'69 GMC 305 V6 not running right

[DreamRyder1963]

My brother came home this afternoon and said that his GMC was having trouble running and that it stalled out on him on his way home. I figured it probably just needed a tune up because we have never replaced the plugs or wires and they looked horrible. Well after changing those out it still runs horribly. It has no power and the engine is lugging in all gears while backfiring out the exhaust. I could not get it to do even 30 mph. It sounds like it might be out of time but it was running great this morning and the distrubitor is still tight so I ruled that out. While we were changing the plugs we found a vacuum line that was connected to the back of the carb but open on the other end. I tried plugging it and did not seem to have much effect at the time but now I am thinking that what ever it was connected to is causing this. Can someone identify where these lines are supposed to go? I see two of them going to the vacuum advance. Also I thought that the carb may be off a bit. How many turns out should the screw in the picture be set and what does it control? Thanks for your help.

[marvgarr68]

I would still check the timing a spring or adv weight could have come off in the distributer. The idle mixture screw should be turned out about 1 1/2 turns base setting then adjusted tell the engine runs good.

[cdowns]

open dizzy and clean points and set dwell b4 u do anything to carb

[DreamRyder1963]

I opened the dizzy and cleaned the points. No change in the way it runs. I also adjusted the carb to 1.5 turns (it was at three) and it didn't change. I'm now going to try redoing the timing. It is currently all the way advanced.

[68gmsee]

Several things can cause the problems you're having including some of those vacuum lines being open. If in doubt, plug them up. Also, bad fuel pump or clogged filters.

If the above won't help, you need to check the fuel pump to make sure it can pump about 1 pint in less than 30 seconds into a plastic jug (make sure distributor is disconnected).

Then dig into the carb for sediment and/or other buildup. See if you can locate a rebuild kit for it, clean it all out, replace all the gaskets and make sure it doesn't leak. Make sure and replace all the filters also.

I drove one of those back in the 70's that caught on fire due to a leaking/flooding carburetor. Spark plugs on top is what gave it the spark it needed.

[BrianG]

sorry, if I'm a bit ignorant to these point style distributers, but do they have a vacuum advance? if the vacuum line in question went the distributer, seems like that could be the issue.

[68gmsee]

Originally Posted by BrianG

sorry, if I'm a bit ignorant to these point style distributers, but do they have a vacuum advance? if the vacuum line in question went the distributer, seems like that could be the issue.

Yes, They have a vacuum advance. It's primary function is to advance the timing during low idle/lower rpms. As the butterflies/throttle opens and there is less engine vacuum the vacuum advance is less effective so the mechanical advance comes into play. That's why it's important to insure both work.

[DreamRyder1963]

As far as I see there is not a mechanical advance in his distributor.

[marvgarr68]

the adv is under the point plate turn the rotor back and forth and see if its still springs back. Sounds like a vacuum leak somewere.

[bigmac73]

how many miles are on this engine?? Could it be that it is just wore out, cam starting to flatten or maybe valves are toast?? just throwing that out there

[DreamRyder1963]

Originally Posted by bigmac73

how many miles are on this engine?? Could it be that it is just wore out, cam starting to flatten or maybe valves are toast?? just throwing that out there

Around 60,000. It problem started all of a sudden so I doubt that's the problem.

[DreamRyder1963]

Originally Posted by marvgarr68

the adv is under the point plate turn the rotor back and forth and see if its still springs back. Sounds like a vacuum leak somewere.

I agree about the possible vacuum leak since we found that spare hose but I can't find where it connected to. Plus there was no change when I pluged it. The hoses don't have a lot of vacuum on them.

[68gmsee]

You might want to replace cap, rotor and if you haven't done so, new points also.

[DreamRyder1963]

That's my plan for tomorrow afternoon. I would have already but like everything else I had to wait for parts. I'm hoping that is all it is.

[Terry Crist]

Could also be a fuel filter clogged or timing chain jumped. Need to check everything BEFORE cranking around on the distributer.

[DreamRyder1963]

Is there a way to tell if the chain has jumped without taking the cover and everything off?

[Terry Crist]

Bump it up to #1 TDC and check to see what plug wire the rotor is pointing to.

[DreamRyder1963]

Originally Posted by Terry Crist

Bump it up to #1 TDC and check to see what plug wire the rotor is pointing to.

Thanks I will try that if the points don't work.

[BrianG]

Is a vacuum hose connected to the distributor?

[70 shorty]

I too was thinking that it might be the timing chain.

[DreamRyder1963]

Yes. Actually two are.

[DreamRyder1963]

I was trying to check the timing chain his afternoon but I could not turn the crank with my wrench. Do these engines have a lot more compression then say a 350 V8?

[DreamRyder1963]

Here's an update on our progress .. I changed out the points and check the timing chain. The chain is good and in the right spot. That still did fix it so I by-passed the fuel filter and while it was dirty it still didn't fix the problem. I only thing I can think of now is that the vacuum advance is not working when it tries to take off.

[marvgarr68]

DreamRyder that dist is much the same as the one in your corvair if that helps. Only difference is the two line vacuum adv and the dist drive. Maybe you can see what is wrong I Know on my 62 monza I had dist problems all the time replaced it never had a problem again. Now to check the adv unit get a vacuum pump one of the hand held ones. Hook up to the outer line on the adv unit and start sucking if it moves its ok. Now check the back line if it moves its ok. If this test is ok and the timing is still ok I would 1st check the carb maybe base gasket blew out. Did it back fire at all? Take off the carb clean it up and replace gaskets plug all the vacuum lines except the two lines to dist. Replace the vacuum lines also see how it runs.

[marvgarr68]

Here is the distributor and they are cheap price
http://www.autozone.com/autozone/par.../N-ir009Z9n80u