Pun intended. 1953 235 (solid lifter) in my '52 coupe (powerglide) has developed a miss and I am pulling what little hair I have left trying to sort it out. Apologies for the following wall of text, but here's what's known and what I've tried. Known: Refreshed this engine this past winter, just gaskets and a rattle can rebuild but I did disassemble the head, lapped the valves by hand (didn't take much they looked pretty good) and new stem seals. After assembly it was timed by light, ran up to temp and set the valves by the book. Ran beautifully the first month or so, no issues besides slow. I'd read that these engines like to have the octane selector on the distributor set a little advanced so this is what I did, then timed by vacuum to get a consistent reading at just shy of 20lbs with no major fluctuations. A few weeks ago I noticed I was developing a miss at idle that seems to go nearly away when under load (missis in neutral and park, nearly goes away in gear even when sitting still). It's barely noticeable as you're driving and I'd honestly just live with it if the miss in park wasn't so terrible. What I've tried: -double checked timing -set carb to manual specs (I rebuilt carb last year and ran it on previous 235) -new plugs -checked wires, can't see a problem -condenser -cleaned point contacts but they looked fine -kicking -swearing Now, I am sure I am missing (har) something simple. I did not have a spare coil or cap to try at home but I could probably get them in short order if needed, I'm just skeptical of it being ignition now that it seems to go away under a load? I know rich mixtures can cause misses so I'm wondering if my Rochester is over-fueling my engine, these carbs are known for bad accelerator pumps after all. I had 2 of my 6 plugs quite a bit darker than the other 4 (cyl 2 and 5 if it matters). I do not have a spare carb to try at home, I have a manual choke one back at the farm I could toss on to see if it isolates the problem. Paging all 235 gurus or even just regular shade-tree hacks like myself who've beat their head against a wall and come through victorious.
Have you pulled each lead off in turn when it’s running to see if it is a cylinder specific misfire? Tim
Sorry, yes - I did pull each and I couldn't locate a specific problem cyl. Mind you I was doing this solo and really should have someone who can stand at the back and help listen, maybe I'll try again tonight when my pal comes into town.
I pour a bottle of Techron, isopropyl drygas or Lucas fuel system treatment in each car's gas tank every now and then. Sometimes it even works.
You probably already done it, but check inside of cap/rotor for carbon buildup.. I had that happen once before.
What type of plug wires did you check? Carbon core can be funny sometimes when going bad. Will be fine at one rpm but not at another rpm.
FWIW You might open the valve cover up and make sure you didn't have a valve stick on you over the winter. My experience has been stovebolt engines bend pusrods very easily that way. I had a miss problem appear that way years ago. Also, I gave up on the Rochester B long ago because I couldn't keep modern China-junk seals and accelerator pumps from going bad during winter storage. I used an old Holley 1940 I had and it was nearly bolt on.
Thanks guys Local jobber had a cap in stock and it was cheap enough I grabbed it, will try tonight. Wires are Standard (Blue Streak) I got last summer and ran on the previous engine. I'll try to spray some brake cleaner around the problematic areas tonight, see if I get jumping RPM. It was just reassembled here over the winter and was running good so I'm fairly sure I don't have a sticking valve but I suppose anything is possible - up to and including bad spring/bent push rod but I'm reeeaaally hoping not.
Manifold leaks used to be common with these. The round metal intake rings do help this if you have them.
Do you have vacuum on the advance diaphragm at idle? This engine was originally set up with ported vacuum so you should have no vacuum advance at idle. I have seen a "no load" miss when the timing is advanced farther than what the engine wants. Try disconnecting the vacuum advance and see if the idle miss goes away. If that isn't the case, then next step is to check the compression. In fact, you should have done that early on.
1320 Fan beat me to the punch, had a pesky miss after years ago replacing a 235 in my 57 pickup, don't recall if a split ring in the intake was missing or improperly seated, couldn't believe the difference once corrected..
I have the intake rings installed, but just in case I'll spray brake clean there too. To me it doesn't feel like it has much shaft play but I don't know how much "too much" would be? Correct, should be ported vac but maybe when I bumped up the octane selector advance I went too far - I will try disconnecting that tonight.
Shade tree hack here. But I've had a couple of the old 6 cylinder engines. Intermittent miss, right? Sort of like blum blum blum blum miss blum blum blum miss blum blum blum blum miss I tend to agree with the guys who are suggesting you might have a vacuum leak. Intake ring is possible. But those little Rochester carburetors have such narrow cross sections on the bottom of the base (the mating surface) that a vacuum leak can easily develop there. Don't be tempted to use gooey gasket sealer to try to fix it, it'll go in tiny holes where it's not supposed to. If you determine it's leaking there, make sure the mating surfaces are nice and flat and clean and you have a nice new gasket and phenolic spacer if you're using one. How do your plugs look?
Plugs are white/brown except for #2 and #5 (last week, before swapping to new - I am going on a cruise for a few hundred km this weekend, will pull and check again once back). Will add the carb base to my "check for leaks" tonight.
If it's a Rochester model B or BC check the two big phillips head screws that come up thru the throttle body flange to attach the float bowl. It's not uncommon for them to work loose and create a vacuum leak. Also check the gasket that the screws pass thru and make sure it's intact.
Run it at night in darkness, if you have any ignition "leaks" you will see them as a flash of light. Hook up a tachometer to it, pull one lead at a time, and narrow it down to one cylinder. If it is not a constant miss look further up the line for something that is common to all cylinders (coil, distributor, etc). Check your vacuum advance by disconnecting the tube and replacing with some flexible stuff, and suck away! The distributor should move a few degrees with a good "suck".
Grab the body of the carb and twist back and forth. I've seen a couple of them that did hust what Claymart said.
Follow up from the weekend, I got home friday night from work and first thing I did was take my handy little 1/4 drive speed wrench thingy (Gearwrench #85035) and snug up those 2 vertical screws holding the body to the base. They didn't move much at all but I think @ClayMart was onto something, it seemed to help quite a bit. It still has a minor pop here and there but nothing I can't live with for the time being. If anything changes you can bet I'll be back bitching and moaning. As an aside, I put on roughly 240miles (386km) this weekend and was rather surprised with my mileage, it was around 13L/100km (18+/- MPG for you guys) which I thought was pretty fair. That's damn near exactly what my 2001 Cherokee with the 4.0L gets average.
Like others said, check carb body screws. Use a can of carb cleaner with the plastic tube to pin point a vacuum leak. Brake clean not effective. Providing the compression test is ok, check spark plug wire ends for corrosion,a plastic spray bottle with water carefully misted on plug wires will allow any broken down insulation to show up, or use ohm meter and wiggle test to check, or just replace if age is unknown. Also check distributor shaft for excessive wear, grab rotor with fingers , check side to side movement.
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