2 months ago I bought a 1965 Mustang Coupe with a '69 351W that has been worked. First I want to say that I'm mechanically inclined when I know what I'm looking at and what I need to do but until then I'm clueless. And this is the first carburetor vehicle I've ever owned. I've put about 150 miles on this car and has run good until now. Last weekend it started "bucking" slightly while at a steady cruising speed. It has gradually gotten worse over the past week to the point now where the car is barely driveable. It will start and idle perfectly, but as soon as you drive it, it is very rough. So it didn't start all at once but gradually got worse. It has a Holley 670 Street Avenger carb and an MSD Ignition.

Any suggestions on how I proceed? I hate to just start replacing plugs, wires, distributor, carb adjustments, etc. if there are tests I can try first. I did notice that this started after the first time I drove it in the rain but I would think that would have dried by now or it at least would get better with time if that is the cause. Probably coincidence.

Fuel pump or plugged filter. Put a pressure gauge on the fuel line and crank it (15psi gauge) it should have ~5 to 6 PSI and when cranking stops (just do it for 10
seconds or so) it should hold the pressure. If not, change the pump, or replace it with an electric pump. Also check the fuel filter. Jim

And this is the first carburetor vehicle I've ever owned... :shock:

Its still the basics bro...

My first thought, and the simplest thing to do, is to pull the fuel filter off, and see if
you can blow through it, without much effort. Could be plugged. Let us know what you find.

Reminds me of a conversation at a swap meet, between a father, and his son. Dad says "These
are for old cars. They're called carburetors". Kinda makes you stop and scratch your head.

I changed the fuel filter soon after I bought it. Very unlikely it could be that. I will check pump pressure.

Check the fuel level in the float bowls those have a plug on each bowl that you remove and an adjustment for
each,Google this and you may find a clip about it,,start there

Primary jets plugged? Holly had a problem with the plating coming off the carbs on certain years.

Aaron

I would make sure the fuel pump puts out at least 5 psi while at your steady cruising speed. Put a T in the line right before the carburetor, get a fuel pressure gauge, and make sure you can read it while going down the highway. Make sure the engine oil doesn't smell like gas if it has mechanical fuel pump on the engine

define msd ignition? , if it is electronic ? then disregard my comment ,because it may not be your
problem . if you have points, if it is anything like my 429 Marquis Convertible built in 69 .they
have a tendency to slip on a worn out distributor plate , whenever the vacuum advance pulls a hard
punch , that results in a fast takeoff to achieve 100 mph just like that !!!.. when she comes back
down ,. it will idle fine , but wont want to take fuel ,.the points mite be sitting too close,..

Like I learned 2 weeks ago. Always start with the points.

(quoted from post at 20:03:53 09/08/17) define msd ignition? , if it is electronic ? then disregard my comment ,because it may not be your
problem . if you have points, if it is anything like my 429 Marquis Convertible built in 69 .they
have a tendency to slip on a worn out distributor plate , whenever the vacuum advance pulls a hard
punch , that results in a fast takeoff to achieve 100 mph just like that !!!.. when she comes back
down ,. it will idle fine , but wont want to take fuel ,.the points mite be sitting too close,..

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The MSD ignition is all electronic, Multiple Spark Discharge when the engine is below 3000 rpm it can fire the same sparkplug up to seven times (20 degree's of crank rotation) to keep the spark plugs from fouling out. The system was designed for racecars first then they started making them for street car applications. You don't want to get zapped by it, video of the coil output https://www.youtube.com/watch?v=LbAcPl95PHU

MSD is very high output electronic

sounds to me like you got a bad tank of gas. pull bottom bolt out of fuel bowl on carb. catch the gas and let it settle. see what you have. you can fill carb through the vent on top of carb with good gas. see if it runs better. may have to drain the gas tank down to get water out. holley carbs are pretty simple to work on. some seafoam should clean it up if you can get it running a little better. vacuum line come off carb or distributer? do you have msd distributor and ignition box?

If it has water in the fuel it would effect the startup, and idle also. Since water settles at the bottom you would have a bog on acceleration since the accelerator pump gets its fuel from the bottom of the float bowl.

nrowles,

double check that the carb secondary blades are completely shut, maybe tap on them with a screwdriver.

D.

Your carb float levels are set to low.

Fuel restriction

(quoted from post at 23:39:42 09/08/17) vacuum line come off carb or distributer? do you have msd distributor and ignition box?

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I don't believe there are any vacuum lines and the other night we spray carb cleaner around vacuum areas and no change in engine so I don't think it is vacuum related. Yes to MSD distributor and box.

(quoted from post at 23:56:39 09/08/17) If it has water in the fuel it would effect the startup, and idle also. Since water settles at the bottom you would have a bog on acceleration since the accelerator pump gets its fuel from the bottom of the float bowl.

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While it started at cruising speed at has gotten much worse over the last 10 miles. When I stay it is now running rough it definitely runs rough on acceleration. This problem started shortly after a "fresh" tank of gas. Hmmmm.

(quoted from post at 02:45:37 09/09/17) Your carb float levels are set to low.

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Don't you think a setting would have shown itself before? It ran fine before and I didn't change any float level settings.

I don't know how to put multiple quotes in one post so that's why all the posts in a row.

I am going to Penn State / Pitt college football game today. Hopefully I can check some of these things out tomorrow. Any more suggestions are welcome. Seems like most of you are going the fuel route rather than electrical/spark.

Bad plug wires can cause bucking. That aftermarket ignition needs special wires.

(quoted from post at 08:53:02 09/09/17) I would make sure the fuel pump puts out at least 5 psi while at your steady cruising speed. Put a T in the line right before the carburetor, get a fuel pressure gauge, and make sure you can read it while going down the highway. Make sure the engine oil doesn't smell like gas if it has mechanical fuel pump on the engine

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And don't forget to check the suction side of the PUMP with a fuel pressure tester... The tester has a vacuum gauge for a reason :wink: You can even go to the tank and check from the tank froward It should pull at the least 12" of vacuum.... If not suspect a bad pump are a leak in a hose are metal tube depending on were you install the gauge.

https://www.youtube.com/watch?v=EYWKo40FDH0

You said the issue appeared after it got wet pull the distributor cap and check for moisture... The only problem I have had with MSD is the trigger the controller is pretty much bullet proof. Even then it would not fire at all and EZ to diagnosis.

baring bad gas put in during the week, im going to say with that msd setup you have a mid rpm miss due to plug wires breaking down, or a plug bad, probably both now, if its missing at mid rpm levels the plug is being fouled by unburnt fuel, as stated that msd requires special wires the usual auto store ones wont last on it , id pull the plugs and see what those tell you you may need plugs too, you mentioned the motor has been worked, but not to what extent, a hot motor needs hot motor parts,

The 351 windsor had a fuel pump with canister on it containing fuel filter . Did you change the filter in that canister?

i did pull the distributor cap and no moisture. The motoor is supposedly all top end stuff and bored .40 over with about 400 hp at the crank. I did pull 1 plug last night while motor was still hot and the plug was a burnt dry tan color and nothing was rounded off. I think it looked good but that was only 1 of 8. The filter I changed was the little one in the canister right before the carb.

(quoted from post at 20:34:10 09/08/17) Like I learned 2 weeks ago. Always start with the points.

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Points, condensor, spark plugs, and then move on to the distributer cap and the plug wires. Since it happened AFTER driving in the rain, I would suspect the ignition system first, and probably the distributer cap.

The first step for me is always to determine whether it is spark or fuel. Ignition problem gives a sharp or abrupt miss, hiccup, buck or fish bite feeling. Fuel will generally be more dull and gradual. If backing off the pedal smooths it out , it is not getting enough fuel into the carb. If nailing the pedal makes it clean out and go, you have enough fuel in the carb , but are lean for some other reason.

My guess would be one or more primary load circuits in the carburetor may be partly restricted/plugged (your 4 barrel has 2 primary load circuits and 2 on the secondary barrels), causing lean fuel under load. Check the easy and cheapest stuff first: spark, fuel pump, before tearing into the hard stuff. If you need to tear into the carburetor, find or download a good manual on it before you take it apart.

A sticky centrifugal advance or vacuum advance would be easy to check with a timing light. Borrow one from an old guy or find one at a garage sale or Goodwill for about $1 for a black one or $5 for a shiny chrome one, LOL. Tune up tools for those cars also included a vacuum gauge, remote starter switch and a dwell meter.

One of the most difficult issues I ever ran across the guy brought a chevy with a 383 stroker. It was the strongest one I have ever driven it would get'er done. He decides he wants different valve covers and air cleaner. I install them a few weeks later he returns and ask I install new plugs in it, it runs like chit.. At idle and light throttle it ran good but would bust up and fall on its face under acceleration at anything above light throttle.

All in and done this went on for weeks it was a head scratchier... Every time I worked on it I put the air cleaner back on it one Sunday I said self you got to get it FIXED. It needed gas as it only got 4 MPG so I just laid the air cleaner in the bed. I pulled out the drive and nailed it, it took off like a bat out of ell...

The new air cleaner was sitting to close to the top of the carb and disturbing the air. I got a 4" element to replace the 2" one it was FIXED... Hopped up engines like there air and plenty of it...

Every thing I touched had a issue like the distributor gear worn on the cam, the fuel pump bad, the lobe on the cam that ran the pump worn out. The wrong spark plugs installed that crushed the first threads in the heads. All in said and done air was the root cause it all goes back to check your basic injected are not...

Well we all can second guess here as to what , But really what is needed is and old fart that worked on those engines when new and built them . Now i am sure your not in my back yard and a road test is out of the question here . many moons ago i worked for a large Ford dealer and headed up there Drag club and kept our two cars running . Built many 302 ,351 Windsors and coutless F E's and the Bosses and the 385 blocks . So really with out a test drive and hands on we would be guessing . Now i am not up on the Holley Avenger carb so i guess i would have to look that one up . If it like the OLD Holley's then i was the wizard on them . So on them first place i would look is the power valve , Those had teltale signs of being bad , (1) Like hard starting , where ya had to crank for and extended time to refill the fuel bowl after setting , (2) hard starting hot acting like the engine was flooded . Now surging can be caused by improper jetting and todays' let build and engine out of the Summit Racing book is the new engine builders dream . as we can not make a call and give the CARD # and UPs will drop my parts off and i can BOLT them on and it will go . I have no idea what your engine is doing on vac. at and idle or on a cruse or WOT as this will determan what power valve and jetting . Timing , i have no idea what your timing curve is as i BUILT all my own dist. for app. some i used a single point set up and some i ran a dual point , some with vac advance and some with out . I have no idea of your compression ratio or the cam your running as here again this can affect the carb set up . . Now as to the MSD myself i have only worked with one MSD system , No take that back two and both were used on pulling tractor builds and BTW both were top winners. when i had had a problem child i had the means at the shop to put them on the scope and run them on the Dyno , Or i could put my small portable scope in the car and drive it on the and see what the ing. system was doing in a real driving situation . As to fine tuning the carb i could stick the TUBE up the pipe and also go ahead and laugh a Sniff test . You could have a timing chain starting to stretch and allowing the cam timing to bunch around . May even have a couple lobes wiping off the cam . rocker arms coming looses bent push rods . I had one 69 ford Torino that had a 351 W 4 Bbl. with a four gear that belonged to one of the girls that was in the drag club that drove me goofy as that car would run great , then just all of a sudden just up and die , they would drag it in on the back of a wrecker and i would jump on it and each time a new set of points and cond seamed to solve the problem only to have it come back a couple days later , sometimes after the ride on the back of the wrecker it would start and run fine for a day or two. at the track it screamed . I ended up taking the car and driving it myself for a solid week before it died on me one morning heading into work and i found the problem while setting along side the road ,it was the resistor wire from the key switch to the coil . And because of this my new diagnostic tool for tracking down this problem was a scavenged dash litebulb socket and a 1895 bulb hooked to the coil and a ground stickup up from under the hood When the light went out you had no juice , replace wire .

Stroke and age makes the mind fuzzy. But wasn't the 351 the one that came from two different plants. One was a great engine the other was a dud.

(quoted from post at 09:10:08 09/09/17) Stroke and age makes the mind fuzzy. But wasn't the 351 the one that came from two different plants. One was a great engine the other was a dud.

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your correct,Cleveland and Windsor.

Before you start changing parts,

In the dark lift up the hood and start it up, give it a couple of revs and watch for sparks at the plug wires.

if it was mine it would have an edelbrock carb on it!

just by your description sure sounds like a fuel pump to me , spurting out just enough to keep the engine running at idle.give it a check and the filter at same time as that will do the same thing. gets worse with time.

Try cleaning the rotor button n in the distributer. When my 1975 Cougar with 351w acted that way, that's what I did and it solved it. Just take some fine sandpaper to the edge of the rotor button.

I am on a phone right now so I will have to read these replies more thoroughly tomorrow. You guys are definitely helping me out with this one. I think I can figure out if I'm getting fuel to the carb. I will probably leave the carb for last other than the easy things to check that you guys mention. I can check plugs to see what they look like.

How do I check wires? Am I pulling the plug and grounding the plug and turning over and looking for spark at the plug?

How do I know if the distributor is failing?

eliminate the fuel problem first. do one thing at a time in order. # 1 is a fuel pump check followed by the filter. you must have a proper flow of fuel reaching the carb! your barking up the wrong tree worrying about plugs.

> How do I check wires?

The traditional test is with an ohmmeter; they should have a resistance of less than one kilohm per foot. But that won't tell you if the insulation is breaking down.

Try firing up the engine in pitch dark. Any crossfiring will be visible.

99.999 % fail at the spark plug end are the dist boot end... LOOK inside the boot... Normally they will be smut black are cooked white... Your eyes are your friend...

BTW the last ford that gave me fittz it would knock off randomly and always would restart once you pulled off to the side of the road no pattern to it. It may run 200 miles are you may not get out of site of the shop.

I was ready to throw in the towel I had drove it 400 miles before I got it to act up once it did it happen regular on a drive, I let it cool off it never happen again... On a whim because I happen to have a used distributor I went after the dist. While removing the plug wires from the cap one wire had pushed back into the boot causing the spark to jump a large gap. I checked them all and got that one back to were it needed to be. Its never stalled again my thinking is it overheated the coil....

I run ethanol in everything however if this car had never had ethanol and that's what you put in it could be the source of several issues including plugged fuel filters.

(quoted from post at 16:10:08 09/09/17) Stroke and age makes the mind fuzzy. But wasn't the 351 the one that came from two different plants. One was a great engine the other was a dud.

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The dud you are talking about is the 351M. In the mid seventies, everybody wanted 351s and Ford couldn't keep up after they dropped the 351C. The 351M came about when Ford put a Windsor crank in a 400. I personally do not consider the 351M a "dud", as it was built under the heavy smog restrictions; it did the job Ford wanted it to do. It met pollution requirements, was the displacement everybody wanted and had enough power for light trucks.

well when ya get down to it there were three , ya had the 351 W then the 351 Cleveland and then came the boat anchor 351 M . some say four if ya include the 351 BOSS but it was built on the cleveland .

I had my bate of'em (351M400)... They stink tho I will admit they were average to good on fuel and pulled dang good... The best part is there were enoufh with 390's you could buy a junker and swap that P.O.S. to a 390...

Wow! I had that exact same car (and problem...). My engine was the 351W, but someone had wired it as a 289. The farmer next door looked at it and said, "I bet that's a 351W". He knew the firing order, switched the plug wires around, and it purred like a kitten. Best engine I ever had...
I got the car cheap because it would idle great, but ran very rough under load. It was just a simple plug wire mix up.

Bye for now,

Troy

ok so here's where I'm at. I haven't done everything you guys mention but I've gotten some progress. I haven't touched the carb yet because that is all foreign to me.

Tested the fuel pump. It put out 6.00 psi with engine at idle and jumped to 6.75 when revved. I left the gauge on after I turned car off and it only dropped to 6.00 psi from 6.75 after about 25 minutes. I didn't vacuum test it but I would think what I've done confirms pump is good.

The car doesn't have a fuel filter canister on the bottom of the pump. I changed the inline fuel filter right before the carb 150 miles ago when I bought the car. This is a little plastic looking strainer thing that you can see though a glass canister it is in. It was absolutely filthy with what I'm assuming is debris from the gas tank. I'm wondering if something got by this filter and is plugged up in my carb somewhere ???

Oil does not smell like gas.

Cleaned MSD distributor inside and out and does not appear to have any moisture present. I also tested the MSD box and it is working and producing spark. Do you know how I can test these MSD distributors? Also, I don't think it has any points. Is that possible?

I tested each wire with an ohmmeter and they all came in around 1,000 so my wires are good.

I could only get 4 plugs out as all of the others I'm not able to get out with the tools I have. That motor is sitting so tight in the engine compartment. Unfortunate but I really don't have an option here.

Another note is that when I go wide open throttle it seems to have all the power and takes off like I would expect it to.

So to summarize my questions, how do I test the MSD distributor? Am I correct in saying these MSD distributors don't have points? Any other thoughts after all this info? After this I'm tearing into the carb.

I'd change the fuel filter if its as dirty as you make it sound, and see what it does first. You not only have to have fuel pressure, but you need fuel volume also. The dirty filter is reducing the volume so its not going to be able to get enough fuel to keep up with what the engine wants.

(quoted from post at 06:56:19 09/11/17) I'd change the fuel filter if its as dirty as you make it sound, and see what it does first. You not only have to have fuel pressure, but you need fuel volume also. The dirty filter is reducing the volume so its not going to be able to get enough fuel to keep up with what the engine wants.

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I did put a new filter in. No change.

If you get full power at WOT I would suspect the carb primary circuit, power valve maybe.

Looks like you get to learn how to work on a Holley 4bbl carb.