Running rough
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Freshman User
Joined: Apr 2006
Posts: 48
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From: Minnesota
Running rough
Hi, Im new to the FE engines and the one in my '74 f100 runs real good at idle, but at any higher rpm it runs rough. It also backfires frequently at speeds in excess of 50 mph, and for whatever reason it only seems to start easily in neutral. Im positive its nothing internal, for I had it running fine the other day. I just bought the truck and it had been sitting since august. Any help would be much appreciated, I work mostly on Austins and VWs so this is new to me.
Elder User
Joined: Jan 2004
Posts: 561
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From: houston
Does it back-fire through the carb, or out the exhaust? Through the carb indicates the fuel mixture is too lean. Through the exhaust indicates the mixture is way too rich or a serious timing issue. Good luck.
Post Fiend
Joined: Mar 2004
Posts: 6,056
Likes: 8
From: Union, Washington
The proper way to do this is do a compression check, then you will know for sure the motor is healthy. When was last tune up? A worn cap, rotor, points or plugs can do this to you. It could be a vacuum advance unit as bertha66 says, but it is more likely something in the actually ignition system, unless you have had a sudden drop in gas mileage.
Senior User
Joined: Sep 2004
Posts: 457
Likes: 0
As bear states, check your inginition system. Since it's been sitting a while, it may be best to go down to your local Napa and buy yer plugs/wires/rotor/cap. Give her some new parts and try er then. If problem still exists......Well, at least you know it aint the ignition system and what......you've got $45 bucks in er?
It's good for those 'ol girls to have new parts once in a while. :thumbsup:
Mike
It's good for those 'ol girls to have new parts once in a while. :thumbsup:
Mike
Thread Starter
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Freshman User
Joined: Apr 2006
Posts: 48
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From: Minnesota
Ok, sounds like it is the timing/vacuum advance/fuel too rich. It backfires through the exhaust. Im almost positive that it is one or all of those three, because it had a tune up before i bought it. Im not so sure how fresh it is, but everything looks very new (coil, points, cap) However the wires may be subject to replacing, they dont look worn out but I doubt those were done the same time as the rest of the tune-up. I also added a fuel filter right before the carb to get rid of any varnish from the tank/lines. It has a 4 barrel Motorcraft carb, so if anyone can give me a hint on where the mix screw is id appreciate it. I usally work on english SU dual carbs and Solex carbs, so im not 100% on where it is. Thanks for the feedback!
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Freshman User
Joined: Mar 2005
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From: buckley, wa
i would make sure the points are good, and that the dwell is set right... something around .008??(someone help me out with that one, not quite sure) my dad had the same problem with the 352 that was in his 66, ran great at idle, but once rpms increased whether in gear or not it would backfire through the exhaust real bad...
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Post Fiend
Joined: Mar 2004
Posts: 6,056
Likes: 8
From: Union, Washington
Try .017" for the points or 24 to 30° for dwell. A bad condensor will cause this also. Idle mixture screws are on the front of the base plate of the carb. They have plastic covers on them to limit how much you can turn them, but they aren't your problem.
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Freshman User
Joined: Apr 2006
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From: Minnesota
Alright, i found my dwell/tach meter and i couldnt find the instructions on how to hook it up...another thing i was having trouble finding was where the marks for the timing degrees, there is nothing i could see to figure the tab on the left hand (passenger) side of the engine, but no numbers. I havent been able to find anything on where they are or what they look like. If anyone has a picture, PM me for my email. I was able to get the timing by ear, but i was still getting some chugging and hesitation in the low rpm that gets better with higher rpm. Im not sure if that means my advance is sticky or not.
Post Fiend
Joined: Mar 2004
Posts: 6,056
Likes: 8
From: Union, Washington
Dwell meter hooks to the the dist,, (negative side) of the coil and the other lead to ground. Timing marks are there on the damper, behind the front lower pulleys on the engine. Marked 10° ATDC (After Top Dead Center) to 30° BTDC (Before Top Dead Center). Sometimes the damper gets dirty and you have to clean it off to find the marks, but if the engine is not running they can be on the down side and you won't see them. Engine running you need a timing light flashing to see them. The tab is just the pointer, number on the rotating damper under it. I doubt your advance is stuck, just base timing is wrong. BTW, the passenger side is always the right hand side of the vehicle, driver's side is the left. Everything is oriented from sitting in the driver seat.
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