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780 Views 8 Replies 4 Participants Last post by  66shawn
Patrick.,.. Have a question for you - I have read many of your
posts/replies and know that you know what you are talking about...
I am a pretty good mechanic too - But I have a problem that I thought you
may be able to help me with...

I bought a 66 converttible last year and had to make some changes to her
last winter.. I pulled the motor, completely rebuilt it, .030 over, .010 on
the crank. Everything is bone stock... My car is by no means a hot rod but
has plenty of umph. I like the original look or all original parts on these

Here is my question... I have the engine all back in now, took her for a
few test drives yesterday. The car has plenty of pickup, and over 2500rpm
she runs like a champ..

When I am kinda putting through a neighborhood, 3rd gear and about
1500-1800rpm the car has a very slight "bucking" that she wants to do.
Almost feels like the timing is too high, or like on a newer car, an egr
valve is sticking open (know the feel I am talking about???)

Anyhow, this car is a stock 66, no emissions or anything - vacuum is dead
nuts at 18 inches at idle.
Appears to be no vacuum leaks around the intake or the carb base and the
carb is untouched from last year when I bought the car. I never felt this
bucking with this carb on the old engine so do not feel that the problem is
carb related.

Another thing, I did convert to a pertronix ignition with the stock wires,
coil and dist cap... I can easily put the points back in and see if my
problem is ignition related but it does not feel like a miss, kinda feels
like a plug wire that fouls out or arcs out - this is usually more
prevelant under hard acceleration though....

One other thing I noticed was that when idling at like 700rpm, the pcv
valve seems to "rattle" like it's opening and closing real fast.. I put mu
thumb over it and the idle drops a bit.. I even pinched the vacuum line off
to the PCV valve and took it for a ride - same minor bucking..
Power brakes are brand new, new booster and a dual bowl master cylinder -
booster holds vacuum overnight, no problem here.

Motor is very strong and I don't know what else to check... Thanks in

1 - 9 of 9 Posts

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10,537 Posts
Hey Shawn,
Do I have anything to worry about with the cruise control on my '85 Ford Diesel pickup?? I've heard sometimes they get a mind of their own...*G*

OK, lets see...what happens if you stick your foot in it at the rpm level where you get the bucking?

Describe the carburetor and transmission type and rear gear ratio please...

From your description, if the car runs fine over 2500, even under WOT, I'd discount ignition and be taking a closer look at the carb...

If you can accelerate in 3rd gear from 1500 without bucking and hesitation, I'd say it's possible you have a chunkie stuck in your intermediate say the idle is fine with 18"hg so I think your idle circuit is working good...

Try this....put the timing light on the engine and run it up in neutral through the problem area while watching the strobe on the timing pointer....any erratic or missing flashes?

When you've got some more details post back and we'll see what we can do....


· Registered
22,556 Posts
Sounds like it could be that, too much timing. Try this, remove the vacuum hose off the distributor and see how it runs. After that, if that's the problem, you can try adjusting the spring rate in the vacuum advance unit, with an allen wrench through the nipple on the advanve unit. Don't forget now that your engine is nice and fresh, timing requirements may be different. Maybe a P.O. made adjustments to compensate for a tired motor before.

Also, how is the vacuum advance hooked up, manifold or ported, if ported go to manifold vacuum.

You can do anything you want to......ONCE!
aka "my 66 coupe"

Hale Boppe comet shot off my roof. See you can use 100 iso at night with no flash!

· Registered
117 Posts
Discussion Starter · #4 ·
Ok, here are the car's specs...
C4- crusiomatic
289 4bbl (autolite 4100)
stock 8" ford 3.00:1 ring and pinion.
Vacuum advance is connected to the carb, above the throttle plates - factory location

I'll check with a timing light around 1500RPM but without a load on the engine it responds fine.. In fact, it sounds very responsive and strong.. I agree that the ignition should be discounted but it was a change I made...

Fuel bowls were drained over the winter and the carb was shelved - Seems unlikly to me that there could be something in the intermediate ckt but I guess that is possible.. Car has a full tank of fresh 94 octane fuel (problem was there before and after new fuel).. Maybe a can or 2 or gumout in this tank and some serious cruzin are all that the doctor ordered!

I can also disconnect the vacuum advance and plug it - see what she does....

One pain on this little 289 is that she has 1 (ONE) 3/8 port on the manifold - I already modified that fitting to connect to the modulator valve on the tranny- I guess I could temporarily install a tee in that hose and pipe it to the dist... Also, never knew that there was an adjustable tensioner in that distributor.. Will look at that possibility.. Thanks again in advance - This has to be the best site on the net!!!!!

· Premium Member
18,946 Posts
I had that ran fine, but under cruise conditions, it had a slight hickup like a miss, but somewhat regular and fast...2 or 3x a second or so. It turned out my timing was too far advanced, and the engine (apparently) was too clean to induce knock or pinging. I'd try retarding the ignition and see what's cheap and easy to do. me check your shorts! My multimeter is just a-waiting! Formerly known as Midlife in the old VMF.
King of the Old Farts *struts*

· Registered
117 Posts
Discussion Starter · #6 ·
Ok, tonight I did take the car for another cruise after finding that I botched installing the new vacuum advance line from the carb to the dist... Was actually talking to another mustanger regarding some parts sale and was showing off my convertible.. I pulled the air cleaner off and was showing him the new stainless line and when I gave it a slight bump it popped out! Turns out the line must have walked out of the ferrul when I tightened it down.. So..... I replaced the ferrul and reinstalled the line.. Went with my wife for a cruise tonight and got the car nice and warmed up - pulled into a subdivision and gave it the test - STILL MISSES but very slightly... It is almost just an anoying miss but I know it is not right.. So, on the way home I was goosing her (the car) and got a very slight ping under acceleration.. I will knock the timing down a few degrees tomorrow and see what happens.. I am sure this is the problem.. I'll keep everyone posted!! Thanks again for your replies.. Everyone is thinking the way I am so that has me assured I am onto the fix!


· Registered
117 Posts
Discussion Starter · #7 ·
Patrick...... Did not mean to blow you off on the cruise control question for your truck...
Turns out that in the mid 80's ford did have a big problem with their servos on the cruise.. Did you check with a dealer to see if Ford issued a TSB on this? Being that it is cruise control coming on by itself sometimes makes me believe that it would be a recall, and no matter what the age/mileage of the vehicle it would be covered since it is a safety issue.. Ford is good about covering their problems that are not safety related or emissions related with dates and miles but I have never seen an emission concern or safety issue have a time frame or mileage restriction to it..
Let me know a little more about the nature of the problem and I will check some documents at work.. E-mail me the vin number and I'll see if I can have someone run it and see if there are any outstanding recalls on it too!


· Registered
10,537 Posts
That's OK Shawn....just a little engineer humor...*G*

My late year Kansas City truck has been exemplary in serving me for the last nearly16 years...

Only problem I ever had with the cruise control was forgetting to put back the clutch pedal safety switch wire when I did maintenance on the pedal bushings...
The diagnostics in the service manual took me right to the problem...

Other than my first car, which was a restored 39 Dodge sedan, I've never owned another make vehicle other than Ford.....that's how much I believe in HF's philosophy....

I would, however, be happy to receive any up-to-date information on issues regarding maintenance on my truck as I intend to keep it indefinitely....I will e-mail you the appropriate information presently...
Thanks for your offer of assistance!

Please keep us posted on your situation as well....


· Registered
117 Posts
Discussion Starter · #9 ·
Problem is GONE!

Ok everyone, my "bucking" problem is gone.. Turned out that it was a combination of the vacuum line not seated in the carb to the dist and a bit too much timing. I reattached the vacuum line correctly and retarded the timing about 2 degrees - Runs like a champ!! Thanks to everyone for their knowledge of these classic cars!!!!
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