carb jetting

[67matang]

i have a 67 mustang with a 351 w heres what is done to it..
twisted wedge heads
roller rockers
extreme energy 274h cam
holley 750
weiand stealth
headers with 2.5" pipe and flowmaster 40s
8.8 rearend with 3.73's
c-4 with shiftkit

my problem is that i changed my 8" air filter to a 14" k&n and now at 3500 + rpms it hesitates and revs up really slow..could this be the jets in teh carb? i changed it back to my 8" and the problem went away.
thanks

 

[Ronstang]

Have you checked to make sure the new air cleaner is not somehow interfering with the linkage on the secondaries....or even the primaries? I would check for interference first as a change in air cleaner should not have that much affect on the jetting of a carb, it could have some but I doubt it would be as significant as you indicate.

 

[brianj5600]

If the smaller air filter is more restrictive, it will act as a partial choke. This provide a stronger pull on the fuel circuits. Might have to richen it up for the bigger air filter.

 

[67matang]

well nothing is interfering..i have a drop base to clear the hood and nothing is hitting..

 

[1969mach1351]

I'd give it a quick drive without any filter to see what happens. Do you have too much oil in the filter? Maybe it starts to suck in the K&N oil at high RPM?

 

[67matang]

well i was thinking that with the drop base and not using a tall air filter...it might be that its not getting enough air because the lid and the drop base might be too close together? thats what im thinking

 

[2nd Mustang]

well nothing is interfering..i have a drop base to clear the hood and nothing is hitting..

Once, while trying to figure out why my engine wouldn't idle, I noticed that when I had the base of the air cleaner off (I also have a drop base with 3" tall filter) the engine wouldn't idle correctly (internal carb problem), but when I put the base back on, the idle would pick up significantly. I also made sure none of the linkage was hanging up or caught somehow, but it wasn't. I think the design of the base increases velocity of air flow into the carb. I think I remember reading something about this phenomenum many years ago in a magazine.

 

[67matang]

when i put the drop base on with the filter then the lid there is only like 1" or less between the lid and the base so could that be causing the problem?

 

[2nd Mustang]

when i put the drop base on with the filter then the lid there is only like 1" or less between the lid and the base so could that be causing the problem?

I guess I'm having trouble picturing your setup. Is it an open element type air cleaner, because the K&N filter should be about 3" tall, isn't it? If you only have 1" between the lid and the base with the filter in it, how does that compare to your original air cleaner housing and filter? It really sounds like an air flow issue.

 

[67matang]

the air filter is just a round 14" like most carbed engines. i looked at it this morning and with the lid on i have a little less than 1" inch between the lid and the base..the old one has about 2.5" (however tall the air filter is) the K&N filter is about 2.5" tall.

 

[67coupestang]

well nothing is interfering..i have a drop base to clear the hood and nothing is hitting..

it should clear without it. Mine does.