LilJayV10

iTrader: (5)

I am about to finish my 406. I have a basic holley 750 DP. I was wondering if one of the carb guru's could give me a good baseline suggestion for the jets/PV and squirter's. My setup is below. Thanks.

406 w/ 10:1 comp
AFR 195 eliminator heads
288XRoller cam, 236/242 @.050
RPM Air Gap Intake
2800 stall 3.23 gears
dyno don's 1 3/4 shorty headers, 2 1/2 y pipe to 4 inch mufflex
Stock HEI ignition

Thanks for any advice.

Jason

sofakingdom

iTrader: (1)

Go here and put in whatever it says it's supposed to have. Then follow the "Holley Tuning" sticky at the top of this page. Once that procedure is COMPLETELY COMPLETE, if it's not perfect yet, we'll see if we can take it further. Meanwhile, everything you need to do and why you need to do it, is in that sticky.

xpndbl3

iTrader: (5)

stall and gears are going to make that motor rather finicky since it'll want to rev freely.

LilJayV10

iTrader: (5)

What do you mean? The car ran high 7's in the 1/8 before and drove like my stock 305 TBI did? I don't understand, can you explain what you mean? Thanks.

I will re read that sticky.

lukn4trbl

which style/PN of 750DP do you have?

Does it look like this:
http://www.americanmusclecarhardware...log/00d7_1.jpg

or more like:

http://www.torinoproject.com/images/...50dp_ennen.jpg

Is it stock? Do you have a secondary power valve, or four corner idle?

If you don't have a secondary power valve, start with

Primary PV Size for your cam specs, CID and compression will be about 4.5

Check idle vacuum with a guage and then subtract two points to get you
very close to optimum.

Primary jets 78, secondary 84

Install at least one new plug before the jet change and then drive around
at cruise. It is best to install one at all four corners to get an idea of the
fuel distribution between front and rear cylinders. Those tend to be the
most lean because of most manifold designs.

Do not go wide open, or use excessive throttle. Check the
plug for correct heat range and mixture.

If it's good, do a wide open test (at the track, or dyno preferably). Shut
it down right away and check heat range and mixture again.

Adjust jetting as needed. If you have access to a wide band 02, you can
monitor the ratio.


If you do have a secondary valve, start with:

Primary 78 / secondary 78 jetting

These are safe jet sizes. You will likely have to jet down.

You don't want to start off too small and run lean! Better safe than sorry.

Worry about the squirters and pump cams later. The squirters have a slight
effect on jetting depending on pull-over amounts/anti-pull over design.

Happy Tuning.

LilJayV10

iTrader: (5)

I messed with the carb some. It's running really rich. The spark plugs are black.

I put on my friends 750 DP w/ a proform main body with four corner idle screws. He is not using it and this is probably the route I am going so this is what I am going to use.

It has 72/78 jets in it now. I don't care about WOT performance just idle and driving now.

I am pretty sure the throttle blades are open to far and it's dumping fuel in from the primaries. I need to take the carb off and look at the idle slots.

Turning the idle screws doesn't have much effect. I unplugged a vacuum hose and the car sped up and smoothed out some. I also turned the idle mixture screws in and the vacuum shot up to 15 inches! These things lead me to believe it's running way to rich at idle.

I bought a holley how to carb book. I "think" I understand the basic concept of a carb, but obviously need to know more.

LilJayV10

iTrader: (5)

sofa,

I know on your sticky one of the later things you do is the PV. But do you think with my setup and problems I should change it first? There is so much fuel dumping in at idle I can't get the engine to calm down.

Thanks.

LilJayV10

iTrader: (5)

I opened the secondary blades just a little bit. Started it and it was running at 10inch's of vacuum. I closed the secondary idle screws and it went up more. I adjusted the primary idle screws and I got 14 almost 15 out of it.

Air_Adam

Very very similar combo to a buddies car... IIRC hes in the 80/82 range, which is probably a decent place to start. I'd follow Sofa's instructions though, he's dead on.

lukn4trbl

Did that solve the idle fuel ratio problem? It seems the idle vac is well above
the PV point (if stock).

If you're still having issues, check the float levels, and fuel pressure at the
bowl inlets.

Anything more would lead to idle bleeds, or IFR's. Both have a dramatic
effect on idle tuning and part throttle cruise ratios.

LilJayV10

iTrader: (5)

Opening the blades up on the secondaries seemed to help. The car sounds a lot better at idle and revs better.

I went and drove the car. Just light throttle cruising. Came back and checked the plugs. They were burning a lot cleaner. They weren't all black and sooty like before.

The primary idle screws are really sensitive now. Before they really didn't seem to do anything. Now I can easily kill the engine if I turn them in to far.

What is the best way to find out how much I should open the secondaries. I know it's trail and error but is there a limit of going to far?

I looked at the innovative motorsports wideband setup. It's pretty interesting. I figure I can get "close" buy doing things the old school way buy reading the spark plugs.

lukn4trbl

I would start by splitting the transfer slot exposure between front and back
(within limits of course).

This is tough to do with carbs that don't have a 4 corner idle, but it beats
having to drill holes in the blades. Most of the time you can get the carb
to idle by tuning the bleeds and IFR's. That takes patience and practice, but
once you get a grasp of the circuit it becomes easier each time.

Reading the plugs is the best method. A wide band gives you a ratio to get
you close, but it can't tell you what the engine needs.

If you were to pull and compare all 8 plugs, you could see which cylinders
are running rich/lean, which need more/less timing, etc.

The wideband just gives you and average of the entire motor.

Stick to plug reading and get good at it. You'll be far better off in the long
run.

LilJayV10

iTrader: (5)

Well my bastard of a car is back on the road again.

I am now back to where I was several months ago. It still doesn't like to run in gear. When I put the carb back on i closed the secondary screw maybe a 1/4 turn. I thought I might have had it open to much. I think I need to open it again. Is there a limit to how much I should open the secondary screw? When is the point I should start thinking about having to drill holes in the primaries to let more air in. I don't think the cam is that huge especially on a 400.

I want to get the thing to idle right before I start any adjustments on anything else.

After the idle issue the car has a horrible off idle stumble. The car sounds like its drowning, its hard to explain but even my wife asked about it. I will deal with that later on.

Thanks for the help. I bought that Holley book. I haven't looked at it in a while. I will do that tonight.

Jason

LilJayV10

iTrader: (5)

I know the throttle blades are open to much. I put the vacuum gauge on the timed port and I am getting about 5 inches of vacuum. If I turn the idle screw down the vacuum will drop. I can get it to zero but the car is idling barely at 600rpms.

The timing is set to 15 initial, it was around 8. I am only getting 28 degrees total. I know it should be around 35 or so with AFR heads. Bumping up the timing has helped the stumble off idle. The exhaust sounds a lot cleaner and not so bogged down.

Once I set my timing lets say at 15, when I rev it up it won't idle back down to the same speed and the timing will be around 25. It's not the carb the throttle is closing all the way. I don't know if the weights are sticking. I have a light and medium spring on the weights.

LilJayV10

iTrader: (5)

ttt

LilJayV10

iTrader: (5)

I found out the intake is leaking today which I don't understand. The intake, heads and gaskets are all new.

I sprayed brake cleaner around the ports and the idle sped up.

Arrgh.

jstoltz

iTrader: (16)

get the vac leak fixed before you try to tune anything else. also check carb gaskets while you are at it. which gaskets do you have on the intake? I always use indian head sealer on them and haven't had a problem yet anyways.

LilJayV10

iTrader: (5)

I replaced the gaskets this weekend. I am using felpro 1205 that AFR recommends. I used that indian head sealer. I sprayed carb cleaner on it last night and it didn't idle up to 14-15 like it did. It was fluctuating(sp?)but I think it's because of the engine lope. I checked the carb gaskets and they aren't leaking.

If I manually open the secondaries up and give it some more air the idle will speed up and the engine vacuum goes to 15. I think I am probably adding a little bit of fuel too from the accelerator(sp?)pump.

LilJayV10

iTrader: (5)

Here are some pics of the primaries. You can see how much of the idle slots are exposed.





Secondaries


Notice how damp it is on the back of the carb flange.

At first I thought it was moisture from the PCV. But when I took the carb off tonight without running the car since yesterday it was still there. Can it be leaking somewhere? It's not leaking externally.

five7kid

iTrader: (14)

Make sure the back of the carb isn't hitting that vacuum fitting, and that the spacer is flat.

five7kid

iTrader: (14)

Actually, that wetness on the gasket is probably just from bumping the accelerator pump while removing the carb.

LilJayV10

iTrader: (5)

The carb isn't hitting the fitting. The gasket looked like that before I put the spacer on it.

Why does the primaries look so dirty? Its clean around the idle transfer slot and the, i think its called the discharge port?

Does it look like the throttle blades are open to much?

Basically I am lost and not sure what to do next.

Thank you for your help.

five7kid

iTrader: (14)

Are you getting any backfiring? That'll blacken things.

The primary blades look too open and the secondary blades not open enough.

LilJayV10

iTrader: (5)

No backfiring. I tried to open up the secondaries more but the screw wont turn. I am going to take the carb off and look at it again later tonight.

I rechecked the float bowl levels and the rear was just a little bit low. I raised it up which raised my idle speed. I am assuming its because the fuel level in the wells are higher?

Thanks for your patience. I hate not being able to figure this out on my own.

What will the engine do if I open the secondaries up to far? I am asking so I will know what to look for if I do.

Thanks again.

xpndbl3

iTrader: (5)

more timing at idle will allow you to close those slots. I would shoot for 20 degrees at idle and 34/36 total. You may have to limit your mechanical advanve.

LilJayV10

iTrader: (5)

I will try more initial timing.

You mentioned that earlier in the thread. Can you explain what you mean? I am not understanding.

Thanks!

xpndbl3

iTrader: (5)

a bigger stall will help with the launch and the bigger gears will put the motor more into its powerband. That is a bigger cam and a 3500 minimum stall should be used with 3.73 or 4.10 gears.

five7kid

iTrader: (14)

The other way around, actually.

LilJayV10

iTrader: (5)

I thought with a larger displacement engine with more tourqe you could use a lower stall and higher gears. I thought using a higher stall and lower gears would "pull" you through your tourqe band faster and would be wasted.

I actually think I fixed the idle tonight. I took the carb apart and ran a small tap through the secondary set screw. There was a casting flash on the base plate that would only let me open the secondaries so much.

Now the car idles in gear and I was able to turn the idle screws in quite a bit.

Apparently I should have not drilled a 1/16 hole in the blades.

I can close the primary idle screw all the way closed and it idles the same. If I close the secondary side some it will die. Now I have tried to open the primary some and close the secondary to put more of an emphasize(sp?) on the primareis but no luck yet.

Thanks for the help. My eyes don't water when the car is idling. Actually being able to adjust the secondary blades, balancing it out makes more sense now.

One last question. I set the idle then go drive it. When I put it back in park it idles high a little bit and will eventually come back down. What causes that?

It's 100% better than it was.