Fuel or air problems on a 70 c10 with 1 barrel Rochester

[BenC10]

Sorry about the long post.

New here and somewhat new to Chevy and classic trucks in general, but I've been tinkering with a 70 c10 with an I6 250 and the single barrel carb.

Engine is rebuilt, installed headers (intake heater is installed), carb had been "rebuilt" by me and the distributor is new/reman.

I've had a lingering hesitation and sometimes downright stall problem when going uphill, or at least that's when it's most prevalent. I thought it was the lack of intake heat so I installed the plate and engine coolant line. While that did seem help, it didn't fix it problem.

Latest problem is that I tried adjusting the fast idle and while reversing out of my driveway the engine dies almost as soon as it tilts back down a hill. First time this has happened.

So I think it's getting flooded. I did have issues with the float causing overflow at a standard adjustment, so I've got a new one on the way, but something else may be wrong that I wanted to get input on...

So when I pulled off the carb, I tilted it back (like driving uphill) about 20 degrees and noticed fuel pouring out of the brass orifice in the middle of barrel. Is that normal? I took off the top end and it didn't seem like there was too much fuel in the bowl, but I also have no frame of reference.

It's also always kept the top gasket saturated, which seems like it could be excessive fuel in the bowl.

[Dead Parrot]

You mentioned a new distributor. Double check the timing and make sure it hasn't self adjusted since you installed it. Also make sure the mechanical and vacuum advance are working. Poor timing can mimic some fuel/carb adjustment issues.

If you have or can get one of the old style vacuum gauges that can also check fuel pressure, double check that as well. Used to be you could trust parts to be pretty close to spec but not so much any more. Possible your fuel pump is putting out too much pressure for the float/seat to handle.

[BenC10]

Thanks for the reply. I did set the timing to 12 degrees base and set the gap and have played around with that (it's around .019" if memory serves). I recently got a dwell meter as well, but haven't tried that yet (carb is still apart).

Vacuum advance seems to work fine with the mighty vac. I do have another guauge on the way to check fuel pressure from the pump and into the bowl.

[BenC10]

Update: I got the new float installed and set back to factory, and while it does seem to be more effective, the main problem is still present, which is that I can barely get it started or keep it running.

First start after installing the carb sounded great, then after a minute it just sputtered out and can barely start. I checked and the bowl was full. I'm starting to think I have an ignition problem on top of the perceived fuel issue.

Checked the coil, getting 1.7 ohms across pos. and neg. and around 9.5k to the middle.

I am getting 12v to the coil however. Is that correct?

[vince1]

I think a 2 ohm coil might need a resistor. Lift the hood at night. If it glows blue around the coil wire it may be getting too many volts. I fried a Delco 2 ohm coil like that once where the original had been a 4 ohm Prestolite without a resistor wire. It's time to check the wiring diagram or get one of the aces involved.

[geezer#99]

Originally Posted by BenC10

Update: I got the new float installed and set back to factory, and while it does seem to be more effective, the main problem is still present, which is that I can barely get it started or keep it running.

First start after installing the carb sounded great, then after a minute it just sputtered out and can barely start. I checked and the bowl was full. I'm starting to think I have an ignition problem on top of the perceived fuel issue.

Checked the coil, getting 1.7 ohms across pos. and neg. and around 9.5k to the middle.

I am getting 12v to the coil however. Is that correct?

Only time you should have 12v to the coil is when starting it. After it starts you should have 7-9v.
Try lowering the float level a bit.

What choke do you have?

[BenC10]

Yeah it's getting 12.5v with the key on. So I guess since one or both wires going to positive on the coil look like they could have been cut that means the resistance wire is probably not working. Would this model have a resistance wire or some sort of resistor?

It's a manual choke now, but was thermal on the manifold.

[AussieinNC]

Sounds like the float has a crack in it and is filling up with fuel and sinking in the bowl.

The 12 volts at the coil with key in On position usually means someone has bypassed the ballast resistor or replaced the resistor wire in the circuit.

Having 12 volts to points all the time will usually burn them up a little faster than normal. It should not be causing the issues you have detailed.

Tilting any carb back to 20 degrees and having fuel run out is a sign the float level is too high or the flaot is cracked or the needle and seat has the needle in backwards...the angles point on the needle goes into the seat first.

Good luck

[BenC10]

So does the ballast work with the resistance wire or will it only have one or the other (not sure what the ballast does)?

The needle is pointy side down . Since working on the carb again, I also hooked up a fuel pressure gauge. It's holding steady around 3-4 psi for several hours, so at least now with the new float I think it's okay.

[Mike C]

Either or with the ballast resistor or the resistor wire. People drop the word resistor a lot when talking about the ballast, but add that back and it helps understand one or the other to accomplish same goal.

I have several 153 ci motors, the old Chevy II or 2/3 of a 250. I have found the 1 barrel Carter choke/idle setup to be VERY finicky and after you bird dog the igntion, give some more time to making sure that circuit is adjusted well/accurately.

[AussieinNC]

Originally Posted by BenC10

So does the ballast work with the resistance wire or will it only have one or the other (not sure what the ballast does)?

The needle is pointy side down . Since working on the carb again, I also hooked up a fuel pressure gauge. It's holding steady around 3-4 psi for several hours, so at least now with the new float I think it's okay.

mmm...Pointy side down....the pointy side of the needle goes into the seat so the pointy taper can seal against the seat....the only time it would be pointing down would be when you are assembling the carb top....when its installed in the carb, the pointy end is actually pointing up....

See this youtube video for a good look at the top overhaul...

https://www.youtube.com/watch?v=pJb9zEutiHc

Ignition ballasts are used when the operating voltage designed for the coil is 7-8 volts rather than 12 volts available in the vehicle.

To aid starting, there is a secondary supply wire from the starter that provides 12 volts to the coil during cranking. (Look on the bottom of the coil can for operating voltage of the coil).

If the coil on your truck is marked for 12 volt operation, the system does not need a ballast resistor. When the key is released into the run position, the ballast circuit takes over voltage supply to the coil.

[BenC10]

My carb isn't the same as the video. On mine, the fuel line goes into a mini filter then up into the valve/bowl. And the pointy rubber bit seals at the bottom of the brass screw on bit.

Also, taking a closer look at the coil I see a yellow wire that goes to the passenger side of the starter and the other black cloth covered wire routes up along the firewall drip edge and terminates into a larger wire where it is spliced into it.

I'll try separating the yellow and black at the coil side and recheck the voltage with the key on.

[BenC10]

Cut loose the yellow wire and I am getting 12.2v from the braid sheilded wire (assuming resistance wire), which is crimped into the larger red wire that feeds the throttle solenoid. The length of the resistance wire is 3 feet and I read that it's supposed to be around 7.5 feet long.

Is it possible to obtain another one of these wires and connect it back where it's supposed to go, or would it be easier to wire up a resistor with regular wire?

[geezer#99]

Likely easier to swap in an hei.

[AussieinNC]

If the coil is a 12 volt coil you can leave the wiring as it is. The downside is the points may erode faster than if the system was supplying 7-8 volts to the coil.

Did you check the bottom of the coil for a voltage rating?

The yellow wire coming from the starter is the 12 volt feed wire usually used to supply 12 volts to the coil under crank conditions to make starting the engine easier.

So long as the needle pointy end is sealing against the seat body you have it in correctly.

These carbs are renowned for being finicky to set float levels with...I usually set the level too low and if fuel starvation seems an issue, I slowly lift the height unto a flooding situation occurs. Then back off a little....

[BenC10]

It doesn't say on the coil itself, but at least one parts store lists it at 12v. I was thinking it's for a 12v system but that's still going to kill the points? I did go ahead and replace the points and set back to .019. I'll give that a rest for now.

I got it to start back up. It sounded fine at first then started getting rough and not wanting to run as it started to warm. It's being starved for something but I just can't tell what it is. I can keep taping the gas to keep it running (rough) but eventually even that won't keep it running.

Tried closing the choke (after warm up) and that seemed to kill it faster.

Pulled the plugs, and honestly it doesn't look like it's really flooding right now (not really wet looking).

I'm going to try the suggestion of setting the float level lower and replace the plugs to help see what's going on when I get the chance.

[vince1]

If you were to try a Chrysler type resistor it might work and then you wouldn't have to play with a resistance wire. 6R1002 or RU11. I think your coil is getting super saturated for lack of a better term. It may already be fried. Better yet as has been suggested go for the HEI. They can still be found in the junkyards. Petronix is another option that some people use in an original distributor.

What kind of carb is that? It is different than the one I had on my 66.

[BenC10]

I don't think so? It just says Chevrolet and Monojet on the side of the bowl.

I did pick up an RU10 because it was available locally and it was rated at 1.8 ohms, but it didn't lower the voltage. I had also read from some that you won't see a voltage drop until the contact is connected, but I didn't test that far.

I really don't want to introduce a new headache by switching to hei (yet) but maybe later.

Ohm readings on the coil were in spec, but I suppose that doesn't always mean it's good.

[vince1]

Take the cap off the distributor and with the points closed hold the coil wire close to ground while opening and closing the points with a screwdriver. You should get nice blue sparks about 1/4 inch or longer.

[BenC10]

Sounds thrilling.

I did try a new coil and plugs and no change.

I hooked up a spark tester light and noticed it was faint and flickering too much. I replaced the last thing I could think of (condenser) and of course, it fired right up and runs perfectly now.

Back to the voltage concern... Both the old and new coil say 12v but to use an external resistor or resistance wire. So, I guess I should try the ballast and see if that keeps everything in working order for longer.

[vince1]

Aha, I knew it was electrical and can't believe the condenser was not suggested. I had to replace one myself a few years ago after putting an old car back on the road. Good find.

I fried my Delco coil that was getting full alternator voltage probably within a hundred miles. Your resistance wire is probably still hiding in there somewhere. Got a wiring diagram?

[BenC10]

I have a few wiring diagrams bookmarked and a Haynes manual (not that it helps much).

Took the truck out for a drive today and everything seemed fine, though too early to tell if the uphill sputtering issue is fixed.

[BenC10]

After several days of running great, the sputtering issue came back with a vengeance and seemingly out of nowhere, it just started dying every time I tried to push it even a little.

I broke down and purchased a summit racing hei dist which should be in this week. Hopefully that will permanently fix it and there won't be any underlying carb issues left.

Question: do I need the starter side coil wire anymore? Seems like I just need to run a 12v (original firewall plug if I can) to the dist and that's all.

['68OrangeSunshine]

Originally Posted by BenC10

Question: do I need the starter side coil wire anymore?

Seems like I just need to run a 12v (original firewall plug if I can) to the dist and that's all.

1] No.
2] Yup. I run a fresh 12 ga wire from Ign Unfused to the + terminal on the HEI. It goes thru a grommet in the firewall.
I left the OEM Or/Ppl/Wht 20 line [resistor lead] in place if for any reason I want to go back to points.

[BenC10]

Thanks. In my case the resistor wire it got ripped out of the plug, so maybe I can repin a new one there.