The Stovebolt Site Forums The Shop Area Engine Shop spark plugs for a 235

Anytime you ask about spark plugs, you get lots of opinions and often some arguments. But here we go anyway. I put a 1962 Chevy 235 engine in my 53 project truck. I don't know anything about the engine except that it had been in an A.D. truck before I bought it. It does run, but now that it's driveable out on the roads, I find that it doesn't run very well. I did not put new plugs in it, I figured I'd try the old ones first. I'm not real good at diagnosing a poor running engine, so I thought I'd start with new plugs. What would you guys recommend for this particular engine?

Plugs and plug wires are about the best thing you can have for a properly running engine. What about the rest of the ignition system? Make sure you don't have old corroded cap and rotor. Make sure points are set properly. Buy a new 200,000 hr condenser from Jon G on this site. New condensers are Chinese Junk.

I've been using the AC Delco 43 or 45 (I can't remember which) for the last 4 or 5 years and 10,000 miles. Runs great and I drive it weekly on local roads and interstates.

Check Rock Auto

AC 45 here. 0.035 gap.

Mike - I'll 2nd Wally info and add some detail. The 1962 235 Truck specs from Chevy show the original equipment plugs were AC45. If it's by chance a transplant from a car, Chevy called for AC46 plugs as the base spec. You can still find NOS AC45 plugs for sale, mostly on eBay, but there are a little more modern equivalents like the AC Delco Gold R45 (a resistor plug) and a whole slew of others listed in this Cross Reference List.

Just my opinion, but I would say go with the base spec plug and probably a new set of wires like Otto suggested. If your plugs are old and tired, chances are your wires and other distributor components (points, cap, rotor, condenser) are likely in need of a refresh too. It's not a ton of money for these items and you may be surprised on what some fresh goodies will do for your engine.

On a note on condensers, I'm a firm believer in folks getting in tough with Stovebolter Jon G. He's developed and offers some superior condensers that you can read about in this Detailed Posting. They out perform off the shelf mostly made in China junk and many folks will attest to this.

For what it's worth, The points, rotor, cap, condenser, and wires are new. I also disassembled the distributor all of the way down to make sure the centrifugal advance was free and working OK. So, I'm pretty confident that those items are OK, and set up properly. My engine did not come from a car. It came from a P series truck, which I think was a step van, like a delivery truck, milk truck. etc. I will try new plugs next, and will report back.

Mike - The added details help as it can eliminate a whole bunch of guessing for folks. Thanks for adding them and looking forward to hearing how the new plugs work out.

I have a '60 235 and I'm using AC-R43 plugs. I couldn't find AC45 plugs locally, but I bought the first plugs the would work. Need to add - My truck is not on the road yet, but hopefully soon.

My truck has a '62 235 which has been running AC c44s plugs for quite a few years and keeps on puuring'

I've been running ACDelco Rapidfire Platinum Spark Plug -# 7 plugs in my 261 w/ HEI ignition for several years.

Champion j12yc or Rj12yc for the resistor version. I have run them in every 235 and 261 motor I have ever built or worked on for 48 years, not one issue ever and they are a common number and still available

OK, I have installed 6 new AC45 plugs, gapped at .035. The old plugs that I removed were Champion RJ12YC. The old plugs were extremely black and sooty. This was the case with every plug, not just a few. So the engine has been running very rich. This might be since I've owned it, or before. I'm guessing that it's since I've owned it because I definately removed the old plugs and re-gapped them months ago when I first started the truck. My carburetor is a Carter YF966S, which I cleaned and put a carb king kit in it, back before initial starting. The carb seems to work OK, but I have to confess, I don't really know the proper way to adjust it. I'm pretty good at many phases of this hobby, but diagnosing a poor running engine is not one of them. I've never been good at that. Here's a clue that seems odd to me: The engine starts right up when cold and full choke on. But when it's warmed up, I still have to choke it most times. That seems pretty odd to me. I have not adjusted the valves yet, and I know that's important. But, it doesn't seem to me that that would be part of this problem.

You have been running rich. There's no need to choke an engine after it starts.

You're going to have to check the basics. Make sure your timing is correct.

Set the octane selector on the dizzy to "0" and then make sure the BB on the flywheel is at the pointer.

The mixture screw on your carburetor should be adjusted out about 1 1/2 turns.

I'm sorry, I should have mentioned that when I first installed the engine, I static timed it by eyeballing it. It was close enough that it started up OK. Then, not long ago, I adjusted it, using a timing light. It was very close and only needed a slight change.

What is the manifold vacuum at light throttle cruise speed? The Carter carb has a mechanical metering rod that controls high speed mixture, not a vacuum operated power valve like a Rochester. It's possible the metering rod needs to be adjusted a little leaner for the best cruise mixture. Idle mixture can also be adjusted with a vacuum gauge. Turn the idle mixture screw clockwise until the vacuum begins to drop, then back it out until the vacuum peaks. Some people suggest going 1/8 turn richer on the idle screw after the vacuum maxes out to help the transition from idle to part throttle acceleration.
Jerry

Mike it is possible the diaphragm in your carburetor is leaking. I've written about this a few times and have showed people how I fix it. In basic terms, there is always vacuum present at the bottom of the diaphragm. That is by design and Carter used that variable vacuum to make the metering rod go up and down as needed (as Jerry mentions above). If the diaphragm is leaking what will happen is two things: raw gas will be sucked past it (the diaphragm) and right into your intake manifold and also there won't be the proper vacuum to make your metering rod work correctly. The lack of vacuum will cause the small part of the rod to be in the up position and that will make things run richer. Not to bore you but when vacuum is high, the diaphragm is sucked downward and this causes the fat part of your metering rod to enter the main jet. When vacuum is less, the diaphragm is not sucked down and the spring pulls the metering rod upward causing the small part of your metering rod to be in the main jet...giving your engine a richer mixture (which would be needed going up a hill for example). The "bonnet" that sits atop your diaphragm rod gets distorted when somebody over-tightens it and the use of the gasket shown in the image below will make things worse. What happens is the corners of the bonnet get pulled down leaving a gap between them. You can see I have shown one side of this one was warped .006 and the other side was warped .008".

To fix it, you'll need to get a nice flat piece of wood and use a drill bit of about 1 1/4 inch diameter to make a hole as you see I've done in the first image below. Then cut a hole out of a small piece of 320 grit sandpaper and 600 grit sandpaper. Then set the sandpaper on the wood piece (start with 320 grit) and rotate your bonnet piece back and forth until it is nice and smooth and all the warpage has been removed. Then follow with the 600 grit paper to smooth it even more. It should look like the second image below. Please don't re-use that gasket if one was in the kit you got.

This is just one possibility. While you have your carburetor apart please check the float settings too. An incorrect float setting can cause a rich-running condition. Hope this helps.

Mike, in addition to what Jon G has nicely demonstrated, those diaphragms tend to tear after several years, especially if you don't run the truck often and the diaphragm dries out. I am betting that all you have to do is replace the diaphragm and you will be back in business.

Kent

Let me add another view. Below is a cutaway showing the diaphragm and the vacuum channel leading to it (sort of squiggly red line). One end of that line leads to your intake manifold and the other is below the diaphragm (with a tiny vacuum air bleed line terminating in the bore of the carburetor. As long as no gas enters the recessed area below the diaphragm, all is okay. Vacuum pulls against the bottom of the diaphragm and this in turn pulls it down against the strength of the lower diaphragm spring. Once there is not enough vacuum to overcome the strength of the spring, you'll start running richer as the metering rod will travel upward placing the smallest portion of the rod in the main jet...which feeds more fuel up through the passage leading to the nozzle and making the mixture richer.

I have a rebuild kit and there is a gasket in it that looks like it goes between the accelerator pump diaphragm and the bottom of the well.
I have never taken a YF apart which had that gasket in it.
The instruction sheet that came with the kit had a footnote for that gasket. It stated that the gasket could be used to correct leaks in the accelerator pump. It is not a hard gasket and would likely compress enough to seal a corroded well or a slightly warped bonnet that goes on top of diaphragm.

Hi Carl. That is the gasket I showed the image of in my post above. My opinion is it makes the warping worse in that it allows the corners of the bonnet to be drawn down further. It doesn't take much effort to warp that potmetal. The gasket was created as a "shade tree fix" of the problem I mentioned. Jon H doesn't include it in the kits he makes for the YF models and while I could make them, I don't include it in the gaskets I provide for the YF either. But Jon can tell you about that gasket and who created it.

The only YFs I've taken apart which had that gasket were those which were "rebuilt" by a commercial rebuilder. It is pretty easy to correct the warping problem using a piece of wood and some sandpaper, but I doubt a commercial rebuilder would ever take the time to do it. My experience has been once that bonnet has been warped the best fix is to make it level again and be done with it. Usually about .005" to .010" is all you need to remove, but any size opening will let gas be sucked in there.

Possibly a Viton gasket made in that shape would help, but it would need to be very thin. Even raising the height of the bonnet by 1/32" is going to increase the tension of the lower diaphragm spring and that means unless the vacuum present beneath the diaphragm increases, the mixture might be richer.

Thanks so much to all of you guys. The collective knowledge of this group is amazing to me. After reading on here about spark plugs, I installed new AC 45 plugs that have been sitting on the shelf in my shop for many years. I haven't driven it since, because I got side tracked with installing my bed. Today I will install tail lights, and get the truck out on the road to see how it runs now, and will report back. If I still have a problem, I feel sure that the carb information here will help me to work it out. THANKS

Sooty plugs, depending on the level of sootiness….might not mean much. If your engine idled for any length of time before you pulled them to examine…will look like that.

Other than the weirdness of needing to choke the warm engine, does it seem to run well and have decent power?

So, today I took the truck out on the highway for a test run with the new plugs in it. It starts correctly now, and runs great. So, I'm going to put a few miles on it and then take a look at the plugs. I have a feeling that they will look good. The sooty old plugs apparently got that way while they were in a previous vehicle, under a different owner.