Rochester B, BC, BV Carburetor

Rochester B, BC, BV Technical Information Here

 

Hi Mike, just talked to you on the phone. Did the rebuild, but now I need to choke the carb in order for it to start, no matter how hot the system is. What can I do to fix this. Its a manual choke. 235 1953 pickup. Thanks John

A couple of things come to mind.

Gas boils at a lower point now and I’m hearing a lot of complaints about peculation problems, especially in the hot weather. You get the engine hot, then when you turn the engine off, the gas starts to boil out of the carburetor. A smell of fuel after stopping might be a hint.

Ethanol is one of the bigger problems. Not sure if it will help the low boiling point, but StarTron will help with ethanol problems.

Unfortunately there isn’t a real good solution to the percolation problem. Some have added an electric fuel pump, which will fill the bowl when the key is turned on. Anything you can do to keep the fuel cooler would be a plus.

You may also be having a low fuel problem not attributal to percolation.This would also cause poor operation other than starting the engine.

  • It may be that the float is too low. Adjust to specifications.
  • The fuel pump isn’t putting out enough pressure. Test the pressure.
  • Make sure all of the passages are cleaned out. This must be done by physically running wire down the holes. Ethanol leaves deposits behind that cleaners can’t get out.

From my friend Jeff:

If he didn’t get the accel. pump to work, then it won’t prime . . . although it really should start without touching the gas unless it has sat for several hours without running.  In reality, choking generally tends to make heat soak problems worse, not better — the engine is already flooded, after all.
Could he have a vacuum leak?  Is he running bad gas?  These will also cause a hot carb to need choking.
Jeff

22 thoughts on “Rochester B, BC, BV Carburetor

  1. Have a Cherolet 3600 with Rochester B. Have installed rebuilt fuel pump, new points/condenser, fuel filter, and have run non-ethanol fuel since it became available. In morning. engine will start and then stop. Cannot get to re-fire without priming. truck then cranks without hesitation for remainder of day. Next day same thing. Forgot to mention complete carb overhaul.
    Do you have any suggestions?

    • This could be caused by percolation: http://www.carburetor-parts.com/Percolation_ep_1870.html
      Also the gas tank may not be vented.
      The fuel pump might be defective. New fuel pumps are more suspect than old ones because they aren’t great quality these days.
      To test for things prior to the gas tank: After stopping for the night, disconnect the fuel line from the carburetor. In the AM hook it back up. If it starts then you know it’s before the carburetor.
      Off chance the gas is leaking out of the bottom of the carburetor. Take the carb off, full of fuel and set it on a paper towel. Come back later to see if any gas leaked out.

      I’ll try to think of some other things.

  2. I figured out my problem Mike…….persistence pays off!
    When I raised the float to carry more gas the problem got much worse so the hand writing was on the wall so I went the other direction and set the float lever so its parallel with the cover face.
    I SHOULD have done that in the first place as I’ve never seen a carb that wasn’t set up that way.
    Tickling the foot feed makes sense now.
    It was to give it air…….not fuel.

    • I don’t think the number you gave me is the carburetor number. The carburetor number location is explained on this page and if the number is not present, then watch the video at the top of this page about how to select the correct kit. Just a little bit of homework will get you the correct carburetor kit.

      Thanks
      Mike

  3. hi ..
    I have a 235 in a 56 chevy pickup. It has the manual choke 1 barrel with the oil bath. I changed it out for a period style foam element filter. Runs fine at idle but coughs and splutters, misses and backfires through the carb when trying to get moving. Do i need to rejet it to make it run properly and if so what do you suggest? Also …what threads do the fuel fittings use?

    Any advice welcome

    Rory.

    • Not likely that the coughing is due to jets. You didn’t indicate if you just rebuilt the carb or not. If not, then start there. Backfires can be caused by a lot of things. Valves, electrical as well as the carburetor.

  4. I have a 1964 chevy c10 with a 292 engine – The carburetor is a Rochester manual choke that has been rebuilt sometime before I owned the truck – It appears to me that the top half of the carburetor has been replaced, the tag is missing so I can’t determine what I have – The main pump is round but I’m not sure if the pump seal is removable – I don’t have any problem doing the rebuild myself just need help to figure out what kit and parts to buy – Any help is welcome.

  5. Hi there Mike. I have a canadian pontiac with a factory 261 engine with a 2 spd. I am trying to get it through aircare. I rebuilt the carb and it passes on the idle but way to rich on the driving. the carb is perfectly set up. the only other thing is the main jet. my tag number on the carb is 7020080. was wondering if you could tell me the factory main jet size ? i see i can buy main jets from you so i am going to try and downsize it for the test. I see i can buy jets from you. thanks jeff

  6. I have the same basic carb you rebuilt in the video. I have rebuilt it a few times but I can’t seem to get it to squirt fuel into the intake when I pump the throttle. I know the float bowl has fuel in it and I adjusted the floats as required. Any thoughts?

    Thank you for your time

  7. MY 235 IL6 HAS A “B” MODEL SINGLE BARREL W/MANUEL CHOKE. RUNS GOOD BUT HE CARB HAS DEVELOPED A FLOODING FUEL AT IDLE AND OVER RUN AT THE THROTTLE PLATE SHAFT AT SHUT DOWN. I SOLVE THE PROBLEM BY RUNNING ABOUT A HALF CUP OF COLD WATER OVER THE BOWL AND THROTTLE SHAFT AREA AND THE FUEL RUN OVER STOPS. WOULDYOU HAVE ANY IDEA WHAT IS GOING ON? I HAVE READJUSTED THIS CARB OVER AND OVER SEVERAL HUNDRED TIMES AND IT CONTINUES.

    • A couple of things come to mind. One is a peculation problem. This occurs when the engine gets hot, then at shut down, the temperature jumps up and the fuel boils out of the carburetor. Gas these days have a lower boiling point. I don’t know what the weather is like where you are, but over the summer months we hear about this problem a lot. If this is the problem, then see what you can do to cool down the fuel inlet line.

      The other possibility is that the carburetor is simply flooding over due to too much fuel. Could be a bad float, too much pressure from the fuel pump, etc.

  8. Great video. Thanks. I’m ready to order a kit but my Rochester “B” has slack in the throttle shaft. The bore on the base measures about 0.31. A 0.31 rod will pass through with no slack. The throttle shaft measurement varies from 0.302 to 0.308. Should I install a new shaft and install bushings or just a new shaft? Are you able to supply new shafts? Thanks for the advice.

    • Shafts are not available for the B and I can’t tell by your measurements if it is too loose. I have to wiggle one back and forth, or spray some carb cleaner around the shaft when idling. If the rpm picks up, or the idle smooth out, then it will need to be re-bushed, or replaced.

  9. on this web sight you have a 3 part video rebuilding a rochester “b” 1 barrel carb .(manual choke) just like mine .My engine number shows its a 54 year engine. My carb looks just like your’s in the video. I need a rebuild kit for it but cant find it on your web sight.Can you give me the price and what number kit it is. The only number I find on the carb is at the base hard to make out the 4th and 5th number but looks like 7004022.Thank you much.

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