Engine Stumbles

[hetrickw]

351w starts, BAD stumbles not surge(almost shuts off) then recovers most start ups but always when run for more than a few minutes. But intermittently runs smooth then real rough. Plugs are new/clean, checked spark going to distributor (what should be going from coil to dist? constant 12 volts? or not), timings good. Gas is full. Battery is new, alternator working fine. Fuel pressure constant @ 4/5lbs to carb. New plug wires, coil, condenser/rotor/cap, gap correct. Any way to rule out electrical before I rebuild my Holley again? I've had trouble with my carbuerator and have rebuilt it numerous times, last time being w/in last year. I am positive the carb settings are good, sine it ran great the weeks before and runs great intermittently. What should be the voltage coming off the coil and should it be constant voltage? Thanks, I appreciate the input.

Bill (San Antonio)

 

[Don C]

If you have points in your distributor you will only see a battery voltage reading when the points are open on the negative side of the coil (the wire that runs from the coil to the distributor). When the points are closed the voltage reading will be zero. Assuming the wire that runs from the ignition to the positive side of your coil is original, when the points are open you should see close to battery voltage and around 6 volts when the points are closed. These readings are when using a digital volt meter.

 

[T-Tom]

How old is the fuel? If you're not using 100% gasoline then it could be the problem. This ethanol crap is only good for about 30 days. If this is what you are using, drain it and replace it with fresh fuel, preferably real gas. You can never be sure how old your fuel actually is because you are getting it from a station's storage tank.

 

[hetrickw]

How old is the fuel? If you're not using 100% gasoline then it could be the problem. This ethanol crap is only good for about 30 days. If this is what you are using, drain it and replace it with fresh fuel, preferably real gas. You can never be sure how old your fuel actually is because you are getting it from a station's storage tank.

fuel is a couple months old, 10% ethanol (only available locally), I also use ethanol treatment every time I add gas.

 

[csgt428]

Does it have a rebuilt distributor? I've had really bad luck with stock rebuilds. Same thing, stumbles as soon as the vacuum advance kicks in. Try disconnecting the vacuum and see what happens.

 

[T-Tom]

There's a place in Hondo, C&W Fuels, 670 Fm 462 N.

http://pure-gas.org/index.jsp?stateprov=TX

 

[hetrickw]

There's a place in Hondo, C&W Fuels, 670 Fm 462 N.

http://pure-gas.org/index.jsp?stateprov=TX

Dist 10 years old only 50 miles on motor. (bought new)

removed vacuum from dist to carb and she ran great for 10 mins....then cleaned conncections between firewall and coil (connection) noticed frayed wires @ firewall. moved the harness a little and she shut down....so vacuum great idea....i'll re-do wiring and eliminagte, then move back to vacuum....and dist....headed in the right direction. at least I can PUT her back in the GARAGE now w/out pushing it..........great IDEAs AGAIN GUYS...........

HONDO is a good 40 miles, but a GREAT OPTION. Thanks

 

[mustang7173]

hetrickw,

How old is your Holley? I have chucked several Holley's due to internal cracks. I could never get them to idle right. Just a thought.

mustang7173

 

[hetrickw]

hetrickw,

How old is your Holley? I have chucked several Holley's due to internal cracks. I could never get them to idle right. Just a thought.

mustang7173

The 650 is about 10 years old, i'm thinking its fuel. I removed vaccum line into carb and played with hot to coil, not so sure those were actually the issue (ran a little better - intermittently ). I'm tending to believe i over did it or the powervavles blown, or something. It ran great for a good while, but it's still a severe stumble. A lot of my friends hate holleys but I had one for 10 years back in the 80's with not problems......guess ill pull carb, unless any other suggestions.....thanks

Bill

 

[TommyK]

Your fuel pressure sounds a bit low. Holley's are calibrated for 6 psi. 6-7 is usually considered an acceptable range.

What list number 650?

Is the float level correct?

 

[MotoArts]

Here's a free, old skool Holley trick.

Get the engine up to temp.

Manually run the idle up to about 2-3K RPM or so from under the hood.

Briefly close the choke blade, maybe for a second or 2. No need to gag is so bad that it stalls.

Repeat a time or 2 if necessary.

Carb should swallow the bug or dirt chunk if there was one.

Done.

Yeah yeah, some may find reasons not to do this but I've "fixed" one or 2 this way. Didn't cost me a thing.

 

[barnett468]

.

set the gas level in the carb to just below the inspection window when it is idling and leave it there forever.

plug the distributor advance hose and leave it plugged until the problem is resolved after which connect it to ported vacuum, not manifold vacuum.

tell us what the timing is at idle . . should be around 6 - 12 btdc.

turn one fuel mix screw in until it stops then turn it back out.

do the same thing with the other screw and post results.

.

 

[hetrickw]

its a 650 and the floats are set good, it finally went no start yesterday....i'm thinking it's the timing chain now. I tested for spark which I was getting but not sure it's on the right timing now. I've never replaced the chain on this one. I saw a neat trick on youtube to see how much play/slack is in the chain by turning crank forward/stop/reverse while obvserving rotor with dist. cap off.....i'll try that ....it it's the chain mayble i'll put better cam in while i'm tearing out the front end..... just another day in the life of this mustang.........going on 36 years with her this year.....