Engine hesitation/stumble
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From: Eastern, NC
Engine hesitation/stumble
Ok, I have searched this forum and am still lost. I have a 79 ford f-150 4x4 with a 1971 ltd 429 w/ dove-c heads a lunati cam, edlebrock performer rpm intake, holley 770 truck avenger, msd 6a ignition, powermaster starter/alt. I was having a slight stumble off idle so i switched the old holley 750 for this one. Then I noticed my dizzy bolt was loose, I set the timing by playing with it and the problem is even worse than before. The truck runs awesome from about 15 mph on. But from a slow roll it will almost bog. I bought the truck second hand and am unsure of the timing/advance and am also a rookie in that department. I noticed that when I changed carbs that the vac line from the dizzy was plugged at the carb and completely disconnected from the dizzy. Do I have an egr on this year? What does it look like? I was thinking that it may be a vac problem, so I connected the vac line to the dizzy and it did not help any. I am lost any help will be appreciated.
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From: okc
make sure that vacuum line is ported(only has vacuum when the throttle is applied) that is pretty crucial........then get yourself a timing light and set your timing at 10 degrees BTDC, then test drive, then you can adjust the timing up or down 2 degrees at a time until you find the performance you like......i say to do it this way because people use many different cams and timing gears so this will help you dial it in......its pretty much impossible to time a Ford engine by ear, you will never get it right, i threw away my old 360 because i thought the motor was shot, turned out i didnt know how to time it back then and it ran just fine........silly me, since i learned how to time these Ford V8s i kick my self for getting rid of it.....
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From: okc
ported will be on the carb above the base, a ported vacuum has no vacuum at idle, it has vacuum when the RPMs are increased, the reason for using a ported vacuum is that a direct vacuum off the manifold or bottom of the carb looses vacuum when the throttle is first pressed, then the vacuum rises as rpms get higher,that doesnt help for off the line performance...... a ported vacuum is different in that the vacuum increases when the throttle is applied then levels out,this does help for off the line performance.....i hope im not confusing you..........
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From: okc
im sorry, i reread my post and need to clarify......the port above the base will be on the side of the carb above the metering screws, there is a port down low above the base thats not ported.......if thats where you have yours, the next step is timing the engine like i said above.........
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From: Eastern, NC
OK, still not fixed. I can't read the timing marks, but I am using a light to adjust the timing and I still can't get it dialed in. If I go to high on the timing I get a spark knock going up hills. If I go to low the stumble is still present and there is barely enough vacuum to work the brakes. The stumble will go away after I drive the truck for like 30 minutes. But on short trips like 12 miles or less it is still there. It never stalls, but I have to feather the gas to get it going. Thanks in advance
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From: okc
only way it would be a choke problem is if the choke isnt opening when the engine is warmed up, i personally dont use my mechanical choke at all.....only thing i can think of off hand is to clean off the timing marks so you know where its set, the go a half degree at a time to dial it in where you need it....that slight stumble is real tricky to get rid of, only way i got rid of mine was tweaking the distributer over and over till it was right, its gotta be dead on....you might try putting the vacuum advance on a direct vacuum, i know i said otherwise before, but sometimes it works better, mine is on a direct port now because my carb doesnt have a ported vacuum, yet....but it works fine like that for now......hope you get it figured out......
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From: Eastern, NC
It is running like a champ now. The float level was a tad too high. It is amazing how much that little difference made. Now I just have to fine tune my timing. Thanks for your help.
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From: okc
i cant believe i didnt type that in here already, i had to reread everything to be sure!! thats usually one of the first things i tell people to do, guess ive typed it in so many other threads that i thought i did here too.....sorry bout that....glad to hear you got it figured out, these motors are so much fun when everything is dialed in and running smooth.....
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