The Stovebolt Site Forums The Shop Area Engine Shop '57 235 with Rochester B (in a '53) - tuning q's ?

Hiya folks.

My dad rebuilt the Rochester B carb(numbers say it is a '59 carb) for his '57 235 which is in his '53 chevy truck.

That is a mess of parts...

Anyway, when he first put rebuilt the carb., he could not get it to idle. He decided to take it back apart and double check everything.

Yesterday, he got it all back together and fired up the truck. He adjusted on it some and it would idle nicely on it's own once it got warmed up, then he played with the distributor timing some.

Then he seemed to back it off a little too much on the carb. idle adjustment and it died. Then it didn't want to fire right back up. Pop was officially tired of foolin' with it and called it a day.

So, we can get it cranked, and eventually warmed up but is there some adjusting somewhere that we are missing?

-W

Once it is warmed up:

1. Adjust the idle speed to the desired rpm.
2. Adjust the mixture screw for maximum vacuum.

Some people adjust the timing to maximum vacuum, also (I usually adjust to the timing mark).

W - i have same carb ( from a truck ), but a 55 motor . i threw a kit in the carb & i can't get it to idle . it runs rough & i had to set r.p.m.'s up to keep it running . otherwise it accelerates well etc. can you ask what your dad did to fix idle problem & let me know . thanks ...............

For a "ballpark" idle air screw setting, turn it to the right until it begins to tighten (do this gently) then back it out 1 1/2 turns.
On a cold engine, make sure the choke is working, this should also provide you a higher idle speed because of the idle cam on the choke. Once the engine is warm follow tclederman's procedure above.

project 39,

I'll send him the link to this thread and maybe he can come in here and explain whatever he did. I think he just took it all back apart again and cleaned all the parts in the carb cleaner tank.

tcelderman and waldo53, thanks.


-W

This is Woogeroo's dad. I've done all the things you have suggested and it still won't idle. I took it apart Tuesday and cleaned it again with carburetor cleaner and took special care that I put it back together using the instructions with the kit. It still won't idle. I don't know if the kit is wrong or what. If you have any more ideas, please post them. Thanks!

Could be a vacuum leak. Check EVERYTHING that is connected to the carb or manifold. Pull the hose off the vacuum spark advance mechanism (distributor end) and plug it, see if that makes a difference. Same for vacuum wipers if you have them. On your first post you said "he played with the distributor timing some". I would recheck the point gap (seems to be a trouble spot on these old distributors) then set the timing right back on the mark. Keep looking, you'll find that pesky little gremlin!!

in mine , i thought maybe a vacum leak , so i took a butane torch ( the gas ) & held it near the carb base & around the intake gaskets . no detectable change . i'm thinking it's in the idle circuit - but where to look ? ( i am going to try disconnect vacum advance & see what happens . ( i checked plugs - reset points ) i also will pull each plug wire one at a time to see what happens ( a poor wire ? but they are new ).

plugged the vacum - pulled each wire - did the propane thing again ------no change ------ melvin , did u check your intake gaskets ?
could a weak coil cause this problem . keep me posted on your progress ......... thanks all ......

Melvin L Hardin,

My thought would be the float level. If you aren't real savvy with carburetors, this can be a touchy setting. If it is too low, it probably won't idle worth a hoot. I think the directions show how it is done..with gasket in place maybe?

Stuart

Another thought on this: I think the last "B" kit I got came with 2 different carb base gaskets. Make sure you use the one with the notch that matches the vacuum port on the carb base AND that it's oriented right (vacuum port is visible).

just installing new parts some time is not the answer,,if internal passages need cleaned it will have to be soaked in a cleaner also make all adj that came with the kit instructions,,if float is brass check for a leak,,if float is comp replace it....doc

I found on a Rocky B that polishing the power piston/metering rod using very fine steel wool(000) made all the difference in the world, I also polished the hole it rides in as good as I could using small bits of steel wool & a matchstick. Brian

thanks for that tip brian . i have a fuel pump tip . got a new one that would not work - found out it was put together backwards . took screws out & turned it 180 degrees , so it would have suction on the correct side . frank

waldo53 , i noticed the newer ( 59 ) carb has 2 ? idle cicuit holes ? at the base of the carb. the insulator block lines up w / the larger hole & the second hole is blocked off by the insulator . the junk original carb has only one hole . my wells kit came w / only one gasket & says not to use if there is a insulator block . do i have to notch out the insulator for the second hole , so both holes recieve vacum ?thanks for any help ! frank

Just a guess here Frank, I'm not familiar with the '59 carb, but sounds like your carb and base don't match. My thought is - what do you have to lose? Grind or file a notch in the base to match the carb and give it a try.
Maybe someone else will chime in here too.

Wasn't the original complaint that the carburetor wouldn't idle. Isn't the only purpose of the vacuum hole in the base to allow manifold vacuum, or lack of it, to signal the power valve to stay closed, or to open. This valve injects additional fuel into the carburetor under low vacuum conditions...heavy load/throttle conditions.

Unless the little port was blocked and dumping excess fuel into the rig at idle, which would stall it out, then having this covered wouldn't be the main suspect in a no idle situation...would it?

If it wouldn't idle because it was way over rich...flooded to death, then you would see black smoke and smell raw gas. This is how I understand it.

Stuart

there is no black smoke . when i try to adjust the idle screw , it just seems not to do much , unless i turn it way in , then the motor really slows . i did the propane thing again & cannot detect any change in the way it runs . i took carb off & re-cleaned it ( saw nothing )floats are @ specs. valve adj. is good . points i reset to .016 ( from .019 new ) . it has to be one of three things : ign. - vacum or carb . she's got gas ! thanks for helping .

I'm out of my league, talking about carbs. But I remember CarbKing mentioning something about a fuel valve (?) in rebuild kits. Frequently the kits are sized for other applications of the same carb, such as a 300 c.i.d. Ford engine instead of a 235 c.i.d. Chevy. There is no way you can "adjust out" this feature of the kit. You have to have a kit that really is built for the carb that you have on the bench, not a similar one because the kit suppliers have a different definition of "similar".

I'm sure a search under CarbKing's posts will turn up the thread. As I recall, it was related to a Carter YF/Rochester B topic.

Bill

bill , thanks for the input . the kit came w / new gaskets & new accelerator pump & 2 balls w / springs , only ( i did buy a new float also ) no new jetting . yeah i wish i knew just a smidgen of what the carbking knows ! frank

I've messed with B carbs quite a few times. There is a lot of interection between ignition timing/dwell and idle settings on the carb. I've got mine dialed in pretty well. Initially I couldn't do it. It turned out that the distributor was worn out and the dwell angle walked around all over the place. I swapped it out for a good one and set the dwell and timing, then did the carb. A few minor tweaks on the idle mixture and float setting and it runs great now- no leaks, starts easy after months of sitting, etc.

You never want to mess with both timing and carb stuff simultaneously- if you are doing a tuneup, do the ignition first and drive it a few days before you mess with the carb. Carbs get blamed for bad ignition and bad ignitions get blamed for bad carbs. I never set the point gap with a feeler gauge any more- I use a dwell meter. Its ok to set timing by ear but dwell is a lot tougher to do. Once the distributor gets old the point gap isn't a reliable indicator of dwell angle any more.

As lousy as the "B" is, it can be made to idle really well- as long as it isn't dumping gas down the throat. I had to replace the float on mine to get it to work right, its been reliable for 3 years now.

And for Pete's sake, never change the condenser unless you know its bad. The new ones are such poor quality that you'd better buy 3 or 4 until you get a good one.

the machinest looked the dist. over at rebuild time & said it was in good shape . i took new plug wires off & put old ones on - it then ran worse . my son put oxygen ( from torch ) around intake - no change - i took carb apart changed float just a little - no change . it has power on acceleration - just cannot get it to idle down smoothly . a slight surging & rough running . i'm old enough to know what it should sound like . ( it sounds like a motor with a hot cam in it ).thanks 4onthefloor

you can look in the carb throat as engine idles with a light if you see gas dripping them you have a flooding prob,, either seat leak or float level wrong or float bad,,,jet size or PV setting shouldnot alter idle adj unless fuel is flowing over cluster and dripping..the idle screw willnot cause the carb to be rich while driving if you have this the prob is with seat leak,,high float,,power valve sys bad,,main jet to large,,timing late,,vacum adv non working...doc

thanks for the valuable info doc . frank

The other thing to look for if you can't find a vacuum leak is a bad valve- it will act just like a vacuum leak. Re-check your valve adjustment, and check the compression to make sure all the cylinders are even. I like to run my valves slightly loose. They tick a little but run smooth.

Also, don't forget the vacuum wiper motor. Sometimes they leak and a torch won't find that unless its in the cab.

thanks 4onthe floor , i did recheck valves , they have a slight tick , so i must be close : ) the wiper is plugged off . i thought i would redo the intake gaskets . trying to eliminate things one at a time .
WOOGEROO - did your dad get going ? frank

I also had what I thought was a bad carb. I had to set the idle higher than it should be to keep the engine running at idle, and I also had a problem with the engine running rich based on the condition of the spark plugs. After fiddling with the carb, I finally checked the distributor. That's where the problem lay. The engine runs great now. At this point, I would check the dwell with a dwell meter instead of just a feeler gauge, make sure all wires are good by measuring the resistance from the cap to the spark plug end, and check the cap and rotor itself while you have it off. More likely a dwell or timing issue, but you might as well check the other items while your at it.