The Stovebolt Site Forums The Shop Area Engine Shop Rochester B jet size for early 216

Somebody put a Rochester B from the later 216s on my 1948 216.
The jet size is #52 right now and it's too rich.

What is the correct jet size for a 1948 216 on a Rochester B?

Wish it still had the original Carter W-1...

Make sure you have the proper bottom gasket before you worry about the jet size. You may just have a power valve that is stuck open. There needs to be a notch to allow for the hole in the base of the carb to see manifold vacuum.

Gasket is correct and the hole on the carbbase is free.

Took the whole carb apart yesterday and everything is good, as it was recently rebuilt.

I just spoke to my local carb source for parts - he thought I should go with a #49 jet.
Ordered one and will go from there.

I just like to keep driving the original 216 until my 261 is ready....

My first 216 experience. Having a good time, getting it to run smoothly again.

The 52 sounds about right. Did you check the float for having gasoline in it? You might try setting the float level a little lower than specs.

Sure thing - these monojet carbs are no rocket science.
Float is good. I set it to spec and subtracted 1/32 because of modern fuel.

I wait for the smaller jet and play with the float level again, if that wasn't it.

But it really feels like too much fuel in the mix.
If you accelerate slowly and carefully, the engine goes up in rpm evenly.
If you push harder on the gas, it just gets too much fuel and you can smell it.
The power valve and spring is also OK.
Maybe the earlier Rochester Bs had smaller passages and different power valve sizes..?

Idle mix screw also needs to be turned in more than normal.
I'm thinking - too big a jet.


Typical Rochester B(S)....
I have had experimented with several Rochester Bs and different bore/jet size over the years on my truck and the late 235.
I learened to stay away from them and rather go with Carters or Strombergs.

I just want to cruise around town while I'm waiting for my new engine.

The Rochester Catalog
lists 51, 52.

If it is running too rich, check the top and center castings for warpage. Warpage can cause an internal vacuum leak, causing the power valve to be open all of the time. The Rochester B is infamous for this issue.

And even though you are dealing with the Rochester B, remember that 93 percent (at least with real carburetors ) of all carburetor problems are ignition!!!!! The perfect mixture, combined with a weak ignition will generally run rich and blow black smoke. Items often causing issues are old or incorrect spark plug wires, and old are generic (thus incorrect) coils.

If it is the carburetor, one other possible issue is the fuel valve. The original fuel valve was a smaller orifice than comes in many modern repair kits. This can cause the fuel level in the bowl to be too high (as can too much pressure from the fuel pump).

And if everything else fails, remember the ABC's of carburetion (A)lways (B)uy (C)arter!

Jon.

Just reread the entire thread. Your comment that the idle mixture control screw must be turned in further than normal indicates issues OTHER than too large a main jet, as fuel for this circuit is NOT dependent on the main jet. See my previous post.

Jon.

That's my experience with the B's that I have played with, too.

The differance between a 49 and a 52 jet is too small for you to notice that kind of a drivability problem. Also, under acceleration, the power circuit is much more of a dominant fuel provider. The main jet really only affects cruise on the "b", really just plug fouling and fuel economy.

I'll bet you either need a new float (they get leaky, even the brass ones), or a level adjustment. I fought my B until I got that problem fixed, and its been reliable for 4 years since- haven't had to touch it.

I like to chamfer the edge of the fuel valve that comes with the kit by placing one of the old steel balls from the rebuild kit in it and giving it a light whack with a punch and hammer. This gives the viton seat of the needle a bit more surface area to seal and keeps it from sticking. It means you have to adjust the float level by checking the amount of gasoline in the bowl instead of measuring it, but it seems to work well.

I learned that trick from messing with the fussy Keihin carbs on my motorcycle that have floats that are too small for the design.

Thanks for the great tips and the link.
I was looking for that page, but couldn't find it. There are so many links on the old online manual site now.

Ignition has all new parts, just done.
I was wrong about the mix screw - it's 1-1/2 turns out, which seems OK.

Thanks for all the info. Looks like the jet size is correct.
Definetly the typical Rochester warpage on this one.
I get way too much leakage around the gasket after driving around the block.

I will lower the float in small steps until at least the leaking stops.
If the engine responds better after that as well, that's maybe all there was to it...
I find out later this afternoon.
Thanks again for all the helpful tips and info.

Finally had time this weekend to play some more with the carburetor and the timing on the old 216.

Lowered the float to 1-11/32 (stock 1-9/32) and found the sweet spot on the timing, which as usual is quiet a bit more advanced than the stock setting.
Got everything running pretty well.
Still got one issue that seems to be carb related.

I can punch the gas and the engine gets the boost and responds normal in any gear, without hesitation.

However I always have to be careful not to leave the carb throttle open too far.
The engine accelerates but eventually reaches a point where it starts sputtering like it gets too much fuel in the mix.
I have to let of the gas slightly and the engine recovers again.
If I want more rpm, I have to VERY gradually open the throttle and not get 'ahead' of the engine with the gas pedal, so it doesn't start sputtering again.

If I do that, the engine goes up evenly with the rpm and deceleration in gear is also no problem without any sounds.

I guess, I will lower the float another 32nd and see what happens.

Anybody had something like this before and was able to cure it?

I wouldn,t go any lower with the float. It could be to much spark advance. Some engines if you get too much advance will run rough at part throttle. Try it with the vacuum line to the advance disconnected.

Lowering the float another 32nd helped but not much.
Advance is as good as it gets right now. More or less gives more sputtering when the gas pedal is pushed more.

Could be just an old motor - it has never been rebuilt. It does burn a little oil but less each time I drive.
When I got it, it had about 2 quarts too much above the max. fill line....