250 xflow - 350 holley jet sizes?



I'm sure this isn't an uncommon question, but none of the Carby places round here seem to want to help us out.

I have a 84 FalconS 4.1L 250 Xflow, redline manifold, with a 350 Holley, which I understand is a very common setup here in Aust. The carby has come off an 8 and it floods when you put your foot down.

I would like to know approx what jet sizes to start with, so I don't have to spend lots of $$ trying many jets.
Do you mean it stumbles momentarily, or runs rough when it's cracked wide open, all the time? Holleys are a simple carb, but the "fuel curve" is the tricky part. The best fix - proper dyno tuning may not be affordable, but with a few more details, you ought to get some workable suggestions coming your way.

You can change jets, pump settings, power valve and fuel metering block hole sizes. That's why it's important to get as many baseline references as you can.

Have you done any other work on the engine, and what is the tranny? How do you drive the car? What are your own skills like, and what tools do you have?

Cheers, Adam.
It runs very rough under load from 1/4 to 3/4 Thottle unless you nurse it up to 2300rpm then it runs ok except for the unburnt fuel out the exhaust.
When it's not under load the engine revs fine.

I'm having to set the idle screws nearly all of the way out to make it idle without spluttering, and that appears to make nursing it up to 2300rpm a bit easier too.

The engine has had a little work done.
Extractors, Exhaust, Cam, OS Valves & guides, and I've just changed from an old Webber with the standard ford manifold to a redline with the holley. It's got the standard BWarner 3speed tranny.

I know I've got to change the jets, it just a matter of finding a size to start with and go from there.

Cheers Adam,

I'd change the vacuum power valve first (to one that stays closed longer), then jet it like a stock 253. Try backing off the accelerator pump one hole in the linkage.

Are you in Sydney, or Melbourne? Sydney - a good place is Howarth's ("Carb. Service Co.")for parts. But service or reco is pricey (good, though). Not much suggestion for Melbourne - Noel - any ideas?

Did this just start with the carbie and manifold change? Was the engine running ok before.
From what you say much too much fuel is needed/flowing into the engine.
Pull the front off the carbie and check what is in it. Make sure what is supposed to be there is in it.
Not the first time a carbie has been put together to sell with what ever was left over.
Look first and get back to us.
I have a holley 350 on my iron head xflow, running #63 jets... im not sure what the power valve etc was, its been a while since i put it in :)

it runs pretty well, but isnt really tuned properly ( easy to stall if you give it too much throttle @ low RPM...), but I have never really bothered because the car is run on LPG 99% of the time.

check you float level, it could be whats causing you to get huge amounts of fuel... my car 'seemed' perfect in the shed with #53 jets (what we started with), it would idle and rev perfectly... as soon as it was under load it was a piece of shit tho, until we bumped them up to #63 (FYI, it came off a 253 with #53's installed)
Float level is what is next to look at. This is simple but explanation is long and involved.
P.M. me and I will type this out.
Try a #65 power valve, and #58 jets. Adjust your float level so that on level ground the fuel in the bowl is just on the lower lip of the inspection hole. You need to remove the brass screw on the side of the fuel bowl.

alternately as you have the carb apart, the rough and ready way is to attatch a bit of fuel line to the inlet of the fuel bowl which is long enough so that you can blow in it and see the angle of the dangle of the float.

undo the set screw for the needle and seat. Blow into the hose(doesnt need to be hard) and lift the float till the air is stopped by the movement of the float up. Adjust the seat by turning the hex nut under the set screw so that the air stops when the float arm is parallel to the top of the fuel bowl housing. Retighten the set screw again. This is about right, unless the float arm has been previously bent. You should get some flow of air when you move the float down.

Note you should also adjust your accellerator pump cam for minimum stroke and adjust that little by little till you get nice drivability. You can also change the accellerator pump jets but I don't have my holley book to hand.

Misaligned Holley's can be real Fuel Hogs, most people make the mistake of trying to make them flow more fuel than necessary, believing that its the way to more power.

Hope this helps you get started. :)