Hi Guys
I have a 225 I'm trying to tune to work with my 390 4bbl holley. I put 51's in the primary and 54's in the secondairies, installed the secondary metering plate, used the stock secondary vacuum spring in the pod, and went to a 6.5 power valve. I ran it for awhile, pulled the plugs and they are black around the top part of the plug electrode, with some brown around the tips. My engine build is 9.7/1 compression oversize valves, headers erson 280/270 cam and cifford intake with a stock bottom end. I have read that some use the 600 cfm with this type of build, and was wondering if it would be a better choice,,or stick with the 390 and figure out the puzzle. Any input on this would be appreciated..

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Brian Long

I have lived in your Holley world for four years with perhaps a bit lumpier cam. Until I installed an o2 sensor and A/F ratio gage I was in the tuning weeds. I have tried every combination starting with power valve plug to 10.5, jets from 51 to 60, secondary springs from lightest to black.

First you need to make some vacuum readings at: in gear idle, park idle, and on up each 300 rpm to 3000.

Attach a long vacuum hose to gage, run gage into cockpit and make some tests while driving looking to see how the gage reacts to coasting downhill, constant throttle on flat ground, light throttle up hill, and WOT all at different speeds. Make notes; a friend is good to have on board for this task.

Before making the above tests, a few questions on idle quality:
Is car an automatic?
Dose engine idle in gear (D) with a lope, or is it smooth and what rpm?
What is in park idle rpm, and vacuum reading?

Do idle mixture adjustment screws react to adjustment, and how many turns out from bottom are they. Should be 1 ½ turns.

You are idling pig rich, and need more air at idle to lean it out.

Remove choke and secondary spring diaphragm chamber to check vacuum passages.

When you shut down engine at idle, the plugs will show idle mixture combustion at that moment. Yours shows pig rich. Dose the engine shut down without any spin-back?

If you pull off cap from center front vacuum tap on carburetor to manifold vacuum, dose idle improve, and idle adjustment screws become responsive to adjustment?

Proper PCV valve must be installed which supplies additional air needed for correct A/F mixture.

Once you can provide the information requested we can move to phase 2.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

I had literally same setup I ran for awhile with two different cams on erson 270 and a bigger one, ran fine for me once i got vac leak taken care of. If i recall i had a 4.5 maybe pv 56 or 58 jet in front light spring in secondary, big pump squirter like a 50 but it always seem to run better the more pump shot plugs looked decent in my case sandy brown. Maybe that helps? im sure our setups would differ somewhere but that was a pretty good street tune for my car when it was auto or stick. Never had an issue with rich idle i would check to make sure your pv is not blown and letting gas in at idle maybe? or just lean the mixture screws.
Oh the only problem i had tuning wise with that carb was a bog if i just went from idle to wot then it was fine but i believe that turned out to be because of a vacuum leak if memory serves.
Kev

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The car is an automatic,,idles at 800 in park,,down to 500 in drive. Idles with a lope, with a rich mixture at the tailpipe. The mixture screws does affect the way it runs..I have them set at 1 1/2 turns I have the center port on the front of the carb plugged..when I take it off the idle jumps up and smooths out. I don't think the carb is having issues,,its brand new. sometimes the engine does run on after I turn the key off. I do have a pvc valve installed,,but not sure if its the proper one..just bought one off the shelf and stuck it on..

chek this out http://www.youtube.com/watch?v=A4kCofAXP5w&feature=plcp

give you some vacuum readings.

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Brian Long

Need to see them readings, they are going to be your guide to tuning the carb...

Since you now have an engine that is not "factory" and more cam duration, you may need to have more idle speed to keep it happy... the stock-ish Erson has a little lump and lower rpm tends to aggravate that.

I'd check for the vacc. leak first...put the car in park in your driveway and using brake cleaner or carb cleaner spray a bit at the carb base, and at the spots where the intake runners meet the head...if the idle changes then you have found the location of one leak...

The port under the bowl at the front of the carb is where you should hook up you vacc. gauge, it will give you the reading that the carb sees...also if you drive with the gauge in that location, you will be able to judge how much your throttle plates are open while driving...

With the Holley 8007, I think your jet selection is OK, you may need to floor it on the road and check the vacc gauge to see if at WOT you are at zero vacc. or have some left (if you have some left the carb is too small for the build-no problem there, that now means you have a carb that will provide better mileage and get better signal from the motor....you will also need to change the PV).

Run on would be an indication that the throttle plates may be too far open, and you may need to adjust the idle screw, check to make sure your throttle cable is adjusted to allow the plates to close all the way...or find that pesky vacc. leak causing the run on...

If you have an O2 sensor, and a vacc. gauge you should be able to dial the carb in over the course of an afternoon.

I would also suggest getting the Dave Emmanuel Book on Holleys.

Other things that may affect your carb tuning: proper valve lash, and timing (if you have a hot rod setup and are still using a stocker distributor, if you recurve, you may need to 'fiddle' with the carb settings again)....

Good Luck,

-D.Idiot

i posted a video of the vacuum readings..see if this helps you some
thanks

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Brian Long

I encourage you to stay with the 390 carb and not go to the 600. You will not get much more (if any) power, and driveability will be worse and tuning harder.

Lou

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Home of Slant6-powered fun machines since 1988

Do you know the Lobe Seperation (Lobe Centers) for your cam?
What are the lash setting you are currently running?
DD

Whats the duration of your cam at .050 and the lsa, the cam in my turbo motor is 220@ .050 on exhaust and intake lsa 114 pulls over 15in vac at idle, I could be wrong because this was with the old motor but i though even with the bigger cam i had over 10 in vac or more at idle still that cam was 238@ .050 108lsa 510lft. When you nail it and get a slight hesitation i'd say your lean for a second considering that what my afr gauge told me during tuning and stuff. Try a bigger pump shooter may help cover up that split second lean spot or maybe a little more main jet but that will richen up your normal driving, as far as the rich idle i'd make sure you got a good pv in there and lean out the mixture screws. Your video the vac gauge stuff looked normal as far as the driving and what i look at on my gauges. somebody else metioned timing couuld take a look at that the 225 does like a fair amount of initial timing that may help the initial grunt.

Kev

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Actually if he opts for a 600 with all annular boosters instead of the crappy stockers, it will do better on the street...but he will need to go with a stiffer spring in the secondaries (I run a brown in this combo)...and gas mileage will suffer compared to the little 390....(about 4-5 mpg average)

That being said...the annual booster 600 vs. the 390 at the track with the right combo is worth about .5 seconds if in the 15-16 sec bracket.

-D.Idiot

well after looking at my cam card harder,,seems erson screwed up on the grind. At .050 intake is 220 and exhaust is 230. shouldn't that be the other way around on a split duration 280/270? And the card has intake 270 and exhaust 280. I wish I woulda realized this be4 the install. I have a lift of 310 both exhaust and intake. intake center line is 108, have the valves at .022 lash. I degreed the cam 3 degrees advance and went with that. It smokes the 26" tall tires i'm running, with the 3:23 gears. It's just that rich eye burning idle thats the issue. Could this be due to the screwed up grind on the cam erson did? Can it be fixed without changing the cam??

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Brian Long

twister6,

[quote]What I got from the video:
Idle in P: 800rpm, 11â€￾ Hg
1000 rpm, 15â€￾ Hg
1500 rpm, 18â€￾ Hg
Idle in D: 750-800 rpm, 9â€￾Hg
1000? , 12â€￾hg

Light throttle:
2000 rpm, 13-14-15â€￾ Hg

Off throttle:
1500 rpm, 15â€￾hg
2500 rpm, 20â€￾Hg
WOT: through rpm range to 4000 rpm, 3â€￾hg[/quote]

I have to say most of those vacuum readings are not bad, a lot higher than what I get. What rear gear & converter stall speed are you running?

I did not hear much of a lope in gear at idle.

As Doc was wondering, what is lash adjustment?

[quote]I have them set at 1 1/2 turns I have the center port on the front of the carb plugged..when I take it off the idle jumps up and smooths out.[/quote]

With manifold vacuum tap uncapped adjust idle speed back down to 1000 or 900 Re adjust idle mix screws, and report how far out they are if there is a change. Go for a ride, look for change in off throttle flat spot. Report back results.

Do you recall how much of transition slot was showing when throttle is closed when mounting carb? (This adjustment is made by idle speed screw).

Is there any surging at steady throttle position on flat ground where engine seams to pull slightly then let off?

WOT producing only 3â€￾Hg is a bit high, should be close to zero. Two causes come to mind, too small or dirty air filter, or too little carb. I don’t think 390 cfm carb size is the problem with a 225 cid engine in this case where rpm never went past 4500 rpm.

Can you find a larger filter with more area to run more WOT tests with manifold vacuum tap capped? Or, perhaps a quick unfiltered test where where you can pull filter off, run a WOT from stop for 1/8 mi, and then replace filter (don’t recommend unfiltered running with hood insulation).


When you ran second WOT test, and let up slightly keeping throttle over half open, and could feel engine continuing to pull; that is the secondary circuit continuing to open. If you were to let off, and get back on it the engine would feel weak for a moment until the secondary’s reopen. In other words two barrel operation is not keeping up with engine demand at that moment.

Back to original query, “rich idleâ€￾, I think you need more air, and less transition slot showing at idle. I’m going to say the secondary idle circuit hopefully is correctly set from factory. Stock 6.5 power valve is good for now.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

Sounds like Erson did not understand that you wanted an RDP (reverse dual pattern) cam.

Try loosing the exhaust lash as much as you can, see if it will lash at .026 or even .028 with-out a lot of "ticking".

Basically, this grind (at 108 LSA) has a good amount of overlap and is leaving the exhaust valve open a long time, after TDCE. Doing this lets a lot of intake charge, flow out the tailpipe.
DD