Hot Rods AD_NAPCO's 39 GMC Rocket 324 Build

No cooling lines on those.

 

Ok... So I have had it running but I can't get it to idle lower than about 1800 RPM. I have the cam dwell rock solid at 29 degrees. I put the timing light on it, and set it to 5 degrees and can't seem to get it even close to the timing marks before it stalls out and that's usually approaching 1600 RPM's is where it dies. I have the mixture screws out two turns and I think I have the choke adjusted right.

As far as the fast idle screw and the idle screw... Well, I'm still trying to figure those out.

Just to verify, should tightening the idle screw raise RPM's or lower RPM's, and the fast idle screw seems only to have to do with the choke and therefore initial idle speed.

Initially, the engine fires, and with the choke manually held mostly closed, it runs around 2500-2600 RPM's and after 45 seconds or so I try to let the choke open some and it drops RPM's, but as soon as it gets around 1600 is when it dies. Any ideas where to start diagnosing this?

 

The motor needs to be up to operating temps and idling at lower rpm before doing the idle mix screws. Idle mix screws won't work on higher RPMs, because the carb is not running on it's idle circuit.

Forget the timimg light for now, unless you want to try to check that the mark is correct with looking into #1 plug hole at the top of the compression stroke. I'd time it by ear just to get it warmed up and be able to get it to idle.


Screwing in the curb idle screw will raise the "hot" idle. The high idle runs off the choke. There is a book spec on that, once you get closer to dialing it all in.


How long. in years, has this motor sat unused? Heat is your friend on long dormant motors.

 

I'm thinking it's been between 40-45 years since this thing has run... Based on the degree of rust on the grenaded third member I found in the bed, and the last registration.

I've had the motor up to operating temp, and the choke spring relaxed to the point where it definitely doesn't want to stay closed anymore, yet I have to choke it to keep it running.

I'm thinking maybe I have a vacuum leak somewhere?

One thing I was noticing when reading the manual again, is that the vacuum throttle return diaphragm on this carb is specific to Jetaway equipped cars. I'm thinking I'm going to remove that part from the equation and plug the port it's running from and then look for vacuum leaks around the carb, and intake.

 

sounds like you might have a vacuum leak, or the idle circuit is plugged, you could try pulling the idle mixture screws and blowing air in them and then reinstall the screws, how about taking some nice pic of all 4 sides of your carb so maybe we can see whats going on, i have had carbs that you needed to keep them revved up because the float had sunk, you can tell if thats what is happening by black smoke pouring out the exhaust.

 

Setting timing by strobe can't be done unless it is at normal idle speed. Also, the damper mark may have shifted, so I would get it coming up to TDC on #1 compession stroke then use a probe or plastic straw on the piston to find exact TDC; then look where the mark is. While you do that, use a test light clipped to the minus terminal on the coil. As you start to get to #1 TDC, the light will come on as the points open. (with key ON) Then see where that exact point is on the front pulley.

If all that is OK, also check the vacuum advance unit to see if vacuum will move it.

Maybe check to see if the secondaries are completely shut and sealing well. Flashlight down the rear barrels to look for misadjusted flaps.

Then get some run time on it. Heating cooling cycles may free up stuck rings and help seat the valves if they have light rust on the faces.

 

I bought a so called rebuilt 4GC for a '62 Olds many years ago,
I could not get it to run right or respond to idle adjustment

turned out one of the percolator tubes had a glass bead jambed in it
the rebuilder had glass beaded all the small parts!
luckly I still had my old carb and swapped out the ruined part.

not saying that's your problem
just beware that just because the carb is supposed to be fresh..
it's just as old as the rest of the motor
and just as likely to have unforseen issues

as for the potential vacuum leak
you sure you have the right base gasket under the carb?
is the vacuum line to the fuel pump hooked up?
is the vacuum diaphram in the fuel pump good?

if you haven't already, one way to check for vacuum leaks
is to squirt starter fluid around all potential areas while the engine is running
the motor will speed up when the fluid finds the leak.
but you already knew that.

 

Turns out it's exactly where it should be. I checked exactly the way you described.

I have been running with the vacuum advance disconnected, and the vacuum ports at the base of the carb plugged. I'll see if I can hook my vacuum pump to the advance and see if it works. Would be good to know regardless.

They look to be okay to me...

I haven't been able to get the bastard to really run all morning. Even after checking for points opening at TDC, and making sure the dwell is set at 29 degrees per the manual.

Which brings up a dumb question. Cam Dwell vs. Point Gap. It's the same adustment, so why have two different specs? Gap the points at .016 or set dwell at 29 degrees? Six of one and half dozen of the other? Is the point gap meant to just take the place of the meter when the meter isn't available? I probably just answered my own question, but by all means, feel free to learn me something.

I see where you're coming from, and if I can't get something working soon, I'm going to dig back into the carb and see if it's not something stupid like that.

Looks correct to me... I can double check that there's no vacuum ports blocked or open that shouldn't be.

No. Both the engine and wiper ports on top of the fuel pump are open. When I got the vehicle, they were blocked off. I rebuilt the pump a few days ago, and when I spoke to the guy at the company that made the kit (who also does rebuilds) he said to leave them both open if I didn't know where the port for the engine side was, and also since I don't have a wiper motor to hook to.

It's all new.

I actually did already know that, and was planning on using that method this morning, but i haven't had any luck keeping it running, even at high RPM's.

 

Are you running a ballast resistor in your hotwired setup? If not, and if it's not an internal resistor coil, the points could now be intermittant due to overvoltage..

Unless crud got loose in the carb, why would it not run today compared to before...That goes back to Pauls rebuilt; dirt getting loose, but worth checking the Ignition also.

If you can fight it to run at higher rpms, I would think you should see some fuel mist at the venturies if the jets aren't plugged. You could bench test that with a high volume blow gun with the carb off, and blowing down through each venturi.

 

I'm definitely running a resistor, and the coil is marked for use with external resistor.

Just had the carb off. Took the vacuum throttle return diaphragm off and plugged the port. Checked the base gasket. I can't see any conflict there. Put the carb back on and tried to fire it. I think the rear main might have just gone south. Lost a bunch of oil out the back end and initally thought it might be tranny fluid but I checked the oil in the block and it's way low.

So, I'm praying it's just a seal and not something much worse.

Either way, I'm thinking I need to go ahead and pull this motor out and open it up.

I need to separate the tranny anyway and get it over to the shop for an inspection and pray that all it needs is cleaning, adjusting and resealing.

Fun stuff!

I'm sure I'll be asking a lot of questions about the motor teardown and rebuild as that process moves along.

 

Oil leak also could be the oil filter can or oil pressure sender.

The rear seal is rope so I doubt it would "just now" start pouring out...but you never know.

 

Oil filter can is pretty well solid. I checked that. There had been a leak already from the side pan on the tranny, but now it's coming out the tail shaft as well and there's a LOT... It seems to have gone from moderate to severe very quickly.

Where is the oil pressure sending unit located? I haven't spotted anything in the manual about it.

 

It should be above the oil filter casting., so it should be pouring down that side. The center part of the sender is plastic on mine and they shrink after 60 years, and then the rubber gasket under the plastic, starts leaking.

Those motors come apart real nice and quick, too. I did mark the two halves of the torus, just out of habit, so they will go back together in the same relation. I don't know if the any of the 32 bolts are offset to make it fit only one way or not.

To get my 56 to a bare block took a half hour with air tools.

I'd like to see if you have stuck rings. My 303 does for sure; I can tell by the noises it makes while turning with a ratchet. I believe the noises come from the slight bore tapers and that some of the rings stuck at the bore tops and some lower; so the rings that stuck up high, are too tight to ride to the untapered part of the bore...and it almost squeaks I have it soaking, but that won't help IMO. Not enough compression yet and a ailing starter is not helping. I was hoping to get the 40 yard drivable because with only one work bay, I'd need to push the car in an out to another door, when I need the bay.

 

Wise to mark the torus halfs. The two dowel pins are very slightly different sizes. Mix them up and you will warp the torus.

 

Well, I checked the sender, and it's definitely not leaking there. It's dry as a bone up there.

So, tomorrow will be cleaning up and organizing day. Gotta get the shop all douched out and make plenty of room to work clean and organized.

Thanks for the help so far fellas... Something tells me this is only the beginning!

 

Josh,been awhile since I messed with a 4G carb so bear with me.Your idle and stalling issue sounds like a low speed mixture issue mentioned by Paul.Top of the carb comes off,a few screws pulls the primary venturi cluster.Look at the brass tubes on the cluster,two of them have a restriction to control fuel flow for idle and off idle,up to about 1600 rpm at light load.Check them for crud inside.Gently stick a pin drill or cut off a piece of #12 standed wire and use one of the strands as a probe.Then carb cleaner and compressed air.
Of course it can be just a vacuum leak or secondary throttle open a bit.

 

Paul and Tony... I will definitely open up this carb and check those passages for bits of junk... Thanks for the heads up on that stuff. Today has been a massive excercise in organizing, cleaning up, and throwing shit I don't need away. I'm wanting as much clean space and light to work in as I can. Unfortunately all I have is a crowded one car garage to work with for a shop and so I'm trying to uncrowd it as much as possible. The fun continues.

 

i would of said pull the top off your carb but thats not what i would do first, i say pull the idle mixture screws and squart some fluid in there, carb cleaner or WD-40, then blow some air in them while you hold the choke open and watch for the fluid shooting into the throat, then reset the screws, 30 seconds and your done, the screws should come out just to be checked for condition anyway.

 

Hey Add__Napco,

Just to give you some more work to consider, check the condition of the oil breather chamber on your Olds engine, the one located laying on its side at the rear of the valve chamber under the valve chamber cover. It's roughly shaped like a small frozen lemonade container.

On my old unrebuilt 303 motor, this chamber was plugged solid with engine crud, and it took three trips through the machine shop's degreasing machine to clear it. Once we re-installed the breather, the excess crankcase pressure was relieved, and consequently all the oil leakage from around the engine seals quickly stopped. Also, check and clean the oil pump screen while you're at it, and remove any sludge from the bottom of the oil pan that happens to be present.

All this re-sanitizing work made my old 303 run quietly with acceptable oil pressure and without any oil leaks! Best of luck to you.

mr50s

 

Experience overcomes brash actions. Seems like you were bang on correct. Cleaned up the top and sides of the lower boss, as well as the lower edge of the top bore as best I could. Hit everything with some degreaser, carefully lined up and twisted and out she came. Thanks again for the advice.

Now, any tips on removing the camshaft?

 

How are we doing on the running problem?


I thought I'd update you on my 303 with stuck rings and collapsing lifters.. I did get it to run mid afternoon today. Anyways, despite very low initial compression from 10 to 50psi, and weak lifters and a 4GC that was only cleaned out without a kit, and mismatched plugs and old wires...... it idles like silk. No kidding.

So I just can't believe yours needs to come apart yet, because it won't run?

I know I am still TDC or ATDC, lifters bleed down in seconds after shutdown, and my flywheel is just the lightweight front piece of the torus. I am amazed at how it runs/idles. I almost started to tear it down last night after fighting with it for 2 days...but I was too tired.

 

i find it hard to beleave there is much of anything wrong, the video shows it running and just stalling because it was running out of gas.

 

One of many things I tried today to get mine going, was to tighten the choke super tight. I did that because it fired on most cyls for a split second and stalled.

After I got it to run and stay running, I had to manually open the choke after 2-3 minutes run time because it was loading up at half choke.

That video reminds me of the 56 Buick thread by 3spd. His would fire and die and he said it was because the pre-oiling of the cyls got enough compression to start, but not enough to keep running. He ended up re-ringing his, but his last roadtrip video shows lean-out flaming up the carb, and constant stalling while letting the clutch out. More of a carb or timing problem, rather than compression at that point..

 

in the last two weeks i have started four engines that have been sitting for awhile, two of them have been sitting sence 1990, one sitting for 5 years, on all three i locked the choke full open, i have a spray bottle with gas in it to give them a drink before i try starting and then to keep them running, one of them i didn't have gas going to the carb just my spray bottle, it idled and i could rev it up, just a matter of how hard and fast i sprayed the gas, it takes some trying but anyone can do this trick.

 

Long story short, I mixed the top and bowl/butteyy fly plates between two confirmed 7007000 4gcs because one had a semi stripped gas line inlet. The bottom I rebuilt and have a bad stumble unless the engine is totally warmed up. 160 degree thermostat thinking I should go to 180. Some of this stumble I think is due to the carb body being worn where the primary shaft runs through. The unrebiult body seems a lot tighter so I'm thinking rebuild that and use it with the top it came with. Question: Where can I get a rebuild kit that will be compatibale with todays swill for gas?

 

Quick update... There really isn't one. I got call last weekend for a short freelance gig working on a Ford commercial so I have not touched the old Rocket motor since the day of my last post.

You guys are probably 100% right. I don't doubt it at all. My biggest concern at this point is still keeping oil in it while I run it. I'm tellin ya... It pissed a LOT of oil out. When I noticed it and checked the level, it was not even showing oil on the dipstick.

So that's my biggest concern at this point and why I'm tempted to go ahead and dig into it to check and see if there was any damage.

I'd hate to keep trying to run it and compound anything that happened. I'm hoping to get some time this weekend to work on it.

 

Hey AD_NAPCO, any updates over the past two weeks?

 

Olds guys don't mind an update with no progess.....it gives the hamb more Olds threads at the top..


The motor damage: I can't see how you hurt it yet. A motor can run at idle a long long time with zero pressure, and I am sure you had at least some pressure.


Yes, you need to find out exactly where the oil leak is. With it leaking a lot, it just makes too much stress when trying to deal with other issues.

If it leaks as much as you say, it would seem that it must me a pressure-fed leak, rather than something like a valve cover, or the gasket on the rear road draft connection, or other gaskets.


Just refill the oil, and try to dry the lower parts of the engine, and only run it a few minutes at a time, then shut it off, to crawl around with a light and maybe a mirror, to try to find it. If it leaks a lot, oil will still be dripping from the area for a few minutes after shutdown. No harm done by doing this.

 

Well, I got busier at work, and extended for a few more days and still haven't gotten anything done. In the meantime some low-life bastard broke into my storage unit and made off with about four grand worth of winch, trailering equipment, camping gear and tools... Luckily all that stuff is replaceable. I just hope the insurance treats me fairly.

Also lucky the dumb sonsabitches didn't know how valuable the old car and truck parts in there were!

I'm in the process of trying to find a used engine hoist around these parts at a decent price. I sold mine off a couple years ago when we moved and and downsized things and weren't flush enough with cash to pay for off site storage...

I am fairly certain I'm gonna need the hydra-matic gone through at least inspected and resealed because it's leaking pretty badly.

I probably should just go ahead and pull them both and go from there, right? Maybe try one more time to get it to run on a stand before I dive into tearing it down?

 

I don't know your goals or budget.


Yes, it should run and idle sweet, with what you have for compression. But, if it remains under specs after a while of running, it either needs rings or even a rebore.

Some owners run them, some just go through it all. No point in running it again unless you are not sure you "must" rebuild it.

My 303 runs very nice, but the blowby, after a few good heat/cool sessions, has me convinced that the rings are stuck badly. It will need to come apart when i finish the body.