Pete, Yup. OR a misfire which dumps unburned fuel into the exhaust where it fires. Been there, done that.

Dennis, I don't think so. Bigger ports might just make it Lazy down low, but they should (obviously) work better higher up. Maybe the Advance can leaks? You read plugs yet? could be Jetting, but that's pretty severe. usually they'll surge when they're too lean on the mains, or the floats are set too low.

Frank/Rebop

Bristol, In ( by Elkhart) 

Dennis: I have no idea why your having the current problem..but an issue to look at later, is that you state that your new engine is like the old 239, it has no crank damper. Might want to get some expert advice (from someone like Ted?) on that point, especially since you race your truck. Ford put dampers on the later engines for a reason..

Paul

Well, Dennis, you've got us all scratching our heads.

Based upon all that has been discussed to date, consider going at this in a different way.

Locate a vacuum gauge. Hopefully, you’ve got enough running time on the engine that you’re comfortable dropping the engine idle speed down to ‘normal’.

The numerical ‘normal’ vacuum gauge reading on your engine will likely be lower than an everyday grocery-getter because of the Isky E-4 cam you’re running. -Your cam probably has about 40 degrees of valve overlap. Sooo… In doing vacuum gauge readings, the action of the gauge needle will generally be more telling than the numerical gauge reading.

Run your engine until it is at operating temperature. Connect the vacuum gauge to the intake manifold.

At engine idle speed, what is the movement of the needle indicator?

-is the vacuum gauge needle steady?
-does the needle drop 1-7 inches at regular intervals?
-is there a sharp, intermittent drop of the needle?

-does the needle drift either side of your 'normal' reading?

-if the needle does drift either side of your ‘normal’, how many inches does it drift each way?

-what is the numerical reading of the vacuum gauge at idle?

-what is your idle speed?

At a steady engine operating speed of 2000 rpm, what is the movement of the needle indicator?

-does the needle fluctuate rapidly at this engine speed?

-if the needle does fluctuate rapidly, what numbers does it fluctuate between?

-if there is such a fluctuation, does the fluctuation amount increase as the engine speed is increased?

I’m in hopes that this test will tell us something we don’t know.

NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York

Do you have a bigger intake to try just to rule it out?

I wonder if the secondary carbs need to open sooner. Using an online airflow calculator, your 283 requires about 164cfm @2500rpm. Everything else being the same, that's about 10% more than before, and 20% more than the 239. I think when Ted was doing the 3-2 dyno testing, he said they flow about 150cfm each. If I'm remembering that correctly, then you may be exceeding the limits of a single carb which is why you have the stumble with only one carb and all 3, if the other 2 have not yet begun to open.

I can bring my B intake and an Edelbrock 600 to Columbus for you to try if you like. I can also bring my points distributor, but aren't you running the 239 drive gear?

The Edelbrock didn't like my engine combo, the air valve wasn't right for it but that doesn't mean it wouldn't work for you. I would get a stumble with it but it was at a much higher rpm.


Lawrenceville, GA

I'll put a gauge on it when I get a chance. Had a viewing last night, model rr club tonight, another viewing friday night and the funeral sat.

  Dennis in Lititz PA

Charlie,
I have 3 B intakes, but no carbs. I also have an offy 3x2 with big ports, but Ted suggested using the edelbrock.

Yeah, I have the 13 tooth gear on mine.

I have a spare 292 that still has the distributor in it, and a complete 239 that I could use the gear and make up another distributor combo.

  Dennis in Lititz PA

I got a chance to get a vacuum reading. At 500 rpm it would bounce between 11-12. At 750 rpm 13-14. At 1200 16 and steady. At 2000 17 and steady. When I would blip the throttle it would just touch the outer carb butterflies a hair. It would dip down to 5 and up to 22 when it snapped shut.

I'm thinking more and more it's carbs. The intake sat on the shelf for 4 months.

  Dennis in Lititz PA

I think your vacuum is low. I get 15 at about 750rpm, with a little bigger cam. Do you know what it was with the previous build?


Lawrenceville, GA

I seem to remember 13 and 17 from the old engine.

  Dennis in Lititz PA

Progress! I talked to a retired mechanic at the funeral today. He suggested changing one jet in each carb.
I had .53 in the center carb and .51 in the front and rear. I put one .57 in the front and one .57 in the rear.

I still had a stumble sometimes around 2500 but when I got over that it was pulling nicely in 3rd gear up a long hill. I let off at 3500, felt I was going fast enough. I think I'll try putting the other two .57 jets in and try again.

Like it is, I should be able to go to the ford race at Maple Grove tomorrow.

  Dennis in Lititz PA