help me fix my missing 302HO

I just bought a 65 mustang and its got a 302HO in it with a miss that i've been trying to figure out. I hate when things like this happen because it seems like you just have to guess as to what the problem might be and you end up replacing a lot of stuff that you dont have to to fix the problem. Its a 87 302 with a F303 cam, air gap intake, holley 750 double pumper, world windsor jr heads, msd large cap distributor, msd wires, 6AL ignition, and NGK UR4 spark plugs. I pulled the plugs and they were the wrong kind for the heads, they were like a .700 reach plug where the heads need a .460 reach plug and I thought that would have fixed it, but it only runs a little better after I did that. I cleaned all the terminals in the dist cap and that also helped some but there is still a miss. I was thinking about getting new taylor plug wires next but the wires on it look like they are brand new and i think it would probably be a waste of money. What do you guys think I should do next?

well i messed with it. I changed the plug wires to taylors, new NGK UR4 spark plugs, cleaned the terminals on the dist cap.

I got it running much better now and I only have a little missing when I am at cruise speeds. Say i'm cruising along in 5th gear and give it some throttle it will stumble/miss. I have the idle mixture screws 2.5 turns out now and its still a little lean because when I stop at a light the car wants to die for a second if I dont tap the throttle. I'm thinking it may be lean on the transition circuit on the carb so i'm gonna open up the IFR's a little more to see if it helps.

a thing that is really bugging me is the clearance with the plug wires on the headers on the drivers side. I have world windsor jr. cylinder heads and the headers were "clearanced" by the PO with a big hammer...but the plug wire boots are still touching the headers. I have the heat boots over them but I dont think its going to help much since they are in direct contact.

D.Hearne said:

The idle mixture screws aren't going to affect what it's doing at cruise speeds. If you've got a stumble there, it's in the accellerator pump circuit. The dying at idle, tells me the idle speed screw is giving it enough air and/or the mixture screws are too lean. Might also not have enough initial timing

Click to expand...

18* initial timing

yea the idle mixture screws dont have anything to do with adjusting the mixture at the transition slots, but i'm thinking that since they are already 2.5 turns out opening up the ifr's will get the idle screws back down to about 1.5 turns out and opening up the ifr's will also fatten up the transition circuit some which will help with the lean misfiring at low rpm cruise. I dont think the car is into the main metering system since the rpms are so low. It seems to do fine above 2500rpms when i think the mains are activating

I dont think its in the accelerator pump circuit, its like its at a constant state of misfiring surging at just the tiniest big of throttle movement, and i already got the squirters to a 40p and 35s