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Joined: Jun 2007
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Those nylon sprockets were notorious for clogging oil pickup tubes.


GB2

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Originally Posted by northern_dave
well, if something is leading to a short stroke or intermittent stroke on the mechanical fuel pump.... it could starve for fuel (power)

Also, lean pop (backfire through carb)


whistle

You just never know.

flat fuel pump lobe, worn pump push rod, weak pump return spring...

(I could do this all day)

Lol!



well ...

A carbed engine would stumble if there wasn't enough fuel in the float bowl. It wouldn't run smooth under a load, especially at WOT, and have an overall lack of power.

(we could do this all day) laugh

Just havin' fun.

You've been spot on. smile

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The problem is the placement of the distributor. They belong in the front, not the rear. Just kidding.

Does it have a quadra-junk carb on it?

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Originally Posted by northern_dave
if you are backfiring through the carb you may have an intake valve issue, either chipped, bent stem or not closing well. Intermittent could be due to something like a broken valve spring which would have you relying on compression to slap the valve shut. Broken or weak valve spring could also cause some return lash (excessive) in the whole rocker, push rod, lifter, cam lobe motion delivery.

dig?

Pull valve covers and twist on each valve spring with valve in it's closed position. This will be the spring's most relaxed position, it should offer some preload on the seated valve, holding it closed.

A broken one will be obvious, weak springs could be random here or there caused by the spring fatigue or possibly a sunken valve.



You probably got it pegged Dave...what kind of odds would you give as to the cam being boogered?

To the OP...since this is your only transportation vehicle & you seem to be on a limited budget, I'd suggest finding a runner (engine) on craigslist that you can temporarily install until you can get your engine rebuilt. Since your current engine is an unknown quantity, I don't think I'd bother trying to chase down noises...especially if they are "nasty sounding"...chances are that this engine has had more than a few "easy fixes" & is more than ready for a full rebuild. You might be amazed at what you find once you start tearing the old one apart. Find a good, reputable machine shop & talk to them as to cost...swapping out an engine shouldn't take more than a day...maybe two if you take frequent breaks...
Another thing you might consider (if you go the "beater" route) is to find one in a similar vintage & keep it as a "parts truck" for tranny, axels etc. good luck

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Compression check first. If all the cylinders are good you can move forward. You can look all day at stuff but if a cylinder is down you are way ahead in time wasted. And you truck ain't exactly cramped for space to do this smile

If a low cylinder rotate till valves are closed then blow air into plug hole and listen to see if it is escaping through intake or exhaust. If a valve is leaking you can hear it. If not then rings or head gasket.

Ticking noise that goes away with rpm sounds like something sticking or pressure related (or both). Sticking or failing lifter maybe.

Also stupid thought but hit your intake manifold with some carb clean at the gaskets to see if there is any vacuum leaks. Dont blow yourself up but your idle will jump if there is a leak. Also a source of a lean pop.

Vacuum check first then eliminate the compression issue. Just my .02

W

Last edited by woofer; 07/13/14.

"I would build one again, if it were not for my 350RM (grin)."

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One note on what woofer suggested on the leak down test. When you pump air into the cylinders, make sure the piston is at the bottom of the stroke. Too much air will rotate the crank and turn over the engine. Scares the crap out of you especially if your leaning over the fan.

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You can also do a dry, then "wet" comp test as a way to evaluate rings.

Make one lap around the engine with the comp tester on dry cylinders. Write down your comp numbers for each cylinder. Then get a little bottle with a pointy cap, the type of cap that comes on 90wt gear oil bottles. Give each cylinder an ounce or 2 squirt of engine oil in through the spark plug hole before threading in the comp tester. Repeat the test for each cylinder and record the "wet" numbers.

If you see a big difference in pressure on a particular cylinder(s)between your dry and wet numbers, this would indicate a ring/cylinder problem. The oil will typically raise the number a bit, but if you have a low pressure cylinder and the oil trick doesn't bring it up into the range of the other cylinders, this points to valve issue.



Something clever here.

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My old 350 did about the same thing. Didn't have $$ to take it to a shop so talked to an old shade tree mechanic in the neighborhood. #5 cam lobe was toast. He had a good one so I grabbed a gasket set, he came over, we both wrenched at the same time and fired it up that evening over some beverages. Had it another 6-7 years after that.


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I have seen timing chains so loose on 350's they wore a hole in the timing cover. But, the motor still performed admirably.


Throttle fixes everything. If it doesn't fix the problem, it’ll end the suspense.
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Had a spark plug come loose and sound like a knock...
I wouldn't put too much money I to an old motor. A good rebuild is not expensive and can be swapped out on that old77 in a weekend...

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Another possibility to add to all the good ones already listed.

Check the roll pin that holds the drive gear on the distributor shaft. An ignition timing check can show if there's an issue, but best way to look is to pull the distributor and look. Don't forget to index the timing marks on the harmonic balancer and the location of the distributor body to the intake and the distributor shaft to the distributor body. Makes reassembly a snap.

Typical symptom of this is timing constantly moving until finally it won't run when the gear moves too far.



-Brian-
Whatever you do, do well.
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