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I have an 83 F250 I recently put a "new" (junkyard rotating assembly aside) engine in and did some mild uprades on the engine during the process. It's a 351w with Edelbrock Performer 2181 intake, 1406 carb, and Gt40 heads with long tubes and dual exhaust. Right now she's running pretty decent but I'd love to get her tip top. Timing and all maintenance items have already been done. Here's a few things I'm hoping to get pointers on.
1. Usually takes a couple pumps of gas to get it fired up, however every once in a while it fires up no problem. I understand some of this is normal.
2. Pulling a bed full, as well as a 5x10 trailer full of firewood up hill, at 65mph full throttle maybe 3500rpm there was a significant surging problem. I slowed down a little and eased back into the throttle a little and it seemed to be ok then.
3. Currently getting about 11mpg which isn't terrible but more is always better. I do have bigger tires which I'm sure doesn't help but I've got 3.55 gears which is better than it could be for economy.
Hopefully someone smart out there still remembers how to use these!
I would look into how much total advance you are getting in relation to your engine surge issue - it sounds like timing to me and not a carb issue. Hopefully someone else can make a more insightful suggestion.
Get in the older tune-up manuals. Compression first, make sure piston rings and valves are in good shape. If it doesn't make spec or has uneven compression it won't tune-up no matter what. Plug looks pretty good, at least that one I guess, if compression test checks out focus on other tests. Ignition.
Vacuum test with a mechanic's gauge will help diagnose faults and help sneak up over time on a sharp tune. Make sure the centrifugal weights in the distributor, the ignition curve is correct all the way from idle to high RPM and everything in between, and the vacuum advance is doing its thing. If the timing curve and carb mixtures are screwy it can drop highway economy especially by quite a lot.
Vacuum leaks always cause trouble, timing derangements, weak thermostat, poor grounds and cables, weak charging etc. Remember compression, ignition, carburetion. Compression test, and vacuum test will tell the tale, they don't lie. 150psi compression across the board say, and maybe 20" steady needle on the gauge vacuum test at factory idle and ignition settings are what you want to see. A tune-up won't turn your truck into a Festiva but you can make it run to its potential.
I would look into how much total advance you are getting in relation to your engine surge issue - it sounds like timing to me and not a carb issue. Hopefully someone else can make a more insightful suggestion.
I agree. But also make sure the vacuum advance is working. If it's not, it'll run weird like that. Plugs look fine
It's been since I set up the engine that I did the leak down test and since I tuned with a vacuum gauge. Leak down looked great, all in the green. I was able to get vacuum at idle to about 19-19.5. New cap, rotor, wires, plugs. Upgraded to the 130A 3G alternator off a 3.0 Windstar.
It's been since I set up the engine that I did the leak down test and since I tuned with a vacuum gauge. Leak down looked great, all in the green. I was able to get vacuum at idle to about 19-19.5.
Where exactly did the initial ignition timing end up at to achieve that vacuum #, a high manifold vacuum is a good indication though for actual engine diagnostics it should be measured at the factory timing of say 6° or 8° BTDC, something like that, what is important to see is that the manifold vacuum reaches spec at factory idle timing specs.
Sometimes the manuals are a little vague or too generalized, they'll say something like "normal" is 15" to 20", that is a huge spread. Altitude plays a role with the highest # that can be achieved but without regard to that the higher the # the better if talking about a stock engine. If an engine pulls 15" or 17" when it really should be 20", or lots of initial ignition timing has to be added to achieve it, that isn't really "normal" and indicates a serious defect somewhere. A worn timing set and chain will cause late valve timing and lower manifold vacuum and sluggish response.
I'm not sure exactly what timing is at super high RPM as the MSD tape flew off and my makeshift paint pen marks are hard to read. Initial timing is still 10, at high RPM I want to say 25 or 30. The advance seems smooth up and down and doesn't jump.
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