17059272 on a ford 300

[F250 Restorer]

First, I want to say that the last time I used this forum I was really frustrated b/c I could not get my qj to run correctly, and may have spoken badly of a certain qj's mother.  It was beyond my skill set. I apologize.

I have since started anew, keeping it all oem.  This time around I found a qj from an equal size engine.  Now I can get it to idle fine, with 72 primary jets and 52 rods, as it came from GM. But tip in tells me it's lean.  I've tried apt thru it's range.  So I tried changing to cliff's 44 rods, and couldn't get it to idle.  It seems to have great power when floored from a stop.  However, when I step on it at 40 mph, it just bogs out and I have nothing.  I'm thinking that I have the apt too far out, and rod goes to rich on acc. and gives it too much.

Anyway, this time around I am following Cliff's advice.  I'm going to lock out the secondaries and find the best primary jets, then use a rod about 30 diff.


Any help would be appreciated.

I'm not blocking secondaries

[Cliff Ruggles]

The metering rods aren't part of the idle system.  If you see a change there, the metering rods would have to be a restriction in the jets.  Going from 52K to 44's would not be a restriction in the jets, unless the wrong jets are installed in the carburetor and the primary metering rods are too deep.

72 jets and 44 rods in that carburetor are fine, and with the APT system will provide full control of the A/F at part throttle.

Being a 301 carburetor, it has cross drill secondary fuel nozzles, and limited airflap open angle.  The secondary throttle plates may also be limited on the open angle.

I would set the throttle plates for full open (90 degrees), install solid fuel nozzles in the airhorn, and grind the stop for the airflap so they come to full opening.

Install a new secondary cam/spring as well.

Most, if not all of the parts from your other rebuild should work on the new carb......Cliff

[F250 Restorer]

I installed Cliff's .044 rods.  I also went with a slightly stiffer power spring.  As Cliff suggested, I adjusted the secondary flaps to open fully, and altered the air flap stop to allow it to open fully.  When I started it with the new rods, changed from the oem .052, I could immediately tell the difference.  I set the idle and the mix, and there is no longer a bog when I hit the gas at 30-40 getting on the freeway.  What a pleasure. 

Cliff, why should I change from the cross-drilled secondary nozzles? If it works better, of course I'll do it.  I just wanted to know the reasoning behind it.

One question though: I adjusted the mix in till it changes idle, then out to the highest vac. reading. I noticed though, that using the tip-in, it is running a bit lean at idle.  I tried to adjust the apt to compensate, but could not.  There is also a very slight hesitation transitioning off idle. How can I resolve those issues?

Thank you for the help.

I also have to say that I'm curious why GM would have used the larger bore qj for a 301.  Any thought?

[Cliff Ruggles]

Fuel distibution is poor from the cross drilled nozzled once you open up the secondary airflaps past the angle the factory set them at.

"Tip in" at idle speed?

The APT is not a player at idle speed, and not used to "compensate" idle fuel requirements.

Idle fuel comes from the idle tubes, then idle down channel restrictions, then to the mixture screws.  There are two idle airbleeds in that carb, but the stock sizes for them are fine.

If you need more idle fuel for what you are doing, install larger idle tubes.  They are right at .034" in that carb stock from what I can remember.  A few thousanths larger and maybe a few thousanths more down channel will help with the lean off idle deal.

The "large bore" q-jet is fine for small cid engines, and they never made any front inlet later style BOP q-jets with the smaller bores anyhow.  A few later model Chevy units still used the smaller bores, but disappeared around 1979-80.......Cliff

[F250 Restorer]

Thanks for the help, Cliff. I'll be ordering the tubes from you.

kevin.

[Cliff Ruggles]

Thanks....Cliff

[F250 Restorer]

I haven't addressed the lean idle issue yet, but soon will, work permitting. 

There is one other issue I need to ask about:  I really enjoy the QJ, but have noticed I'm getting only 7.8 miles per gallon, driving a mix of 80% street, and 20% freeway.  Maybe I got on it a couple of times while getting on the freeway, but mostly I'm driving conservatively. I know that mpg can't be correct, and need some feedback regarding how to raise that mpg.

It's not smoking. Choke opens completely. The only vacuum line not plugged is the dizzy advance.

[Cliff Ruggles]

Yikes, should be getting nearly double that mileage.  I owned a 79 Blazer with a 400 SBC making over 350hp, TH350, and 3.08 gears that got 15mpg's with a q-jet on a stock intake. 

Something isn't quite right someplace, I'd expect at least 11-12 mpg combined city/highway and closer to 14-16 highway mileage.

Have you done a "tip-in" test with the APT screw?  Set it for 100-150rpm's increase when the choke flap it tipped in slightly.  This will be slightly lean, but should delivery good mileage.....Cliff

[F250 Restorer]

Thanks. I'll try it.

I don't have the throttle response I was expecting. As you suggested with climbing a hill, when I'm climbing and hit the gas at 30, it just seems sluggish. Is that a sign of too big a pri. jet? 

[Cliff Ruggles]

Climbing a hill and "hitting the gas" puts the metering rods on the tips.  Assuming you are staying on the primaries, the 72 jets may be slightly lean in that carb number.  We usually set those up with 73 main jets, and 44 tapered metering rods.....Cliff

[F250 Restorer]

Cliff-- This carb came with two v. pull offs, one at rear, and one in front.  Do I need both?  I'm having a bit of trouble with the choke.

Also, the electric bulb mounted for for throttle shaft, what is that?  How would I set it up in an older vehicle?

Thank You. 

[Cliff Ruggles]

The rear pull-off is not needed, it is just a back-up for the front pull-off.

Don't know what an "electric bulb" is?  Fast idle solenoid for the A/C???.....Cliff

[F250 Restorer]

Thanks, Cliff. 

Recently I removed the carb.  I have a dual port manifold that separates the pri. from the sec. side of carb. I noticed that inside the secondary channel/runner it was wet.  I still have the cross drilled nozzles.  The secondaries don't open until really getting on it with pedal to the floor, and come on briefly, then the trans shifts.

Since this is an auto trans, If I tighten the air flap control, they would barely open b/f the trans shifts.

I have the CH rods, and the M hanger.  Advice?

[Shark Racer]

Your comment on the manifold confuses me; dual ports that separate the primaries from the secondaries in the manifold? If this is the case, then you'd have to have two sets of intake runners to each cylinder, one for primary feed and one for secondary feed...

Is there any chance you can post pictures of this setup?

[Cliff Ruggles]

The adjustment spring for the secondary airflap is used to get smooth transition and help prevent stumble/bog from having them come in too early.  The choke pull-off is also a player here, as it holds the flaps tightly shut at idle and cruising and helps prevent them from "whipping" open too quick causing a lean condition (bog).  Winding the spring too tight hurts engine power and performance.  With the right pull-off, the secondary spring should be about 1/2 to 3/4 turns clockwise after it contacts the pin.

If you have modified the opening angle of the secondary airflap on the 301 carburetor, then it needs solid secondary fuel nozzles, or there will be fuel distribution problems when the secondaries are used.......Cliff