The Stovebolt Site Forums The Shop Area Engine Shop Help! I need to rejet my Rochester B.

I just moved to Denver, CO from St.Louis, MO. Wohoo!! Only problem is my '49 w/'59 235 ,HEI, and Rochester B won't accellerate worth a crap. Don't even try to pull a mountain grade. I found a place to get jets, but at $10 a pair I can't just buy a bunch. It ran fine at 500ft, so I don't want to ditch the carb.
Can anybody at high altitude give me a ballpark to start at? I'll keep looking locally for another carb that might be jetted good. Someone suggested getting rid of the oil bath air filter. Will this help?
Thanks,
Scott

Since you're in an area of thinner air, you need leaner jets. Carburetors mix fuel and air by weight, so when the air is less dense, the carb runs rich unless smaller jets are installed. I can't say how far you need to go, but if you can find a jet a couple of steps leaner, that's a good starting point.
Jerry

I just didn't know whether to go down a couple sizes or 6. It's probably cheaper to find some 216 carbs & take jets out of them. Jet interchangability is unknown territory for me. Like Carter to Rochester to Holley.
Now I just have to watch craigslist & figure out where a good salvage yard is.

The ideal fuel:air mixture is 14.7:1, by weight, not volume. Therefore, it takes nearly 15 pounds of air to burn one pound of gasoline. Since atmospheric pressure at sea level is 14.7 lb./sq. in., and the atmosphere peters out at about 100,000 feet altitude, it takes a one square inch column of air 100,000 feet tall to burn one pound of gasoline. Gas weighs a little over 6 pounds per gallon, so it takes a 100,000 foot column of air about 3 1/2 inches square for every gallon of gas! A clean air filter is essential, and it doesn't really matter if it's a paper pack or an oil bath, as long as it's free-flowing. I've got a stash of Rochester B's that are mostly junk. I'll see what the main jet thread diameter and pitch is, and compare it to some Holley jets I've got stashed away from my racing days. I don't think they will interchange, but it's possible something could be fabricated to adapt them temporarily. Holley jets are cheap! If so, the Holley jets could be used to tinker with the mixture, and the correct diameter Rochester jet could be selected once you're satisfied with the performance. Just an off the wall idea- - - -it might be totally impractical.
Jerry

I have had good luck soldering them shut then drilling out to a smaller size. Its not 100% accurate but will get you in the ball park. Once you get close, look for the correct jet in that range.

JOE

i would rejet it with a holly webber 2 barel
brand new from stovebolt engine company for 190 bucks. philip

Basically a sliding scale:

sea level ~ 4000 feet - use stock jet
4001 ~ 6000 feet - subtract 0.002
6001 ~ 7000 feet - subtract an additional 0.002.

Jon.

Correcting the mixture is necessary if you’re gonna run it around Denver but it won’t give you back the performance you had down at sea level. As long as you’re dealing with a normally aspirated engine the power output will continue to decrease and it will get more sluggish the higher you go.
At a mile high the air pressure on a standard day is only 12.2 in.hg. Your engine is only going to let in about 80% of the air volume available at sea level at full throttle.
There are bunches of paved mountain roads in CO. that are at of above 10,000 feet. The pressure of the atmosphere up there is now down to 10.1 in.hg. and an engine is only capable of producing less than 70% of its sea level power.
On your run up to the summit of Pikes Peak you gonna be down to about 55% and probably wouldn’t have enough power to pull the old Stovebolt.
And that’s why they invented superchargers……
DG

Thanks, everybody. I used to have a bunch of spare 1, 2, 4brl carbs I could have tried seeing if jets would swap, but I've never had the need. I gave most of my stuff away due to moving. That webber sounds nice, but can't afford that right now.
Carbking, that's awesome info! Looks like I'll still have to buy 2 or 3 sizes. One for Denver & a couple for the mountains.

What size do you have in there now? I have a few different ones & I can send one to you.

I just checked Summit racing. They have jet kits starting about $40. The size is 1/4-32 for jets 64 thru 99. A couple kits have 5/16-32. The kits that state a brand say Holley.
I found a site: chevy.oldcarmanual.com (lots of good tech info)that shows the jet size as .057 or .058 for a '54-'56 235 w/Rochester B. Doesn't give thread size. I assume jets 64-99 are .064-.099?
Another site: carburation.com (Carbs Unlimited) has jets for the B, size 41-72 for $10 each. No thread size.
So, it looks like the kits from Summit are too big. I will open my carb up & check the jet size. Then I'll see if I can get some jets from a local carb shop or order from carburation.com.
Man, I wish I could afford to inject this baby!
Scott

Wrenchbender, I haven't checked yet, but should be a .057 or .058. I guess I need to be around .055 for Denver.
Scott

A couple of years ago I rebuilt a Rochester that i had sitting around and installed it on my 216. I suddenly had all kinds of power that I didn't have before. I then puleed the plugs and they were all covered in carbon, which they weren't before. I looked at the jet and it was stamped "58". I found one with a "51" jet and put it in. I lost some power but my plugs returned to the grey white color that they had been before.

I just opened up one of my junk carbs. The main jet thread is 1/4-28, same as a 1/4" National Fine thread bolt. The Holley jet rethreads very nicely by running it into a 1/4-28 die- - - -I just tried one. It looks like A Holley #56 or #57 jet should lean yours out a little. If you have access to a lathe and some number drills, you can turn out Rochester jets by the dozen by machining a piece of 5/16" brass rod. I just might set up my lathe and build a few for myself!
Jerry

The 235s I've seen come with 56-58 jets.
The 216s I've seen come with 51-52 jets.
You might start with a 216 jet and drill it out.

Sorry to disappear. Had to go to work. Time snuck up on me. I'm currently living out of a suitcase in my brother's spare room until I find an apartment. So no access to anything but a couple of toolboxes of regular hand tools.
Thanks everybody! Now I'm not as ignorant as I was yesterday. I hate trying to buy stuff without all the info I need. The 216 jets sound right for the mountains. Course, never know what I'll find around here.
Hotrod, didn't mean to give you another project, but you could probably finish that before finishing the first beer.
Scott

I like my beer, Phillipine San Miguel from a tub of salted ice at a little pub in Angeles City if possible, but beer and machine tools don't mix! After 50+ years of tinkering with machinery, I've still got all my fingers, and I intend to keep it that way. My other hobby, gunsmithing and reloading, is also very unforgiving of mistakes. Once the machinery power is off and the guns are back in the case, bring on the cooler!
Jerry

I wouldnot get too wild & make a large excursion. About .002 smaller is all you need. I also wouldn't mess with it much till I got settled in. Ive driven cars out to Co. for 60 years from Mo. & never had a problem with fuel mixtures. Of coarce you do loose some power. Ive been up & down Pikes peak about a dozen times the first time in a 53 ford with a flathead v-8. They used to have places to pull off with a water hose you poured water over your rad. to cool it down. Co. is my favorite vacation spot. The scenery is spectacular & the people are friendly.

Hey Jerry, I hope you always 'Candled' your San Miguel before you took a sip, often found sludge on the bottom of it down there on Fields Avenue. Since I was down there every night of the week from Nov of '66 to Mar of '68 with the first Mob, I'll bet we crossed paths a few times.
DG

I was there a little later, from July 75 to November, when Korat AFB in Thailand closed down and we got PCS'ed to Clark for the rest of my 1-year unaccompanied tour. You're right, sometimes there was a bt of sediment in the bottle, but San Magoo is still some of the best-tasting beer I've ever had. The "export" stuff that's available here in the states just isn't the same!
Jerry

Wasn't that the finest Airmans club you've ever seen??? I spent a lot of evenings in there also before I headed down town.
Yep the PI was one of my better memories of my four years service.
DG

The stag bar snack menu at the club was my favorite- - - -a bowl of chili cost $1.00, but for 75 cents, I could get a "chili dog" with a big hot dog, a bun, and as much chili on it as they served in the bowl! Good eats, especially with all the chopped onion topping a customer wanted to add!
Jerry