Fuel/Carb problem?

[1972Blaze]

I was driving the other day with no problem. The truck ran fine. 72 Blazer, 350, original q-jet rebuilt a year or so ago. I got in a few days ago and started to drive and it started acting like it was not getting enough fuel. If I gave it enough throttle it would stay running, but rough. After a couple of stops it ran fine for a mile or so before having issues again. I parked it and pulled the fuel filter in the carb. It looked okay, but I put a new one in. I checked the pump pressure and it is at 8. I don't know what to do next. Is the pump pressure okay? It is a new one I put in 8-9 months ago. I do not drive this truck much, but it has done fine since putting it in. At one point while trying to warm the truck up and see if the fuel filter helped, I got a backfire through the carb (only once), but I do not know what that may tell me about a fuel issue. Any help is appreciated. Thanks.

[geezer#99]

Your backfire could be because it was lean (no choke) and a cool intake plus a lack of initial timing.
You don't use it much so you could have crap in your carb plugging it up. Filter isn't the problem. It's the fuel.

What's your initial timing?

[1972Blaze]

I pulled the fuel tank out suspecting that the sock on the pickup might have a bunch of trash on it. It was not too bad, but it was ripped. There was some debris in the tank I can get cleaned out, but I'm sure some was sucked into the carb. But what about the little bit of rust? These pics show the worst of it, but there are a couple more similar spots. Do I need to change my tank for this? Thanks.

[cadillac_al]

I wouldn't worry about the rust in the tank. It is worse than any car/truck tank that I work on but my garage queen motorcycle has more rust than that in the tank. Keeping fuel in it will keepit at bay and the filters will catch some if it gets pumped toward the engine. I have a hell of a time trying to put new socks on a sending unit. They won't fit tight and I tried to tack weld one on and it melted on 1 spot weld. Some guys run without them but they do help pick up fuel when you are running low and every vehicle should have one..

On my Cadillac I actually used a sending unit from a 72 Blazer because it was the cheapest I could find and cut the suction tube off to connect to my Caddy sending unit.

[1972Blaze]

Originally Posted by geezer#99

Your backfire could be because it was lean (no choke) and a cool intake plus a lack of initial timing.
You don't use it much so you could have crap in your carb plugging it up. Filter isn't the problem. It's the fuel.

What's your initial timing?

I believe my initial timing is 12*. I decided to pull the tank out and clean it since I did not know the history and figured it could have some trash. It is now clean with 5 gallons of fresh fuel and a new sending unit. I did not expect cleaning the tank to change the running condition of the truck and it did not. So what do I need to do now? Is there a process to clean out the carb that does not include a complete rebuild?

[geezer#99]

When it's running rough, look in the carb. You shouldn't see any raw fuel.
If you do it's flooding a bit likely due to trash in the needle/seat, a sunk float or the needle hung on the float wrong.
Who rebuilt your carb?

[1972Blaze]

It was done by Lars Grimsrud. He mostly works with Corvette guys.

[geezer#99]

THen it was done right!
Still, look inside,
Tell us what you see.

[68gmsee]

Agree with above -- check for flooding. Extra fuel in intake can cause the backfiring. Have someone check the exhaust for dark grayish smoke which indicate carb running rich. Usually removing the top, spray cleaning it or forced air can clean out passages that my have become clogged.

If above checks out, look for ignition problems. Distributor cap and rotor, arcing, etc..

['68OrangeSunshine]

Is that a hand-carved wooden float in Post#3? Cool idea.
If your tank has a lot of grunge and rust, plus debris from new fuel formulas dissolving old school insulation, you might want to pull the tank and have it hot tanked at a radiator shop. It is a big hassle, but until it's totally clean, you'll always have FOD issues.

[1972Blaze]

Originally Posted by '68OrangeSunshine

Is that a hand-carved wooden float in Post#3? Cool idea.

No, not wood. Original style brass. It does look kind of interesting though the way it reacted with the fuel and anything else it was exposed to over the years.

['68OrangeSunshine]

Originally Posted by 1972Blaze

No, not wood. Original style brass. It does look kind of interesting though the way it reacted with the fuel and anything else it was exposed to over the years.

OK. One of the drawbacks of not being there in person. But it gives me an idea. I wonder if a wooden float would be bouyant in gasoline. Would it saturate or even decompose in an all fuel environment?

[Coley]

Couple of quick questions:
1) What type of ignition/distributor do you have? HEI? Pertronix? Points?....and any idea of condition?
2) Have you ever taken a carb apart, partial or otherwise...and are you comfortable with that?
3) Have you thoroughly....very thorougly, checked for vacuum leaks? This could be a small missing hose, loose fitting, base gasket/insulator now leaking some air.

All good
Coley

[garyd1961]

How long has the fuel been in the tank? Gas doesn't last very long these days. Just asking because you said you don't drive it very much.