Hi there everyone. I have been enjoying my truck after getting all the ignition and timing sorted, no leaks since I installed the new brass fuel inlet fitting and it starts every time now with no fuss (it's faster to fire up than my 2007 Honda...;-). The only issue is that I am concerned that I believe it is running lean. When driving, it seems to pull pretty good and responds to the throttle well, but I have no reference point for what a 235 should feel like. It's a 235 from 1954 with a Rochester B.
To test the jetting, I drove it for 25 miles on the freeway at about 50mph and when I pulled the plugs, they were bone white at the porcelain (see attached). The strange thing is that the jet it came with was stamped 52, but when I compared it to the new 56 jet I have, the 52 looked much larger, but did not have the eased edges on the 56 (it looks like a straight drilled hole - see pic). I am guessing that someone drilled out the 52 to try and make it work in the 235. From what I have found, the factory jet size should be a 58, and I wanted to know is... - if it is running lean with a jet that looks much bigger than the 56 I have, would I need to go bigger than the stock 58, or do I need to be looking for something else that could be making it run lean? Does the chamfered/eased edge of the jet opening make it mix fuel better? Maybe i have a vacuum leak? I am getting right at 21hg at the port that the wiper vacuum hose connects to on the manifold.
Any chance you have a carb number? From a united motors service bulletin 9C 305 (10/15/1954) the standard main jet for 53-55 Chevy truck Rochester model b is 7002958 (.058) and the lean jet is 7002957 (.057). For 54-56 car motors with Bc carb, the main jet for 54 was .058. For 55 it was .057. For 56 it went back to .058.
Unleaded gas doesn't follow the same rules of thumb that most of us oldtimers learned- - - -"Tan to chocolate brown" for the right mixture. The lead additives in the older gas were what gave plugs their distinctive color. Unleaded goes from white to sooty black for a too-rich mixture with very little variation in between.
I'd suggest getting a few Holley main jets (they're cheap and plentiful) and running a threading die over them to make them fit the Rochester carb thread. Then you can take a set of number drills and a pin vise and make up a set of experimental jets in various diameters to tinker around with the mixture. Once you find the sweet spot, you can either leave the test jet in place, or modify an OEM Rochester jet to the same size. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Does it run OK? Does the exhaust smell? fuel smell or hot lean smell? you will know the difference..... Does it surge when driving steady? Do you have to really step into it to climb a hill? Hows the fuel mileage? Hows it start? Hows it smell a few minutes after shutting it off hot?
And last question, why do you think it's lean?
I run a wideband air/fuel ratio gauge on my truck with a 250 cubic inline six. Mine runs best at 15.5 -16.0 to 1 air fuel ratio, this sounds lean when you hear people talk about A/F ratio's because most only understand WOT for racing. If it runs well, leave it alone for a while and see how it looks after a couple hundred miles. Watch the oil for fuel smells, tail pipe soot, plug color, and most of all, fuel mileage.
When I was working on Rochester Model H, Corvair carburetors, ( three at once ) I would solder the jets shut, then drill out to the size I wanted to try. If it worked, I purchased the correct factor jet, if it needed more, it was no problem to drill a little more solder out.
Dragsix, I don’t have the ID tag to know the specifics of my carb. My guess is that it was originally on a 216 since it had a 52 main jet, but that’s just a guess since my truck is a 1949 with a 1954 motor.
HRL, it sounds like with modern gas, reading plugs is not as easy as before, and jetting becomes more of a seat of the pants thing unless you have access to diagnostic equipment, which I don’t have. It seems to run well, but I might experiment with the Holley jets to see what it means to be too lean or too rich.
Wrench bender, I’ve read that the ethanol gas makes them run lean, so a bigger jet makes sense. Will experiment per HRL’s notes.
Joe, it seems to run pretty well and pull pretty hard at most any throttle input in the city or on the highway, so I must be close (I have no reference point for what a healthy 235 should run/feel like, but it keeps up with traffic for sure). I don’t smell like I spilled fuel on me when I get out after and here in Houston, our “hills” are highway overpasses ;-) and it seems to just need a little input to maintain speed up those uphill conditions. The reason I thought it was lean is because the plugs were bone white when I checked them and the jet was stamped 52 when a 58 should be stock (check out the pictures in my original post)
What I am finding from all the responses is that I am likely in a good place with what I have right now and am more than likely not lean given the size of the jet compared the known 56 that I have. I was concerned about being lean and burning a valve because I have lower compression in one cylinder (95 vs 110 in the others) I will check mileage and experiment with the jets.
Joe, I do smell something other than oil after on the dipstick after a while of running, but I thought that was because my road draft tube is missing from the part that plugs into the block (maybe it’s not pulling out the gasses.). I need to install a pcv or get a correct draft tube set up. It doesn’t smoke or have a strange exhaust smell either.
I've noticed my 53 235 runs much better with non alcohol fuels. It is 4 bucks a gallon but worth it to keep the rochester b happy, IMHO Had to jet it up when I ran 10% alky fuels before the rebuild though
Last edited by sstock; 08/05/20182:09 PM.
1953 Chevrolet 3100 261 cu inch, sm420, 3.55 rear, torque tube still,omaha orange, still 6 volt, RPO green glass, side carrier spare, all done In the DITY Gallery Video of the 261 running
1964 GMC 1000 305 Big Block V6, sm420, the next cab off restoration
The only thing I will add to this is that you might try to find a 54 235 carb. That 216 carb is a tad small and all of the calibrations and jetting, from the idle circuit, through off idle, to wot, are all engineered for use in the smaller motor. On a 235, if I am using 216 carbs, I am using them in a dual set up because the 235 dual carb set ups tend to run a little better with two smaller 216 carbs. So to get your motor running it’s absolute best, find a carb that it was meant to run on. I think you will be better off in the long run.
Resurrecting this one because I stumbled on a post about stuck heat risers potentially causing a lean condition if they freeze up in the "heat on" position. So I popped the hood and tried to twist the heat riser counterbalance by hand... and it appears to be frozen in the horizontal "heat on" position. From what I have read in the forum and in my manual if the valve is stuck in the heat on position, the manifold gets too hot, the gas expands too much and creates a lean condition. My guess is that the PO drilled out the jet so large to compensate?
I've been soaking the riser shaft with PB Blaster and lightly tapping back and forth with a hammer to get it free and no luck so far. Hopefully, I can free it up, then do a highway run re-test on the spark plugs to see if it runs a little richer with a functioning heat riser. If I get the riser working again, I wonder if it will then become a rich condition. Will pull plugs and see.
Also have what seems to be a sticky valve or two because I am getting a constant chuff chuff sound once it warms up. Any thoughts on how to fix them? I'm trying some MMO on the stems, and read about spraying Kroil on the valves, but I'm worried it will catch on fire or something.
When faced with a rusted nut or a pulley that is rusted on a shaft, one thing that has worked well for me is to mildly heat them with a propane torch and melt some wax (hold a candle to the hot metal) onto the shaft. The wax wicks down the shaft and provides enough lubrication to get the stuck part off.
Maybe this technique would work for the riser shaft.
Keep at it with the penetrating oil and tapping. Sometimes it takes several days to get it loose. Don’t give up.ðŸ›
Martin '62 Chevy C-10 Stepside Shortbed (Restomod in progress) '47 Chevy 3100 5 Window (long term project) ‘65 Chevy Biscayne (Emily) ‘39 Dodge Business Coupe (Clarence) “I fought the law and the law won" now I are a retired one! Support those brave men/women who stand the "Thin Blue Line"! Hug a cop! USAF 1965-1969 Weather Observation Tech (I got paid to look at the clouds)
