The Stovebolt Site Forums The Shop Area Engine Shop Tuning Rochester B

I had the carb rebuilt. They told me that they tuned it and it should be plug and play.

Once i got the engine warmed up and tried to take around the block. It idled well, but once I put it in gear it sputtered. I couldn't get it to run much unless I closed the choke half way.

I got it back and adjusted the idle to 600, down from 1000 with the choke open. Drove it again, same problem.

I screwed in the fuel mix screw all the way, backed it out 1.5 turns. From there if I back it out any further the RPMs drop. If I turn it in, the RPMs drop. As I understand that is the ideal spot.

I tried driving it again, it did a little better, but as I got a little more speed on it and shifted into second it back fired twice, blowing the air cleaner into the street. I ran it over

Now what? I don't seem to have a mark on the flywheel to adjust the timing, but before I had the carb rebuilt it, timing wasn't an issue.

Any other ideas?

Send a private message to HotRodLincoln. I have 2 Rochester Bs but I have been having issues for a year and I would not be any help.

Turn that mixture screw until you wear the threads out- - - -it doesn't change a thing except the idle mixture. Your "rebuilder" shouldn't be working on anything more complex than a hand-cranked can opener if he can't make a Rochester B run at least reasonably well. Even at its best, a Rochester can't hold a candle for a Carter carb to go by!
Jerry

I know this is a thread about a Rochester B, and I think everyone knows my opinion about them But not sure that is the culprit here. Wouldn't want the B to get unwarranted abuse

However, a backfire through the carburetor strong enough to blow off the air cleaner is virtually never the fault of the carburetor. Virtually always valve issues or ignition. Locate top dead center, then make your timing mark, and time according to specifications.

Unless you have done one recently, a compression test would be in order to check for a sticky or burned intake valve.

If you think about it; you get a backfire through the carburetor WHEN there is fire in a cylinder AND an intake valve is open.

Jon.

I don't know if the wrong carburetor base gasket will cause the air cleaner to blow off, but it is an easy thing to check.
There is a small hole at the bottom of the carburetor base which corresponds with a small hole in the intake. The wrong base gasket will block the hole and bad things happen.
Carl

Agree completely. Check your firing order vs dizzy cap wiring. Check Timing as said, ASAP. I hope you don't have one of those organ grinder monkey hat air cleaners. If it idles well, I wonder if that means valves are OK? Not sure. Is there a potato or rat stuck in the exhaust pipe?
Had to close the choke..hmmmmmmmm? Running lean or it thinks it's running lean. Runs good, gets carb rebuilt, runs bad. Provided you are not forgetting something else you did, no matter how slight, it points to the carb. But symptoms aren't right, as Jon says.
I say you took the dizzy out and didn't put back correctly.

Sounds to me like the float level is too low. Can you take the carb back to the "rebuilder". Or with a little help from the guys here you could check it yourself.
You could just advance the timing a little using the Octane selector & see what happens. It has a scale on it so it is easy to see what you changed & go back if necessary
I like to adjust the idle mixture screw about 1/2 turn open from the point where it starts to slow down.

Georgeeeeee

The Rochester B models have been vilified greatly around here and in many cases they're 100% deserving of the complaints. But I doubt this backfiring is due to the Rochester. I believe Jon got it right. Somehow fire is occurring at the same time an intake valve is open and that's what you need to stop. I'm not certain why running it overly rich would make it run any better. Many Rochesters run overly rich naturally due to their basic design.

You can check manifold vacuum (not ported vacuum) at idle for a quick view of things. Adjust the distributor so as to (more or less) maximize it. Once you've done that see if the vacuum needle is steady or fluctuating and go from there. If vacuum drops in an intermittent fashion at idle, one (or more) valves could be sticking, hanging open or maybe burned. If vacuum is steady while idling but lower than normal, your timing may be retarded. If it is higher than you think it should be at idle, your timing may be overly advanced. See what you see and let us know. Good luck. Sorry you ran over your air cleaner.

It may be better to help them fix what they have, what they want to use. It's easy (I am guilty at times) to say, "just switch to something else".
At times it's better to switch if you can't fix it.
I realize the vilification in this case are the B models (284). It represents a small section of all the Rochester carbs. It just so happens, on this site, our motors used a lot of them. I don't think the pros hate the whole line of Rochesters. I can not dispute the many who say the YF is fool proof. I think CarbKing Jon just likes them because they don't need a tag

I ran a B on my '52 for years without issue. I even rebuilt it with out having a tab. I will say though, that I prefer the Carter Y that I am running now. I do not have the notorious dead spot on acceleration which has been mentioned by many to be common to the B.
There is not much to lose by trying to make what you have work, tag or not. Kits are cheap, rebuilding a B is easy. If it doesn't work, find a correct Carter Y.
Carl

Well, I agree with Bartamos. It's so easy to say "replace the Rochester B with something else". Well does the new carb fit w/o an adapter? Do you need to change the throttle linkage? Change fuel and vacuum lines? Change air cleaner? Change choke cable or change to automatic choke? Kick down if you have an automatic?

Seems like a opening a can of worms.

Finally, is the new carb you bought a lemon?

Seems easier to rebuild the old carb.

OP: take advice in the above posts above. I would start with checking timing and vacuum.

To hark back to the backfiring issue, I still don't think the carburetor is the root problem, but since the discussion seems to have devolved into comments about helping fix the Rochester B and BC models that people are using let me hark back a few months.

All the work I did late summer/fall of 2018 was to help anyone inclined to do their own work to see and understand more about why I believe their carburetors AREN'T working better. I've kept an open mind and haven't dwelt on all the negatives but even with a very open mind I think anyone will come to decide these are examples of myopic engineering and possibly worse than that most of them have gone through the "rebuilder's parts mixmaster" enough times by now that they're mutts at best. Little Frankencarburetors. Does anyone remember that one of the carbs I opened up was missing the pick-up tube? I suspect some rebuilder knocked it off, but it should be obvious the thing never worked right again. At least until I showed how to make a new one. An example of "professional rebuilding" and how you want to spend your money? Well, it was an example of something.

The project is still ongoing, but stalled until spring. Even though I have some doubts about whether these can successfully be used with ethanol gas, I'm still keeping an open mind and still looking for answers, alterations, anything that might help. But I gotta tell you I'm starting to feel like a neighbor we had who told the same old joke time after time after time.