Ignition questions
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Senior User
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From: Kingston Springs tn
Ignition questions
I recently inherited a 1982 f150. The truck has 351 windsor out of a 1977 ltd II. The engine was rebuilt to stock specs (assuming!)(25 years ago) but bored .030 over. As far as I know stock everything was used except bearing and rings and such. It has a motorcraft 2 barrel carb. Still has the Duraspark II ignition. assuming it has the stock distributor. Also all the smog equipment was deleted, this is Tennessee after all.
My question is, the truck in general doesn't really run all that great. It has a rough idle and doesn't rev cleanly until you get on it. Almost like it has a miss. Is the stock duraspark II a piece of junk and need to be replaced? Should i replace the distributor and coil?
Keep in mind i intend to do a full top end on this truck once i get it semi reliable. (i.e. gt 40 p heads, aluminum four barrel intake, four barrel carburetor, and a better cam, lifters, pushrods.) I would like to be able to keep up with my 5.4 3v.
I'm pretty new to deep dealings with pushrods and carburetors. Mostly just worked on modulars before.
My question is, the truck in general doesn't really run all that great. It has a rough idle and doesn't rev cleanly until you get on it. Almost like it has a miss. Is the stock duraspark II a piece of junk and need to be replaced? Should i replace the distributor and coil?
Keep in mind i intend to do a full top end on this truck once i get it semi reliable. (i.e. gt 40 p heads, aluminum four barrel intake, four barrel carburetor, and a better cam, lifters, pushrods.) I would like to be able to keep up with my 5.4 3v.
I'm pretty new to deep dealings with pushrods and carburetors. Mostly just worked on modulars before.
FTE Legend
Joined: Jul 2010
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From: Northeast, OK
The DS-II ignition is good, and there's no reason to replace it on your truck. My guess is that the air/fuel ratio is very rich, causing the rough idle and poor acceleration until it is rev'd up. If so, the Motorcraft 2150 carb may have a blown power valve. You can read up on it here: Motorcraft 2150 - ???Gary's Garagemahal.
On the other hand, it may be that you have burned valves. I had an engine, oddly enough a 351W in an '82 F150, that had several burned valves. It idled horribly and didn't have much power until floored, but ran well on the highway. When I did a leak-down test I discovered the burned valves and a valve job fixed the problem.
On the other hand, it may be that you have burned valves. I had an engine, oddly enough a 351W in an '82 F150, that had several burned valves. It idled horribly and didn't have much power until floored, but ran well on the highway. When I did a leak-down test I discovered the burned valves and a valve job fixed the problem.
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From: Kingston Springs tn
Thank you! I doubt highly burned valves are an issue, although entirely possible. I would suspect the never been rebuilt carb is suspect. Thank you for such a quick response!
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From: Kingston Springs tn
Also forgot to add that this truck is bitch to keep running until fully warmed up. Choke flap will not stay closed enough unless I gently force it closed with a screw driver.
FTE Legend
Joined: Jul 2010
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From: Northeast, OK
That's a different problem - but still a carb issue. My guess is that the hot air tube has rotted off, as most have, and the choke wouldn't open because there was no hot air coming in from the exhaust manifold. So the PO adjusted the choke where it would come off - but it won't close completely.
Laughing Gas
Joined: Apr 2013
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Your rough idle could be caused by a number of things.
Bad wires will do it every time. If the ignition system is due for cap, rotor, wires and plugs, that could be the source of a lot of trouble.
Next, inspect for vacuum leaks. Broken or disconnected hoses. Inspect them closely for cracks. Check your carb mounting bolts not too tight, but snug.
With the motor running spray some carb cleaner here and there around the intake and base of the carb. If the motor suddenly smooths out and speeds up you've found a vacuum leak!
Finally, spray the springs at the base of the carb with carb cleaner to clear out and crud that could cause them to bind then maybe a tiny bit of oil to ensure they operate freely.
Bad wires will do it every time. If the ignition system is due for cap, rotor, wires and plugs, that could be the source of a lot of trouble.
Next, inspect for vacuum leaks. Broken or disconnected hoses. Inspect them closely for cracks. Check your carb mounting bolts not too tight, but snug.
With the motor running spray some carb cleaner here and there around the intake and base of the carb. If the motor suddenly smooths out and speeds up you've found a vacuum leak!
Finally, spray the springs at the base of the carb with carb cleaner to clear out and crud that could cause them to bind then maybe a tiny bit of oil to ensure they operate freely.
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From: Virginia
If you want this thing to run nice and have a chance of keeping up with your newer truck, I would throw some money at it, replace the intake with a 4bbl and put a nice small holley 600 or edelbrock 4bbl carb on it with your choice of manual or automatic choke.
All new, and a nice power increase.
All new, and a nice power increase.
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Cargo Master
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From: Somewhere n North America
What about your EGR System, leaking Exhaust in to the Intake at Idle ?
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From: Kingston Springs tn
I suspect it may need new wires as some of the wires were definitely chewed on by a small roden.
I rebuilt the carb over this past weekend, new needle and seat, new power valve plus lots and lots of cleaning. The starting issue is completely resolved. It still sounds like it has an intermittent miss but overall idles and runs 10x better.
As for the more power response (I'm on my phone so I can't quote you as well), I figure the stock 1977 heads are only good for scrap iron at this point with gt40 heads being so cheap and plentyful. Used edlebrok four barrel intakes are relatively cheap and easy to find. My question would be cam lifter and pushrod choice when combined with a stock mechanical fuel pump. Also I want to do all the work for $2,000 or less and shooting for 300 hp.
Y'all are awesome, thank you for the help.
FTE Legend
Joined: Jul 2010
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From: Northeast, OK
I'm not sure 300 HP is a reasonable goal - especially for a 351. That is, if you are going to have good low-end torque that's needed for a truck.
I say that because I got 384 HP @ 3800 RPM from a 400 with aluminum heads & 10.5:1 compression, roller cam and lifters, and a 750 CFM carb on a Weiand intake. But, the build was geared for low-end torque for a truck instead of high-end HP like a lighter vehicle would need, and it churned out 500 ft-lbs.
So, with 7/8's the cubic inches and much lower compression you shouldn't expect the same power.
I say that because I got 384 HP @ 3800 RPM from a 400 with aluminum heads & 10.5:1 compression, roller cam and lifters, and a 750 CFM carb on a Weiand intake. But, the build was geared for low-end torque for a truck instead of high-end HP like a lighter vehicle would need, and it churned out 500 ft-lbs.
So, with 7/8's the cubic inches and much lower compression you shouldn't expect the same power.
Thread Starter
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Senior User
Joined: May 2007
Posts: 128
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From: Kingston Springs tn
I'm not sure 300 HP is a reasonable goal - especially for a 351. That is, if you are going to have good low-end torque that's needed for a truck.
I say that because I got 384 HP @ 3800 RPM from a 400 with aluminum heads & 10.5:1 compression, roller cam and lifters, and a 750 CFM carb on a Weiand intake. But, the build was geared for low-end torque for a truck instead of high-end HP like a lighter vehicle would need, and it churned out 500 ft-lbs.
So, with 7/8's the cubic inches and much lower compression you shouldn't expect the same power.
I say that because I got 384 HP @ 3800 RPM from a 400 with aluminum heads & 10.5:1 compression, roller cam and lifters, and a 750 CFM carb on a Weiand intake. But, the build was geared for low-end torque for a truck instead of high-end HP like a lighter vehicle would need, and it churned out 500 ft-lbs.
So, with 7/8's the cubic inches and much lower compression you shouldn't expect the same power.
FTE Legend
Joined: Jul 2010
Posts: 32,875
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From: Northeast, OK
Agreed. I could have probably gotten close to 500 HP out of mine according to Tim Meyer. But that would have been with a single-plane intake and a lot longer duration cam, both of which kill low-end torque. Instead we dialed back the duration and went with a very good dual-plane intake. Now I have a stump-puller that will probably rival the 460 in Big Blue, which has an Edelbrock Performer cam, intake, and carb - but with much less compression and stock heads.
Post Fiend
Joined: Apr 2002
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From: Waterloo, Iowa
Have to work around the EGR as someone else noted. The engine was originally tuned for that, the ignition curve for one thing. If it was deleted they probably had to back way off on the timing and now it may not run right. Not saying this is exactly the issue but that's the kind of thing to keep in mind at this point.