My father and I rebuilt my 1976 F150 360 in the past few weeks. We've been extremely articulate when it came to putting the engine together, so I would find it hard to believe we've screwed things up internally. But, when at idle the truck runs like hell. Like it's missing or something. So, we bought a new carburetor, replaced the rotor and distributor cap, new plugs (gapped at 44), new spark plug wires--- basically, everything's brand new. What else could be the problem? It's failed the emissions test twice now. The first time it failed on " Idle " in both hydrocarbons and carbon monoxide, this time it failed in only the hydrocarbons. If anyone can help, it'd be greatly appreciated.

 

ok is the timing set right. im not too sure about the gapping question tho. the timing would prolly be the answer to the rough idle, or try speeding or slowing down the idle speed on the carb. also make sure all the vaccum is connected and there are no leaks

 

Did you check the conditon of the harmonic balancer and the outer? I don't know much about 360/390, though. Is the firing order correct? Sounds like an ignition problem to me.

 

We did the timing, and then had the timing checked at a shop because of the fact that the idle was so rough. Would bad compression in cylinder(s) effect the engine at idle speed?

 

 

Hey,

Do you have access to a vacuume gauge? Hook it to the mainfold vacuum somewhere and start the engine.

It can show you allot of info, and give clues at to what is going on.

Here is a link to a site that may help you,

http://www.centuryperformance.com/vacuum.htm

-Brents.

 

Wid,
Are you getting any backfire? Under load?
Do a compression check ASAP.
Valve adjustment is not a given on a new build. Hydraulic lifters can fool you easily. Compression check will varify that adjustment is correct/incorrect. This could throw off emmisions, maybe. The emissions test is pointing to fuel. A high carbon monoxide is showing a lean run condition. A high hydrocarbon counts is a rich condition. For an emmision test to show both means you've got some cylinders running lean and some running rich. This could be valve timing and or valve adjustment.
What kind of emmisions equipment is on your vehicle? EGR? PCV? CAT?
KingFisher

 

Kind of sounds like a large vacuum leak. maybe under the manifold or in the EGR system. Also you might double check your firing order.

Bear

 

Well all, my father and I have found out some bad, but good news simultaneously. When we rebuilt this engine we noticed that there was a pit near the exhaust port for the EGR valve in the intake manifold and it didn't seem all that deep, nor did it appear to be at eroded at the edges. I suppose we should've fixed it or replaced then, but we didn't. We just took the truck in to a mechanic to see if they could find a vacuum leak, etc, and when they found that after removing the carburetor they said that was definitaly either the problem or the main problem, at least. Whether or not that's true, we'll only know when we have this fixed. I don't have the pocket change for a new manifold and most of the machine shops said they weren't sure if their machines could shave it down to a level surface. So, we're using JB Weld and have already sanded it, but there's one small area that needs a little more. After this is finished we're going to take it back and let them search again for any other leaks— that is, if it's not running great after we fix the manifold. I just cost myself $89 bucks for not dealing with it when it was apart. At least I'm learning how to take things apart faster with each time I redo my previous work! :-X11