I just picked up a 85 bronco it has an offy intake with a 390cfm holly on it. It has a serious hesitation under load right off idle. No load it revs fine and seems fine. It acts as if it wont take fuel? I have replaced the intake/exhaust gasket and checked the float level on the carb. checked for a vacuum leak. I am stumped. I will run thru plugs wires etc... tonite. Any help would be great

 

That is probably the most common of performance problems with these set-ups and is usually a very lean condition at tip-in. https://www.holley.com/support/ There you will find info on setting-up a carb and rectifying problems in performance. A lighter vac secondary spring, more aggressive pump cam, larger pump squirter, bigger power valve are some things to consider.

Also, if there is no heat plumbed to the intake manifold, no adjustments in the carb are going to help. https://www.ford-trucks.com/forums/1...ires-heat.html

 

Good job, Harte3! I bet it is the latter... snowfighter lives in cold country.

 

Yep, my first thought was, "Is the intake manifold heated?" If not, that's your problem.

 

If you really have an "OFFY" intake, it probably has exhaust manifold heat unless you have headers. Also the air intake system (non-stock) may not allow for good drivabiilty when severely cold weather hits. Especially on some days Carb icing may actually play a part when not using the OEM warm air intake. I have this problem myself on my 2BBL /Clifford arrangement even with manifold heat when first started and conditions are just right.. Then there is always the actual carb itself as others have said for the stumble problem

 

"...and conditions are just right.."

Yup, get a lot of those kind of days where I'm at.

 

 

I drove it home 340 miles with the stock exhaust and offy. I put efi manifolds on it and new gasket with duals. Both ways it runs the same. I am wanting suggestions on intake heating?
I changed plugs wires cap fuel filter checked time and found the vacuum advance diaphram split. I will have a new one tomorrow.

 

https://www.ford-trucks.com/forums/1...-tomorrow.html

The usual method is to plumb the manifold for water heat. There is a pic on that thread that shows what to use for this.

 

It's been a while since I've had an Offy Dp but isn't that carb mounted backwards? I thought the primaries were closest to the cylinder head.

And you might want to check out the accelerator pump squirter. You might need to install a larger one.

 

Not sure on carb mounting I have no experience with this setup.

 

The factory recommended orientation of the carb on a DP is with the primaries next to the engine. A few have oriented the carb the way yours is done. For all practical purposes there might not be any difference. But, you must have heat to the intake manifold. After that the focus will be on possibly a larger pump squirter, a more aggressive pump cam, different vac secondary springs, possibly bigger power valve, etc.

 

Heating the intake will help all around, but if the accelerator pump isn't squirting as soon as the throttle moves that's what's causing the stumble.

 

The DP has smaller runners for whichever side is facing the valve cover (which is supposed to be the primaries), and then larger runners for the other.

The reason for this is that the smaller passageways help boost the throttle at low RPMs. You're never really going to have the secondaries open at low RPMs, so this effect is wasted on them the way you have it oriented.

However, like others have said, it might be so minimal you'll never notice. But, you won't know that unless you try both.

 

UPDATE
So I have it driveable now here is everything I found
no vacuum spark advance
spread bore gasket under the spacer on intake
It had a 6.5 power valve in it the hot vacuum is 19 I put a 8.5 in it
had an orange accelerator cam Replaced with a brown
It had a 31 nozzle I put a 37 on it
I turned the carb around so the primary's are next to the head.
I am not sure which thing fixed it just glad its driveable.

Abandoned bronco what kind of mileage are you getting?

I plan to make the heat plate this weekend