aholiday

I recently had a "reputable" shop rebuild my Rochester 4bbl carb for me.
After receiving the carb and installing back on my car (1955 olds S88 w/ original 324 V8), the car would run rich no matter what external adjustments I made. I talked to a repair shop that I had previously used and...long story, short...they suggested that two reasons why this could be is stuck or maladjusted floats, or wrong metering jet size installed.
Not wanting to send the carb back to the "reputable" shop, I decided to check it myself.

I found the float adjustment to be a little off (very close to shop man. specs.) so I adjusted it. I also found the brand new primary float valve to be sticking (cleaned and checked and it appears to be in fine working order now). The biggest surprise was that the Primary Jet size was changed to 67's. Yeah...67's, way bigger than the stock parts list of 49's for my year suggested. The secondary jets were not changed... still the old 49's with gunk and varnish all over them.

I swapped the 49's from back and the 67's from front as a temp. repair and the car is running much better. New 49's are on the way, I also have 57's and 59's in the garage available.

Ok...on to my question...I am running stock engine with 10w40 oil in florida heat, pertronix ignition and coil, a 3x14 summit paper air cleaner instead of the batwing and everything else is stock and I am currently using 90 or 93 octane non-ethanol fuel.

Should I stay with the 49's or move up to get richer with my current setup? Should I try to have larger secondary jets like some caddy's and/or other GM cars did back in the day? If yes to the above questions, how about a recomended size difference and why.

The car is my daily driver and I will be moving to Cape Cod this summer. Hopefully driving my car the entire route...fingers crossed!

Also...No, I will not be buying another carb or changing anything else out until it breaks or I win the lottery.

I know this is a long post but I wanted to give all relevent(maybe) info up front.

Thanks.

oldcutlass

I would base my jet choice on what the sparkplugs look like. The engine knows what is best!

aholiday

Spark plugs "told me" that 67 jets where ricockulous rich. Black as bad oil.

Before the Carb. rebuild, my car seemed to be ok...at least not too rich or too lean. Based on what I found, so far as the jets that were installed by the shop, 67 is waaay too big for my application. 49 seems ok for now, but I know 67 in the secondary is likely too big also.

Shotgun maintenance and "see what the plugs tell me" is not the ideal situation/answer.

I was hoping for someone with specific knowledge or experience to tell me what direction I should go.

jag1886

If you want to get the right jets without plug testing, go to a local shop with a dyno and have them do a pull or 2, there O2 senser will tell you if it's OK or you need to move up or down a step. I did this to my car after the engine build and it was worth it.

brown7373

I don't know specifics on that carb, but the Doug Roe book on Q-jets suggest no more than about a 5% increase (if memory serves), and that may be too much too, unless you have made some engine mods that require richer mixture. Richer doesn't necessarily mean more power or better operation. I had an 11.0:1 69 Corvette that I was SURE would benefit by richer than the tiny 66 primary (with metering rods, of course). That was a mistake. Larger that 66 just bogged the car down. It screamed with the stock 66 jets, and I never changed them again. Some people have said that with ethanol, a little richer is needed. I run my 72 Supreme 350 with stock jets and it runs fine.

BILL DEMMER

run the 49 jets. the factory got it right.


bill

aholiday

Yeah, right now with the 49's in primary, the car is running really better than it has in the 3+ years I have had it. I have also been able to finally master the timing with what I have on the car and jets are the last thing I am willing to adjust if needed. I'll keep that 5% in mind but I agree that 49's seem to be ok. I can get a bit of a squeal out of the tires and still not burn too much gas. I'ts just that my 0-40 is slow but 40-70 is quick with this big iron beast.

Bill,
I am starting to trust the factory a bit more each time I clean, refinish, or properly adjust what is needed to be done. The hard part sometimes is trusting the work with some of the modern variables due to gas, upgrades, etc. to be most efficient, powerful etc.
Forums like this one help with the learning curve sometimes...sometimes.

Tedd Thompson

It's going to be hard to make your stock 55 olds with 200 HP and packing 4000+ LB's into anything but what it was intended to be, just a classic neat old cruiser. Stock works for that.....Tedd

compedgemarine

I dont think you can add your opinion Ted, your car is so fast it blew the hood off

Ross Racing Engines

Using Todays gasoline..... with these old cars/carbs.....They usally can stand to be 2-3 numbers richer than stock/factory jetting.....this is what we find when tuning on one.....in order to get the A/F ratio and EGT's under control.

Tony

aholiday

Thx Ross,
That was kinda what I was wondering and also near that 5% spoken of earlier.
Tedd,
My 88 and I aren't that fat. At least not yet.
"drivability is my concern" for what it's worth, not blowing my hood off.

brown7373

It is still a trial and error type thing. If you make changes, do it in small increments and only change one thing at a time. The factory did start making carbs a little leaner into the 70s, for emissions reasons. That wasn't a concern in the 50s. I agree with you, that in most cases, the factory did get it right. Aside from the ethanol issue, if you haven't made any performance mods, you are probably about right with the factory settings. My 72 350 4bbl is not a screamer, but still starts, runs and drives about as well as I could hope for with factory jets and rods, and much like yours is a real good cruiser.

Tedd Thompson

Yes it was, not so much now.....Tedd

compedgemarine

how are the repairs coming Ted? I have a 64 Impala at the shop right now that had the same thing happen except the owner is the one who didnt close it. he got lucky that the only damage was the hood hinges were destroyed and the back corners of the hood got dinged.

Tedd Thompson

I could of picked it up Friday and played with it this weekend then returned it for the windshield replacement on Monday but it looked like rain and I have the wiper motor out of it so I left it there, everything else it done and looks good......Tedd

PS I'm having them do a few extras while it's there nothing big just buff and polish type stuff.