Tuning advice

[Norwoodx55]

OK, I just hooked up a Innovate LM-1 to check my A/F ratios. It confirmed what I suspected, I am running rich. Idle seems OK at around 14.9. Cruise and under power are rich, 12.6-13 and 11.8-12 respectively. These numbers are aproximate, I have been looking out of the corner of my eye to get them. Should I got straight to the primaries to raise the cruise ratio or is there another curcuit I should start with? How much will this affect the WOT ratio before I mess with the secondaries? Approximately how many tenths of a point in A/F ratio will each jet # change? I am running a 3310 with a Proform main body and secondary main block(adjustable jets as apposed to metrering plate) now. I would like to get this carb close and gain tuning experience. I will be using a 4779 mech. secondary with the HP main body next, and this will be the one I really want to get right.
Thanks in advance, Brett

[68Formula]

Start with the cruise circuit. Based on your readings I would say 4 jet sizes down on the primaries should get you nearly dead on.

You will also find that your WOT readings will increase to a lesser degree when you do this, probably also getting you right in the range you want there without even touching the secondary jets.

If you have any stumble issues on acceleration then you have to address that circuit.

[Shaker455]

I would like to get this carb close and gain tuning experience.
Thanks in advance, Brett

Brett,
If you want to gain experience in tuning the first thing to do is map out every aspect of your carb and engine combo follows:

Jets
Airbleed sizes
Squiter size
Pump cam color
P.V. size F&R
IFR (idle feed restriction) size in metering blocks
Type of metering block and size and amount of emulsion holes
Float level
Throttleblade position ( amount of transfer slot exposed F&R) should look like a small square
4-corner idle?

Engine size
Cam specs
intake
Dist,
initial, mech advance & total
heads & aprox flow
Exhaust system

Jeff

[Norwoodx55]

Brett,
If you want to gain experience in tuning the first thing to do is map out every aspect of your carb and engine combo follows:

Jets
Airbleed sizes
Squiter size
Pump cam color
P.V. size F&R
IFR (idle feed restriction) size in metering blocks
Type of metering block and size and amount of emulsion holes
Float level
Throttleblade position ( amount of transfer slot exposed F&R) should look like a small square
4-corner idle?

Engine size
Cam specs
intake
Dist,
initial, mech advance & total
heads & aprox flow
Exhaust system

Jeff

Jeff, I have most of the info: Jets 74 78 Airbleeds primary 75 idle 36 main sec. 45 idle 36 main Squirter 31 Pump cam Orange (I think) PV 6.5 Float level Prim. level with bottom of hole Sec. slight dribble Throttle blades prim. square slot sec. height half of width No 4 corner idle Unsure of specs on metering blocks. Don't know the types or have pins to measure holes. Engine specs. 420" SBC 10.25:1 CR Cam specs. 236/242 .565/.571 108 LSA solid roller Intake RPM air gap Dist. vacuum adv. (MSD) Timing 16 initial 34 total Heads AFR 195 approx. 260 [email protected] Not sure if you are recommending I know this info just for my own good, or if you are wanting to help a little more and need the info. I would appreciate your input, but do understand you have a business doing this too! Mike, your advice of dropping 4 primary sizes sounds logical too me. This will probably be the first thing I try. Thanks for the input fellas, Brett PS, I tried twice to get this to post in list form. It keeps grouping it into a paragraph though.

[Shaker455]

Brett,
My advice is free and posting your info is so I can see what you have going on.

How much vacuum are you making at idle & in gear?

How many turns out is you mixture screws?

Have you been reading your vacuum at the A/F points in question?

[Norwoodx55]

Jeff,
-Idle vacuum is 11, same in gear(manual trans.).
-I have not checked vac. while driving. I could tape the gauge to the windshield to get this.
-I forgot to add in my last post the exhaust info. 1.75" headers into 3" dual, over the axle.
-Mixture screws are just over 1 turn out.
-Another possible consederation is that I am a mile high here in Colorado. This altitude blows for making power.

[68Formula]

If you're running a vacuum booster try taking about 4 degrees out of the mechanical advance and set the initial at 22 (increase in 2 degree increments while the engine is hot and make sure the starter load is ok).

[Norwoodx55]

Hey Mike,
I am running hydraboost so no vac. booster. Is this suggestion for improving brake feel w/ vac. boost or for tuning the carb? I could see higher manifold vac. pulling more fuel at idle and light load?

[68Formula]

If you're idle mixture screws are turned for the highest vacuum reading and you only have 11", then the engine would probably like a little more timing down below. This will help the idle a little bit and improve throttle response, but with a manual trans I doubt you will drive it in such a way that you will feel the difference.

The other issue with such a low vacuum is the power valve setting being correct, but I think in your case, you're ok.

[Shaker455]

Okay Brett,
Your airbleeds...Your primary side is different from your secondary?

If so I would like see them all the same...do you have access to different airbleed blanks?

Example: Curb airbleeds (outers) .070" front and rear

I would drop the front jets to 72's

Hi speed airbleeds: .036" front and rear

I like the # 330 pink cam

Also you do need someone to ride shotgun with you and read the vacuum gage, A/F & RPM where it's going rich at cruise as with your low vacuum it may be opening the powervalve too easily.

You may need a PV from 4.5 to 5.5

[Norwoodx55]

Jeff,
-Yes, I double checked the curb bleeds. Is that typical for a vac. secondary carb maybe. The HP main body I will use on the 4779 has the same bleeds front and back, 75/36.
-I don't have any other bleeds or blanks other than what is in the other main body. what is a good source for them? I thought I had seen a kit of them from Holley once, it was a bit pricey.
-I have the #330 pump cam I can put in.
-I will have to get better "on-the-fly" info with someone else in the car, it is a bit busy checking things while driving.
-I think I will try a lower # PV.
- I am going to be working out of town the next couple of days. The weather is still testy in March so that will limit my chances to get the car out too. I will let you know what I find with these changes.
Thanks for your time, Brett

[Shaker455]

Brett,
Yes that is typical but I square them up like the Mech sec and I have airbleeds if you need some (Sales Pitch)...LOL

I get a piece of vacuum line long enough to string into the car and hang the gagae from the rear view mirror with the line wraped around it a few times.

Okay I'll look for your results.

[Norwoodx55]

Jeff,
Hope to get some time with the car this weekend. Sending you a PM about the airbleeds.

[Shaker455]

Hey Brett,
Got your PM, look forward to hearing from you.