw here, ported vaccum hose there.. etc etc.

I think I am going to see how far the carb can be tweaked before modifying the jetting and so on, once I figure out how to actually do so. It may not be a big deal to customize a carb for you guys that do it on a daily basis but in my eyes if its going to take a decent ammount of time to do so I may as well just put the effort into rigging up a TBI on the leaning tower....
Author:  Pierre [ Tue Dec 03, 2002 10:24 pm ]
Post subject:  hoses
DD,

Yep the vaccum advance feed to the distributor is being fed by the bib 1/2 way up the metering block. Then the PCV, the biggest bib on the carb is on the left side of the carb (when facing the carb from the passenger side of the car, say looking at the eletronic choke unit). Then I have a small piece of hose going from the bib that enters the same cavity shared by the air coming in through the air cleaner to a bib next to the electronic choke unit (only two bibs on the carb I found that were the same size, figured that had to be right..) THe last bib I found, under hte primary fuel bowl, I just kept plugged up. Im assumign this is an accessory vaccum outlet you can take to whatever needed vaccum?
Author:  dgc333 [ Wed Dec 04, 2002 2:09 pm ]
Post subject: 
I have a shaved head and a mild cam in my 225 with the 390 and 6 into 2 headers. The following is what I did to my 390 to get the car running well.

The stock primary main jets are 52, I went to 55's. Didn't change the secondary metering plate.

The stock accelerator pump cam is red, I have it in the more agressive #2 postion.

The stock vacuum secondary spring is plain (ie; no color code). I use either the long yellow (two steps softer) or the purple (one step softer). The purple is really the better choice but I like the feel of the secondaries opening so I use the yellow.

I have a ever so slight light throttle tip in hesitation that would likely be fixed going with the 7.5 or 8.5 power valve (stock is 6.5) but it's so slight I have just not bothered to pull the carb apart to change it.
Author:  Pierre [ Wed Dec 04, 2002 3:05 pm ]
Post subject:  carb parts
The engine was rebuilt to be completely stock. I don't think the block was shaved at all, just bored out 30 over, and the head was planed only very lightly... I cant remember the exact figure but it was only .02 or so to get rid of some light scratches.

Hm dgc, so you actually put in bigger jets then stock? I thought the consensus seemed as if they needed to be toned down a bit. Was this because of your cam change?

I just realized that an efi setup might take too long for me to implement before I go back to school. Probably will resort to tweaking the carb...

I was just hunting around and I noticed for the power valve and jets there are several different versions.. which ones should I go for if I were to change anything? Keep in mind my goal is best fuel economy here at the same if not more power/torque then stock.
Author:  dgc333 [ Wed Dec 04, 2002 4:24 pm ]
Post subject: 
My car was running lean, that was the reason for the bigger jets. The jet size also fell in line with what an old Direct Connection build up article recommended. The cam is a Comp Cam 252S which is pretty mild about the same a the mild Mopar Performance cam. My head was planned 0.060".

The car actually ran pretty well with the carb right out of the box. I would let the plugs tell you which way to go on the jets.

I would just get standard jets, same with the power valves.

If you do a search on Amazon on Holley there is a book on tuning Holleys that is very good. I got it at the local Borders for $20.
Author:  Doctor Dodge [ Thu Dec 05, 2002 4:18 am ]
Post subject:  Carb Tunning
Sounds like you should do a little adjusting then drive it for a while, then "read" the plugs and decide on jetting then.

Float level, idle mixture, vacuum advance "tip-in", and accelator pump shot "timming" would be the first adjustments to do. Getting these correct does not require opening-up the carb and should correct the stalling & bogging problems.

Start with setting your distributor timming and make sure the valves are adjusted. Carbs run off of engine vacuum so be sure you have a strong vacuum signal before starting-in on carb adjustments. (add-in as much ignition advance as you can without pre-ignition) Do you have a vacuum gauge?
DD
Author:  Pierre [ Thu Dec 05, 2002 12:08 pm ]
Post subject: 
The valves were adjusted when the engine was put in it a month or two back. I'll double check them and start adjusting the carb. Yea DD, I have a vaccum gauge somewhere in the garage. If not I'll go make a trip to the local Kragen/Napa/Whatever autoparts store is open at the time and get one. I can't do anything to the car on the weekdays because I leave home when its dark and get back when its dark :( And on the weekends I wake up past noon so a good chunk of daylight is lost that way hehe. I'll let you know how it goes. Thanks for the input all
Author:  Pierre [ Sat Dec 07, 2002 6:55 pm ]
Post subject:  newbie question time...
So I start fiddling with it today, and of course it doesn't go as smooth as I thought it would.

The float adjustment was fine, the level was right underneath the site hole and no fuel came out while running. Shake the car just a bit and it'd start to leak out.

Then, on the metering block there are two screws. One on the side of the carb with the accelerator pump, underneath the ported vacuum outlet, and another on the opposite side. They are both towards the bottom. By all the diagrams I've seen, the one towards the accelerator pump side is idle mixture. Is this right? And then what is the screw on the other side for? Something to do with the secondaries?

I hooked up the vacuum gauge to the manifold vacuum outlet underneath the primary fuel bowl, and it read at about 16 (i'm assuming the scale is in inches? it goes from 0 to 30, each tick incrementing by 1, in ~ 4" diameter circle). but to get any significant change id have to turn the screw more then 1.... maybe 1.5 turns each way. and even then it would change by less then 0.5. Is this normal? Maybe a very inacurate gauge? Or do I just need one with a more sensitive scale? I don't see how I am supposed to get within a 1/4 turn of whatever the "sweet spot" may be if the gauge is bearly moving with over one turn of the screw.

Then pretty much giving up on the gauge I did everything by ear (which I knew was a even more hopeless shot in the dark) it sounded like everything was pretty smooth and it drove well. One hitch though. Whenever I punch it and keep my foot down its fine, but if i punch it quickly and let go it dies as soon as I pull my foot back. I have a feeling this has something to do with the accelerator pump/nozzle?

Whew, ok that was long winded. If my questions are out of place here I apologize, just let me know and I'll quit bothering you guys about this.
Author:  dgc333 [ Sun Dec 08, 2002 5:48 am ]
Post subject: 
They are both idle mixture screws. One for each venturi on the primaries. If you have to work back forth on each to get the best adjustment.
Author:  Doctor Dodge [ Sun Dec 08, 2002 10:45 am ]
Post subject:  Idle Screw Adjustments
Yup, they are both idle mixture adjustment screws. Check to see if they are out about the same amount.

With the engine off, I would screw them in until they lightly seat and count the turns as you go, write it down. Then back them both out the same amount, If one went in 2.5 turns and the other went 3 turns, back them both out 3, then start the car and do some adjusting by turning them the same amount, a little at a time, to see what runs best. On front to back carb. mounting, the valve cover side screw will have more influence on the idle so get the best idle with both screw even then fine tune with the outboard. (usually will go in a bit more, (leaner)

Your "quick lift" stall may be too lean of an idle mixture setting or a mis-matched power valve. Get a long hose and drive the car with the vacuum gauge hooked-up and in the car where you can watch it. See if you can find a "soft spot" or stumble in terms of a vacuum reading, that will help you select the proper power valve rating.
DD
Page 1 of 1 All times are UTC-08:00
Powered by phpBB® Forum Software © phpBB Limited
https://www.phpbb.com/