Holley Tuning Help

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Walker434

Walker434

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I have done plenty of searching and reading but I need some help. I have a 71 dart with a magnum 360 stock bottom end, comp cam (Specs below), edelbrock air gap, Holley 750 DP 4779-9, MSD billet Dist, 6 AL box and blaster 2 coil, Cheap 1 5/8 headers to 2.5 flowmasters.

Comp custom grind:

Duration @ .050 - 230/236
Lift .506/.513
LSA 110
Intake C/L 106.0

I am one of the youg guns and this is my first engine build. Swapped the engine last weekend so now I am just working out the bugs and trying to get it tuned right. I have the both blue springs in the distributor and the black 18* bushing.

Timing at idle is 18* and I'm all in with 35* at 2,500 RPM. This is a brand new 4779-9 Holley. I have adjusted my float levels and it runs HARD at With open throttle! I have also adjusted my 4 corner idle mixtures to get the most Vacuum at idle.

At idle I have 11 in of vacuum and that drops to 9 in when in gear. I know thats not a lot of vacuum but I have manual brakes. It idles great at 900 RPM in park and about 750-800 RPM in Drive. I love the way it sounds but when I go for a drive it likes to die at stop signs. Is my cam aggressive enough that I will have to up the idle to 1,000 RPM?

Also cruising at say 40 when you stomp it, it bogs then runs like a raped ape.

The only other issue is when its warm it doesn't want to start unless you give it full throttle like it's flooded?

I eventually plan to get an A/F guage but don't have it yet. Sorry for long post just trying to give all details. THANKS for any help!!
 
scrap the highest vacuum reading thing and put all the idle screws at 1 1/2 turns from all the way in. lightly seat them only. with the motor at idle rip the throttle open as fast as you can and leave it go back to idle just as fast. if it bogs up the squirter size until the is no bog. take it for a lap and test it.
 
Shouldn't have to idle that high with the 230 at .050 cam.
 
^^^^ Yep

If the OP needs a bushing to allow 10 or 14* of mechanical advance I have them for sale.
 
Bob, I will try this test to see if I can cure the bog issue. Cracked, I was reading about these 10* and 14* bushings on another thread. Be easy on me as I am new to this but would these replace the black bushing I have in the distributor now?

Is my current black bushing limiting me to 18* mechanical or advanced? I understand that I need to get the timing where the car wants it before I worry too much about tuning the carb. I guess I just don't understand exactly what the 10* and 14* bushing do, but if these will make my car run better you can bet your *** I will be buying them from you!!!

Thanks for all the help!
 
Walker434 said:
Bob, I will try this test to see if I can cure the bog issue. Cracked, I was reading about these 10* and 14* bushings on another thread. Be easy on me as I am new to this but would these replace the black bushing I have in the distributor now?

Is my current black bushing limiting me to 18* mechanical or advanced? I understand that I need to get the timing where the car wants it before I worry too much about tuning the carb. I guess I just don't understand exactly what the 10* and 14* bushing do, but if these will make my car run better you can bet your *** I will be buying them from you!!!

Thanks for all the help!
Click to expand...

Yes, they replace the black bushing which is ~18* mechanical.

The bushing limits mechanical advance. Basic timing is two pieces, initial + mechanical = total

The bushing allow you to run more initial timing while not exceeding you total number.

Bump up the initial timing to find the highest vacuum reading you can get at the same base RPM. As long as it starts OK with out killing the starter, you're good. Set it to the highest initial timing point of starter kickback or vacuum reading whichever is lower. I'd expect that engine to run at 850-900 rpm without issue in park and 750-800 in gear.

Once you get the two pieces of timing, initial and mechanical figured out, you can mess with the springs. Usually the light silver and blue springs work really well on most cars.
 
to your answer on the cam needing to idle that high I would say yes ,I have used cams like yours in short track engines, with high compression before and they all idled at 1000rpm or more. If you look at the tune up specks from 60's engines like yours with big cams 302/290-350/350-ford 302 boss/290 they all idled at 950/with man. trans. and this was before emissions came in!
 
Thanks Cracked Back! I think I'm starting to understand this now. I sent you a PM.

I now have my idle set to about 950 in Park and 850 in Drive and it doesn't die at stop signs anymore. I am going to try to get my hands on some 10* and 14* bushings and play with the timing and go from there.
 
Walker434 said:
Thanks Cracked Back! I think I'm starting to understand this now. I sent you a PM.

I now have my idle set to about 950 in Park and 850 in Drive and it doesn't die at stop signs anymore. I am going to try to get my hands on some 10* and 14* bushings and play with the timing and go from there.
Click to expand...

PM crackbacked...he makes those bushing and sells them....

I had the same cam in a 360 with a hell of a lot initial advance in it...it purr like a kitten...
 
Low compression doesn't help and usually needs more initial timing to be efficient.

I replied to your PM.
 
The 10* and 14* bushings are in the mail so I'll let you guys know how it runs with more advance timing. I can't wait!
 
Ok everyone. I installed the 14* bushing and got my initial timing to 22*. That is the most I could run with out the starter kicking back. I think this about right anyway becuase this puts me at 36 total. The car pulls more vacum now, idles better, starts better, smells better and seems to run better!!!! THanks Cracked Back!

This also seems to have helped by WOT bog but didn't cure it completely. My carb came stock with 28 and 31 squirter so when this weather ever gets better I am going to move my 31 up front and I have bought a 35 for the back. I am hoping this cures my hesitation but I'll let you guys know.

At least now I have my timing dialed in! Now its time to start working on traction again!:cheers:
 
Good to read.

Don't mess with the rear squirter just yet. What you might do is take the link/arm out that connects your primary and secondaries. Then tune the primary so the bog goes away. Then reattach the secondaries and adjust that squirter. You may need a pump cam change as well.
 
Ok from what I understand my carb came with the pink cams in it. Does the number 1 position or the number 2 position give a more aggressive squirt?

I am going to look tonight and see what position I'm in but maybe I should just go to a more aggresive pump cam all together? Maybe white?

I plan to un hook the secondaries this weekend and get the primaries tuned come hell or high water.
 
Quick update. Got home from work last night and changed out my primary side pink pump cam for the green in position #1. This helped my WOT bog a little. Then I uped the front squirter to 32. This helped a LOT!! The bog is nearly gone!

I will diconnect the secondarys tomorrow to see if I can get the bog completely out of the primarys. I get off work at 5 so by the time I get home there is very little daylight left and I am working in my driveway. Tomorrow I'll have all day to mess with it.

Question: Does holley not make a 33 or 34 squirter? It appears that they jump from 32 to 35. I will try a 35 up front this weekend but I am afraid that might be too big. I guess I could always get the drill out.
 
35's your going to need the hollow screws to get the full use of that size squirter. Try keeping the 32 and chaging the accelertor cam to the the hole marked #2 and make sure you have .15 clearance between the accelertor arm and the bolt with the spring. This done with the engine off and at wide open throttle , this so there is no bind on the pump
 
I will try this. Do you mean #2 cam hole in #1 carb hole? Or #2 cam hole in #2 carb hole?
 
I had some time to tune on the car this weekend and I got the Bog/hesitation whipped! I unhooked the secondaries and found that part of my bog was there. I ended up with a green pump cam in position 2 with a 35 squirter in the primaries to cure that bog. I then hooked up the secondaries and found that I still had a bog. I ended up with a 35 squirter in the secondaires and moving the pink pump cam to position 2. Now the bog is completely gone!

Thanks to everyone who helped with this!
 
Ok, I'm subscribing to this thread because I have nearly the same engine specs and I have the same model carb (Holley 4779-9), same distributor too (MSD Pro-Billet), an MSD 6A ignition box, and crappy Hooker headers. All with similar issues.

Walker434, could you post some pics of what you've done to tune your carbs, such as the pump cams and stuff like that. I'd like to see exactly where on the carb these things are and what you meant by the cam and carb holes. The last time I tuned a carb was in the 90's but it was a Carter carb. Thanks!
 
Walker434 said:
I will try to take some pics tonight. Maybe with pics this will be more clear.
Click to expand...

Awesome! Yeah, should make things more clear and also help people like me with your exact issues. These guys here are tons of help too.
 
Those are some nice cam numbers you spec'd. Not bad at all. That should make a nice street screamer when its dialed in
 
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