help!! my flathead v8 has a miss

[ratrod52]

Just a note this car sat for 8 years in a pull barn under a cover
I just purchased a 52' business coupe. My first flathead!! The motor is stock. it ran very rough and would not idol or stay running. I replaced the usual suspects cap, rotor, points, condenser, also rebuilt the carb with great care and replaced the fuel pump. I got it to run and set the timing, mixtures screws and fast idol. Now it turns right over and idols @ 425-450 rpm, but has a very noticeable miss at any RPM. I did not replace the plugs or wires yet. the plugs did not looked fouled and wires are newer. I did re-gap the plugs to .30 Any ideas on where to go next??
Oh yes it still has the old gas in it. Draining tank tomorrow. would gas cause that significant of a miss???

[jim1932]

I'd like to have a miss.... but the Mrs. says no....

[G.M.]

Drizzle some Marvel Mystery oil down both sides of the carb keeping it running for a few minutes. Put the rest of the quart of MMO in the fuel tank. After the MMO treatment go for a 10 mile drive. Then short each plug to ground to ground while idleing to see if all cylinders are fireing. G.M.

[ratrod52]

i will try that. just curious what does the MMO do to improve my situation?

[Scott H]

Originally Posted by ratrod52

i will try that. just curious what does the MMO do to improve my situation?

yes 8 year old gas will make it run crappy

the MMO will dissolve gummy deposits and help smooth it out if its a fuel-related problem

[ford1]

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MMO is great for freeing up sticking valves, first thing, run a compression check, if the compression is with in specs, then change spark and coil wires, two ways to find a dead cylinder, hook an induction timing lite up to one spark plug wire at a time, if its a plug or wire the lite wont blink, the other way is have the hood open, then have some one start engine, then quickly touch the exhaust manifold with your fingers, the exhaust will be a lot cooler on the cylinder that is not firing than the one that is firing, its best if you can have a friend check the other side, be careful and quick, you only have about 30 secs to check

[Barry WNY]

I alsoguess stuck valve, probably exhaust if compression is not coming back into intake. pull wire to find out what one? I have resurrected a few sat a long while, valves and seats had rusted some. 37 engine Ran great from the getgo, then started missing. During usual tune up type remedies tried would barely run, I concluded compression was disturbing air flow going in. Sure enough heads off nearly all seats had pitting, ground & lapped them all.
Another, friends 8RT ran good on test stand, after 10 min. cooling and oil pressure was good, I said let's put it in, he chose to run another half hour. It went sour, we ended up changing 3 seats and grinding the valves and seats.
Like ford1 says, find out what one will give a good guess as to what side to start with. Oil bath cleaner, oily rag in exh. and vent would have helped

[Mart]

I used some old gas in my 58 f100 and it caused a valve to stick.

Don't use it with that old gas, it will not run well.

Get some fresh stuff in there and some added lube (mmo or fuel injector cleaner) and drive it gently until it begins to feel better.

Of course you can't rule out that there may be something wrong, but the crappy gas will completely mask any other problem.

Mart.

[G.M.]

Hey Ford1 If the valves are sticky a compression test isn't going to free them. I do the easy things first. Then if the problem still exists move to the next less invasive move. You mentioned some simple tests but the order they are performed in needs to be rearranged. Not referring to your post but there are so many that get posted on here tearing thngs apart before doing simple progressive testing. G.M.

[Mike51Merc]

You can mist some water from a spray bottle and look around the engine compartment in the dark to find a bad ignition wire. Look for sparks and listen for sharp clicking sounds.

I'd put ignition wires and plugs just as a matter of course.

I'd check compression and vacuum to try to diagnose a sticky or burnt valve. Low compression or erratic vacuum are both indicators of valve problems. You could also listen in the carb throat (with a hose up to your ear, not with your ear up to the choke!) for a periodic squeeking or huffing sound.

Perhaps your miss is just the normal flathead sound. They do idle with a syncopated rhythm.

[ratrod52]

Thanks for all the good advise everyone. I am going to replace the wires and plugs, get fresh gas in system with some MMO also a compression test i will let you know what I find! Again thanks everyone!

[ratrod52]

UPDATE!! The miss is gone. It was either a bad plug or wire. all replaced and it runs great now. Also drained tank and added non ethanol gas and some MMO
Thanks everyone for your advise. Hope to make it to BTT50's this year