The Stovebolt Site Forums The Shop Area Engine Shop Rebuilt Carb now Spark Plugs Keep Fouling

Need a little help. I have a 1954 chevy 235 with a single barrel rochester B carburetor. I recently rebuilt the carburetor with a kit from Mike's Carburetor parts because the truck would not keep running. I checked everything and narrowed it down to an issue with the carburetor. Now it is running better but it seems like the idle is too high and maybe my mixture screw is not set right. After running it for about 45 minutes, it cut off on me and wouldn't crank back. I pulled the spark plugs and they were black as soot. I know adjusted the mixture screw to 1 1/2 turns back out after it bottoms out. It feels like it is running too high but when I adjust the idle screw back out a quarter of turn more, it slows down and cuts off. Any suggestions??? I burn 93 octane non-ethanol gas. I have the octane retarded a few degrees. Should I advance it a few? Does the mixture screw need to be adjusted more? Could the spark plugs be bad? I have a new coil. Condenser is about 5 years old. Could the condenser be causing this?

Check the top carburetor casting for warp. Rochester Bs are notorious for getting a bowed-up top casting that causes a vacuum leak. This forces the mixture to go full rich by holding the power valve open constantly and there's nothing you can do to adjust it away. You could also have set the float level slightly too high which will cause the carburetor to flood at idle and soot up the plugs.

The fix ix simple- - - -Use the Rochester for a paperweight ( a stinky one because it's had gasoline in it) and install a Carter carburetor. Like Carter's advertising slogan in the 1950s said- - - - -"The ABCs of carburetion are Always Buy Carter!"
Jerry

No good reason to run 93 octane. Some bad reasons though. If it is going to work at all you will need to advance the timing, not retard it.

When it was running, did adjusting the idle mixture screw in or out cause a change in the RPM?

Did you put a gasket between the carb and intake manifold? The kits include one, but it shouldn't be used as it may block the vacuum port on the base of the carb.

I run the higher grade fuel only because of the non-ethanol component to it. That is the only octane available in non-ethanol at the local gas station. Yes adjusting the idle mixture screw does change the RPM. Wondering if my float is too high or main jet too large. I will try advancing the timing a few degrees and see what it does then.

I do have a gasket in between the carb and the spacer but the gasket has a slot cut out of if so as to not block the vacuum port on the bottom.

I may eventually break down and get a Carter! Hoping to avoid the expense for now.

Power piston may be bound up in the power piston bore. I common problem with Model Bs. Carb cleaner and a nylon brush with the correct diameter to fit the bore works well. Make sure that your springs and check ball are correctly in place under the little T retainer too.
Shake your float to make sure that it doesn't have gas in it. Adjust the float level and float drop according to specs.

52Carl,

I have totally gone through every part of the carb and put float, needle, seat, balls, springs, idle mixture screw...

Hi Pastor Matt. Please try an adjustment of between 1/2 turn to 1 turn and set your idle speed to something like 475rpm. Anything over that will cause you to run too rich at idle and waste gas. Also, Jerry is 100% correct. The vacuum leak caused by warped body castings will cause the power piston to fail and that means your Rochester will run very rich constantly. A few years ago I wrote quite a lot about the problems of the Rochesters and a way "everyman" can straighten these using his gas bbq grill.

The Carter YF is an excellent carburetor, by the way. Completely different than the Rochester.

Please also make certain the power piston is freed up in your carburetor. I've seen these which were "professionally rebuilt" which had power pistons that were stuck in their bores and they always stick in the down position.

High octane gas burns much slower than regular, so it needs advanced timing to prevent exhaust valve damage as it is still burning well past the power stroke. Red hot exhaust manifolds are not uncommon when burning premium gas in an engine designed for regular.
Jerry

I am coming late to this thread.

No advice on the Rochester B (other than replace it), but a few comments on the fuel.

As Jerry said in the post above, high octane fuel burns much slower than regular, thus advanced timing is mandatory, or a bunch of the fuel is going out the tailpipe unburned.

Don't take my word for it, but use Google or whatever search engine you prefer, and investigate octane ratings.

There used to be two systems of measuring octane; the (R)esearch method and the (M)otor method.

Of course, the supporters of each system stated that the system they supported was the superior system.

Finally, the government had enough, and did something intelligent for a change. The didn't support either group, they just averaged the two ratings. The new rating scale was called AKI for (A)nti (K)nock (I)ndex. Used to see at the pump the rating was listed as (R + M / 2).

93 octane on the AKI scale is about equivilent to 100 octane in 1954. Your Chevy will run MUCH better on 87 (or less, if you can find it) octane from a name brand station.

Alternately, you could disassemble the engine, install 14:1 compression pistons, a full race camshaft, etc., etc., etc. and just maybe the engine could use the 93 octane.

Put the savings in a piggy bank, and apply toward a Carter carb.

Good luck.

Jon

Good advice, Jon. The speedway in Nashville where I built engines for several car owners mandated that we buy our gas ONLY from the pump in the pit area, which was Pure Firebird racing gas- - - -105 Octane! Then they limited us to 9.5:1 compression engines in the class we ran- - - - -"Street Stock"- - - -which made the engines run really lousy on the $5.00 a gallon gas the track was selling. I'd show up with half a tank or a little more of the cheapest regular gas I could find, and only buy a few gallons of track gas. My engines had an annoying habit of outrunning everybody else! (Yes, I was cheating like Smokey Yunick, but the tech inspectors usually didn't catch me!)
Jerry

Matt,

I use ethanol 87 octane in every one of my vehicles except those with high compression engines like the Cadillac and the Toronado. It works just fine. Your engine (and mine) has a compression ratio akin to a Briggs & Stratton lawn mower. I've never suffered an ethanol related fuel problem in any of my vehicles. That being said, I drive my cars all the time and gas doesn't get a chance to go bad.

You might not be aware that pure ethanol has a higher octane rating than pure gasoline and is used to boost the octane rating on premium fuels. It isn't 10% so it isn't labeled as such.

Anyway, my truck had a FrankenCarter (various year Jeep spec parts) on it when it came to me and it ran pretty good until it didn't. I purchased a rebuildable Carter core and it has run flawlessly ever since. The money spent today on a proper carburetor now is long forgotten when you're driving down the road without any fuel problems. Close to 7000 miles in the last two years. I even commute in rush hour traffic and the truck runs like a noisy sewing machine.

If you want to raise the octane rating a little to be able to advance the ignition timing, and still be able to run 87 octane gas, add 5% Diesel fuel to the mix- - - -1 gallon of Diesel to 19 gallons of gas. It raises the specific gravity of the fuel, slows down the burn rate, and allows the initial timing to be advanced an extra 5 degrees or so without getting detonation. It's a trick we used on the round track cars when we ran straight pump gas with blue machinists' Dykem added to mimic the blue-dyed gas the track sold at an outrageous markup.
Jerry

Your race track cheating stories crack me up, Jerry.

In the immortal words of Smokey Yunick- - - - -"It ain't cheatin' unless ya get caught!"
LOL!
Jerry

"GO FAST- - - - -TURN LEFT!" Everything else you do must be done with that end in sight! Another adage that a successful racer needs to remember- - - -"Nobody wins a race on the first lap!"
Jerry

Thanks Jon! I had a guy flatten it back out for me 2 years ago but not with a gas grill. That sounds interesting! I'm going to adjust the idle mixture screw in as much as I can to see what happens. I assume turning it in more will reduce the amount fuel. I was told if I can get it all the way in and it still idles then I must have the float drop too high.

Otto,

Thanks for the advice. I had a few guys around town tell me I should use the non-ethanol because vehicles back then were not made to burn gas with ethanol. I may advance the timing 10 degrees and see if that helps any.

Jerry,

Thanks for the advice. I had a guy flatten back out the warped casting 2 years ago. I may have to look into the Carter. You got a link for one or any recommendations? Truck is 1952 Chevy 1/2 Ton but running a 54 235 engine on a 6 volt system.

"Carb King" (Jon) is our resident guru on carburetors in general, and Carter in particular. He has posted a pretty comprehensive list of Carter model numbers that are direct replacements for 235 engines that came from the factory with Rochesters. When GM stopped buying Carter carbs for new Chevy engines in the late 1940s or early 50s, and started making their own carbs, the CEO of Carter vowed to sell a million replacement carbs for the OEM Rochesters. It took a few years to actually accomplish that goal, but when the one millionth Carter replacement carb for Chevy engines came off the assembly line, it got gold plated and presented to the CEO of GM as a "GOTCHA!" move!

https://www.stovebolt.com/ubbthread...dentification-carter-yf.html#Post1531510

It looks like a Carter YF #2101 carb is a direct replacement for a 1954 235 engine according to the above list. Have fun!
Jerry

Matt,

Believe me, I'm no fan of ethanol but as long as you don't let the stuff sit in the fuel tank for long periods of time, you won't have problems with it.

Remember when they took lead out of gasoline? Everybody swore you had to put a lead substitute in your tank or your exhaust valves would burn themselves up. Never mind that AMOCO had been selling premium unleaded fuel since 1923.

When whale oil was banned from use as a friction modifier for ATF, old timers swore that transmissions would never shift right again.

Nobody likes change but it isn't always as grim as it seems at first.

The float bowl gasket will show if there is a warp causing a leak. I think a problem could also be just old and worn power piston and bore. Yeah what a bad design, what were they thinking.
Then there is the vacuum supply issue at the flange.

WOW Jerry! That is an incredible story and great history to learn as a backstory to the Rochester and Carter carbs! Made me laugh out loud. I wonder who has that gold plated 1 millionth Carter carb. Should be in a museum somewhere on display!

Thanks again Otto. How long is too long to let it sit? I usually park my truck for 2 or 3 months during winter and don't mess with it too much during that time.

Adding a healthy dose of Sea Foam to the gas and driving a few miles before storage is a good idea. It helps keep carb gaskets from drying out and/or that white chalky residue that "deathanol" causes from forming. I do that to my Harley every year when the weather gets too bad to ride it regularly.
Jerry

I've had decent luck with a product named StaBil 360. You add it to ethanol laced gasoline and it keeps rubber parts from deteriorating and the gas from going bad. Actually it is probably most noticeable in a lawn mower because you only have one cylinder so starting can be more problematic if you have weak gas. About 3 years ago I took 3 small jars and put gas into them...one month apart. I posted the results here but as I recall they were in with another post. What I learned was just sitting for one month made the gas turn sort of orange and smoke a lot when burned. 2 months caused it to be a little worse and 3 months made it pretty honey-colored and it really smoked a lot when burned.

The Carter carb may be better than the Roch. but the Roch. is not all that bad. There are many thousands of them still out there running around.
There is no doubt it is running way too rich. It is easy to remove the air horn & check it out. Make sure the power piston is free to go up & down. You need a clear vacuum passage from the intake to the piston. Like has been said previously check the float level. Make sure the float does not have gas in the pontoons. The float drop is not material to this problem but make sure it is correct.
You will need to clean the plugs to get it running.
Turn the idle mixture screw about 2 turns open, start the engine & with a slow idle slowly turn it in till the engine starts slowing down. Then back it out till it speeds back up. That should be the perfect setting.

George

RE ethanol: Over time it will swell neoprene hoses and other plastic parts. When I drove a tanker we had no end of problems with hose gaskets when hauling ethanol. I always carried a complete spare set. Leaking 4-inch hoses are not fun.

The only ethanol related problem I've experienced since ~2007, when ethanol was mandated by the Feds for metro Atlanta, was when it stretched out the diaphragm of the original 1956 fuel pump in my Cadillac. That happened 2 months after introduction of corn juice.

Since then, all new parts for my vehicles seem to have been manufactured with ethanol compliant rubber. No other vehicles have suffered ethanol problems and they virtually all use it, all the time. It's quite difficult to find non ethanol gas around here.

George,

Thanks for the advice. I cleaned the plugs, put on new wires going from coil to distributor and regulator, and advanced the timing 5 degrees by using the octane selector. Fired right up with the choke pulled. I let it run a minute with choke pulled then pushed it back in all the way. It was idling too high so I adjusted the idle mixture screw and throttle idle screw till I got the idle mixture screw turned in as far as I could without until it starting slowing down then backed it out a quarter turn. I revved it up several times and it slowed right back down to idle and idled smooth for 45 minutes with me revving it up several times throughout. After all that, I cut it off then cranked it right back two or three times. I was feeling pretty good. However, when I pulled the spark plugs they were covered in black soot again (not wet, just black carbon fouling). So.... apparently it is still running too rich. I feel like my only next step is to get a lower size metering jet. Any further thoughts????

Are you able to use a timing light to see what exactly your timing is currently set at?

I wouldn’t draw too many conclusions after 45 minutes of idling. It would be pretty normal for 235 plugs to look sooty following that. You’d have to go for a drive and see how it behaves.

Pastor Matt, if you can find a tachometer (could be part of an old style motor analyzer or something similar), get your idle speed set for around 475 to 500 rpm first. Then set your idle mixture. If you have your idle mixture screw out too far you may think it is good but this can fool you. Too much and you'll just run too rich at idle. If you can find a simple timing light (you probably can borrow one of each of these from an O'Reilly's or AutoZone), check both using those. If you can find a vacuum gauge, that can reveal all sorts of things, also. As others have said idling rich is not uncommon. You could change the main jet size. For us that is a mystery at this point. Please let us know what size you currently have.

JW51,

I had a friend of mine tell me the same. I'll take it out for a drive later this week and see what happens.

Otto,

Timing is pretty close. My timing light doesn't flash very brightly. I probably need a better one. But I painted the BB white and it does appear in the bell housing window when the light flashes with timing light on number one plug. I can't quite make out if the BB is appearing right on the pointer, before or after. But it is appearing within that window. I will probably borrow a better timing light from a buddy.

Thanks.

How did you "clean the plugs"? Unless you have some sort of abrasive blaster, the areas that need to be cleaned can't be reached effectively. Back in ther dark ages (1950s) Champion spark plug company sold a sandblasting machine that used high pressure air and fine grit abrasive to blow away carbon deposits from the plug shell and the porcelain insulator. I haven's seen one of those machines in use in at least the past 40 years. If you happen to have access to a a glass bead blasting cabinet, it can be used to accomplish the cleaning procedure. Back when I was crew chief on a racing team, we kept several sets of spark plugs on hand, cleaned them up every week, and ran the same 40 or 50 plugs all season. It was not uncommon to go through 3 or 4 sets of plugs while adjusting the carburetor mixture to atmospheric conditions during practice before a night's racing.
Jerry

Jon G,

That is good advice. I really didn't realize that it could idle rich like that. Mike's Carburetor site said mentions that you can test the jet size by "operating the vehicle for 20 minutes at sustained speeds." Then I would pull the plugs and check for carbon fouling. I think I just read that wrong and thought I could idle it for a while and get it warmed up. My grandfather had run the truck for years and I doubt he ever changed out the jet size.

I have a friend in our church who is much smarter than I am when it comes to all this. He is going to come by with the tachometer, timing light, and vacuum gauge and help me check all that more precisely.

Thanks for your help!