Is it timing, carburetor or something else?
 

I have a '69 C10 292 4speed. Bone stock. It's never really run great to begin with but I have made some improvements over the years.

Anyway, lately it's been having power issues. It has no power until you get to 1500rpms. It literally chugs along, blowing out black smoke until you get past that point. I've played with the timing, swapped out three carburetors, including another known good one yesterday. So far nothing has changed.

I have not pulled the valve cover or the head simply because I'd like to think that the problem is external first. What should I try next?

Re: Is it timing, carburetor or something else?
 

stuck choke? I'm not familiar with that carb intake combo but sometimes the choke heater and pull rod is the manifold thus swapping carbs would not alleviate.
Thereafter, if you're confident timing is correct, I'd run leak-down and compression tests.
Good luck and let us know what you find

Re: Is it timing, carburetor or something else?
 

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It does sound like it is running rich from your description. After it is fully warmed up check the choke plate and make sure it is opened up all the way, as member bw46 mentioned.

LockDoc

Re: Is it timing, carburetor or something else?
 

Thanks. I'll check the manual choke. The carb is a Rochester MV. I'm more familiar with the BVs but these can't be that much different.

Re: Is it timing, carburetor or something else?
 

Does it have the diverter. in the exhaust manifold to help with warm up? And does it move freely?

Sounds fuel related, but you have changed carbs which points me towards exhaust diverter.

Re: Is it timing, carburetor or something else?
 

Sounds like a carb/fuel issue but....a compression test covers a lot of bases.

Re: Is it timing, carburetor or something else?
 

The choke is working the way it should. I let the engine warm up and hooked up a vacuum gauge. The needle vibrates between 10 and 15hg. Looks like it could be either a stuck valve, burned valve, broken valve spring or a loose valve guide. I'll pull the valve cover off tomorrow to see if I can see anything.

Re: Is it timing, carburetor or something else?
 

It vibrates with the exhaust pulses. I can't tell if it actually works anymore.

Re: Is it timing, carburetor or something else?
 

Leave the valve cover on and set your initial timing at 12 degrees. Plug off the vacuum to the vac pot when you set initial.
The idle should increase. Turn it back down and adjust the mixture screw to achieve the smoothest idle.
If the diverted vibrates just manually move it to see if it moves freely.

Re: Is it timing, carburetor or something else?
 

If you do pull the valve cover off also check for bent pushrods. One of my 292's had two and was running rough.... My other 292 I bought was running bad so the guy pulled it out and replaced it with a 350. It had a bad head gasket. I now have 2 good running, and inexpensive, 292 engines, one with power steering..... :)

LockDoc

Re: Is it timing, carburetor or something else?
 

Today I pulled the valve cover off. Checked for broken springs and didn't see any. Started it up and the rockers all move at the same rate. Nothing unusual there. I guess the next step is to pull the head and see what the valves/cylinders and pistons look like.

Re: Is it timing, carburetor or something else?
 

If you are not getting any popping out the intake or exhaust you can be pretty sure that you don't have a stuck valve. The rapid oscillation of the vacuum gauge indicates worn guides. If the heat riser valve is wiggling, it's probably OK, but you can check it with the engine cold by simply moving the dead weight on it. It should go 1/4 turn from closed to open.

Re: Is it timing, carburetor or something else?
 

What do the spark plugs look like?

Re: Is it timing, carburetor or something else?
 

Do you need a separate image host to post videos or pics here?

Re: Is it timing, carburetor or something else?
 

I did sort of a half ass test last summer and the majority of the cylinders have somewhere between 115-125. Number 3 has 95.

Re: Is it timing, carburetor or something else?
 

No separate image host needed for pictures. Here is how to post pictures
http://67-72chevytrucks.com/vboard/s...d.php?t=627506
And here is one about videos that you put on youtube
http://67-72chevytrucks.com/vboard/s...d.php?t=773558

Re: Is it timing, carburetor or something else?
 

Here are three videos I made yesterday:

Exhaust clip: https://www.youtube.com/watch?v=psMOGTle4LA

Engine running: https://www.youtube.com/watch?v=F3f6EHQPp1g

Engine running with the vacuum gauge: https://www.youtube.com/watch?v=L7lY1-nq_3E

Re: Is it timing, carburetor or something else?
 

Before you pull the head, do ALL the "easy" stuff first. A leaking intake manifold gasket will produce the same "dead cylinder" symptom as a burned valve.. So will an oil fouled sparkplug.. A fouled sparkplug and a leaking gasket will not effect compression.. Do a "full blown" compression check (as opposed to the "sorta half assed one you did previously).. Prop the throttle open a ways, and do the same for the choke.. Spin the engine until the compression gauge needle stops advancing.. Check all six cylinders and note the compression number for each one..15% difference between the highest and lowest is about maximum differential..

Re: Is it timing, carburetor or something else?
 

So here are the plugs with their compression readings relative the cylinders.

The intake/exhaust gasket is good. I replaced it two months ago and the old one didn't leak.

Re: Is it timing, carburetor or something else?
 

You got yourself an oil drinker and the spark plugs are being fouled by all that oil.. A new set of spark plugs should cure the dead cylinder(s)… Number 4 is down on compression, but you've got bigger problems that a "valve job" won't fix..

Re: Is it timing, carburetor or something else?
 

Believe it or not, it doesn't actually "drink" that much oil. The oil you see on the outside of the plugs is from a leaky valve cover gasket. I was a bit surprised to see oil on the inside of some of the plugs but I'm guessing the "drinking" is on the minimal end.

Re: Is it timing, carburetor or something else?
 

I didn't listen to this 'cause I don't want to wake my wife up but see if it offers any help to you.....

https://www.youtube.com/watch?v=lVCs5gWLUyI

LockDoc

Re: Is it timing, carburetor or something else?
 

>>RustyPile, Before you pull the head, do ALL the "easy" stuff first. A leaking intake manifold gasket will produce the same "dead cylinder" symptom as a burned valve. <<

X2

Spray carb cleaner around base of carb and intake manifold.

A carb problem can cause it to blow black smoke, but you said you tried three carbs. I see too many wires. Loose that piece of crap pertronix. A really weak spark with those plugs may be giving you the smoke. Ignition Points are far more reliable, they just need more maintenance.

Those plugs are so grungy, it's hard to see what I'm looking for. The head does appear to have plugs for A.I.R. smog tubes, but that alone doesn't tell me it's a later head that uses tapered seat spark plugs. You should inspect the spark plug hole to see if it is supposed to have the earlier style gasketed spark plugs.

Re: Is it timing, carburetor or something else?
 

To be honest with you, I have no idea on the history of the engine. I do know that it's not original. For all I know it could have been cobbled together out of spare parts. The plugs I got were all I could find at the parts store. What years should have the gasketed plugs?

But how do you know I have a Pertronix system?

Re: Is it timing, carburetor or something else?
 

Thanks, Doc. It appears the last plug is my situation at least for three cylinders.