i have a 64 ranchero. everything mechanical has been rebuilt wiring as well.
replaced 289 heads with 351w 's and put flat tops in it with a small cam. timing is on the mark and all my diagnostics read good but motor misses heavily as soon as you rev motor past 1000 rpm. were the 351 heads a bad combo? is my 600cfm carb causing this? maybe too much cfm? i am at a loss with it for right now. stumps even the local ford guys and the mechanic i paid over $500 to. lousy mechanic couldn't even come with explaination. what and where should i go from here.

 

the parts selection sounds fine, it's been done a million times. what more can you tell about the missing? is there any popping from the carb or exhaust? first thing is double triple check everything you can on the outside. like the firing order around the cap, and that all the plug wires are pushed on correctly. what kind of distributor, stock points? if so, that would be my first suspicion. check to make sure the plugs are gapped right and one doesn't have the gap smashed shut. it's not hard to crack a plug during removal/install. a vacuum leak can cause a miss also. how much work was done just before this miss came to be? any friends in the area that are knowledgeable?

 

hhhmmmmm, i have seen distributors cause it, and i have seen carbs cause it. you dont say what kind of dizzy you are running, or brand on the carb. if you are still running points, check the dizzy real good. breaker plate could be floating, stuck, or the dizzy could be just flat worn out. make sure the vac advance is working properly. unhook the vac advance and rev it then, if it still does it see if it seems worse or better.

i have a six right now with a bad carg that is doing it also, just havent had time yo mess with it lately.


let us know what you find.


jim

 

Perhaps check your coil also. You didn't state if you have points or electronic ignition. If electronic try a different module. If points check your advances( mech and vacuum) along with the points themselves( point float from weak spring). Cracks in the dist cap, bad condenser.How old is the carb? Has it sat with old fuel in it?( varnish in the jets)Loose throttle plate? Intake leaks? 351 heads have the bigger ports everything match there? (intake to heads etc).How's the valve springs? Did you check your valve to piston clearances for your cam.( bent valves/valve interference)Good Luck

 

yes it has points distributor. i have bought two different distributors and same results. edelbrock intake system is all new as well. without vaccum advance hooked up it still performs the same, but a bit slower due to no advance hooked up. i started out with 2 barrel that had been modified to feed a sufficient amount of fuel to motor. after awhile my boyfriend convinced me that the 2 barrel did not let the motor "breathe" properly. i thought we were conserving on gas until we switched to the 4 barrel, and then it got better fuel economy. the miss has always been there, but now it is getting really bad. we have only put 25000 on the motor. also a noticeable clatter comes from timing chain hard to explain but it is like a ticking noise. at cruising speed i can hear it in the cab. i just do not know what to think everything was brand new 25000 mi ago.

 

debra, sounds like you have a real pickle here. what size are the main jets? could be way to fat, that would explain the cutting out. i am guessing you have swapped out the plug wires a time or two, and the plugs along with them. dizzy's new, rebuilt, or used.

i am thinking more in the carb since it is happening at or slightly above 1000 r p m, it is getting just out of the idle circuit when it starts.

have you tried moving the timing around a little to see if that helps?


jim

 

Ticking at the front? This is just a theory but what if it's a lifter that keeps bleeding down. This would create a ticking ...and produce a miss especially when the RPMs go up. Did you isolate the cylinder that's missing( pull a plug wire off one at a time and replace until you find the one that doesn't make it sound different)?Once you have done this you can check the lifters by taking off the valve cover and push on the rocker as the motor is running. The one that ticks is the bad one. The only other thing at the timing cover is the fuel pump....how's that? I would check it too! Good luck.

 

i'd investigate that timing chain noise, and check for a bent pushrod or broken valve spring too. gotta start eliminating some possibilities. you say the miss has stuck with you through the carb changes? still a possibility. a simple trick i use sometimes is to spray a shot of water with a squirt bottle onto the header tube right near where it attaches to the head. a dead cylinder is easy to identify by the way the water reacts.

 

hello and thanks for all input. distributors are both brand new or whatever it was i could get for o.e.m. replacement. i have spent several long weekends trying to tune in this engine. when ever i try moving timing a few degrees ahead or back all it changes is how soon or late the missing starts. the way motor reacts altogether is odd. start up is excellent barely get half a rotation and it fires up cold. idle is as smooth as should be. but this is what is odd; i get in car raise idle up at around 1000 to 1500 rpm i hear several misses ocurring through exhaust, but motor doesn't get jumpy or rock? now if i retard a few degrees the misses are a little bit better, but i lose power out of the motor. advancihg just kills the motor. motor has good vaccum. i keep pressure gauge hooked up as i tinker with adjustments on carb. and i definitely don't get any odd readings on pressure gauge. all parts i've put in motor were new. the things i have determined were bad i replaced with new. except for my harmonic balancer. i had to hunt down a pre 70 mustang parts yard in rio linda,ca for a replacement of what was on motor proir to ownership. a certified mechanic checked my valvesprings and rocker assembly said everything still new to him. yet he had no clue as to what was going on with my motor. go figure.

thanks alot for any input

 

i wondered if carb pulls to much vaccum and advancing to quick. gauge always reads 20 at idle. anybody i've talked to localy isn't quite sure becuase their books don't go that far back.

 

When you put that small cam in did you get the timing mark on the gear lined up, you also said that there is a noise coming from the timing chain, maybe a a tooth is damaged and it's slipping a little.

 

longshot, but... is the cam in the engine for a 302 or a 351W? they use different firing orders. i'm not sure how bad an engine would run if the wrong firing order was used? the factory manual says a 302 goes 15426378, and the 351W goes 13726548. 4 cylinders are different.

 

never even thought about that. i think most aftermarket cams use the 351 firing order, and that would cause the problems they are having. best thing i have heard.


jim

 

It may make the harmonics rough but I fail to see why it would miss when the R's pick up.It would back fire and all kinds of other stuff if that many plugs were wired wrong even at an idle. The ticking in the timing cover along with missing at off idle makes me really suspect the fuel pump. Even new, these can go south. Try to find a fuel pressure gauge and see what happens when you hit the gas. Just a thought.Best of luck.

 

that's what i figured too, 4 wires wrong and it's gonna really let you know. but maybe not? what i want to know is, when is the last time someone actually checked the firing order ? and not just put it back the way it was?