[updated:LAST EDITED ON 02-Jan-03 AT 03:55 PM (EST)]i have replaced the plugs and wires, cleaned out the carb with one of those cans of spray. it still misses though. when i replaced the timing chain, i timed it to 0. it ran the best there so i just left it. i plan on getting a new cap and rotor. one of those accels with the brass connectors. the thing still misses. i think it may be the timing. what do you guys think? it is cold here in ohio, i have a manual choke, but once its warm it still misses at idle and if i hold it down to about 2000 rpm it still misses. my brother says its a Modified and thats all the better it will ever run. help me prove him wrong
oh, by the way its a holley high performance two-barrel. i think its 500 cfm with a 50cc accelerator pump

 

you might want to think about a cylinder leakage test.use compressed air to fill the cylinders to see where it comes out.this might show a leaking valve,you would hear air coming out the carb or exhaust.

 

Seth,

You might try pulling the spark plug wires one at a time to locate which cylinder is missing. Another trick to find leaking/cross-firing wires is to run the engine at night and lift the hood and search for any blue spark leaking from the wires or plugs. You can pull the plugs to see if one of them is fouled, either sooty or oil fouled.

I've been able to cure misfires with extended tip plugs. Worked on a Toyota 3RC engine, a Ford 223, and others. If you don't have extended tip plugs, I'd do that first.

Make sure there's a good ground from the engine to the battery. Make sure that all the ignition wires have a good connection. I had a misfire that was making me crazy. I tried everything, even pulling the cylinder head off to look for a bad valve. Turned out to be an intermittent connection on the coil!

Beware of running spark plug wires too close together. Parallel wires can induce a current in the adjacent wire. Strange but true.

Good luck.

 

i think i will get a compression tester, check for crossed wires and try to find which one is missing by pulling plug wires. thanks guys anything else?

 

If you are saying your spark timing is at 0 degrees at idle it's way to low! at least 16 with everything hooked up.

 

well this was the first time i've ever used a timing light or tried to time an engine. im only 17. i kept the vaccuum to the dist hooked up. it idled fastest at where i have it. before i think it was a 12 retarded or something and it would hardly start. it turns over easily now and runs alright except for the miss. what do you suggest?

 

Seth, have you hooked up a vacuum gauge yet? It should have a steady reading. If a compression/leakdown test reads good another thing to check if you want to go deeper would be to see if all of the valves are opening properly. Could be a flat cam lobe. To check, pull off the valve covers and with the engine running see if any of the valves are just barely moving. Just something else to check.
Greg

'77 F-250 Camper Special 400ci driver
'76 F-250 Supercab 360ci current project
'71 Mach I 429CJ in storage
'79 F-150 for parts
huct on foniks wurkt fer me

 

[updated:LAST EDITED ON 04-Jan-03 AT 12:21 PM (EST)]i had one of the vavle covers off about 2 months ago when i changed the timing chain. i didn't look to see how much they were moving. it's snowing right now and freakin cold. im gonna wait a little while before i work on it. it's still driveable and everything. what kind of a connector do it need to blow air into the cylinder? and how do you do a vaccuum test?

 

i put in the new cap and rotor and it didn't help. can someone please answer some of the questions in my previous post. thanks

 

Seth, try advancing the timing a little at a time. If its starts to kick back when you start it (warm) you've gone too far.

 

>i put in the new cap and rotor and it didn't help. can
>someone please answer some of the questions in my previous
>post. thanks

I ended up having to replace the distributor in my '79 F-250 4X4 400 with 134K on it. It was worn out and allowing the timing to wander up to 9 degrees. As far as pumping air into the cylinders the easiest way is to get a compression tester then just temporarily remove the schrader valve (use a tire valve stem removal tool or very small needle nose pliers) and hook it up to an air hose. When you're done just reinstall the schrader valve and it's as good as new. As far as vacuum tuning goes here's a link with some good info:

[link:www.centuryperformance.com/vacuum.htm|Century Performance Vacuum Tuning]