Need 235 Chevy Carb/Timing Advice

I recently purchased a '60 C10 - neat story, I bought it from the 2nd owner here in town (he's 85!). I have successfully gone through everything and replaced many parts, wires, tires, etc., and I'm just about ready to head down and get a safety inspection, but I'm having carb problems.....

The truck sounds like its starving for fuel. I installed a rebuild kit and a new choke cable a few weeks ago and that cleared up several issues. I adjusted the floats per spec. It was majorly hesitating, and I couldn't see any fuel squirting in from the accelerator pump. I took the carb apart again today and found that the "leathers" on the little pump had rolled up and were binding. I swapped out the accelerator pump and it squirts nicely now as it should.

However, even though the truck accelerates better now, it's still hissing/sucking loudly and has trouble accelerating smoothly. I also replaced the fuel pump, filter, and lines today (thinking maybe it just wasn't getting enough pressure), but the problem still persists.

When I had the fuel lines off, gas was flowing freely from the tank, so I know there's nothing slowing fuel down from the tank to the fuel pump.

One adjustment I don't know how to make, is the air screw (not sure wha the technical term is) at the base of the carburetor. I basically screwed it in until the engine started to die out, and then backed it off a bit. I that right?

Could it be an intake manifold leak? What's a good way to test for this? Spray a little carb cleaner on the manifold seals and listen for a change in the idle?

What else could it be?

One other question - how do I time this engine? There are no marks on the harmonic balancer, or a timing marker/pointer that I can see? The owner's manual references using the flywheel, but I can't see how I would access the flywheel from engine bay?

I loosened the distributor hold down bolt and thought I'd just play with the timing by ear, but a) there's so much play (from the vacuum advance movement), and b) I couldn't get the distributor to turn beyond the play of the vacuum advance.....

It's a really neat little truck, and in pretty great shape! 52,000 original miles, no rust to speak of. The original owner only used it to launch his boat and go to the garden center. The old fella I bought it from babied it, gave it a new paint job in '83, but stopped driving it about 15-20 years ago, so lots of stuff was rotten......

Thanks in advance for any help,

Heckler

 

check for a vacuum leak,especially around the carb base isolator.I use wd40 and spray all areas that have the potental to leak. There will be a rpm increase when you hit a leak. Some bellhousings had a cover or plug over the timeing hole,on the starter side of the engine

 

Hi Heckler. Congrats on your new truck!

To view the timing mark, look for a fairly large hole (approx. 1 1/2" dia.) facing the front of the vehicle, on the front of the bellhousing, on the passenger side. Once you've found it, turn the engine over slowly until the timing-mark appears. Then use a grease-pencil or something similar to mark the...ummmm...mark!...lol. Then time your engine. If you've got the engine running pretty good, I'm sure it's already close to correct. Yes, the distributors on these engines don't adjust very much by simply loosening the hold-down bolt. I believe you can loosen the clamp part of the adjusting mechanism...the part that clamps around the base of the dist. If you can't get the timing to where you want it, change all the spark-plug wires at the dist. one position toward the direction you need to adjust it to. Then you'll be in range, and can fine-tune it within the limits of the dist rotation.

On the carb...you did pretty good with the "air screw". It's called the fuel-mixture adjustment screw, btw. Turn it in as you did, but don't force it...you can easily damage the needle and seat. Then turn it out about 2-3 full turns for now, or where it seems to run best...for now...'cause you need to resolve the other issue...the possible intake leak...then go back and re-time and re-adjust the mixture screw. You've got the right idea about checking for the possible intake leak...spray around with carb-cleaner, with no straw on the nozzle, while listening for an rpm change...just as you said. When you think you've found something, put the straw on the nozzle, and spray smaller amounts in particular areas 'til you find exactly where the leak is. I'm willing to bet it's at the base of the carb...if there is one. But those old Rochester carbs have such a narrow cross-section where it seals against the intake/gasket, that leaks are common. Pull the carb, look at the bottom, you'll see what I mean. Also, you using a phenolic carb-spacer? If it's old, it can become brittle and cracked...and leak. And because of that, some guys are tempted to use some gasket-sealer there. But be careful of using too much...there is a small hole in the bottom of the carb casting that matches a hole in the intake, and a hole or notch in the carb-spacer. That hole runs all the way up to the upper portion of the carb...it's a vacuum-signal port for the idle circuit. If that hole gets clogged, it'll keep your engine from idling well. A vacuum leak at the base of the carb will also keep the engine from idling well. Is the engine idling as it should, or does it want to die? When you choke the carb, either with the choke or just your hand somewhat over the carb, does it seem to run a little better...idle better? If so, I'd bet there's a leak at the base of the carb. These carbs are also very sensitive to whether the float is adjusted to the correct height or not...both in upper position, (when the float-bowl is full) and in lower position. (when the float-bowl is empty) Judging from the "hissing" sound, again...I'd bet on a vac leak at the base of the carb...but...don't overlook vac hoses, etc. Does the carb have an electric choke? Be sure that the cover of the choke adjuster is sealed aroung the edges. (spray with carb-cleaner to check) See the threaded male port there? That is the heat-riser port...meant for heating the carb/choke. Is it open with no hose or fitting? If so, put your finger over the hole...you'll feel vacuum when the engine is running. Can't have that open...gotta plug it somehow...rubber hose and a small bolt, tape, bubblegum, something for now. (just kiddin' about the bubblegum)

I've got a link to an excellent article on tuning/rebuilding the old Rochester carbs. I'll look for it, and add it here. If you have any questions, send me a PM...happy to help if I can. - Rick

 

Sorry Heck...can't locate the web site now. If you need teck help on the carb, do an internet search...quite a bit of info. Good luck.

 

Decker, Thanks for the tips! The truck idles very well currently. It's just when I'm going down the road and giving it some gas that it hisses and has issues.

I'm going shooting with some friends this morning, but I'm going to try spraying around with some carb cleaner later today.

I think I see the plug/hole on the bellhousing you mentioned too. I'll fiddle with it too this afternoon.

Thanks!

 

I've never seen a hole in the intake to match the carb hole (the spacer has one) - what normally happens is that the carb gasket has a slot in it that allows manifold vacuum to the hole in the carb. Original-style gaskets had 2 slots 180 apart, you can put them on wrong and seal-up the carb hole; most replacement gaskets have 6 slots 180 degrees apart. Make sure the holes line-up with the slot in the spacer.