air filter

Dave here,

I'm embarrased to ask this but can't find anything searching the archives and must be missing the obvious. I have a 1954 235 in my 49 1/2 ton, carb looks like a 54+ rodchester with an automatic choke.

The truck came with a very small aftermarket air filter, which quickly gets so dirty that the truck runs way too rich even when I lean it as much as possible (excuse my grammer).

The carb throat measures 2 3/8" od while the aftermarker air filter canisters in the local flops all measure 2 5/8" od. I want to put in a larger air filter with more surface area, what are you guys using?

 

Dave, i don't even know where mine is right now, much less what kind it is! i've got both the dry type and oil bath (somewhere). Hopefully before long, i'll have to make that choice. I'll probably go with the dry type because i hate the mess of the oil bath filters.

 

I have a 55 235 in my 51 3100, with the same carb. I have a 2 1/2" tall 4" wide chrome air cleaner from autozoo, It is 2 5/8" but it came with a plastic insert that makes it 2 3/8". I've never had any problems with mine running rich.

Henry Allen

 

Thanks Henry. It sounds like we may be using the same chrome, vented aftermarket air filter. I'll stop by autozone to see if I can pick something bigger up with the spacer/reducer.

If I take the filter off the truck runs great, but its really sputtering (black smoke, wet tailpipe, black sote on the sparkplugs) at low rpm's even with a new air filter. It may be that the float needs adjusting, but it seems that I'm constantly working on this carb as it can't seem to stay adjusted, and I think I see a carter carb in my future! I've tried turning the fuel mixture screw all the way end, but still runs rich (or at least, idles rich).

 

Dave ;

Sounds like your float level may be off a bit . when measuring the float height
hold the carby so the inlet is facing _up_ and the float hangs , this way there's no heavy pressure on it to mislead you in the height , you do know to have the air horn gasket in place when setting float height ? .

Also , if you're not running any fuel filter , tiny bits of crud will usually stick on the tip of the float needle , allowing it to flood a bit , this causes rich running too .

I'm sure you know that before you can even touch the carby , it is _imperative_ to properly adjust the valves , dwell and ignition timing as you cannot possibly adjust the carby properly with tight valves and timing drifted.

It is possible the road draft tube is clogged up with sludge , this will cause too much smoke and oil vapor to puff out the oil filler cap and then get sucked into the air filter , clogging it .

Lastly , oil bath air filters are the very best and once properly cleaned out and set up . are simple to maintain . soak the gauze element part with several cans of engine de-greaser and allow to sit over night then rinse clean , you'll be amazed at how much black silty stuff will rinse out . allow to drip dry (again may take a few days) then re-fill to the mark with fresh _ATF_
as this will make the oil bath typ of air filter self cleaning ~ you'll soon see lots and lots of silt or sludge in the oil cup , just wipe it out and re-fill with ATF each time , your engine will love you for it .

Remember , the tiny cute little chrome paper element air filters are -way- too small for the needs of your engine ~ think of you engine as a large air pump (that's what is it after all) , it pumps massive CFM's of air through it every few minutes so you need a large , efficient filter else you're going to have problems .

 

Put in a 9 inch air filter and problem resolved. However, the carb is leaking gas in a steady stream out somewhere on the driver's side (can't see exactly where the hole is). Is this a consequence of the float being too high? When adjusted, how high is the float supposed to be?

In any event, the carb clearly needs to be rebuilt.

 

My Rochester Runneth Over

A ' steady stream ' ? this is bad , serious dribbles maybe but no streams .

The venerable Rochester ' B ' series carby is dead simple and can usually be overhauled without removing the base from the engine . just lift the air horn carefully off the bowl after undoing throttle & choke cables , inlet fuel line .

Look at the fuel level in the float bowl , it should be 1/4" or so below the upper edge , if it's up to the edge , it's flooding , if the floats are not sunken (shake to hear/feel fuel inside) there's spooge on the float needle , a very common problem -OR- perhaps the DPO wasn't carefull when re-assenblng the air horn to the bowl and put pressure on the floats , this raises the float height too much and promotes flooding / leaking .

just replace the float needle and seat then clean out all the dirt and crud from the float bowl , if you remove the power valve , it'll have longitudale scratches in it , polish them out with Brasso or other brass polish , do not use sand paper ! the power valve needle should easily slide up and down with finger pressure once it's assembled , often they're bent off to one side so the tip of the needle doesn't depress the steel ball when released ,it is a simple thing to gantly bend it back then twirl it to ensure it'll work in all positions as it tends to rotate as it's working .

These carbies tend to seep and dribble from the seam no matter what you do
~ I've _glued_ a few to-gether to end cutomer complaints but then you'll have to soak it in a tub of alcohol to get it apart next time .

 

Thanks for the details Nate, I'll take the carb off and check the float (may not get to it until next weekend). The rochester carb has always "dribbled" a little, but the last two times I watched it was dribbling a steady stream while the truck was running (and I was remembering my old high school chemistry teaching saying "fire requires three things; fuel, air, and a spark!"). Kinda scary watching gas hit your hot exhaust manifold and turn to vapor. Needless to say I'm not driving it until a) the carter carb I ordered arrives or b) I rebuild the rochester.

 

Fire Safety & Carbies

Amazingly , it's quite unlikely to bust into flames as the sparks are on the other side of the engine and a hot exhaust manifold isn't going to ignite dripping gasoline...

By all means , do replace the Rottenchester with a world beater C@rter YF 2600 but just for grins and to show your self you can do it , I'd say take just the air horn off and repair that leaky old R.P.O.C. (Rochester Piece Of Crap)
as NO new parts should be needed , just cleaning and carefull re-use of the old gasket .

FWIW , Chevy Duty and others all sell top quality rebuilt Rochester carbies , rebuilt by....CARTER of all paople but they do a good job and re-bush the throttle shaft so there's no air leaks screwing up a good idle .

 

okay, the carter carb is on back order and I took the plunge and rebuilt the rochester carb. Actually I took parts of the current rochester with auto choke, a manual choke rochester that i got when I bought an intake manifold from ebay (lord knows what it was originally on, I had to modify the linkage) and a rochester rebuild kit to make one rebuilt rochester with a manual choke. I have the factory manual and the one barrel carb is so straight forward that its east to see how it works.

Anyway, i carefully cleaned all parts, replaced parts as appropriate, put back on truck, added gas lines, linkages, etc and tightened everything down.

The new manual choke worked perfectly. I turned the engine over and fired it up. It ran fine but when I looked under the hood, it appeared to be leaking gas at a fast drip out of the hole for the "pump plunger assembly" and was rapidly seeping gas from a number of other spots. In less than 30 secs there was pool of gas running down the intake manifold.

Arrgh! While its been many, many years, I was a fair shade tree mechanic in the old days. I rebuilt an engine, transmission, etc so this isn't my first time with a wrench in my hand. I rechecked all the bolts, screws, etc and everything is tight (I had gradually tightened everything down in a "crisscross" pattern originally). I checked the float levels, clean out all passages with compressed air, etc.

What in the world is going wrong? There is no fuel leaking out of any fuel line connection, but just about every gasket is leaking. I did not use any type of gasket sealant.

 

Most imortant question :
Did you install an inlet fuel filter (I can see the answer is no) ? .

A tiny bit of dirt or spooge can lodge in the float valve's needle and cause just this you're describing ~ it sounds like flooding to me and I've had it happen many times , this is why I won't operate _any_ engine without a see through fuel filter on the carby inlet .

ANY engine .

I got tired of the poor quality dirty American fuel always causing me flooding problems about 30 years ago , no further problems since adding an inlet filter to each and every engine I own or work on....

DO NOT overtighten the four air horn screws ans this will cause it to leak worse...

 

Hi Nate,

Although you can't see it in the picture, there is a Fram G-2 fuel filter in the fuel line. I've replaced it twice now since last Nov, including just before this carb rebuild, although currently the gas looks clean in the filter.

I thought about tightening the screws too much causing warpage, especially when there are relatively few pressure points/screws. That's why I like torque wrenches and torque specs, you know exactly how tight you need to go and when you're there!

Unfortunately, it appears this carb (just like the last one) has its major leaks in place(s) that don't involve replaceable gaskets and therefore isn't repairable. I don't know enough about the carb to understand exactly why and how this is happening, but I can see it. If it was just a gasket leak I would go back and rebuild with some homemade gaskets, etc.

Any chance that the fuel pressure is too high and a pressure regulator would help this problem?

In any event, I would move on to a Carter carb but its backordered. The local NAPA doesn't offer one at all.

I'm looking at a holley-webber 5200 with adapters through Langdons, but the chokes are automatic. I'll have to explore the feasability of retrofitting it to a manual choke since that's what I really want.

I'm a function before style type of guy, I'd like the truck to stay as stock as possible, but first and foremost it has to be driveable! Any other suggestions for carburetors?

Thanks

 

O.K. , IIRC the Fram F-2 is a very small filter , designed for old VW Beetles .

I'd swap in a WIX/NAPA 3001 filter .

One place these things like to internally leak is : at the flat ring gasket underneath the inlet valve _body_ ~ you did use a gasket there didn't you ? .

I use a fiber or copper flat ring gasket there , some carby kits come with steel flat ring gaskets , not for use there as it won't seal and will cause flooding .

Your NAPA is incompetent , NAPA does a huge business in rebuilt carbies as many FLAPS don't anymore . I don't have my good NAPA books anymore as the dufus on night shift tossed them all out last year so no part nukbers , sorry 'bout that .

The Carter YF series carby is very good and a direct bolt up replacement -but- it's also very popular so look for a N.O.R.S. rebuilt over on E-pay , don't pay over $125.00 (EEK !) though as there'll be no warranty .

BEWARE of used Carter YF carbys ! pay scrap valuse and expect to need three to make one good one .

I have a few old Rottenchester 'B' series carby cores here ~ someday I should rebuild a matched pair for my Offy intake and then service and sell the rest off...

I think you should check for float seating by inverting the carby and sucking on the inlet , absolutely -NO- air is allowed to pass else it'll flood .

I've saved a few junker , warped carbys by carefully _glueing_ the air horn gasket to both air horn and float bowl , be aware this is a Hail Mary , last ditch plan as once it's buttoned up and dry , only soaking the entire carby in alcohol will ever get it back apart as I use Permatex 1-H , this is the fuel proof kind that hardens when it dries .

Do you have a Parts Plus auto parts dealer near you ? ('phone book) they should have listings for this carby , you have a 235 correct ? ask for a 1959 Chevy 1/2 ton pickup with stick shift carby , that'll get you the correct one .

DO NOT let your old carby out of your sight untill you have one on the truck and running well including passing the panic stop test as internal leaks will cause stalling when you screech to a rapid stop .

 

Thanks for the tip on the gas filter, I'll switch over.

I have to admit that I don't know what the "flat ring gasket underneath the inlet valve _body" is, I've reviewed the Carburetor layout in the shop manual but I'm still not sure. I think you might be referring to what the layout calls the "float needle, seat, gasket assy.

If that's so, I did put in a new gasket "but" the kit had several to choose from that were similar size/shape and perhaps I chose the wrong one. Looking over the "left over" gaskets, one is definitely a small flat round hard fiber gasket.

Today I started the truck again to check for leaks. Pulled choke out and truck started right up and continued idling. Jumped out quickly and looked for leaks, for several seconds everything looked okay. However, a steady stream of gas drops soon started quickly falling out of the driver's side of the carb, again it appears to be coming directly out of the outlet hole that the pump plunger assy goes up into.

As I understand it, in order for that to happen the carb interior would have to be flooding (just as you said above)to get high enough to pour down the top of this hole. I turned the engine off and gas continued to pour out the plunger assy hole for 4-5 more seconds and then stopped. Looking directly down the carb throat I could see gas still pouring down the throat from the main discharge nozzle. I would guess this confirms the interior is flooded and gas pours out until the level drops down to "normal"?

And the problem would be that either a) the flat ring gasket isn't sealing properly when the float needle shuts and gas is getting bye it and flooding the interior or b) the floats are sticking or adjusted too high so the float needle isn't closing soon enough, again resulting in flooding the interior ? (the floats appear to be almost new and in perfect condition)

And, if I stop the interior flooding the gas seeping out the air horn gasket is likely to be greatly reduced?

Curses, it all seems to be fitting into a pattern with the end result being the rochester isn't the @#$!!*&@! I was calling it and I may have to apologize to it! We'll find out this weekend unless you disagree with my conclusion.

Thanks Nate, no way would I have thought this through on my own.

Dave

 

My Rochester Runneth Over

Yeah well ;

You rebuild a few thousand of these and you learn some of the anomalies...

So , you're describing classic by-passing or slight flooding symptoms so I'd check that 1st. and go from there

Any time you have the air horn off and in your hand , it should be inverted and checked for proper float valve operation .

The flat ring gasket should fit fairily snugly around the float valve base's threads .

If you take it apart and realiaze there's -no- gasket there ~ that's your problem .

Have at it and see what happens as it's either this or the float needle isn't seating .

This Rochester 'B' series carby will still seep from the air horn gasket when it's all to the good , you can lower the float lever a bit to reduce this seepage but then of course , your engine will be running leaner.....

 

There is a flat ring gasket there that I didn't notice, and it is steel. When I put the second gasket on top there were obvious problems. I took the second gasket back off, checked the floats, put the carb back together and turned the engine over. Same flooding.

Now I'm thinking that old ring gasket has to go, to be replaced with a new fiber gasket. However, getting it out of the hole is turning into a real struggle. I'll keep trying, any secret tips on getting it out?

Dave

 

Steel ring causes flooding every time .

I just flip the air horn over the the steel ring drops into my hand....

Maybe a small magnet or dental pick from Harbor Freight store? .

 

Hmmmm. Steel ring gasket out, fiber ring gasket in, put together and still gas streaming out the pump plunger inlet. What the!!!

So, I go down to the junkyard and which only has three 1950's chevy trucks and get the one and only rochester carb there (I also got the wet air filter and carb hanger for the throttle cable which I needed anyway). Took the top off the carb, washed with carb cleaner and replaced springs and gaskets, blew compressed air through it, made sure floats were hanging at exactly 1 3/4 " to bottom with air horn gasket on, put everything back together and on truck.

Truck starts and gas streams out the pump plunger inletshaft!

I've now had three different tops on this bowl, and they're all leaking heavily out the pump plunger inlet shaft hole. The first top leaked before I ever touched it, the second I completely rebuilt, and the third I did minimal work on (that would seem to remove me as the cause of the leaking).

The interior of the carb must be flooding for the gas level to reach high enough to pour down the pump assymb shaft hole, but what could be happening to all three tops that's causing this to happen.

As far as I can see there is nothing in the bottom bowl itself that could be a factor in the flooding? There is only one valve/outlet and thats a vacumn outlet to the distributor?

By the way, one of the trucks (1 1/2 or 2 ton) had a carter carb, I thought I'd hit the motherload but the base was smaller than the rochester (i.e., the two mounting holes were closer together on the carter). I thought the carter was supposed to be a direct bolt-on?

Thanks
Dave

 

Nate, I should mention that I inverted the Carb and sucked on the gas intake inlet, absolutely no air. That means, I guess, that the flat ring gasket and float needle are capable of sealing properly.

Dave

 

O.K. , did you neglect to tell us there's an electric fuel pump on this truck ? . any more than about 3 # pressure and it'll flood no matter what .....

Time to put a 10 # pressure gauge in the fuel line , use a 'T' right at the carby and see what the running fuel pressure is .

The Carter you saw was prolly on a 216 , those have a narrower base .

I've seen 216 intake manifolds on 235's....

Surely it's gotta be fuel pressure or spooge in the fuel line between the filter and the carby inlet (this is why you're supposed to mount the fuel filter right at the carby) .

keep hunting , it's gotta be simple and almost in view......

Now you have your own little Rochester carby collection , once it's figgered out you can peak & tweak 'em and sell for decent $ on E-youknowwhere...