I'm at my wits end with my truck.

[thedudeabides86]

Good evening gearheads,

I have a problem, perhaps several problems. My '72 C20 with a 350 and a Holley 600 carb will not cooperate at all. Here's the gist of it all.

I got customer mufflers put on last November, NASCAR style. I should back up a few months and mention I had the brakes bled by a shop and the guy mentioned the motor was running rich. I hadn't addressed that issue when I got the new mufflers put on. So, the mufflers get installed and once they're in, I can't get the truck started. It would fire, but wouldn't run at all. This was in November. after several attempts at starting it, it kicks over and runs long enough to make the 11 mile drive back to my garage. After sitting for a week, I attempt to start it again and take it for a spin. She runs for 10-15 minutes and then stalls. Every time I gave it gas, it would peter out. It took me another several attempts to get it started long enough to get it into the garage. Fast forward to last week, on first startup in idles for 5-7 minutes and dies. I adjusted the thermostat back to the factory setting, (matching the hash marks on the thermo cover and the carb body) and checked the vacuum on the PCV Brake booster port and got a steady 17Hg. I moved the idle mixture screws in and out to the same settings on each side and still nothing. I tried it tonight and it barely wants to stayed started and if it does succeed and stay idling roughly, it dies when I hit the throttle. I'm not a carb guy or an electrical guy, so I'm learning as I go here. I do still have the points system in it and that's about it.

So, any of you who read all that, if you have any suggestions or advice, I'd greatly appreciate it because I can't take it anymore. It's driving me to drink. I guess that ain't so bad. Thanks for reading.

[cornerstone]

[QUOTE=thedudeabides86;8500403]
I adjusted the thermostat back to the factory setting, (matching the hash marks on the thermo cover and the carb body)


I'll give it a go, but I think you may be confusing the choke with the thermostat... Care to elaborate on that?

[thedudeabides86]

[quote=cornerstone;8500415]

Originally Posted by thedudeabides86

1. I got customer mufflers put on last November

2. I adjusted the thermostat back to the factory setting, (matching the hash marks on the thermo cover and the carb body)


I'll give it a go, but first please help me out on this...what are "customer" mufflers?
Also, I think you may be confusing the choke with the thermostat... Care to elaborate on that as well?

Ah shoot. Sorry, custom mufflers and sorry again, yeah, the choke. I adjusted the choke back to the factory hash marks. I guess I mentioned it as the thermo since the coil inside heats up and adjusts the choke plate and after typing this I realize that "thermostat" is nothing at all like what I'm describing. Uffdah. Gonna crack a beer. Haha.

[Warship2k15]

Ok you need to start by troubleshooting what you are missing to make it run right.
Ignition, fuel and air/compression.
Is it getting fuel to the carb??too much fuel to the carb?(fuel soaked plugs)
Is it getting a good spark.Test the spark.Also check the timing.
Good air flow and compression.
Check to make sure the carb choke is opening.Do a compression check.

[thedudeabides86]

Originally Posted by Warship2k15

Ok you need to start by troubleshooting what you are missing to make it run right.
Ignition, fuel and air/compression.
Is it getting fuel to the carb??too much fuel to the carb?(fuel soaked plugs)
Is it getting a good spark.Test the spark.Also check the timing.
Good air flow and compression.
Check to make sure the carb choke is opening.Do a compression check.

What might be the recommended setting for the idle mixture screws? It is getting gas to the carb because I can see the jets spraying fuel.

What's the best way to test spark? Can you check timing correctly when you can't get the engine to run? The choke plate is opening accordingly, I think. Checking compression is checking each cylinder once you remove the spark plug and turn the engine over one revolution?

[cornerstone]

From your description of how its acting, I'd venture a guess and say that it may be a combination of a closed choke and a rich carb... Take a spark plug out and see what direction that points you in.

[GASoline71]

Wire the choke open and just pump the gas a few times and get it cranked up. You'll have to feather the throttle to get it to stay running until it warms up a bit. If it will run and drive with the choke wired open, then you had the choke adjusted improperly.

Run the idle mixture screws in all the way and gently bottom them. Turn them 1 1/2 turn out on both sides. There's your baseline. The screws do nothing but control idle mixture. After that it's the accelerator pump (which you see squirting as you move the throttle), and then it's on the primary fuel metering circuit.

Gary

[clay68c10]

Originally Posted by thedudeabides86

It is getting gas to the carb because I can see the jets spraying fuel

What exactly are you seeing spraying fuel? If it’s the accelerator pump squirters when you move the throttle open, good.
Anything else that is doing that, not good, your float level is too high. Easy fix tho.

If that’s ok, then proceed on with the post from GASoline71

[A1971Blazer]

floats too high or power valve is faulty

[HO455]

Does the truck have electronic ignition? If so it is possible when the mufflers were welded something may have gotten fried by stray current. Years ago I lost an alternator after getting new mufflers, which really sucked at the time, since I had spent all my cash on the mufflers.

Fuel starvation could be an issue; on my 69' FJ40 I had the same symptoms; dirty carb was my culprit. On the other hand, as posted above, there could be many issues that cause that problem. m

[prodjay10]

Dirty gas tank clogging carb

[jdalexa84]

It could be heat soak possibly try putting a plastic carb spacer. my truck did something similar and the plastic spacer fixed the problem

[garyd1961]

You were fine until you installed "customer mufflers", I would remove mufflers and see what happens. Maybe they are clogged with grease rags or rat nest or they just have too much resistance.
Watched a mechanic chase a miss for several days before he found a grease rag stuck in one of the intake runners.

[franken]

A vacuum leak is also possible. Might spray brake cleaner around the base of the carb to see if the idle changes and look for open ports or broken lines.
If you changed the choke, that's a possibility too.

[Astro-Balls]

I had a friend with a el Camino who went through a similar problem, changed the carb, checked fuel pump, went through everything, finally found out the exhaust pipe inner wall collapsed like in this pic..
https://rennlist.com/forums/attachme...ed-exhaust.jpg

[rpmerf]

If there is a clog in the exhaust, you can use a vacuum gauge to see it. It should start out with normal manifold vacuum then slowly drop to 0.

[68 TT]

I had a similar problem on a car I bought years ago that sat quite a bit before I got it. Adjustment of the air/fuel mixture screws did little to nothing on the vacuum gauge due to accumulated evaporated fuel residue in the metering blocks. Tore it apart and found a ton of gunk and residue in every possible location fuel could have been. Nothing could have worked right in that carb the way it was. I'm surprised it ran at all before I rebuilt the carb. You could have a similar problem causing you grief.

Did you see much of a change in the vacuum readings when you adjusted the mixture screws? These small passages are the easiest to get clogged with fuel residue or even dirt particles if the truck was driven without an air filter. You should be able to make severe changes to the vacuum readings from these adjustment screws so if you don't have that ability then the carb is most likely dirty internally and could benefit from a good clean out and freshen up kit with all new gaskets and accelerator pump diaphragm plus a set of fresh needle & seat assemblies.

The kits are cheap and the 600 Holley carb is really simple to take apart and reassemble properly unlike a Q-Jet so it is something a first time carb rebuilder could handle if they have just basic mechanical skills. I'm sure there are some videos out there to guide you through the process that could be helpful to you.

[kazoocruiser]

Originally Posted by thedudeabides86

I do still have the points system in it and that's about it.

So, any of you who read all that, if you have any suggestions or advice, I'd greatly appreciate it because I can't take it anymore. It's driving me to drink. I guess that ain't so bad. Thanks for reading.

Have you made sure that the point gap hasn't closed down to almost non-existent?

[Myself]

First, take a spare spark plug and pull off a wire to hook to it. Crank it and look at the spark. Make sure it's bright blue and will jump to ground from 1/4” away. If that test shows no good then start looking for a bad condenser, weak coil, or bad pickup coil if hei.
If you have good spark then check the fuel. While trying to get it to idle you should see some fuel dripping into the primaries on the carb. You should not see fuel pouring in, and you should not see fuel dripping into the secondaries. If you see excess fuel then either a float has hung, a needle valve went bad, or the fuel vent is plugged.
Last, if nothing else looks unusual pull the fuel line off going to the carb. Add a piece of rubber line to it and grab a container. Crank it over and see how much fuel is pumping out. Just cause somebody says it's running rich doesn't mean they know what they're talking about. If you're barely getting any fuel it will stall out when you open the throttle. Could have a failing mechanical pump or even a pump lobe worn off the cam.

[kazoocruiser]

Did this problem ever get fixed?

Originally Posted by kazoocruiser

Did this problem ever get fixed?

Am curious as well. My guess was fuel starvation but as others have pointed out could have been many issues or a combination thereof.

[thedudeabides86]

Hi Everybody,

Sorry for the lack of updates on this issues. A fellow coworker mentioned that I should add some HEAT to the gas thinking perhaps I had water in the gas. I added a couple bottles of HEAT and changed the distributor from points over to and HEI and it's been starting up and driving like a hotrod. I'm not sure where the problem was, but as long as it's driving forward and starting, I guess I'm happy. Next project on it is an alignment and hopefully some new tires.

Anyone know what the widest tire is you can put on the rear without any complications? I've always liked the look of the wide tire in the back.

[PepperTreeGarage]

Originally Posted by thedudeabides86

Hi Everybody,

Sorry for the lack of updates on this issues. A fellow coworker mentioned that I should add some HEAT to the gas thinking perhaps I had water in the gas. I added a couple bottles of HEAT and changed the distributor from points over to and HEI and it's been starting up and driving like a hotrod. I'm not sure where the problem was, but as long as it's driving forward and starting, I guess I'm happy. Next project on it is an alignment and hopefully some new tires.

Anyone know what the widest tire is you can put on the rear without any complications? I've always liked the look of the wide tire in the back.

Running this on the rear of my '72 C20. 255/70X16 on a 16X8. I'm lowered 5.5 inches in front and about 7 inches in the back.

[rpmerf]

Originally Posted by thedudeabides86

Anyone know what the widest tire is you can put on the rear without any complications? I've always liked the look of the wide tire in the back.

265/75R16 are the same diameter as the 235/85/16, but an inch wider. I had these on my truck for a bit. Not sure what rims they were mounted on (width, backspacing). Factory rims are 6" and shouldn't have wider than a 235, but you CAN fit wider.