Carburetor Woes

[1972K20]

I've got a 1970 C50 that had been sitting for about 10 years. Ive got the truck running, but it still has some problems. First of all, it won't run with choke completely open. It has to stay partially closed or it will quit running. It doesn't accelerate good and when pulling hills, it won't go over 15-20 mph. It starts and runs great, but it seems like the carb is stopped up.

Here's what I've done so far:
New fuel pump
New fuel filter (in-line, the filter at the carb was removed before I got it)
New fuel tank
New sending unit
Blew out the fuel lines with air
Fresh gas
Added Seafoam and sprayed carb cleaner in the carb
New air filter

Is the carb stopped up? What's the best way to clean it out?

Thanks!

[71K20chevy]

It sounds like you're just running lean?

But I'm wondering if it could be ignition related too.

[67 cst swb]

Rebuild the carb.
Kits are very affordable.

[BLT gmc]

In this situation, I have removed the carb. Disassemble and submerge is the best carb cleaner I could find for 1 to 7 days- depends on how dirty it is and how big of a hurry I am in. I then spray all the passages out with pressurized cleaner. re-assemble with a re-build kit. Then finally adjust as needed to idle/run/accelerate. Good Luck, Bruce

[Coley]

Originally Posted by BLT gmc

In this situation, I have removed the carb. Disassemble and submerge is the best carb cleaner I could find for 1 to 7 days- depends on how dirty it is and how big of a hurry I am in. I then spray all the passages out with pressurized cleaner. re-assemble with a re-build kit. Then finally adjust as needed to idle/run/accelerate. Good Luck, Bruce

Absolute ditto on BLT/GMC's comments here.
You have to get inside the carb and clean out the passages, bowls, etc to get a good baseline.
Whatever you do....don't try to solve this by leaving the carb on the truck and 'putzing' and poking from outside. Remove it (takes 15 minutes tops) and get it on a bench.
The first thing I would do is to get the top (air horn) off of it and take a look in the main fuel chamber to see what sort of crap is in there. At this point you haven't affected or adjusted anything...simply investigated.
If you haven't rebuilt a carb before don't panic.....just proceed carefully.
Keep us posted and remember...remove the carb, get it on a workbench, take your time and proceed carefully....it will pay dividends over 'screwdriver' putzing from the outside.
Very Important Note: Before you start anything....take some pics as you go, so you know and remember exactly where everything went and where it should go back to.
My two bits.
Coley

[1972BlueC20]

man why does that carb look so small? I'm new to these trucks, but my stock q-jet was much bigger looking.

[BLT gmc]

This is a 2 barrel, likely your carb is a 4 barrel.

[Coley]

Originally Posted by 1972BlueC20

man why does that carb look so small? I'm new to these trucks, but my stock q-jet was much bigger looking.

Its not a Q-jet (quadrajet, ie: 4bbl).
Its a 2 bbl Rochester, this is why it looks so much smaller.
Coley

[1972K20]

Ok, good advise guys. Thanks

However, I have a few more questions. I've never done much to one of these carbs, so I want to do it right.

What's the best solution/carb cleaner to soak the carb in?
Who makes a quality rebuilt kit?
How do you clean the tiny passageways in the carbs?
How do you adjust the carb to the correct setting?

[davepl]

For soaking you're going to be limited to what the local autoparts store carries. And I can only find 1-gallon cans these days, which are too small to soak the carb body in (on a Q-Jet anyway, you might get that one in there). The warmer the fluid, the better (but it's flammable, don't be dangerous). In the old days this stuff would strip the minerals out of a skeleton, but now it's environmentally safer. Which is a mixed bag... stuff doesn't work as well anymore, but you old guys didn't have to pour your used motor oil down the storm sewer either :-) At least my Dad flushed it down the toilet...

I think the best rebuild kit is probably the one you can actually find.

Tiny passages can be blown out with compressed air. Wear hearing and eye protection. The latter is essential, the former just a good idea.

If you can give me the actual model number I've got a decent book that covers 8 or so Rochester carbs, I can probably find initial setup info.

And don't throw ANYTHING away until the truck runs right again.

It's almost certainly the carb as all above have said, but there's a slim chance it could be a vacuum leak somewhere and 'choking' the motor makes up for it.

[Coley]

Originally Posted by davepl

For soaking you're going to be limited to what the local autoparts store carries. And I can only find 1-gallon cans these days, which are too small to soak the carb body in (on a Q-Jet anyway, you might get that one in there). The warmer the fluid, the better (but it's flammable, don't be dangerous). In the old days this stuff would strip the minerals out of a skeleton, but now it's environmentally safer. Which is a mixed bag... stuff doesn't work as well anymore, but you old guys didn't have to pour your used motor oil down the storm sewer either :-) At least my Dad flushed it down the toilet...

I think the best rebuild kit is probably the one you can actually find.

Tiny passages can be blown out with compressed air. Wear hearing and eye protection. The latter is essential, the former just a good idea.

If you can give me the actual model number I've got a decent book that covers 8 or so Rochester carbs, I can probably find initial setup info.

And don't throw ANYTHING away until the truck runs right again.

It's almost certainly the carb as all above have said, but there's a slim chance it could be a vacuum leak somewhere and 'choking' the motor makes up for it.

....definitely agree on these tips and....oh yeah, double agree on the eye protection, getting even a drop of bounce back spray of carb cleaner in your eye is a serious drag and danger, it will stop and drop you in your tracks. Don't ask me how I know.
all Good
Coley

[1972K20]

Great, thanks. I'll look for that number.

[crazy longhorn]

That old 2 jet, is an easy carb to rebuild....that said, it has a govener, on the side on that big truck....I am damn sure that the carb needs help, after the yrs of sit time.....before you even try to dial the carb, points/condenser ,& timing 1st....dial the carb last Longhorn

[1972K20]

Haven't had a chance to take the carb off yet, but where is the model number located so I'll know where to look?

[BADAZ chevy guy]

Originally Posted by 1972K20

Haven't had a chance to take the carb off yet, but where is the model number located so I'll know where to look?

I don't remember the 2 brls having a stamped number (I could be wrong) they had a stamped metal tag on one of the top horn screws.