What happens when cam timing is off?

[averagef250]

A friend just did a quicky backyard 360 overhaul and while it ran fine before, but with no oil pressure it now cracks, pops and runs extremely rich regardless of distributor timing. It acts like the distributor timing is extremely advanced, but it runs cold, rich and dumps fuel out the exhaust.

He installed a summit roller timing chain on the original cam and while I was there when he did it I don't recall checking to insure he had the cam timing right on.

I've never experienced an FE with cam timing off and before tearing the front of the engine off to fix it I'm curious how exactly I could diagnose this? At first I thought he may have used some pushrods that were too long so we put some 1/16" washers under the rocker shaft stands just to see if that helped any. Made no difference. Firing order is correct, the distributor timing can be run from 25 before to 20 after and the engine still runs.

I believe this engine has the OE cam for a 74 F100 and the intention was to install it straight up without cam retard.

Any help is very appreciated.

[fordman]

it does sound like you got the right answer. but i can't confirm it.

[averagef250]

I don't know what else it could be. Did a compression test last night and they're all around 140 which sounds good to me for an engine with low compression that hasn't seated rings yet (they're used rings anyway). The oil's still clean and brite with 30+ minutes of run time and no fuel smell.

The 2150 carb ran great before. I rebuilt the carb for him while he tore the engine down and I even switched carbs to another known good 2150 and it runs exactly the same.

I guess the work involved isn't that bad really to pull the pulleys, waterpump and timing cover to figure out what's going on in there, just don't want to do it if it's something else. At this point though even without being able to pinpoint cam timing as the issue I think it's a safe bet it isn't anything else.

[fordman]

i think one way to check is to put the enigne on tdc and take off the valve cover to see if any of the number 1 valves were open or closed.

[Happy_Camper]

Check compression.
Doesn't matter if the cam is advanced or retarded, compression will drop evenly across all 8 cylinders.
As an example, if standard compression is 150 psi across all 8 cylinders, on a cam that is mis-timed, the compression will run down around 130 or maybe less across all 8 cylinders.
Make sure to block open the throttle plates, and start with a good battery.
Good luck! I hope you find something silly, like a loose wire on the coil.

[averagef250]

Cam timing is spot on, the chain was correctly installed. Last night we found the point gap in the dizzy had opened up to .035" and set it back to .017. Also found one new spark plug with a loose insulator and vacuum leak under the carb.

The engine starts, idles and revs up without crackling but still shakes and now runs nice and smooth with partial choke, poor with no choke. It now seams like it has a moderate vacuum leak somewhere now. I am leaning towards the intake manifold to head.

Would it be acceptable to idle the engine without valvecovers and spray starting fluid or propane around the port surfaces to pinpoint a leak? I've never done this before, but can't thin of any other way to find a leak here.

[Happy_Camper]

Good news on the cam timing!

If it had a vacuum leak under the the valve covers, it should suck oil, and that would be visable on the plugs, and crankcase vacuum would be higher than normal.
I would look at the vaporizer. When the vaporizer starts to plug up, the venturi can not draw enough fuel at idle. Closing the choke partially will cause the negative pressure to increase through the venturi and cause more fuel to be pushed from the float bowl through the vaporizer section.
The easiest way to spot this is to remove the air cleaner, and, with a face shield on , look down the throttle bores. At idle it should be a very fine fog. If there are any droplets at all (even small ones), the vaporizer is partially plugged. Normally the plugging is aluminum corrosion, and isn't repairable. Depending on the carburetor, the vaporizer may be replaceable with a NOS piece.
I just went through this with my friend on his old Scout. Took two vaporizers before we got one that worked correctly (thanks to a really awesome Scout dude up in Oregon). Now it runs great.

Good luck amigo!

[averagef250]

Thanks a bunch! I have noticed drips on the venturis at idle on both carbs we tried on this engine. One was assumed good as it runs OK on another 360. Realisticall they could both be bad and my brain has been out of the gas engine world too long to think right.

If it is aluminum corrosion would it be worth a shot to acid dip the vaporizer section? I have a whole mess of hydroflouric acid that works quite swell for quick cleaning alloy wheels and just about anything else aluminum. I suppose there isn't much to lose either way.

[warponyxlt]

that acid you mentioned is that like alumabrite or newbrite or some thing like that

[Happy_Camper]

If you've got the stuff all ready, it's worth trying. Maybe put it in a spray bottle and try spraying it through the passages. Need to clean both the fuel and airways. The corrosion happens when the passage ways dry out. In the old days before reformulated fuels, the passage ways would get coated with a gel, and a good carb dip would clean out the gunk. With the reformulated fuels, the passage ways are stripped bare, and left to corrode from the moist air. So that's what you'll be working on. The vaporizer passages, are metered, so it can be tough. But like you said, it doesn't need to be perfect to get the truck into driveable condition.
I've got my fingers crossed for you.

[averagef250]

Yep, concentrated lumebrite. Got it from a friend who washed semi trailers. I'll give it a whirl and post back.