3.0 misfire at all rpm

1988 3.0 miss fire, conventional ignition (and keeping it) all tune up has been done every season, filters etc... I do have 1.2 ohms on purple to coil + , and 11.50 v to coil on that wire, cannot see a miss on spark tester, carb rebuilt and has good fuel press(6) and idles smooth at 650-700 but a miss here and there and then bogs and will die at wot. Fuel tank check valve replaced also. Ordered a new resistor wire, the coil points condensor cap wires plugs, all new and replaced every season, weather it needs it or not. Just can't figure out this misfire/bogging problem. Also carb swap with buddy's and his runs great with mine ,mine same w his, compression is all good 145-150 across the board, new head gasket, manifold, just cause I'm a ford tech and its a very simple job for me, and age of boat, I've owned since new, But I'm stumped on this one guys

Are you 100% sure you have the firing order correct?

1342

What is your dwell (point gap)
What spark plugs and gap

What points rotor and condenser are you using?.......

Condenser is supposed to be .18-.25 micro farads
Plug RV9YC or AC R42TS gap .035
point dwell 28-34 degrees or .022"

4-6 degrees BTDC timing

Have you confirmed the timing is advancing also have you looked at the advance weights and springs under the point plate to make sure they are clean and working?

What is your idle vacuum?

Check fuel tank vent is clear.......

When this bog occurs if you add more fuel does it go away? (either by rapidly moving the throttle to activate the accelerator pump circuit or adding additional fuel by hand)


if you are 100 % sure of all of the above

then swap coils with your friends boat and see if that may do it.

Other wise it may be a mechanical issue such as a bad valve, valve spring or lifter/pushrod
or worse case a cam lobe has gone round.....

Firing correct, dwell 28,timing 6btdc, I rebuilt dist, new bushing weights ok and advances 32 degrees at about 1800 rpm,vent is clear , when I did head gasket , I sent to trusted machine shop I been using since 1978' valve job showed up just a lapping needed, flatness was .001 , used multiple coils, condensor may be an issue at this point, I'm leaning towards flat cam tho, going check lift in next few weeks , after a long needed vacation. So much for 20 years of synthetic oil, also has AC mr43t plugs,I'll try the 42s next, did not vac check, no port, would have to install one and check base engine, I'll let ya know what I come up with as I won't give up until it's right. Thanks for input, Kevin

Years ago, 1990's I had a '72 Nova 350 auto. Bought it with 89,000 original miles.

It had a slight skip from day one. Over the first couple of years I replaced the stock two barrel with a aluminum intake and holley 4 bbl.
ran like a raped ape.............
I could never get the skip out of it no matter what I tried. I reworked the carb so many different ways with tuning parts and modifying some of them myself.

After about 30,000 miles of use I started getting a back fire thru the carb on hard acceleration. Not under normal load driving only hard acceleration.

found two exhaust lobes went round, simply pulled the valve covers and watched the rocker arms............. new cam, lifters, pushrods, timing chain and a old but good set of heads I had sitting around.......

After rebuild and slight tuning at 110 mph I had 1/4 gas pedal left to go...........motor ran as smooth as could be, no more skip......

I was running a point ignition also but was using Accel parts only.

I also had switched to mobile one as soon as I purchased it.........oil does not matter so much As does how often you change it based on usage.

sad thing is boat don't see more than 25-30 hours a season if that ,and oil changed every season along with ign system, stored in doors heated garage always, and seen rain 1 time. im goin to tap 1/4 n plug under carb in manifold and check vac, then ill remove valve cover,and check cam lift

Still at it guys, going out Monday , checked rockers for worn cam, seem fine all nice lift, removed fuel tank from the boat had it cleaned at a radiator shop, all ready runs good on muffs, will keep ya updated on progress

Gotta 'em crossed for you!

Jeff

Ok, seems like that 27 year old tank and bad fuel was the problem, ran out fine today, all day .
took fuel sample to work and tested for alcohol and passed, but failed deposits. Clean them old tanks boys!!!

Damn good advice. Glad to hear you're okay.

Jeff