FS: DaVinci 950
 

For Sale: DaVinci Prepped Holley 950cfm "HP" double pumper, mechanical secondaries. Like new, works fine (just not well suited for my engine). No choke or horn. Lists for $1070 on DaVinci's website. Asking $650 plus shipping.

What seems to be the problem, Joe?

Basically, unless I drive at higher RPM all of the time, it runs too rich. I've jetted it so that it is perfect a/f ratio at WOT, but for some reason (probably the big cfm), it runs too rich during normal driving. And I don't want to have it go lean when I romp on it, so I have to live with rich when cruising, which I don't like.

I understand your frustration, Joe. Sometimes enough is enough, cut your losses and start over.

I have a KC Shelby 482 stroker. It has taken some time to sort and fine tune the carb. Works well now. I am no expert, but trial and error over the last 4 months have provided me with some insight (Along with valuable tech information from Dave, Holley and a couple of other carb guru's.)

If you are dead set on a new carb that's cool, I understond. If you want to sort through the problem and I can be of any help, just let me know. No promises, but we will give it a shot.

Bret.

I'm open to suggestions...only thing I can think of to do with this one is bump up the power valve...what are you running?

Joe

Your carb sounds like it needs a few things checked Joe. From what you have described I would check the power valve seating. Make sure you have one on the primary side and that the gasket is seated properly. Power valve itself may be defective also. A 6.5 is fine for street/strip unless your engine vacuum is way low, say...below 9 or 10 inches. Then a 3.5 or 4.0 may be needed for a power valve. Secondly, when you received the carb, it may have been jetted very rich out of the box. I will assume all your rejetting, to get a good A/F ratio, was done on the secondary jets only(?). If so, that would leave the primaries still in a rich/cruise mode. I would suggest getting an A/F sniffer up the pipe and a chassis dyno under the wheels. Run the motor to 3000 rpm under a light load and check the A/F ratio. Should be 13.5 - 14.0 at cruise. After you have dialed in the primaries, do a full pull, watching that the new A/F ratio doesn't lean out the motor. You may need to richen up the secondaries for a final A/F ratio of 12.5 - 13.0. This is all based on speculation.

Finally, make sure that the throttle blades have not opened so far as to expose the transition slot too far while you were adjusting the idle speed. If you are farther than .040" exposed on the slot, you will get a very rich idle mix that won't clear up until you are on the primary jets.

Zoom...thanks, but I've done all of that. If I jet for a WOT A/F ratio of 13, I'm cruising in the 10.8-11.2 range. Carb is fine, except for maybe my PV is too low...carb is just a little big, I believe.

Joe,

I am using the originally installed 6.5 power valve.

I have no flat spots, idles @ 850 all day and provides a grey plug and pipe soot after cruising @ 3000 rpm for 30 min. WOT is right now, no stumble, no hesitation, all the way to chipped redline (6500 rpm).

Zoomer hit on some important points.....all very good. I will explain my system, join the two and hopefully correct the problem. We're pullin' for ya :)



Go back to the beginning: (and I am sure you have covered these points, but I missed two small pieces of -AN rubber core stuck in my float!!)

1. Very Important!! Fuel pressure - REGULATED @ 6#s, unrestricted. Be careful if using a return line to the tank, you must have sufficient back pressure. I am using a dead-head system. Too much pressure will lift the seats - when the engine heats up, at idle, you can actually see the fuel dripping in the back bowls. Your fuel floats are preset and should be fine, but very small particulate can hamper their operation.

2. Presuming your carb is clean the idle/transfer circuit is the next place to check. If any idle screw needs to be turned out more than 2 full turns, STOP. You have other problems. If <2.....great, then make sure all four corners are equally adjusted. The transition slot should already be adjusted, but can be checked when the carb is off. Simple way: slot hole should look like a "square" not rectangle.
Set idle @ ~ 850 rpm and set timing.

3. Altitude. I am @ 399' ASL. Higher altitude requires less jet, ~1 jet per 4000' adjusted altitude.

4. I use the originally installed jets.

These are fundamentals, give these a shot. We will move to more complex adjustments if necessary.

GOOD LUCK, Joe.

Edit: You may be trying to compensate for a shooter/accelerator pump adjustment with a fatter power valve. If your A/F is OK from transition to mid range, you may need only to adjust accel pump/fuel delivery cam.

Just thinking out loud here............

Joe

Stick a piece of .032 safety wire in the Idle ckt...... to reduce the volumn of fuel on the idle side....

And increase the air correction for the idle ckt.... so it just pulls off idle....

The rest will settle down....

Morris

..............or what Morris said.;)

Bret, are you running a 950?

1. I'm regulated at 5-6psi using same regulator as Morris. Line sizes per Mallory's recommendations.

2. Idle settings are fine. In fact, my a/f ratio is fine at idle. The problem is after I'm out of the idle ckt, but before WOT. Ie, cruising sucks.

3. I'm at Kentucky altitude. ;)

4. The problem was worse with the originally installed jets. They were 4 sizes larger on front and back.

5. My shooters are dialed.

Morris, see #2...idle is okay.

Thanks for the help! Again, PV is the only thing I think I'm out of line on (@2.5).

Joe

......................................

Joe,

I am also running a 950 Divinci Super Series carb. Basically a Holley 4150 - PN# 80496-1.
Jeeze Joe............ I know this can be real frustrating, but I have a feeling you are quite mechanically inclined and like myself will not let a *#cking carb get the best of me.

Size wise of your carb, you should be OK using "the math": engine cu.(482) in X Max rpm (6500) divided by 3456 is 906 cfm. Bump to the next HIGHER closest carb.........

Sometimes the math is not always right.;)

Anyway,
One last thought..................
Using the original jets, did you check the secondary throttle plate position before WOT (idle/transfer/pre-secondary). The throttle plate being completely closed can cause a rich condition. Sometimes by cracking it open a little more it will lean out your midrange mixture and also allowing the secondary circuit to "prepare" for additional fuel delivery.

Just a thought....

Good luck Dude.:)