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Discussion Starter · #1 ·
My car is running pig rich at idle ever since I swapped the 69/78 jets for 72/80 jets. I have to keep my foot on the gas at stops or it will stall out on me. Once I'm up and running, it seems ok. It fouled out the plugs I had so I bought a brand new set, drove it for a mile and now they're black!
I'm noticed raw fuel dripping from one secondary ventri when it's idling. I don't think that's supposed to happen...is it?
What would cause this? Is there anything I could have done when swapping jets? I fail to beleive that 72/80 jets are too much jet for my setup.
Why is raw fuel dripping into the secondaries at idle and still drips after the car is shut off?

My carb. is a 750dp(4150) with 72/80 jets, 6.5hg PV(none in rear), 30cc pumps, 31/28 squirters.
Car ran fine before the jet swap......
 

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Sounds like the float level is too high, check that first and let us know
 

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Discussion Starter · #3 ·
Which float...front or rear float? They weren't too high last week when I checked them but I'll check again....
 

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The jet sizes will have nothing to do with the richness of the idle.

#1 you may have you rear bowl inlet jammed. The new holley blue gaskets eeryone seems to like, flake off little blue particals and get jamed in the bowls. Take it apart again, and clean very carefully, just one partical will jam the inlet valve.

Also check to make sure you used the correct gaskets. If the secondary has a pumper and it is the wrong gasket, you will spill fuel into your vacuum hole.
 

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Still sounds like high secondary float level or bad secondary needle and seat
 

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On 2006-06-11 05:45, My427stang wrote:
Still sounds like high secondary float level or bad secondary needle and seat
I'll second that! A jet change won't account for your problem. Also, be aware that if you're running a large (.110" ) needle/seat assembly, if your fuel pressure is too high it can overcome the float. Simple hydraulics. The larger the surface area being acted upon at a given pressure, the greater the force applied. It happened to me!! Just a thought..... Now get that thing sorted out, dude... I wanna hear what ya got! LOL!!

Best of luck,

Kevin

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'72 Gran Torino Sport...357W w/TFS TW heads, RPM AirGap intake, Bigs 750DP, CompCam XE274, RHP re-curved Duraspark dizzy, FPA long-tube headers, full 3" X-pipe exhaust w/ Hooker Aerochambers, C6 w/ 2000+/- stall converter & 3.50 gears w/ Powertrax locker

<font size=-1>[ This Message was edited by: OleDutchD on 6/11/06 11:27pm ]</font>
 

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I'd check the needle/seat. Could need replacing or there could be an obstruction holding the needle off the seat.

Or maybe too much fuel pressure blowing the needle off the seat.
 

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Discussion Starter · #8 ·
I pulled the secondary bowl off again and the metering block, blew out all the passages, checked float leve and the problem seemed to have corrected itself.
I did notice one odd thing though. The idle/air screws up front wants to be all the way in or the car idles funny. What does that mean?
Other than that, the car runs really strong especially when the secondaries come in. I might go up to 82 jets later in the rear.
 

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Sounds as if maybe the primaries are cracked too far open and you're running off of too much of the primary idle transfer slot.
Can't say what will work for you, but in MY case, I had to crack the secondary butterflies till I had about .030" of the transfer slot exposed. That allowed me to back off the primary butterflies a good bit, and that gave me the most stable/decent idle quality. It also gave me back my tuneability with the secondary idle adjustment screws.

Just my $.02

Kevin
 

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Discussion Starter · #11 ·
JAM1775, I should check vacuum with car in gear.....correct?
The last time I checked my vacuum, was back when I still had the 3310, and it was 15hg but that was in PARK though.

As far as the air bleeds, I'm not sure if they are removable or how to tell if thay are. I'm not sure exactly even where they're located at.
I do have a vacuum gauge that I'll be installing in the car in the very near future.
 

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On 2006-06-11 10:21, 82GT wrote:
I pulled the secondary bowl off again and the metering block, blew out all the passages, checked float leve and the problem seemed to have corrected itself.
I did notice one odd thing though. The idle/air screws up front wants to be all the way in or the car idles funny. What does that mean?
Other than that, the car runs really strong especially when the secondaries come in. I might go up to 82 jets later in the rear.
That means that you are still pulling in too much fuel from somewhere, do as the fellow above suggested and re-set the secondaries to give about .03-.04 of the transfer slot open so the front butterflies are allowed to open a little more and allow A/F adjustment for idle conditions (under 900 rpm's only).

Then you should have the engine fail when the idle screws are all the way in, if the car still want's to run with the idle screws all the way in then you are having even more excessive fuel issues and may have to lower the float's even more.

Love to hear more after you accomplish this!

FE

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<font size=-1>[ This Message was edited by: FALCONAROUND on 6/12/06 11:41pm ]</font>
 

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Discussion Starter · #13 ·
On 2006-06-12 08:39, FALCONAROUND wrote:
On 2006-06-11 10:21, 82GT wrote:
I pulled the secondary bowl off again and the metering block, blew out all the passages, checked float leve and the problem seemed to have corrected itself.
I did notice one odd thing though. The idle/air screws up front wants to be all the way in or the car idles funny. What does that mean?
Other than that, the car runs really strong especially when the secondaries come in. I might go up to 82 jets later in the rear.
That means that you are still pulling in too much fuel from somewhere, do as the fellow above suggested and re-set the secondaries to give about .03-.04 of the transfer slot open so the front butterflies are allowed to open a little more and allow A/F adjustment for idle conditions (under 900 rpm's only).


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<font size=-1>[ This Message was edited by: FALCONAROUND on 6/12/06 11:41pm ]</font>
Ok, now can you or someone tell me exactly how do to this?
I know VERY little about carbs.
 

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Discussion Starter · #14 ·
I just took a vacuum reading and I have 14-15hg at idle in PARK and about 13hg with the car in gear. Is my 6.5 PV ok then?
I adjusted my timing until I got the highest vacuum reading.
 

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Take the carb off and flip it over. You'll find a small recessed set-screw under the secondary butterfly linkage, that you can only access from the bottom. As it is, you probably only have the curb- idle discharge hole exposed. Turn the secondary adjustment screw about 1/4 of a turn, or until you have about 1/32" of the idle transfer slot exposed. It doesn't take much. Then back the primary idle speed screw off, put the carb back on... and start over with your idle mixture adjustments.

When it's all worked out, you should have more equal settings for the primary and secondary butterflies.

That's what I had to do, because the primary idle speed adjustment was cracked open so far to hold a "good" idle that it exposed too much of the idle transfer slot and ran it too rich at idle.

Give it a try and see what happens.

Good luck,

Kevin
 

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Discussion Starter · #16 ·
On 2006-06-12 12:01, JAM1775 wrote:
Yeah....that seems okay if that is what you are
pulling with the vac advance off, vac port plugged, at idle.

The idle air bleeds are 8 small carb jet like fittings (4F/4R) on front back along the outside of the carb body. If it is a standard 4150 you may not have them. If it is a 4150HP you do. If you have the HP yoou can use them later to fine tune.

<font size=-1>[ This Message was edited by: JAM1775 on 6/13/06 3:11am ]</font>
FWIW, I have mechanical advance dizzy and a standard 4150 carb. Thanks for the advice guys!
Maybe I should read more of my SUPER TUNING AND REBUILDING HOLLEY'S book. It would probably tell me all of this stuff.
 

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I have noticed a lot of folks are going to aftermarket Throttle Plate assemblies, the entire base plate that is...whatever name you want to put to it.

These are all set up for 4 corner idle, thinner throttle plates, thiner shafts...ect:

One important thing though is this throttle plate housing can not be used with 2 corner idle metering blocks.

In the bottom of the Throttle plate housing are the idle discharge holes. On a stardard two hole carb from Holley, you will have two large idle discharge holes in teh front, and two tiny little discharge holes in the rear.

The new aftermarket throttle plate housings have two huge idle discharge holes in the front and two huge ones in the rear.

Now, if you use a regular metering block ( no idle adjustments) on this type of throttle plate with the large discharge holes, then basicly you have an uncrontrollable dump of gas into the engine, enough so that the fronts are not needed at all....

Lots of tricks to these carbs that are not found in any book....
 
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