351w backfire at high rpm...WHY!?!?!?!

[gadget73]

Duraspark has no spout connector.

[91_351police-special]

its not like i beat the hell out of the car. its an older car...i done found out what beating the car all to hell does with my older civilian '88 crown vic. since my p72 only has 2nd gear, drive, and overdrive selections i just leave it in drive or overdrive so the trans is shifting by itself so if its over revving im not causing it to. i replaced the cap and rotor and plugs and wires in the spring. i did check the cap and rotor a few weeks ago and there was alot of build up on the contacts so i scraped it all off. and yes its duraspark ignition. lastnight i tried just turning each screw out a full turn and it increased the idle a bit but that was about it. i just set it back to what it was. today im going to go by the instructions and hope ill get close by ear. if not my boss will let me use his vacuum gauge monday. i would buy my own but being a student and only getting 20 hours a week makes money kinda tight.

[91_351police-special]

alright. idle mixture screws set. i looked all over the carb to see if there was leaking gas or any signs of something wrong and on the back right corner of the carb where the fuel goes into was wet along the bottom of the fuel fitting and the edge of the gasket prolly an inch down each side of the carb....so idk if the fuel fitting is leaking slightly or if the backfires out the carb have damaged the top gasket that covers up the bowls and its leaking and causing the bad studder/ bog under load?

[import convert]

i would try and get a fuel pressure gauge on the thing and make sure youre getting at least 5 or 6 psi going to the carb. if you have that then you should be getting enough fuel to the car which then should hint towards an ignition problem or a possible gasket leak that could be leaning out your mixture.

[91_351police-special]

ok, ill get on that tomorrow at work if its slow and ima back the timing down from 8 advanced to 5 or 4 advanced.

[1987cp]

Re stumbling on tip-in, which position are you using on the accelerator pump lever? I more often than not find myself using the largest pump shot, especially before more serious tuning takes place (i.e. digging into the EDL-1487 tuning kit). My slightly-hotter-than-stock 351 seems to like two stages rich on both power and cruise as well as using either the 7" or 8" stepup spring.

If you're letting the AOD shift itself, an "overrevving" condition is indeed unlikely, and further, I don't think you'll be turning enough RPM to have to worry about too aggressive a timing curve unless your distributor setup has already been modified.

Remind me which vacuum source you have your advance canister attached to? Like I mentioned, non-EGR cars seem happy with the vacuum advance disconnected entirely.

[91_351police-special]

the left port on the carb.....no vacuum at idle but theres vacuum when you give it some throttle. im almost positive its fuel related.....the car ran like shit this morning...studdering and spitting when driving like a grandma but it eventually cleared up half way to work....but its still fucked up when its close to half throttle or more....usually ill notice it when im accelerating on the highway entrance ramp.

[1987cp]

Have you verified that the choke is opening fully?

[91_351police-special]

yes sir. it works and is set up and opens as it should.

[import convert]

my car has no egr and im using the port on the carb listed for vacume advance and its fine. myself id think that the VV carb would use less fuel then the 4 barrel would as well as the intake. so yea if your pump is weak you could be maxing it out.

i will ask though, have you sealed tightly? id do a vacume test to to make sure youre getting 17-21 inches of vacume to rule out a vacume leak. that could make you think you have a fuel problem and youd be fighting the wrong problem.

[Pirate]

Something I just thought of....have you changed plug wires recently?

[1987cp]

Another thought, what position are you using on the accelerator pump actuator? Sorry to play 20 Questions, but when info isn't forthcoming ...

myself id think that the VV carb would use less fuel then the 4 barrel would as well as the intake. so yea if your pump is weak you could be maxing it out.

A stock Ford mechanical pump works great for entry-level Performer carb setups - either the deadhead style or return style is acceptable. They're designed to put out 5 psi, right in the middle of the range Edelbrock specifies, and the stock 5/16" fuel line is fine for applications up to at least 300 or 350hp (can't remember the exact level at which you're supposed to upgrade). Of course, a bad pump, clogged filter or pickup screen, or kink in the line can always throw a wrench in the works.

i will ask though, have you sealed tightly? id do a vacume test to to make sure youre getting 17-21 inches of vacume to rule out a vacume leak. that could make you think you have a fuel problem and youd be fighting the wrong problem.

Definitely a good thought. I got my Sunpro vacuum gauge for about $16 from Summit, and it's been way worth it. It's good to have as a tuning aid anyway, and less frustrating than blindly spraying water all over the intake manifold wondering if you have a vacuum problem in the first place.

Something I just thought of....have you changed plug wires recently?

I know, maybe he's melted the spark plugs! (though probably not ... )

[import convert]

i wonder if maybe it was just a bad carb? ive sold one or 2 edlebrock carbs htat were bad so i know it can happen but isnt likely

[torquelover]

i wonder if maybe it was just a bad carb? ive sold one or 2 edlebrock carbs htat were bad so i know it can happen but isnt likely

My 1406 had a float bowl out of adjustment right out of the box. What was wrong with the 2 you sold?

[import convert]

honestly im not sure. the guys called and wanted new ones but edlebrock wants any questions or problems to go through them so i never knew what went wrong. but yea, ive seen it happen before. idk if it were a carb problem itd be something on the high rpm side i think. might not be getting the right amount of fuel at high rpms. or i think itd be the secondary feed of hte carb.