The Stovebolt Site Forums The Shop Area Engine Shop troubleshooting a rough idleing 235

I have an ongoing rough idle issue with my 1960 235 that I just cant seem to crack. I thought I might ask here as to what to check next. I'm sure I'm guilty of replacing rather than being able to isolate the problem...but that's why I'm here.

When I start the engine it runs smooth for a moment until it builds oil pressure, and then it starts to run rough. It does not seem to be a consistently timed rough idle, so I had thought an electrical problem was a likely cause.

I tired the following solutions:
-new plugs and wires
-new points and condenser
-new rotor and cap
-timing both to the flywheel mark, and set by vacuum

none of these seem to help so I started looking at potential mechanical causes:

-I sprayed starting fluid around the intake looking for leaks, nothing.
-Then I switched out the carb from a Rochester to Carter YF, but no significant change.
-I've also adjusted the valves. No obvious issues with either lifters (hydraulic) or the push rods.

So...what would you check next? Would a rich fuel mixture cause the issue. I rebuilt the YF myself, so maybe I have the float set wrong. Its getting a bit frustrating, I want to drive my truck.

Are you sure your vacuum advance is working?

Kurt

Thanks for the reply,

No, I haven't tested the vacuum advance. That could make it run rough at idle? I'll give it a shot, thanks.

With insulated pliers pull one spark plug wire at a time with the engine idleing. Compare the amount of change in each cyl. That could point you to cyls that may be effecting the rough idle. You can tell if the vacuum advance works by watching the dist as you accel. the engine. Ifv it is working the dist will turn. This does not effect thje idle though as the 235 uses ported vacuum for the advance & doesn't advance at idle. Take a look at a couple of spark plugs to see if they have carboned up from all this idleing. You probably are going to have to run a compression test.

I would do a compression test like Wrenchbender said but I would also change out the coil are you using a ballist resitor if so change that to,also what # YF did you use?Some have port vac. and some are manifold vac.If you give us the YF# I have a list I can look it up for you.


Pete

Okay, so I ran out and pulled the plugs to check for carbon deposits and it looks like its running a bit rich, less so on cylinders 5 and 6. It was the same when I changed the plugs out, not terrible, but obviously running a bit rich.

I pulled one plug at a time and had about the same increase in idle roughness when taking each cylinder off-line.

When I changed the plugs and wires I also checked the compression. I got between 78 and 85 psi with no real standouts.

I forgot to mention that the coil is new, but I didn't change out the ballast resistor when I changed out the coil. I'll try to pick up one of those tomorrow.

The YF is a model 2101S

Thanks again.

I didnt see if you had checked if your vacuum advance was working, but the reason to do so is that if it is not working, most likely the diaphram is busted and you will then have a vacuum leak. This can affect your idle.

Do have a steel or brass idle screw? My 2100S had a steel screw which was very corroded. This could be another problem.

Kurt

Hi Kurt. Very good point on the vacuum leak. I hadn't considered the diaphragm as a source.

The vacuum advance may be bad, I still need to check it (snowing here at the moment). However, its currently still unhooked from my having set the timing using the vacuum gauge and the line to the carb is temporarily taped off.

I also bypassed the wiper unit to see if maybe that was leaking. It didn't seem to be, but I replaced the line from the intake just to be sure.

I'll have to take a peak at the idle screw to make sure, but if I remember correctly its steel (I'll check ).
I do know its clean. I soaked everything in solvent before rebuilding the carb, and looked for damage that might have been caused by over tightening etc. Not that I couldn't have missed something I guess.

Off to get a ballast resistor...

Installed the new ballast resistor and it seemed to help a little. Not the solution though unfortunately, still running rough.

Idle screw is confirmed steel, not corroded.

I noticed that the intake is frosting up at the base of carb pretty good and a bit on the manifold. I wonder if I might need additional heat transfer to the intake...

Adjusted the float a bit and that seemed to help until I revved it up a bit. it sounds like its missing, but no one cylinder seems to be the source. Maybe my auto choke is causing problems. That's next on the list. I'm thinking of rebuilding my old Rochester just to see if the symptoms will change.

I was watching 100 years of Chevrolet on Velocity this morning and really got the urge to drive my truck. So,I went out and started it up this morning. In retrospect I don't think adjusting the float helped at all. The lower portion of the carb, whatever the spacer is called between the carb and the intake is frosted up. But the problem of running rough precedes the new carb so I don't know if this is an issue or not. I'm at a loss and feel like just setting fire to the darn thing.

Any ideas on what I could be missing here?

thanks much,
-Chris

Dont get out the gas can or matches yet. Double check your heat riser on your exhaust manifold. I had the same problem with my 60 235 in my 52 3100, freed up the heat riser and it runs a lot better, I also replace the coil with one that is a internal resistor(less wire connections to deal with). This made a big difference in the way it runs.

Thank you for the suggestion.

I had today off, so I pulled the intake and exhaust manifolds.
The spring is missing and the flapper is stuck such that it wont allow hot air to the intake. I shot it with some PB blaster and let it sit for the night. I'll see if I can find a replacement spring assembly tomorrow.

Chris,

I'm no help here, but I wanted to let you know that reading about your troubleshooting steps and results is helping me a lot. I have similar issues with my 235 but am nowhere nearly as mechanically inclined as you. Your frustrations will help others, so please don't throw in the towel!

Best,

Jim

A little update.

Thanks again to Roberr54 for suggesting the heat riser. I got it together and buttoned up today, along with a new oil line and a fresh set of plugs.

Its running very well down the road, and idles much smoother now.
the rich condition I had observed earlier on the plugs seems to be resolved (so far anyway).

It still has a bit of a burble when idling and I can hear a lifter tick that's annoying me (I think I may have a bad hydroloic lifter) but the darn thing running a ton better than it was.

Pulling the plug wire from my number two cylinder now seems to have little affect on the idle, so I'm thinking that might be my burble source.

-Chris

Chris thats good news, now that you have it so it runs and idles better you may want to play with the timing a little, also you may want to adjust the lifter again while it is idling,as for the lifter tick, could be some dirt in the lifter, next time you change oil add some ATF drive your truck around a little before the oil change. Good luck have fun with your truck

Rob